An optimization method, system, device and medium for a single-effect two-stage coupled lithium bromide absorption refrigeration cycle with large temperature difference

Abstract

The present application relates to lithium bromide absorption refrigeration technology field, especially a single effect-two stage coupling lithium bromide absorption refrigeration cycle optimization method, system, equipment and medium of big temperature difference refrigeration, the heat source medium is connected in series to drive single effect generator, low pressure generator and high pressure generator and constructs the step heat drive generator sequence, makes the heat source outlet temperature fully reduce, the low pressure side two section series generation-absorption cycle and high pressure side single stage regeneration cycle are coupled in the intermediate pressure interface, two road vapour condenses and is sent into the evaporator to the cold water system output cold quantity after converging, with component level steady state balance equation as the foundation, with high and low pressure side cycle ratio as cross cycle coupling iteration amount, global simultaneous iteration convergence strategy is used to solve, with unit heat source mass flow refrigerating capacity as performance evaluation index, realize the quantitative optimization evaluation of compound refrigeration cycle thermal performance.

Description

Technical Field

[0001] This invention relates to the field of lithium bromide absorption refrigeration technology, and in particular to an optimized method, system, equipment, and medium for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle. Background Technology

[0002] Absorption refrigeration technology uses lithium bromide solution and water as the working fluid pair. It converts low-grade heat energy into cold energy through a solution generation-absorption cycle. The coefficient of performance (COP) is generally between 0.6 and 1.2. Compared with mechanical compression refrigeration, absorption refrigeration does not require a large amount of electrical energy and can directly use industrial waste heat or hot water as the driving heat source. It has a wide range of applications in industrial waste heat recovery and building air conditioning cold source supply.

[0003] Currently, lithium bromide absorption chillers driven by low-temperature hot water mainly have two circulation modes: single-effect cycle and two-stage cycle. Single-effect cycle units generally require a heat source temperature of 80-100℃, with a small temperature difference between the inlet and outlet on the heat source side. The cooling capacity corresponding to a unit heat source flow rate is limited, resulting in poor overall cooling economy in scenarios where the cost of heat source water resources is high.

[0004] Although two-stage circulating units can utilize low-temperature heat sources of 70-80℃, their coefficient of performance (COP) is only about half that of single-effect units, resulting in significantly lower cooling efficiency. When the heat source inlet temperature is high and the heat source outlet temperature needs to be significantly reduced, both existing single-effect and two-stage circulating units struggle to simultaneously meet the dual requirements of utilizing a large temperature difference on the heat source side and achieving a high COP. This leads to high heat source water consumption and limited economic viability.

[0005] Furthermore, when a single-effect cycle is coupled with a two-stage cycle to form a composite refrigeration system, the system involves multiple interconnected heat exchange and mass transfer components. The state variables exhibit strong nonlinear multivariable coupling characteristics, making it difficult for the traditional sequential module method to achieve stable convergence. There is a lack of global modeling and performance optimization methods suitable for this type of composite cycle, which restricts the engineering design and widespread application of composite cycle systems. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the problem to be solved by this invention is how to address the limited temperature drop range on the heat source side of existing lithium bromide absorption chillers, which require a large amount of heat source water to achieve the same cooling capacity, resulting in insufficient cooling economy in situations where heat source water costs are high; the complex modeling of composite systems with single-effect and two-stage cycle coupling, the strong coupling between the state variables of each component, the lack of a globally accurate simultaneous solution method, and the difficulty in making complete prediction and quantitative optimization of the system's thermodynamic performance.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, embodiments of the present invention provide an optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle, which includes connecting a heat source medium in series through a single-effect generator, a low-pressure generator and a high-pressure generator, driving the lithium bromide solution at each stage to desorb the refrigerant vapor respectively, forming a stepped heat drive generation sequence; The refrigerant vapors generated by the single-effect generator and the high-pressure generator are condensed by the single-effect condenser and the high-pressure condenser, respectively. The condensate is then combined and evaporated in the evaporator, outputting cooling capacity to the chilled water system. After the lithium bromide solution in the low-pressure absorber is pressurized and heated, it enters the single-effect generator and the low-pressure generator in sequence for two-stage desorption and concentration. The concentrated solution is cooled and returned to the low-pressure absorber. The low-pressure absorber absorbs the refrigerant vapor generated by the evaporator, completing the low-pressure side cycle in the dual-path absorption-generation coupling architecture. The lithium bromide solution in the high-pressure absorber is pressurized and heated before entering the high-pressure generator for desorption and concentration. The concentrated solution is then cooled and returned to the high-pressure absorber, which absorbs the refrigerant vapor generated by the low-pressure generator, completing the high-pressure side cycle in the dual-path absorption-generator coupling architecture.

[0009] As a preferred embodiment of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method of the present invention, the formation of the stepped heat drive generation sequence includes: the heat source medium enters the tube of the single-effect generator from the high temperature end and exchanges heat with the lithium bromide solution sprayed outside the tube; the lithium bromide solution desorbs the refrigerant vapor under the corresponding pressure, and the solution concentration increases. After the heat source medium flows out of the tube of the single-effect generator, it enters the tube of the low-pressure generator and exchanges heat with the lithium bromide solution sprayed outside the tube. The lithium bromide solution desorbs the refrigerant vapor under the corresponding pressure, and the solution concentration further increases. After the heat source medium flows out of the low-pressure generator tube, it enters the high-pressure generator tube and exchanges heat with the lithium bromide solution sprayed outside the tube. The lithium bromide solution desorbs the refrigerant vapor under the corresponding pressure. After the solution concentration further increases, the heat source medium flows out from the low-temperature end of the high-pressure generator.

[0010] As a preferred embodiment of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method of the present invention, the lithium bromide solution in the low-pressure absorber is pressurized and heated, and then enters the single-effect generator and the low-pressure generator in sequence for two-stage desorption and concentration. Specifically, the lithium bromide solution at the bottom of the low-pressure absorber is pressurized by the low-pressure generator pump, and then passes through the second heat exchanger and the third heat exchanger in sequence to absorb heat and heat up. It then enters the outside of the tube of the single-effect generator and exchanges heat with the heat source medium inside the tube in a spray manner. The lithium bromide solution desorbs refrigerant vapor in the single-effect generator, and the solution concentration increases. After the lithium bromide solution flows out from the bottom of the single-effect generator, it is cooled down by the third heat exchanger and enters the outside of the low-pressure generator tube. It exchanges heat with the heat source medium inside the tube by spraying. The lithium bromide solution desorbs the refrigerant vapor in the low-pressure generator, and the solution concentration increases further. After the lithium bromide solution flows out from the bottom of the low-pressure generator, it is cooled down by the second heat exchanger and returns to the low-pressure absorber, where it comes into contact with the refrigerant vapor from the evaporator for absorption. After the solution concentration decreases, it accumulates at the bottom of the low-pressure absorber.

[0011] As a preferred embodiment of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method of the present invention, wherein: the lithium bromide solution in the high-pressure absorber is pressurized and heated and then enters the high-pressure generator for desorption and concentration, including: the lithium bromide solution at the bottom of the high-pressure absorber is pressurized by the high-pressure generator pump, absorbs heat and is heated by the first heat exchanger, enters the outside of the high-pressure generator tube and exchanges heat with the heat source medium inside the tube by spraying, and the lithium bromide solution desorbs refrigerant vapor in the high-pressure generator, and the solution concentration increases; After the lithium bromide solution flows out from the bottom of the high-pressure generator, it is cooled down by the first heat exchanger and returns to the high-pressure absorber, where it comes into contact with the refrigerant vapor from the low-pressure generator for absorption. After the solution concentration decreases, it accumulates at the bottom of the high-pressure absorber.

[0012] As a preferred embodiment of the optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle described in this invention, it further includes: establishing component-level steady-state equilibrium equations for mass conservation, lithium bromide composition conservation, and energy conservation for each heat exchange and mass transfer component in the refrigeration cycle. The high-pressure side circulation ratio and the low-pressure side circulation ratio are incorporated into the equation system as cross-cycle coupling iteration quantities, and together with the working pressure of each pressure level, they form the core iterative state vector, thus forming a multi-variable coupled equation system for the entire system. Using the core iterative state vector as the solution object, a global simultaneous iterative convergence strategy is adopted to solve the multivariate coupled equations of the entire system. In each iteration, the enthalpy value and saturation temperature of the lithium bromide solution at each node are updated synchronously until the global residual satisfies the convergence condition. Based on the convergence results, the cooling capacity per unit heat source mass flow rate is used as the evaluation index for large temperature difference refrigeration performance, and the performance of the refrigeration system is quantitatively evaluated.

[0013] As a preferred embodiment of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method described in this invention, wherein: the high-pressure side circulation ratio and the low-pressure side circulation ratio are used as cross-cycle coupling iteration quantities, including the high-pressure side circulation ratio being determined by the ratio of the concentration difference of lithium bromide solution at the inlet and outlet of the high-pressure generator to the inlet concentration, reflecting the lithium bromide solution circulation mass corresponding to the unit refrigerant output on the high-pressure side; The low-pressure side circulation ratio is determined by the ratio of the concentration difference between the inlet and outlet lithium bromide solutions during the series generation process of the single-effect generator and the low-pressure generator to the inlet concentration, reflecting the overall desorption efficiency of the two-stage generation process on the low-pressure side. The high-pressure side circulation ratio and the low-pressure side circulation ratio are interconnected through the heat exchanger mass conservation equation and converge synchronously during the global iterative solution process.

[0014] As a preferred embodiment of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method described in this invention, the synchronous convergence during the global iterative solution includes: rearranging the steady-state equilibrium equation of the entire system into a residual function about the core iterative state vector, constructing the system Jacobian matrix with the current iterative state variables, solving the linearized correction equation set to obtain the state variable correction vector, and introducing a damping coefficient to control the correction step size; In each iteration, the current temperature and concentration state variables are substituted into the lithium bromide solution property equation to update the enthalpy and saturation temperature of each node. This process proceeds synchronously with the state variable corrections until the global convergence condition is met.

[0015] Secondly, embodiments of the present invention provide a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization system, which includes a heat drive sequence construction module, which connects the heat source medium in series through a single-effect generator, a low-pressure generator and a high-pressure generator to drive the lithium bromide solution at each stage to desorb the refrigerant vapor respectively, forming a stepped heat drive generation sequence. The dual-circulation operation module has refrigerant vapors generated by the single-effect generator and the high-pressure generator, which are condensed by the single-effect condenser and the high-pressure condenser, respectively. The condensate is then combined and enters the evaporator to evaporate, outputting cooling capacity to the chilled water system. In the low-pressure side solution circulation module, after the lithium bromide solution in the low-pressure absorber is pressurized and heated, it enters the single-effect generator and the low-pressure generator in sequence for two-stage desorption and concentration. The concentrated solution is cooled and returned to the low-pressure absorber. The low-pressure absorber absorbs the refrigerant vapor generated by the evaporator, completing the low-pressure side circulation in the dual-path absorption-generation coupling architecture. In the high-pressure side solution circulation module, the lithium bromide solution in the high-pressure absorber is pressurized and heated before entering the high-pressure generator for desorption and concentration. The concentrated solution is then cooled and returned to the high-pressure absorber, which absorbs the refrigerant vapor generated by the low-pressure generator, thus completing the high-pressure side circulation in the dual-path absorption-generator coupling architecture.

[0016] Thirdly, embodiments of the present invention provide a computer device, including a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program instructions are executed by the processor, they implement the steps of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method as described in the first aspect of the present invention.

[0017] Fourthly, embodiments of the present invention provide a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program instructions are executed by a processor, they implement the steps of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method as described in the first aspect of the present invention.

[0018] The beneficial effects of this invention are as follows: This invention constructs a tiered heat-driven generation sequence by connecting a heat source medium in series with a three-stage pressure generator, allowing the heat source medium to release heat gradually and fully along the temperature drop direction, thereby reducing the heat source outlet temperature. The cooling capacity per unit heat source mass flow rate is improved compared to existing single-effect and two-stage cycles, solving the problems of narrow heat source temperature drop range and high heat source water consumption in existing units. The two-stage series generation on the low-pressure side expands the comprehensive gas release range of the lithium bromide solution, reduces the cycle ratio, and decreases pump power consumption. The refrigerant vapor generated by the low-pressure generator is directly introduced into the high-pressure absorber, thermocouples the two solution cycles at the intermediate pressure interface, and balances high thermal coefficient with large temperature difference operation, solving the problem that single-effect and two-stage cycles cannot simultaneously balance thermal coefficient and heat source temperature difference utilization. The global simultaneous iterative convergence strategy solves the problem of poor convergence of the high and low pressure side cycle ratios as coupling constraints, overcoming the shortcomings of the traditional sequential module method under strong coupling conditions of multiple variables, and realizing stable prediction and quantitative performance evaluation of the thermodynamic state of the composite cycle system. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A flowchart of an optimization method for a single-effect, two-stage coupled lithium bromide absorption refrigeration cycle with a large temperature difference. Figure 2 A computer device diagram for optimizing a single-effect, two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle; Figure 3 A schematic diagram of a refrigeration cycle system for optimizing a single-effect, two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle; Figure 4 A schematic diagram comparing the water-saving performance of a composite system (STAC) based on an optimization method for a single-effect, two-stage coupled lithium bromide absorption chiller with a large temperature difference refrigeration cycle, and a conventional absorption chiller. Figure 5 A comparative schematic diagram of the composite system (STAC) of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method with RXZⅢ-ZH2M2 and BDH8.6XⅡ. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0024] Example 1 Reference Figure 1 This is the first embodiment of the present invention, which provides an optimization method for a single-effect, two-stage coupled lithium bromide absorption large-temperature-difference refrigeration cycle, including: S100: The heat source medium is connected in series through a single-effect generator, a low-pressure generator, and a high-pressure generator to drive the lithium bromide solution at each stage to desorb the refrigerant vapor, forming a cascade heat drive generation sequence.

[0025] S200: The refrigerant vapor generated by the single-effect generator and the high-pressure generator is condensed by the single-effect condenser and the high-pressure condenser respectively. The condensate is then combined and enters the evaporator for evaporation, outputting cooling capacity to the chilled water system.

[0026] S300: After the lithium bromide solution in the low-pressure absorber is pressurized and heated, it enters the single-effect generator and the low-pressure generator in sequence for two-stage desorption and concentration. The concentrated solution is cooled and returned to the low-pressure absorber. The low-pressure absorber absorbs the refrigerant vapor generated by the evaporator, completing the low-pressure side cycle in the dual-path absorption-generator coupling architecture.

[0027] S400: After the lithium bromide solution in the high-pressure absorber is pressurized and heated, it enters the high-pressure generator for desorption and concentration. The concentrated solution is cooled and returned to the high-pressure absorber. The high-pressure absorber absorbs the refrigerant vapor generated by the low-pressure generator, completing the high-pressure side cycle in the dual-path absorption-generator coupling architecture.

[0028] It should be noted that the low-pressure generator plays a dual role in this scheme: firstly, the lithium bromide solution flowing out of the low-pressure absorber enters the low-pressure generator for further desorption after the first stage of generation is completed in the single-effect generator, thus completing the two-stage series generation process on the low-pressure side; secondly, the refrigerant vapor generated by the desorption of the low-pressure generator is not introduced into the condenser, but is directly sent to the high-pressure absorber to drive the absorption process of the concentrated solution on the high-pressure side.

[0029] S100 establishes a heat-driven sequence of a three-stage generator driven by a series heat source. The heat source medium releases heat step by step in the single-effect generator, low-pressure generator, and high-pressure generator along the temperature drop direction, thus significantly reducing the outlet temperature and increasing the cooling capacity per unit heat source mass flow rate. S200 condenses and combines the refrigerant generated by the single-effect generator and high-pressure generator before sending it to the evaporator to complete the cooling output. S300 operates a two-stage series generation-absorption cycle on the low-pressure side, and S400 operates a single-stage regeneration cycle on the high-pressure side. The two cycles maintain thermal correlation and flow balance through a cross-path method of providing steam from the low-pressure generator to the high-pressure absorber. The four steps are executed in a coordinated manner, achieving large temperature difference operation on the heat source side while maintaining a high thermal coefficient, solving the problem of the narrow heat source temperature drop range of the existing single-effect cycle and the difficulty in simultaneously achieving the low thermal coefficient of the two-stage cycle.

[0030] Example 2 Reference Figure 1 - Figure 5 This is the second embodiment of the present invention.

[0031] In this embodiment, step S100 involves connecting the heat source medium in series with a single-effect generator, a low-pressure generator, and a high-pressure generator to drive the lithium bromide solutions at each stage to desorb the refrigerant vapor, forming a cascaded heat drive generation sequence, including the following A1 step: A1: The cascade heat drive generation sequence includes the following: the heat source medium enters the tube of the single-effect generator from the high-temperature end, exchanges heat with the lithium bromide solution sprayed outside the tube, and the lithium bromide solution desorbs the refrigerant vapor under the corresponding pressure, thus increasing the solution concentration. After the heat source medium flows out of the tube of the single-effect generator, it enters the tube of the low-pressure generator and exchanges heat with the lithium bromide solution sprayed outside the tube. The lithium bromide solution desorbs the refrigerant vapor under the corresponding pressure, and the solution concentration further increases. After the heat source medium flows out of the low-pressure generator tube, it enters the high-pressure generator tube and exchanges heat with the lithium bromide solution sprayed outside the tube. The lithium bromide solution desorbs the refrigerant vapor under the corresponding pressure. After the solution concentration further increases, the heat source medium flows out from the low-temperature end of the high-pressure generator.

[0032] Specifically, the construction of the cascaded heat drive generation sequence is the core component of this scheme to achieve large temperature difference operation on the heat source side. The heat source medium (hot water in this embodiment) flows in series through the heat exchange tubes of the single-effect generator, the low-pressure generator, and the high-pressure generator, releasing heat to the lithium bromide solution step by step along the direction of heat source temperature drop. All three generators adopt a heat transfer method of spraying lithium bromide solution on the outside of the heat exchange tubes. The heat source medium inside the tubes and the sprayed solution outside the tubes exchange heat non-contactly through the tube walls. After the lithium bromide solution absorbs heat and rises in temperature, it desorbs the refrigerant (water vapor) under its respective operating pressure.

[0033] Specifically, the heat source medium first enters the tubes of the single-effect generator. The single-effect generator operates at a single-effect condensing pressure P. k＇ (That is, the condensing pressure inside the single-effect condenser, at which the lithium bromide solution desorbs water vapor at the saturation temperature corresponding to the pressure). Let the mass flow rate of the lithium bromide solution entering the single-effect generator be... The lithium bromide mass fraction (the percentage of lithium bromide in the total mass of the solution, hereinafter referred to as "concentration") is: The mass flow rate of the concentrated solution leaving the single-effect generator is The concentration is The mass flow rate of water vapor produced by the single-effect generator is: By the law of conservation of mass, the total mass conservation equation for a single-effect generator is given by formula (1): (1) The conservation equation for lithium bromide components is Equation (2): (2) The energy conservation equation for a single-effect generator is shown in equation (3): (3) The specific enthalpy h (heat contained in a unit mass of working fluid, in kJ / kg) at each state point is determined by the current temperature and lithium bromide solution concentration through the property equation. The heat transfer of the heat source medium on the single-effect generator side is given by formula (4): (4) in, The mass flow rate of the heat source medium. Specific heat of the heat source medium and These represent the temperatures at which the heat source medium enters and exits the single-effect generator, respectively.

[0034] The heat source medium flows out of the single-effect generator tube and into the low-pressure generator tube. The low-pressure generator operates at an intermediate pressure P. m P m Below the single-effect condensing pressure P k＇The low-pressure generator receives a high-concentration lithium bromide solution flowing from the bottom of the single-effect generator. The solution continues to be sprayed and heat-exchanged outside the low-pressure generator tubes. m Water vapor is further desorbed under pressure. Let the inlet and outlet mass flow rates of the solution in the low-pressure generator be respectively... and The concentrations are respectively and The desorption produces water vapor at a mass flow rate of 100%. The overall mass conservation equation for the low-pressure generator (5): (5) Lithium bromide component conservation equation (6): (6) The energy conservation equations correspond to formula (7): (7) The heat exchange of the heat source medium on the low-pressure generator side is given by formula (8): (8) The temperature of the heat source medium is further reduced at this stage.

[0035] The heat source medium flows out of the low-pressure generator tube and into the high-pressure generator tube. The high-pressure generator operates at its maximum pressure P. k It receives a low-concentration lithium bromide solution from the high-pressure absorber. The solution exchanges heat via a spray method on the outside of the high-pressure generator tube. k Water vapor is desorbed under pressure. Let the inlet and outlet concentrations of the solution in the high-pressure generator be ω1 and ω2, respectively, and the mass flow rate of the desorbed water vapor be... The overall mass conservation equation for the high-voltage generator (9): (9) Lithium bromide component conservation equation (10): (10) And the energy conservation equation formula (11): (11) The heat exchange of the heat source medium on the high-pressure generator side is given by formula (12): (12) The heat source medium flows out from the low-temperature end of the high-pressure generator. At this time, the heat source medium has fully released heat, and the outlet temperature drops to the lower limit of the usable heat source temperature, achieving the goal of large temperature difference operation on the heat source side.

[0036] The pressure sequence between the three pressure levels is P k >P k＇ >P m >Po (P) o The operating pressure of the evaporator and the low-pressure absorber is the lowest pressure in the medium. The boiling point temperature of the lithium bromide solution corresponding to each pressure level decreases sequentially. The heat source medium drives the desorption of the lithium bromide solution at each level from the high-temperature end to the low-temperature end along the series path, forming a complete ladder heat drive generation sequence.

[0037] In this embodiment, the refrigerant vapor generated by the single-effect generator and the high-pressure generator in step S200 is condensed by the single-effect condenser and the high-pressure condenser, respectively. The condensate is then combined and evaporated in the evaporator to output cooling capacity to the chilled water system, including the following steps B1-B2: The single-effect generator and the high-pressure generator produce refrigerant vapors operating at different pressure levels. The two vapors enter the condensers of the corresponding pressure levels for condensation. The condensates are then combined and sent to the evaporator for evaporation and cooling, outputting cooling capacity to the chilled water system.

[0038] Specifically, the single-effect generator operates at pressure P. k＇ The water vapor generated by desorption enters the single-effect condenser. The energy conservation equation for the refrigerant (i.e., working fluid, which is water in this scheme) side of the single-effect condenser is Equation (13): (13) Describe water vapor in P k＇ The heat of condensation released to the cooling water during the process of condensing from gaseous to liquid condensate under pressure. The heat exchange of cooling water on the single-effect condenser side is given by formula (14): (14) Cooling water enters the heat exchange tubes of the single-effect condenser, absorbs heat and rises in temperature, then flows out of the single-effect condenser and enters the heat exchange tubes of the high-pressure condenser, realizing the series utilization of cooling water. The mass conservation equation of the single-effect condenser is given by formula (15): (15) This indicates that the mass of water vapor entering the condenser is equal to the mass of liquid condensate produced during condensation.

[0039] High pressure generator at pressure P k The water vapor generated by desorption enters the high-pressure condenser. The energy conservation equation for the refrigerant side of the high-pressure condenser is Equation (16): (16) The equation for calculating the heat exchange on the cooling water side is formula (17): (17) The cooling water inlet comes from the cooling water outlet of the single-effect condenser, flows in series through the high-pressure condenser, and then exits the unit. The mass conservation equation for the high-pressure condenser is formula (18): (18) The condensate produced at the bottom of the single-effect condenser and the high-pressure condenser merges through parallel pipes and flows into the bottom of the evaporator. The evaporator operates at the lowest pressure P. o condensate in P o At the low saturation temperature corresponding to the pressure, the refrigerant evaporates into low-pressure water vapor after being pressurized and sprayed by the refrigerant pump. During the evaporation process, it absorbs heat from the cold water system, thereby cooling the cold water and outputting cooling capacity. The power of the refrigerant pump is calculated by formula (19): (19) The energy conservation equation for the refrigerant side of the evaporator is Equation (20): (20) This describes the heat absorbed by the evaporation of liquid condensate. The heat exchange on the cold water side is given by formula (21): (twenty one) Cold water enters the heat exchange tubes of the evaporator, exchanges heat with the refrigerant evaporating outside the tubes, and its temperature decreases, thus supplying cooling to the cold water system as low-temperature cold water. The mass conservation equation of the evaporator is given by formula (22): (twenty two) The low-pressure water vapor generated by evaporation is supplied to the low-pressure absorber, corresponding to the absorption process of the S300 low-pressure side circulation.

[0040] It should be noted that the low-voltage generator is in P m The water vapor generated under pressure does not enter the condenser, but is directly introduced into the high-pressure absorber (both pressures are P). m The steam, which serves as the heat source for driving the absorption process of the lithium bromide solution on the high-pressure side, is the key connection for the establishment of the dual-path absorption-generation coupling architecture in this scheme.

[0041] In this embodiment, after the lithium bromide solution in the low-pressure absorber is pressurized and heated in step S300, it sequentially enters the single-effect generator and the low-pressure generator for two-stage desorption and concentration. The concentrated solution is cooled and returned to the low-pressure absorber, where it absorbs the refrigerant vapor generated by the evaporator, completing the low-pressure side cycle in the dual-path absorption-generator coupling architecture, including the following C1 step: C1: After the lithium bromide solution in the low-pressure absorber is pressurized and heated, it enters the single-effect generator and the low-pressure generator in sequence for two-stage desorption and concentration. This includes the lithium bromide solution at the bottom of the low-pressure absorber being pressurized by the low-pressure generator pump, and then passing through the second and third heat exchangers in sequence to absorb heat and increase its temperature. It then enters the outside of the tube of the single-effect generator and exchanges heat with the heat source medium inside the tube in a spray manner. The lithium bromide solution desorbs refrigerant vapor in the single-effect generator, and the solution concentration increases. After the lithium bromide solution flows out from the bottom of the single-effect generator, it is cooled down by the third heat exchanger and enters the outside of the low-pressure generator tube. It exchanges heat with the heat source medium inside the tube by spraying. The lithium bromide solution desorbs the refrigerant vapor in the low-pressure generator, and the solution concentration increases further. After the lithium bromide solution flows out from the bottom of the low-pressure generator, it is cooled down by the second heat exchanger and returns to the low-pressure absorber, where it comes into contact with the refrigerant vapor from the evaporator for absorption. After the solution concentration decreases, it accumulates at the bottom of the low-pressure absorber.

[0042] Specifically, the low-pressure side solution circulation enables the lithium bromide solution to pass through the low-pressure absorber (operating pressure P). o Single-effect generator (working pressure P) k＇ ) and low-pressure generator (working pressure P) m The closed loop between the two stages of generation processes fully desorbs the refrigerant and absorbs low-pressure water vapor from the evaporator in the low-pressure absorber, causing the solution concentration to fluctuate during the cycle. The low-pressure side cycle has one more generation process than the high-pressure side cycle, which is equivalent to multi-stage generation, allowing the low-pressure side solution to make more efficient use of the heat source temperature drop.

[0043] Specifically, the lowest concentration lithium bromide solution (concentration ω3, corresponding to...) is stored at the bottom of the low-pressure absorber after the absorption process is complete. Figure 4 The solution at state point 9 (solution state). The solution is pressurized by a low-pressure pump from P. o Pressure rises to P k＇ The power of the low-pressure generating pump is calculated using formula (23): (twenty three) In the formula, the subscript of head H indicates the pipeline between the two components through which the solution flows.

[0044] After being pressurized, the solution flows sequentially through the second and third heat exchangers to absorb heat and increase its temperature, thereby reducing the external heat input required to subsequently enter the generator. In the second heat exchanger, the low-temperature side solution (from the bottom of the low-pressure absorber, concentration ω3) exchanges heat with the high-temperature side solution (from the high-concentration lithium bromide solution at the bottom of the low-pressure generator, concentration ω5): the low-temperature side solution absorbs heat and increases its temperature, while the high-temperature side solution releases heat and decreases its temperature. Neglecting heat loss, the heat balance equation for the second heat exchanger is Equation (24): (twenty four) The equation for calculating heat exchange is formula (25): (25) The solution flows further through the third heat exchanger and continues to heat up. In the third heat exchanger, the low-temperature side solution (from the low-temperature side outlet of the second heat exchanger) exchanges heat with the high-temperature side solution (from the high-concentration lithium bromide solution at the bottom of the single-effect generator, concentration ω4). The heat balance equation of the third heat exchanger is Equation (26): (26) The equation for calculating heat exchange is formula (27): (27) After being heated through two stages of heat exchange, the solution enters the outside of the single-effect generator tube and exchanges heat with the heat source medium inside the tube via a spray method. k＇ Water vapor is desorbed under pressure, completing the first stage of the process. The solution concentration increases from ω3 to ω4. The corresponding mass conservation equation is (1): (1) Lithium bromide component conservation equation (2): (2) Energy conservation equation (3): (3) The heat exchange equation for the hot water side is formula (4): (4) After the lithium bromide solution flows out from the bottom of the single-effect generator, it is then processed by P. k＇ Reduce voltage to P m The solution enters the high-temperature side of the third heat exchanger, releasing heat to the low-temperature side solution for cooling. After cooling, the solution enters the outside of the low-pressure generator tubes, where it exchanges heat with the heat source medium inside the tubes via a spray method. m Under pressure, water vapor continues to be desorbed, completing the second stage of the process. The solution concentration further increases from ω4 to ω5, and the corresponding mass conservation equation is (5): (5) Lithium bromide component conservation equation (6): (6) Energy conservation equation (7): (7) The heat exchange equation for the hot water side is given by formula (8): (8) After the lithium bromide solution flows out from the bottom of the low-pressure generator, it is controlled by P. m Reduce voltage to P o The solution enters the high-temperature side of the second heat exchanger, releasing heat to the low-temperature side to cool down. The cooled, high-concentration solution (concentration ω5) then enters the low-pressure absorber, where it is cooled by heat transfer. oUnder pressure, the solution absorbs heat through contact with low-pressure water vapor from the evaporator, causing the solution concentration to decrease from ω5 to ω3. Consequently, the solution temperature decreases, and the absorbed heat is released to the cooling water. The overall mass conservation equation for the low-pressure absorber is (28): (28) Lithium bromide component conservation equation (29): (29) The energy conservation equation is given by formula (30): (30) The equation for calculating the heat exchange on the cooling water side is formula (30): (30) Cooling water flows through the heat exchange tubes of the low-pressure absorber, carrying away the absorbed heat before flowing out of the unit.

[0045] Low-pressure side circulation cycle ratio f SG (That is, the mass of lithium bromide solution required to generate 1 kg of refrigerant vapor on the low-pressure side) is defined by formula (31): (31) The venting range is the range of change in solution concentration within the generator, i.e., the concentration difference between the solution entering and leaving the generator.

[0046] In the generator, the total amount of lithium bromide remains constant. Therefore, the circulation ratio can also be calculated using the concentration of lithium bromide solution entering and leaving the generator, and the calculation formula derived based on the conservation of lithium bromide mass is shown in formula (32): (32) like Figure 4 - Figure 5 As shown, the wide-temperature-range lithium bromide refrigeration cycle consists of two cycles: a high-pressure solution cycle and a low-pressure solution cycle. The specific calculation relationship of the cycle ratio of the high-pressure cycle is shown in formula (33): (33) in, This refers to the venting range of the high-pressure cycle.

[0047] The cycle ratio of the low-pressure cycle is: (34) in, This refers to the venting range of the low-pressure cycle.

[0048] f SG The value is determined by the combined venting range of the single-effect generator and the low-pressure generator connected in series. The larger the venting range, the greater the f...SG The smaller the value, the lower the power consumption of the low-pressure generator pump and the higher its energy efficiency.

[0049] In this embodiment, after the lithium bromide solution in the high-pressure absorber is pressurized and heated in step S400, it enters the high-pressure generator for desorption and concentration. The concentrated solution is then cooled and returned to the high-pressure absorber. The high-pressure absorber absorbs the refrigerant vapor generated by the low-pressure generator, completing the high-pressure side cycle in the dual-path absorption-generator coupling architecture, including the following steps D1-D4: D1: After the lithium bromide solution in the high-pressure absorber is pressurized and heated, it enters the high-pressure generator for desorption and concentration. This includes the lithium bromide solution at the bottom of the high-pressure absorber being pressurized by the high-pressure generator pump, absorbing heat and heating through the first heat exchanger, entering the outside of the high-pressure generator tube and exchanging heat with the heat source medium inside the tube by spraying. The lithium bromide solution desorbs refrigerant vapor in the high-pressure generator, and the solution concentration increases. After the lithium bromide solution flows out from the bottom of the high-pressure generator, it is cooled down by the first heat exchanger and returns to the high-pressure absorber, where it comes into contact with the refrigerant vapor from the low-pressure generator for absorption. After the solution concentration decreases, it accumulates at the bottom of the high-pressure absorber.

[0050] High-pressure side solution circulation: High-pressure side solution circulation enables lithium bromide solution to pass through the high-pressure absorber (operating pressure P). m ) and high-pressure generator (working pressure P) k The closed single-stage regeneration cycle between the two stages completes the concentration cycle of the solution through a generation process and an absorption process.

[0051] Specifically, the bottom of the high-pressure absorber stores the lithium bromide solution with the lowest concentration after the absorption process is complete (concentration ω1, corresponding to...). Figure 4 The solution at state point 5 (solution state). This solution is pressurized by a high-pressure pump from P... m Pressure rises to P k Pressure. The power of the high-pressure generating pump is calculated using formula (35): (35) In the formula, the subscript of head H indicates the pipeline between the two components through which the solution flows.

[0052] The pressurized low-concentration solution enters the low-temperature side of the first heat exchanger and exchanges heat with the high-temperature side solution (a high-concentration lithium bromide solution from the bottom of the high-pressure generator, concentration ω2): the low-temperature side solution absorbs heat and heats up, while the high-temperature side solution releases heat and cools down. The inlet and outlet of the high-temperature side solution of the first heat exchanger are connected to the bottom outlet of the high-pressure generator and the top inlet of the high-pressure absorber, respectively, and the inlet and outlet of the low-temperature side solution are connected to the bottom outlet of the high-pressure absorber and the top inlet of the high-pressure generator, respectively. Neglecting heat loss, the heat balance equation of the first heat exchanger is Equation (36): (36) The equation for calculating heat exchange is formula (37): (37) After being heated by the first heat exchanger, the low-concentration lithium bromide solution enters the outside of the high-pressure generator tube and exchanges heat with the heat source medium inside the tube via a spray method. k Water vapor is desorbed under pressure, and the solution concentration increases from ω1 to ω2. The total mass conservation equation, lithium bromide component conservation equation, and energy conservation equation of the high-pressure generator correspond to formulas (9), (10), and (11), respectively. The heat exchange of the heat source medium is given by formula (12).

[0053] A high-concentration lithium bromide solution (concentration ω2) flows out from the bottom of the high-voltage generator and is then processed by P. k Reduce voltage to P m The solution enters the high-temperature side of the first heat exchanger, releasing heat to the low-temperature side to cool down, reducing the solution temperature to near the absorption temperature of the high-pressure absorber. The cooled, high-concentration solution then enters the high-pressure absorber, where it is heated by P... m Under pressure, the absorber contacts intermediate-pressure water vapor from the low-pressure generator for absorption, reducing the solution concentration from ω2 to ω1 and releasing the absorbed heat to the cooling water. The overall mass conservation equation for the high-pressure absorber is (38): (38) Lithium bromide component conservation equation (39): (39) The energy conservation equation is given by formula (40): (40) The equation for calculating the heat exchange on the cooling water side is formula (41): (41) Cooling water flows through the heat exchange tubes of the high-pressure absorber, carrying away the absorbed heat before exiting the unit. The solution at the bottom of the high-pressure absorber is then pumped back into the high-pressure generator by the high-pressure generating pump, completing a single-stage regeneration cycle on the high-pressure side.

[0054] High-voltage side circulation cycle ratio f HG (That is, the mass of lithium bromide solution required to generate 1 kg of refrigerant vapor on the high-pressure side) is defined by formula (31): (31) The calculation formula derived based on the mass conservation of lithium bromide is shown in formula (32): (32) The specific calculation relationship on the high-voltage side of this system is shown in formula (33): (33) Its value is determined by the lithium bromide concentration difference between the inlet and outlet of the high-pressure generator (venting range ω2-ω1).

[0055] D2: Also includes establishing component-level steady-state equilibrium equations for mass conservation, lithium bromide composition conservation, and energy conservation for each heat exchange and mass transfer component in the refrigeration cycle. The high-pressure side circulation ratio and the low-pressure side circulation ratio are incorporated into the equation system as cross-cycle coupling iteration quantities, and together with the working pressure of each pressure level, they form the core iterative state vector, thus forming a multi-variable coupled equation system for the entire system. Using the core iterative state vector as the solution object, a global simultaneous iterative convergence strategy is adopted to solve the multivariate coupled equations of the whole system. In each iteration, the enthalpy value and saturation temperature of lithium bromide solution at each node are updated synchronously until the global residual satisfies the convergence condition. Based on the convergence results, the cooling capacity per unit heat source mass flow rate is used as the evaluation index for large temperature difference refrigeration performance, and the performance of the refrigeration system is quantitatively evaluated.

[0056] Establishment of the multivariable coupled equations for the whole system: After the cascade heat drive generation sequence (S100-A1), the refrigerant condensation and evaporation process (S200-B1), the low-pressure side cycle (S300-C1), and the high-pressure side cycle (D1) are all established, this scheme realizes a complete mathematical description of the system's thermodynamic state by constructing a multivariable coupled equation set for the whole system, providing a computational basis for subsequent iterative solutions and performance evaluation.

[0057] For all 11 heat exchange and mass transfer components in the refrigeration cycle (single-effect generator, high-pressure generator, low-pressure generator, single-effect condenser, high-pressure condenser, high-pressure absorber, low-pressure absorber, evaporator, first heat exchanger, second heat exchanger, and third heat exchanger), under the assumption of steady-state operation, mass conservation, lithium bromide component conservation, and energy conservation equations are established respectively, forming a total of component-level steady-state equilibrium equations.

[0058] Regarding pump power consumption, since the vacuum pump operates intermittently, this scheme does not include the vacuum pump power consumption, but only considers four pumps: the high-pressure generating pump, the low-pressure generating pump, the absorption pump, and the refrigerant pump. Pump power loss is ignored, and the pressurization process of each pump is considered as isentropic compression. The power calculation equations for each pump are formulas (35), (23), (42), and (19), respectively. The power of the absorption pump (used to pressurize the solution at the bottom of the low-pressure absorber and send it to the second heat exchanger) is given by formula (38). Absorption pump power calculation equation: (42) In the formula, the subscript of head H indicates the pipeline between the two components through which the solution or coolant water flows.

[0059] The circulation ratio (CR) is an important parameter characterizing the system's operating efficiency. It is defined as the mass of lithium bromide solution required to circulate in the generator to produce 1 kg of refrigerant water vapor, and its definition is given by formula (31). The larger the circulation ratio, the higher the pump power consumption and the lower the energy efficiency. Therefore, reducing the circulation ratio is one of the core objectives for improving system energy efficiency. This system has a high-pressure side circulation ratio f HG and low-pressure side circulation ratio f SG The calculation formulas for the two cycle ratios, derived based on the mass conservation of lithium bromide, are shown in formula (41), and the specific calculation relationships for the high and low pressure sides are shown in formula (33). The venting range (i.e., the difference in the mass fraction of lithium bromide at the inlet and outlet of the solution in the generator) reflects the desorption capacity of each generation stage for the lithium bromide solution. The larger the venting range, the smaller the cycle ratio.

[0060] High-voltage side circulation ratio f HG and low-pressure side circulation ratio f SG As a cross-cyclic coupling iterative quantity, it is incorporated into the equation system, along with the working pressure P of each pressure level. k P k＇ P m and P o Together they form the core iterative state vector X, and the definition of the global variable vector is shown in formula (43): (43) Where, 𝑋∈𝑅 𝑛 n=16 represents the number of basic variables. The equations for each component are rearranged into residual form, forming a multivariable coupled equation set describing the thermodynamic state of the entire system. The matrix representation of the overall equation set is shown in formula (44): (44) D3: The high-pressure side circulation ratio and the low-pressure side circulation ratio are used as cross-cycle coupling iteration quantities. The high-pressure side circulation ratio is determined by the ratio of the concentration difference of lithium bromide solution at the inlet and outlet of the high-pressure generator to the inlet concentration, reflecting the circulating mass of lithium bromide solution corresponding to the unit refrigerant output on the high-pressure side. The low-pressure side circulation ratio is determined by the ratio of the concentration difference between the inlet and outlet lithium bromide solutions during the series generation process of the single-effect generator and the low-pressure generator to the inlet concentration, reflecting the overall desorption efficiency of the two-stage generation process on the low-pressure side. The high-pressure side circulation ratio and the low-pressure side circulation ratio are interconnected through the heat exchanger mass conservation equation and converge synchronously during the global iterative solution process.

[0061] Establishment of cyclic ratio coupling constraint: High-voltage side cyclic ratio f HG and low-pressure side circulation ratio f SGIt is the core coupling quantity connecting the high and low pressure dual-path solution circulation. The two are related to each other through the mass conservation equation of the heat exchanger, and jointly constrain the mass distribution of each flow node in the whole system.

[0062] High-voltage side circulation ratio f HG The concentration difference (ω2-ω1) between the inlet and outlet of the high-pressure generator lithium bromide solution is determined by the ratio of this concentration to the inlet concentration ω1, as shown in formulas (31) and (33). ω1 is the mass fraction of the low-concentration lithium bromide solution flowing out after absorption by the high-pressure absorber, and ω2 is the mass fraction of the high-concentration lithium bromide solution flowing out after desorption by the high-pressure generator. The difference between the two is the venting range on the high-pressure side. HG The circulating mass of lithium bromide solution corresponding to each kilogram of refrigerant produced on the high-pressure side is a core parameter for determining the flow rate of each flow node on the high-pressure side (high-pressure generating pump flow rate, first heat exchanger flow rate, and high-pressure absorber flow rate).

[0063] Low-pressure side circulation ratio f SG The concentration difference (ω5-ω3) between the inlet and outlet lithium bromide solutions during the series generation process of the single-effect generator and the low-pressure generator is determined by the ratio of the inlet concentration ω3 to the inlet concentration ω5, as shown in formulas (31) and (34). ω3 is the mass fraction of the low-concentration lithium bromide solution flowing out after the low-pressure absorber completes absorption, and ω5 is the mass fraction of the high-concentration lithium bromide solution flowing out after the low-pressure generator completes desorption. The concentration change from ω3 to ω5 spans both the single-effect generator and the low-pressure generator generation processes. SG The overall desorption efficiency, which reflects the solution's reaction across the two stages of the low-pressure side process, is the core parameter for determining the flow rate nodes on the low-pressure side (low-pressure generating pump flow rate, second and third heat exchanger flow rates, and low-pressure absorber flow rate).

[0064] High-voltage side circulation ratio f HG and low-pressure side circulation ratio f SG The mass and energy conservation equations of the first, second, and third heat exchangers are interconnected: the three heat exchangers respectively handle heat transfer between the high-pressure and low-pressure solutions, ensuring that the circulation ratios of the two paths cannot change independently; a change in the circulation ratio on one side will affect the flow distribution on the other side through the heat exchanger equations. In the global iterative solution process, f... HG and f SG As a key convergence variable, it is iterated synchronously. Its convergence value directly determines the distribution of lithium bromide solution flow rate, concentration, and temperature at the 16 basic variable nodes of the whole system. It is a necessary constraint condition for closing the multivariable coupled equation system F(X)=0 of the whole system.

[0065] D4: Synchronous convergence during the global iterative solution process includes: rearranging the steady-state equilibrium equations of the entire system into residual functions of the core iterative state vectors; constructing the system Jacobian matrix with the current iterative state variables; solving the linearized correction equations to obtain the state variable correction vectors; and introducing a damping coefficient to control the correction step size. In each iteration, the current temperature and concentration state variables are substituted into the lithium bromide solution property equation to update the enthalpy and saturation temperature of each node. This process proceeds synchronously with the state variable corrections until the global convergence condition is met.

[0066] Implementation of the global simultaneous iterative convergence strategy: Since the thermodynamic properties of lithium bromide solution (enthalpy h, saturation temperature, phase equilibrium) are all highly nonlinear functions of lithium bromide mass fraction and temperature, the equations of each component are interconnected through flow rate, concentration, pressure, temperature and heat transfer rate, forming a multivariable strongly coupled nonlinear equation system.

[0067] Traditional sequential module methods solve each component in turn, requiring a large number of nested iterations and exhibiting poor convergence stability. This scheme adopts a global simultaneous iteration convergence strategy oriented towards solving simultaneous equations (i.e., the Newton-Raphson iteration method), which simultaneously solves F(X)=0 as shown in formula (44). This method has a quadratic convergence speed and can quickly solve the 16 basic state variables of the entire system while satisfying all equation constraints.

[0068] Specifically, the implementation steps of the global simultaneous iterative convergence strategy are as follows: The first step is to input the known parameters. These parameters include: cooling water inlet temperature and mass flow rate, cold water inlet temperature and mass flow rate, heat source medium inlet temperature and mass flow rate, and the heat transfer coefficient K (unit: W / (m³)) of each heat exchange component. 2 ·℃) and heat exchange area A (unit: m) 2 The above parameters remain unchanged during the iteration process and serve as boundary conditions for the system of equations.

[0069] The second step is to initialize the core iterative state vector X. 0 Based on engineering experience, reasonable initial values ​​are assigned to each state variable. These initial values ​​should satisfy the physical constraints of each variable: each pressure level satisfies P... k >P k＇ >P m >P o The lithium bromide solution concentration satisfies 0 < ω < 100%, and the cycle ratio satisfies f. HG >1 and f SG >1. The second law of thermodynamics requires that the temperature difference for heat transfer be positive.

[0070] The third step is to enter the iterative loop (k=0,1,2,…) until convergence. The specific steps of each iteration are as follows: a) Call the lithium bromide solution property calculation module, calculate the specific enthalpy h and saturation temperature of each state node according to the temperature and concentration values ​​in the current state variables, and ensure that the nonlinear properties of the lithium bromide solution are updated synchronously with the system equation constraints; b) Substitute the current state variables into the residual functions of each component, and calculate the global residual vector F(Xk) in the matrix form of formula (44); c) Determine the convergence condition - if ‖F(Xk)‖<ε or ‖ΔX‖<ε (ε is the preset convergence accuracy), then terminate. Iteration; d) Construct the system Jacobian matrix J(Xk) with the current state variables, where each element of the matrix is ​​the partial derivative of the residual function with respect to each state variable, and the numerical difference approximation is used for calculation; e) Solve the linearized correction equation system J(Xk)·ΔX=-F(Xk) to obtain the state variable correction vector ΔX; f) Introduce a damping coefficient λ∈(0,1] to control the correction step size, and update the state variables Xk+1=Xk+λ·ΔX. The damping control prevents iterative divergence caused by excessive correction step size under strong coupling of multiple variables.

[0071] The fourth step is post-processing. After iterative convergence, the system cooling capacity is calculated based on the converged solutions of each state node. Wrefri (The cooling capacity output by the evaporator to the chilled water system) is calculated using formulas to determine the hot water side heat exchange of the high-pressure generator, single-effect generator, and low-pressure generator. The refrigeration capacity per unit heat source mass flow rate (RCPMF, i.e., Refrigerating Capacity Perunit Mass Flow, the cooling capacity corresponding to a unit mass flow rate of hot water) is used as the evaluation index for large temperature difference cooling performance. The calculation formula is as follows: in Wrefri For cooling capacity, q 1 represents the inlet mass flow rate of the heat source medium. A higher RCPMF value means that less heat source water is consumed for the same cooling capacity, the system has a higher utilization rate of the heat source, and better cooling economy. By comparing the RCPMF with that of a single-effect circulating unit and a two-stage circulating unit, the performance advantages of this scheme under large temperature difference conditions on the heat source side are quantitatively verified.

[0072] Example 3 Reference Figure 4 - Figure 5 This is the third embodiment of the present invention.

[0073] Jiangsu Shuangliang Company and Changsha Yuanda Company are major manufacturers of lithium bromide chillers in China. This specification compares this invention with single-effect and two-stage chiller units produced by these two companies. The main parameters of the comparative units are shown in Table 1.

[0074] Table 1. Main parameters of single-effect and two-stage refrigeration units used for comparison.

[0075] During model calculations, the cooling capacity of the coupled system (STAC) designed in this invention ( W refri The hot water inlet temperature (t1) and other parameters were set to be the same as those for commercial products. The comparison results are as follows: Figure 4 - Figure 5 The figure above shows a comparison of the RCPMF values ​​between the composite system (STAC) designed in this invention and the four existing conventional absorption chillers listed in Table 1. Arranged from lowest to highest, the RCPMF values ​​of STAC are 134%, 295%, 313%, and 591% for BDH8.6XII (two-stage unit), RXZⅢ-ZH2M2 (two-stage unit), RXZH2A (single-effect unit), and BDH98-500 (single-effect unit), respectively. The RCPMF value of the chiller increases with the increase of the hot water inlet temperature t1. The results indicate that STAC has a higher water-saving rate at high heat source temperatures. In some applications with high water costs, such as geothermal water, using STAC as an air conditioning chiller has a significant economic advantage over current commercial absorption chillers.

[0076] Example 4 Reference Figures 2-3 This is the fourth embodiment of the present invention.

[0077] The above is a schematic scheme of an optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle. It should be noted that the technical solution of this single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization system belongs to the same concept as the technical solution of the aforementioned single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method. Details not described in detail in this embodiment of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization system can be found in the description of the aforementioned single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method.

[0078] This embodiment also provides a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization system, including: a heat drive sequence construction module, which connects the heat source medium in series through a single-effect generator, a low-pressure generator and a high-pressure generator, to drive the lithium bromide solution at each stage to desorb the refrigerant vapor respectively, forming a stepped heat drive generation sequence; The dual-circulation operation module has refrigerant vapors generated by the single-effect generator and the high-pressure generator, which are condensed by the single-effect condenser and the high-pressure condenser, respectively. The condensate is then combined and enters the evaporator to evaporate, outputting cooling capacity to the chilled water system. In the low-pressure side solution circulation module, after the lithium bromide solution in the low-pressure absorber is pressurized and heated, it enters the single-effect generator and the low-pressure generator in sequence for two-stage desorption and concentration. The concentrated solution is cooled and returned to the low-pressure absorber. The low-pressure absorber absorbs the refrigerant vapor generated by the evaporator, completing the low-pressure side circulation in the dual-path absorption-generation coupling architecture. In the high-pressure side solution circulation module, the lithium bromide solution in the high-pressure absorber is pressurized and heated before entering the high-pressure generator for desorption and concentration. The concentrated solution is then cooled and returned to the high-pressure absorber, which absorbs the refrigerant vapor generated by the low-pressure generator, thus completing the high-pressure side circulation in the dual-path absorption-generator coupling architecture.

[0079] The optimized single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle system includes a single-effect generator, a single-effect condenser, a high-pressure generator, a high-pressure condenser, a low-pressure generator, a high-pressure absorber, a low-pressure absorber, an evaporator, a first heat exchanger, a second heat exchanger, a third heat exchanger, a high-pressure generating pump, a low-pressure generating pump, an absorption pump, a refrigerant pump, a vacuum pump, a cooler, an oil blocker, a self-extraction device, regulating valves, solenoid valves, multiple manual valves, multiple temperature sensors (not shown), and multiple pressure sensors (not shown). Figure 3 As shown.

[0080] The system mainly consists of three water circulation systems, two solution circulation systems, and one solvent (which is also a refrigerant) circulation system. The water circulation systems mainly include hot water circulation, cooling water circulation, and cold water circulation. Figure 3 The solid purple line in the diagram represents the hot water flow. The hot water first enters the heat exchange tube (inside the tube) of the single-effect generator, then enters the heat exchange tube (inside the tube) of the low-pressure generator, then enters the heat exchange tube (inside the tube) of the high-pressure generator, and finally flows out from the heat exchange tube of the high-pressure generator. Figure 3 The dark blue solid line represents the cooling water flow path. The cooling water first enters the heat exchange tubes (inside the tubes) of the single-effect condenser, low-pressure absorber, and high-pressure absorber in parallel. After heat exchange, the cooling water in the low-pressure and high-pressure absorbers flows directly out of the unit. The cooling water in the single-effect condenser, after heat exchange, enters the heat exchange tubes (inside the tubes) of the high-pressure condenser, and then flows out after heat exchange. Figure 3 The light blue solid line in the image represents the cold water flow. Cold water enters the heat exchange tubes (inside the tubes) of the evaporator, exchanges heat, and then flows out.

[0081] The two solution circulation processes include high-pressure side solution circulation and low-pressure side solution circulation. In the high-pressure side solution circulation, the reservoir below the high-pressure absorber stores the lowest concentration lithium bromide solution (…). Figure 3(Represented in black), the solution is pumped into the high-pressure generator by a high-pressure pump, where it absorbs heat and heats up in the first heat exchanger. Water is desorbed from the heat exchange tubes of the high-pressure generator, and the concentration and temperature gradually increase. The solution, now with increased concentration, flows out from the bottom of the high-pressure generator and enters the first heat exchanger, where it releases heat and cools down before re-entering the high-pressure absorber, thus completing the high-pressure cycle. In the low-pressure side solution circulation, the storage tank at the bottom of the low-pressure absorber stores the lithium bromide solution with the highest concentration (…). Figure 3 (Indicated by orange), the solution is sequentially pumped into the second and third heat exchangers by a low-pressure pump. After absorbing heat and heating up, it first enters the single-effect generator, where the hot water temperature is highest. The solution desorbs water by spraying outside the single-effect generator tubes, gradually increasing the solution concentration and temperature. The increased concentration of the solution then flows from the bottom of the single-effect generator (…). Figure 3 (Indicated in orange-red) flows out and enters the third heat exchanger, where it releases heat and cools before entering the low-pressure generator. In the low-pressure generator, the temperature continues to rise and the concentration increases. The solution flows from the bottom of the low-pressure generator (…). Figure 3 The solution (shown in red) flows out and enters the second heat exchanger, where it releases heat and cools before entering the low-pressure absorber. In the low-pressure absorber, it absorbs water vapor from the evaporator, further cooling and reducing its concentration. This completes the low-pressure cycle. The low-pressure cycle on the solution side has one more occurrence process than the high-pressure cycle, equivalent to a multi-stage occurrence.

[0082] Solvent circulation mainly refers to the process where water vapor from the high-pressure generator and the single-effect generator enters the high-pressure condenser and the single-effect condenser respectively for condensation, and then the condensate flows into the evaporator to turn back into water vapor. Figure 3 In the diagram, the solid green line represents the solvent (condensate). The condensate from the bottom of the high-pressure condenser and the single-effect condenser flows in parallel into the bottom of the evaporator, and is then pressurized by the refrigerant pump before being sprayed. The vacuum pump, oil blocker, and self-extraction device are mainly used to remove non-condensable gases or leaked air from the unit. This is a standard design feature of lithium bromide absorption chillers, and the specific principles will not be elaborated here.

[0083] This embodiment also provides an electronic device suitable for optimizing a single-effect-two-stage coupled lithium bromide absorption cooling cycle with a large temperature difference, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to realize the optimization method for a single-effect-two-stage coupled lithium bromide absorption cooling cycle with a large temperature difference as proposed in the above embodiment.

[0084] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements the optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle as proposed in the above embodiments.

[0085] The storage medium proposed in this embodiment belongs to the same inventive concept as the optimization method for realizing a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle proposed in the above embodiments. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0086] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0087] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An optimization method for a single-effect, two-stage coupled lithium bromide absorption refrigeration cycle with a large temperature difference, characterized in that: This includes connecting the heat source medium in series through a single-effect generator, a low-pressure generator, and a high-pressure generator to drive the lithium bromide solution at each stage to desorb the refrigerant vapor, forming a cascade heat drive generation sequence; The refrigerant vapors generated by the single-effect generator and the high-pressure generator are condensed by the single-effect condenser and the high-pressure condenser, respectively. The condensate is then combined and enters the evaporator to evaporate, outputting cooling capacity to the chilled water system. After the lithium bromide solution in the low-pressure absorber is pressurized and heated, it enters the single-effect generator and the low-pressure generator in sequence for two-stage desorption and concentration. The concentrated solution is cooled and returned to the low-pressure absorber. The low-pressure absorber absorbs the refrigerant vapor generated by the evaporator, completing the low-pressure side cycle in the dual-path absorption-generation coupling architecture. The lithium bromide solution in the high-pressure absorber is pressurized and heated before entering the high-pressure generator for desorption and concentration. The concentrated solution is then cooled and returned to the high-pressure absorber, which absorbs the refrigerant vapor generated by the low-pressure generator, completing the high-pressure side cycle in the dual-path absorption-generator coupling architecture.

2. The optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle as described in claim 1, characterized in that: The formation of the cascade heat drive generation sequence includes: the heat source medium enters the tube of the single-effect generator from the high-temperature end and exchanges heat with the lithium bromide solution sprayed outside the tube; the lithium bromide solution desorbs refrigerant vapor under the corresponding pressure, and the solution concentration increases. After the heat source medium flows out of the tube of the single-effect generator, it enters the tube of the low-pressure generator and exchanges heat with the lithium bromide solution sprayed outside the tube. The lithium bromide solution desorbs the refrigerant vapor under the corresponding pressure, and the solution concentration further increases. After the heat source medium flows out of the low-pressure generator tube, it enters the high-pressure generator tube and exchanges heat with the lithium bromide solution sprayed outside the tube. The lithium bromide solution desorbs the refrigerant vapor under the corresponding pressure. After the solution concentration further increases, the heat source medium flows out from the low-temperature end of the high-pressure generator.

3. The optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle as described in claim 2, characterized in that: The lithium bromide solution in the low-pressure absorber is pressurized and heated before sequentially entering a single-effect generator and a low-pressure generator for two-stage desorption and concentration. The lithium bromide solution at the bottom of the low-pressure absorber is pressurized by the low-pressure generator pump, and then passes through the second and third heat exchangers in sequence to absorb heat and increase temperature. It enters the outside of the single-effect generator tube and exchanges heat with the heat source medium inside the tube in a spray manner. The lithium bromide solution desorbs refrigerant vapor in the single-effect generator, and the solution concentration increases. After the lithium bromide solution flows out from the bottom of the single-effect generator, it is cooled down by the third heat exchanger and enters the outside of the low-pressure generator tube. It exchanges heat with the heat source medium inside the tube by spraying. The lithium bromide solution desorbs the refrigerant vapor in the low-pressure generator, and the solution concentration increases further. After the lithium bromide solution flows out from the bottom of the low-pressure generator, it is cooled down by the second heat exchanger and returns to the low-pressure absorber, where it comes into contact with the refrigerant vapor from the evaporator for absorption. After the solution concentration decreases, it accumulates at the bottom of the low-pressure absorber.

4. The optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle as described in claim 3, characterized in that: After the lithium bromide solution in the high-pressure absorber is pressurized and heated, it enters the high-pressure generator for desorption and concentration. This includes the lithium bromide solution at the bottom of the high-pressure absorber being pressurized by a high-pressure pump, absorbing heat and heating through a first heat exchanger, entering the outside of the high-pressure generator tube and exchanging heat with the heat source medium inside the tube by spraying. The lithium bromide solution desorbs refrigerant vapor in the high-pressure generator, and the solution concentration increases. After the lithium bromide solution flows out from the bottom of the high-pressure generator, it is cooled down by the first heat exchanger and returns to the high-pressure absorber, where it comes into contact with the refrigerant vapor from the low-pressure generator for absorption. After the solution concentration decreases, it accumulates at the bottom of the high-pressure absorber.

5. The optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle as described in claim 4, characterized in that: It also includes establishing component-level steady-state equilibrium equations for mass conservation, lithium bromide composition conservation, and energy conservation for each heat exchange and mass transfer component in the refrigeration cycle. The high-pressure side circulation ratio and the low-pressure side circulation ratio are incorporated into the equation system as cross-cycle coupling iteration quantities, and together with the working pressure of each pressure level, they form the core iterative state vector, thus forming a multi-variable coupled equation system for the entire system. Using the core iterative state vector as the solution object, a global simultaneous iterative convergence strategy is adopted to solve the multivariate coupled equations of the entire system. In each iteration, the enthalpy value and saturation temperature of the lithium bromide solution at each node are updated synchronously until the global residual satisfies the convergence condition. Based on the convergence results, the cooling capacity per unit heat source mass flow rate is used as the evaluation index for large temperature difference refrigeration performance, and the performance of the refrigeration system is quantitatively evaluated.

6. The optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle as described in claim 5, characterized in that: The high-pressure side circulation ratio and the low-pressure side circulation ratio are used as cross-cycle coupling iteration quantities. The high-pressure side circulation ratio is determined by the ratio of the concentration difference of lithium bromide solution at the inlet and outlet of the high-pressure generator to the inlet concentration, reflecting the circulating mass of lithium bromide solution corresponding to the unit refrigerant output on the high-pressure side. The low-pressure side circulation ratio is determined by the ratio of the concentration difference between the inlet and outlet lithium bromide solutions during the series generation process of the single-effect generator and the low-pressure generator to the inlet concentration, reflecting the overall desorption efficiency of the two-stage generation process on the low-pressure side. The high-pressure side circulation ratio and the low-pressure side circulation ratio are interconnected through the heat exchanger mass conservation equation and converge synchronously during the global iterative solution process.

7. The optimization method for a single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle as described in claim 6, characterized in that: The synchronous convergence during the global iterative solution process includes: rearranging the steady-state equilibrium equations of the entire system into residual functions about the core iterative state vectors; constructing the system Jacobian matrix with the current iterative state variables; solving the linearized correction equations to obtain the state variable correction vectors; and introducing a damping coefficient to control the correction step size. In each iteration, the current temperature and concentration state variables are substituted into the lithium bromide solution property equation to update the enthalpy and saturation temperature of each node. This process proceeds synchronously with the state variable corrections until the global convergence condition is met.

8. A single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization system, based on the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method according to any one of claims 1 to 7, characterized in that: It also includes a heat drive sequence construction module, which connects the heat source medium in series through a single-effect generator, a low-pressure generator, and a high-pressure generator to drive the lithium bromide solution at each stage to desorb the refrigerant vapor, forming a cascade heat drive generation sequence; The dual-circulation operation module has refrigerant vapors generated by the single-effect generator and the high-pressure generator, which are condensed by the single-effect condenser and the high-pressure condenser, respectively. The condensate is then combined and enters the evaporator to evaporate, outputting cooling capacity to the chilled water system. In the low-pressure side solution circulation module, after the lithium bromide solution in the low-pressure absorber is pressurized and heated, it enters the single-effect generator and the low-pressure generator in sequence for two-stage desorption and concentration. The concentrated solution is cooled and returned to the low-pressure absorber. The low-pressure absorber absorbs the refrigerant vapor generated by the evaporator, completing the low-pressure side circulation in the dual-path absorption-generation coupling architecture. In the high-pressure side solution circulation module, the lithium bromide solution in the high-pressure absorber is pressurized and heated before entering the high-pressure generator for desorption and concentration. The concentrated solution is then cooled and returned to the high-pressure absorber, which absorbs the refrigerant vapor generated by the low-pressure generator, thus completing the high-pressure side circulation in the dual-path absorption-generator coupling architecture.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, it implements the steps of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements the steps of the single-effect-two-stage coupled lithium bromide absorption large temperature difference refrigeration cycle optimization method according to any one of claims 1 to 7.

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