Refrigeration liquid supply valve control method based on evaporator tube dryness prediction model

Abstract

The present invention relates to the technical field of refrigerant flow control in evaporator tubes, and more specifically, to a refrigeration liquid supply valve control method based on a dryness prediction model in evaporator tubes, for solving the problem that ammonia refrigeration systems in the prior art generally adopt a relatively high circulation ratio, cannot effectively reduce the filling amount of ammonia refrigerant, are difficult to ensure safe operation of the ammonia refrigeration system, and cannot improve the refrigeration effect of the evaporator; the present invention establishes a dryness prediction model, obtains relevant parameters of the dryness prediction model in the unit, converts the dryness prediction model into dryness changes in the evaporation tube under different refrigerant mass flow rates, and selects the optimal refrigerant mass flow rate, so that the ammonia liquid circulation ratio of the ammonia refrigeration system is lower than 1.2, can effectively reduce the filling amount of ammonia refrigerant, ensure the safe operation of the ammonia system, and can improve the refrigeration effect of the evaporator.

Description

Technical Field

[0001] The invention relates to the technical field of refrigerant flow control in an evaporator tube, and more specifically to a refrigeration liquid supply valve control method based on a dryness prediction model in an evaporator tube. Background Art

[0002] Ammonia is a high-quality refrigerant with excellent thermodynamic properties, zero ODP and GWP values, and other advantages. It is widely used in large and medium-sized cold storages in China. However, ammonia is toxic and flammable and explosive under certain conditions, posing a safety hazard to food and personnel, and has certain restrictions on its use. The potential hazard of the ammonia system is directly related to its charge volume. The "Cold Storage Design Code" stipulates that the total charge volume of ammonia refrigerant in a cold storage refrigeration system using ammonia refrigerant cannot exceed 40 tons. The "Identification of Major Hazard Sources of Dangerous Chemicals" stipulates that a refrigeration system with an ammonia charge of more than 10 tons is a major hazard source. Therefore, the ammonia charge volume of the ammonia refrigeration system must be accurately controlled to ensure the safe operation of the ammonia system.

[0003] The patent application with reference publication number CN116123769A discloses a flow control device of a refrigeration equipment and a refrigeration system, wherein the flow control device of the refrigeration equipment comprises at least one circuit, wherein the circuit comprises a liquid supply branch, a liquid return branch and a control module, wherein the liquid supply branch is connected between the output port of the refrigeration equipment and the device to be supplied with cold, and the liquid return branch is connected between the device to be supplied with cold and the input port of the refrigeration equipment, wherein the liquid supply branch comprises a control valve, and the liquid return branch comprises a flow detection module; the control module is electrically connected to the control valve and the flow detection module respectively, and the flow detection module is used to detect the actual flow value in the liquid return branch; in this embodiment, the control module is used to control the opening of the control valve according to the set flow value and the actual flow value, thereby realizing the flow control of each circuit; the flow control device of the refrigeration equipment is independent of the refrigeration equipment, and when the internal structure of the refrigeration equipment is not changed, it meets the different requirements of the number of circuits output by the refrigeration equipment to the outside, thereby improving the versatility of the refrigeration equipment;

[0004] However, the ammonia refrigeration system in the prior art generally adopts a higher circulation rate, which cannot effectively reduce the charge amount of ammonia refrigerant, makes it difficult to ensure the safe operation of the ammonia refrigeration system, and cannot improve the refrigeration effect of the evaporator; at the same time, it cannot achieve accurate control of the mass flow rate of ammonia liquid in the terminal heat exchanger under different load conditions.

[0005] To this end, we proposed a refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model to address the above problems. Summary of the invention

[0006] The purpose of the present invention is to provide a refrigeration liquid supply valve control method based on an evaporator tube dryness prediction model, which solves the problem that the ammonia refrigeration system in the prior art generally adopts a higher circulation rate, cannot effectively reduce the filling amount of ammonia refrigerant, is difficult to ensure the safe operation of the ammonia refrigeration system, and cannot improve the refrigeration effect of the evaporator; at the same time, it is impossible to accurately control the mass flow rate of ammonia liquid in the terminal heat exchanger under different load conditions.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model includes the following steps:

[0009] Step 1: Use the microelement method to divide the pipeline into several microelement segments, and input the pipeline structure parameters, air temperature t air , natural convection heat transfer coefficient of air on the pipe surface h air , the temperature of the refrigerant at the pipe inlet t e and dryness x e , and refrigerant mass flow rate G;

[0010] Step 2: Preset wall temperature t w0 , using the air side physical parameters to calculate the heat flux density q, and then get the heat transfer coefficient h TP and the total heat transfer coefficient K, based on which the heat transfer Q is calculated, and the actual wall temperature t is inferred through the heat balance principle w and iteratively adjust with the preset value until the accurate wall temperature t is obtained w ;

[0011] Step 3: Based on the accurate wall temperature t w , calculate the heat flux density q and heat transfer coefficient h again TP and the total heat transfer coefficient K, and then the heat exchange Q, the refrigerant outlet enthalpy h0 and the outlet dryness x0 are obtained;

[0012] Step 4: Use the outlet parameters of the current micro-element segment as the inlet parameters of the next micro-element segment, traverse the entire pipeline, obtain the refrigerant dryness distribution along the pipeline and the evaporator heat exchange, and select the refrigerant mass flow rate with an outlet dryness in the range of 0.98-1;

[0013] Step 5: According to the matching characteristics of the dryness prediction model, the mass flow corresponding to the outlet dryness close to 0.98 is taken as the target, and the control valve opening is initially set to 50%. The control valve is adjusted by the step method until the mass flow is close to the optimal value, thereby determining the optimal control valve opening under different loads.

[0014] As a preferred embodiment of the present invention, the outlet enthalpy and outlet dryness of the previous micro-element pipe segment are used as the inlet parameters of the next micro-element pipe segment for calculation. The input parameters of the dryness prediction model are the air temperature outside the pipe, the natural convection heat transfer coefficient of the air outside the pipe, the refrigerant temperature at the pipe inlet, and the mass flow rate of the refrigerant in the pipe. The output parameters of the dryness prediction model are the outlet dryness of each micro-element pipe segment, the cooling capacity, and the pipe outlet wall temperature.

[0015] As a preferred embodiment of the present invention, the heat flux q is calculated by the following formula:

[0016] q=h air (t w0 -t air );

[0017] The two-phase flow heat transfer coefficient on the inner surface of the evaporator tube is an important indicator for determining the outlet dryness and outlet enthalpy of the micro-element tube, which is expressed as:

[0018] h TP =ψh f ;

[0019] Among them, h f is the forced convection heat transfer in the tube, ψ is h TP With h f ratio.

[0020] As a preferred embodiment of the present invention, the most widely used correlation formula Ditus-Belt is used for forced convection heat exchange in the tube:

[0021]

[0022] Among them, G is the mass flow rate, x is the dryness, D is the inner diameter of the evaporation tube, μ f is the dynamic viscosity, Pr is the Prandtl number, k f is the thermal conductivity of the liquid;

[0023] When there is two-phase flow in the tube, the heat transfer is calculated using the Shah Chart recommended relationship. First, three dimensionless numbers are calculated:

[0024] Convective heat transfer parameters:

[0025] Where x is the dryness, ρ g is the gas phase density, ρ f is the liquid density;

[0026] Boiling heat transfer parameters:

[0027] Where q″ is the heat flux, G is the mass flow rate, H fg is the latent heat of vaporization;

[0028] Froude number:

[0029] Where G is the mass flow rate, ρ f is the liquid density, g is the acceleration due to gravity, and D is the inner diameter of the evaporation tube.

[0030] As a preferred embodiment of the present invention, based on the above calculation results, the specific process of calculating the parameter ψ is as follows:

[0031]

[0032] When N>1.0:

[0033]

[0034] At this time, ψ=max{ψ nb ,ψ cb};

[0035] When 0.1 <N≤1.0:ψ bε =FB0 0.5 exp(2.74N -0.15 );

[0036] When N≤0.1: ψ bε =FB0 0.5 exp(2.74N -0.1 );

[0037] At this time, ψ=max{ψ bε ,ψ cb};

[0038] The calculation formula of F in the above formula is:

[0039] As a preferred embodiment of the present invention, the total heat transfer coefficient of the evaporation micro-element tube section is expressed as:

[0040]

[0041] Where d0 is the outer diameter of the evaporation tube, d e is the inner diameter of the evaporator tube, and λ is the thermal conductivity of the evaporator tube.

[0042] As a preferred embodiment of the present invention, the heat transfer capacity of the micro-element pipe segment is expressed as:

[0043] φ=KA0(t f0 -t fe );

[0044] Where A0 is the outer area of ​​the pipe section, t f0 is the air temperature outside the evaporator, tfe is the refrigerant temperature in the evaporator tube.

[0045] As a preferred embodiment of the present invention, the outlet enthalpy value of the microelement pipe segment is expressed as:

[0046]

[0047] Where G is the mass flow rate, A is the cross-sectional area of ​​the pipe section, and h e is the inlet enthalpy of the pipe section;

[0048] The outlet dryness of the micro-element pipe section is expressed as:

[0049]

[0050] Wherein, h' is the enthalpy of the saturated liquid phase under the inlet conditions, and h" is the enthalpy of the saturated gas phase under the inlet conditions.

[0051] As a preferred embodiment of the present invention, the microelement method is used to establish a heat transfer model of ammonia refrigerant flowing in the evaporating tube, the microelement length of the pipeline is used as the calculation cycle step, the outlet thermal properties of the previous microelement are used as the inlet thermal properties of the next microelement, each microelement tube follows the principle of energy conservation, and the following model is established according to the heat exchange conditions:

[0052] Q=KA0Δt=KA0(t w- t air )=m(h0-h e );

[0053] Among them, Q is the heat exchange amount, A0 is the outer area of ​​the tube section, Δt is the temperature difference between the fluid inside and outside the evaporator tube, m is the mass flow rate of the refrigerant, h0 is the outlet enthalpy of the tube section, and h e is the inlet enthalpy of the pipe section;

[0054] Based on the confirmed heat transfer Q, the actual wall temperature is inferred through the heat balance formula:

[0055]

[0056] As a preferred embodiment of the present invention, it is applied to a refrigeration liquid supply valve control system based on an evaporator tube dryness prediction model, including a cloud management platform, a data acquisition module, a pipeline microelementization and parameter input module, a wall temperature iterative solution module, a refrigerant state and heat exchange calculation module, an along-the-way parameter traversal module and a control valve opening optimization module;

[0057] The data acquisition module collects ambient temperature data, control valve inlet and outlet pressure difference data, evaporator pipeline temperature data and refrigerant temperature data;

[0058] The pipeline microelementization and parameter input module divides the pipeline into multiple microelement segments by microelement method, and inputs pipeline structure, air temperature, heat transfer coefficient, refrigerant inlet state and mass flow rate;

[0059] The wall temperature iterative solution module solves the accurate wall temperature through an iterative method;

[0060] The refrigerant state and heat exchange calculation module calculates the heat exchange and the refrigerant outlet enthalpy and outlet dryness based on the accurate wall temperature;

[0061] The parameter traversal module along the pipeline obtains the refrigerant dryness distribution along the pipeline and the heat exchange of the evaporator, and selects the mass flow with appropriate outlet dryness;

[0062] The control valve opening optimization module sets the target flow rate according to the dryness-mass flow rate characteristics, the initial control valve opening is 50%, and the control valve opening is adjusted step by step to the optimum to determine the optimal control valve opening under different loads.

[0063] Compared with the prior art, the advantages of the present invention are:

[0064] (1) In the present invention, by establishing a dryness prediction model, the relevant parameters of the dryness prediction model in the unit are obtained, the dryness prediction model is converted into the dryness change in the evaporator tube under different refrigerant mass flow rates, and the optimal refrigerant mass flow rate is selected, so that the ammonia liquid circulation ratio of the ammonia refrigeration system is lower than 1.2, ensuring the safe operation of the ammonia system while saving costs;

[0065] (2) In the present invention, the dryness change of the evaporator pipeline under the conditions of different loads, different evaporation temperatures, different heat exchange temperature differences, and different liquid supply methods of the ammonia refrigeration cold storage is obtained through a dryness prediction model. The ammonia liquid circulation ratio of the ammonia refrigeration system is set to be lower than 1.2, and the optimal refrigerant mass flow rate under different load conditions is obtained. The control valve is adjusted until the mass flow rate is close to the optimal refrigerant mass flow rate, thereby obtaining the optimal opening under different loads. The data is stored in the cloud management platform. When the cold storage load changes, the cold storage system obtains the optimal opening of the control valve at this time from the cloud management platform according to the load change, adjusts the control valve, and accurately controls the refrigerant mass flow rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 This is a flow chart of the refrigeration liquid supply valve control method of the present invention;

[0067] Figure 2 is a system block diagram of the present invention;

[0068] Figure 3 It is a logical flow diagram of the present invention. DETAILED DESCRIPTION

[0069] The following will combine the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all the embodiments. All other embodiments obtained by ordinary technicians in this field without creative work based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0070] Embodiment 1: Figure 1 As shown, the refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model proposed by the present invention includes the following steps:

[0071] Step 1: Use the microelement method to divide the pipeline into several microelement segments, and input the pipeline structure parameters, air temperature t air , natural convection heat transfer coefficient of air on the pipe surface h air , the temperature of the refrigerant at the pipe inlet t e and dryness x e , and refrigerant mass flow rate G;

[0072] Step 2: Preset wall temperature t w0 , using the air side physical parameters to calculate the heat flux density q, and then get the heat transfer coefficient h TP and the total heat transfer coefficient K, based on which the heat transfer Q is calculated, and the actual wall temperature t is inferred through the heat balance principle w and iteratively adjust with the preset value until the accurate wall temperature t is obtained w ;

[0073] Step 3: Based on the accurate wall temperature t w , calculate the heat flux density q and heat transfer coefficient h again TP and the total heat transfer coefficient K, and then the heat exchange Q, the refrigerant outlet enthalpy h0 and the outlet dryness x0 are obtained;

[0074] Step 4: Use the outlet parameters of the current micro-element segment as the inlet parameters of the next micro-element segment, traverse the entire pipeline, obtain the refrigerant dryness distribution along the pipeline and the evaporator heat exchange, and select the refrigerant mass flow rate with an outlet dryness in the range of 0.98-1;

[0075] Step 5: According to the matching characteristics of the dryness prediction model, the mass flow corresponding to the outlet dryness close to 0.98 is taken as the target, the control valve opening is initially set to 50%, and the control valve is adjusted by the step method until the mass flow is close to the optimal value, thereby determining the optimal control valve opening under different loads;

[0076] The process steps for adjusting the control valve opening are as follows:

[0077] Set the target dryness to x 目标=0.98, set the initial control valve opening to 50%, determine different load conditions (for example: 30% load, 50% load, 100% load), and ensure that the flow, pressure and temperature instruments are calibrated and can be monitored in real time;

[0078] The dryness prediction model is established and calculated using the following formula:

[0079]

[0080] Where Q is the mass flow rate, K v is the flow coefficient of the control valve, △P is the upstream and downstream pressure difference of the control valve, P1 is the upstream pressure of the control valve, and P2 is the downstream pressure of the control valve;

[0081] Set the initial control valve opening to 50% and record the initial mass flow rate Q 初始 and dryness x 当前 , according to the relationship between dryness and mass flow, calculate the ideal mass flow Q 目标 , to achieve a dryness of 0.98;

[0082] Step adjustment process: set the opening change for each adjustment, for example 5%;

[0083] If the current dryness is lower than the target dryness, increase the control valve opening (e.g., increase the opening by 5%);

[0084] If the current dryness is higher than the target dryness, reduce the control valve opening (e.g., reduce the opening by 5%);

[0085] Wait for a while (e.g. 20 seconds) to ensure that the system reaches a new stable state;

[0086] Measure the current mass flow rate Q again 当前 and dryness x 当前 ;

[0087] Compare target flow and current flow:

[0088] If the absolute value of the difference between the current flow rate and the target flow rate and the absolute value of the difference between the current dryness and the target dryness are both within the acceptable range (e.g. <0.01), stop adjusting;

[0089] If it is not reached, it will return to continue adjusting and record the valve opening and flow information after each adjustment;

[0090] Repeat the control valve opening adjustment process under each load condition (e.g., 30%, 50%, 100% load) to determine the optimal control valve opening and corresponding mass flow rate in each case;

[0091] Summarize the best opening and mass flow under different load conditions and compare them with the target. Analyze the relationship between flow and dryness based on the collected data to determine the best working area. Adjust the parameters of the dryness prediction model based on actual operation feedback to improve the accuracy of the model. Record all the data obtained, including the best valve opening, mass flow and system stability information under each load;

[0092] The outlet enthalpy and outlet dryness of the previous micro-element pipe section are used as the inlet parameters of the next micro-element pipe section for calculation. The input parameters of the dryness prediction model are the air temperature outside the pipe, the natural convection heat transfer coefficient of the air outside the pipe, the refrigerant temperature at the pipe inlet, and the mass flow rate of the refrigerant in the pipe. The output parameters of the dryness prediction model are the outlet dryness, cooling capacity, and pipe outlet wall temperature of each micro-element pipe section.

[0093] The outlet enthalpy and outlet dryness calculated from the previous micro-element pipe segment are used as the inlet parameters of the next micro-element pipe segment. The calculation steps of the micro-element pipe are repeated to obtain the outlet enthalpy and outlet dryness of the micro-element pipe segment. This calculation is continued until the last micro-element pipe, and the dryness prediction model of the evaporation pipe is obtained by fitting the node dryness.

[0094] Embodiment 2: The technical solution of the embodiment of the present invention is different from that of embodiment 1 in that:

[0095] like Figure 2 As shown, the heat flux q is calculated by the following formula:

[0096] q=h air (t w0- t air );

[0097] The two-phase flow heat transfer coefficient on the inner surface of the evaporator tube is an important indicator for determining the outlet dryness and outlet enthalpy of the micro-element tube, which is expressed as:

[0098] h TP =ψh f ;

[0099] Among them, h f is the forced convection heat transfer in the tube, ψ is h TP With h f The ratio of

[0100] For forced convection heat transfer in tubes, the most widely used correlation is Ditus-Belt:

[0101]

[0102] Among them, G is the mass flow rate, x is the dryness, D is the inner diameter of the evaporation tube, μ f is the dynamic viscosity, Pr is the Prandtl number, k f is the thermal conductivity of the liquid;

[0103] When there is two-phase flow in the tube, the heat transfer is calculated using the Shah Chart recommended relationship. First, three dimensionless numbers are calculated:

[0104] Convective heat transfer parameters:

[0105] Where x is the dryness, ρ g is the gas phase density, ρ f is the liquid density;

[0106] Boiling heat transfer parameters:

[0107] Where q″ is the heat flux, G is the mass flow rate, H fg is the latent heat of vaporization;

[0108] Froude number:

[0109] Where G is the mass flow rate, ρ f is the liquid density, g is the gravitational acceleration, and D is the inner diameter of the evaporation tube;

[0110] Based on the above calculation results, the specific process of calculating the parameter ψ is as follows:

[0111]

[0112] When N>1.0:

[0113]

[0114] At this time, ψ=max{ψ nb ,ψ cb};

[0115] When 0.1 <N≤1.0:ψ bε =FB0 0.5 exp(2.74N -0.15 );

[0116] When N≤0.1: ψ bε =FB0 0.5 exp(2.74N -0.1 );

[0117] At this time, ψ=max{ψ bε ,ψ cb};

[0118] The calculation formula of F in the above formula is:

[0119] The total heat transfer coefficient of the evaporation micro-element tube section is expressed as:

[0120]

[0121] Where d0 is the outer diameter of the evaporation tube, d e is the inner diameter of the evaporation tube, λ is the thermal conductivity of the evaporation tube;

[0122] The structural parameters of the evaporation tube and the convection heat transfer coefficient of the air outside the tube are given. Therefore, the total heat transfer coefficient is only related to the heat transfer coefficient inside the tube. By calculating the heat transfer coefficient inside the micro-element tube, the total heat transfer coefficient of the micro-element tube can be obtained, and then the heat transfer capacity of the micro-element tube can be calculated.

[0123] The heat transfer of the micro-element pipe section is expressed as:

[0124] φ=KA0(t f0 -t fe );

[0125] Where A0 is the outer area of ​​the pipe section, t f0 is the air temperature outside the evaporator, t fe is the refrigerant temperature in the evaporator tube;

[0126] The refrigerant temperature in the evaporating tube and the air temperature outside the tube are both given. Therefore, the heat transfer of the micro-element tube is only related to the total heat transfer coefficient. By calculating the total heat transfer coefficient of the micro-element tube, the heat transfer of the micro-element tube can be obtained, and then the outlet enthalpy and outlet dryness of the micro-element tube can be calculated.

[0127] The outlet enthalpy of the microelement pipe section is expressed as:

[0128]

[0129] Where G is the mass flow rate, A is the cross-sectional area of ​​the pipe section, and h e is the inlet enthalpy of the pipe section;

[0130] The outlet dryness of the micro-element pipe section is expressed as:

[0131]

[0132] Wherein, h' is the enthalpy of the saturated liquid phase under the inlet conditions, and h" is the enthalpy of the saturated gas phase under the inlet conditions;

[0133] The outlet enthalpy of the micro-element tube is calculated according to the law of energy conservation, and the outlet dryness of the micro-element tube is calculated according to the latent heat of vaporization under the refrigerant inlet conditions;

[0134] The heat transfer model of ammonia refrigerant flowing in the evaporator tube is established by using the microelement method. The length of the pipeline microelement is used as the calculation cycle step, and the outlet thermal properties of the previous microelement are used as the inlet thermal properties of the next microelement. Each microelement tube follows the principle of energy conservation. The following model is established according to the heat exchange conditions:

[0135] Q=KA0Δt=KA0(t w- t air )=m(h0-h e );

[0136] Among them, Q is the heat exchange amount, A0 is the outer area of ​​the tube section, Δt is the temperature difference between the fluid inside and outside the evaporator tube, m is the mass flow rate of the refrigerant, h0 is the outlet enthalpy of the tube section, and h e is the inlet enthalpy of the pipe section;

[0137] Air flows over the surface of the evaporator tube. Due to the temperature difference between the air and the refrigerant in the tube, heat is continuously transferred from the air to the tube wall and then to the refrigerant. In this process, the temperature of the air outside the tube and the tube wall decreases, while the refrigerant in the tube gradually changes to a two-phase flow due to the absorption of heat. Along the flow direction of the refrigerant, the enthalpy value of the refrigerant gradually increases. The heat exchange and outlet enthalpy value of the microelement tube are calculated by energy conservation.

[0138] Based on the confirmed heat transfer Q, the actual wall temperature is inferred through the heat balance formula:

[0139]

[0140] It is applied to the refrigeration liquid supply valve control system based on the evaporator tube dryness prediction model, including cloud management platform, data acquisition module, pipeline microelementization and parameter input module, wall temperature iterative solution module, refrigerant state and heat exchange calculation module, along-the-process parameter traversal module and control valve opening optimization module;

[0141] The data acquisition module collects ambient temperature data, control valve inlet and outlet pressure difference data, evaporator pipeline temperature data and refrigerant temperature data;

[0142] The data acquisition module collects ambient temperature data, control valve inlet and outlet pressure difference data, evaporator pipe temperature data and refrigerant temperature data, stores historical data through the cloud management platform, and simultaneously stores the refrigerant mass flow rate and corresponding valve opening size of the evaporator pipe when the optimal outlet dryness is reached under different loads;

[0143] Pipeline microelementization and parameter input module: the pipeline is divided into multiple microelement segments by microelement method, and the pipeline structure, air temperature, heat transfer coefficient, refrigerant inlet state and mass flow rate are input;

[0144] The wall temperature iterative solution module uses the iterative method to solve the accurate wall temperature;

[0145] Refrigerant state and heat transfer calculation module, based on accurate wall temperature, calculates heat transfer and refrigerant outlet enthalpy and outlet dryness;

[0146] The parameter traversal module along the pipeline obtains the refrigerant dryness distribution along the pipeline and the heat exchange of the evaporator, and selects the mass flow with appropriate outlet dryness;

[0147] The control valve opening optimization module sets the target flow rate according to the dryness-mass flow characteristics, the initial control valve opening is 50%, and the control valve opening is adjusted step by step to the optimum to determine the optimal control valve opening under different loads;

[0148] The cloud management platform is connected to the data acquisition module, the control valve opening optimization module, the pipeline minimization and parameter input module and the along-process parameter traversal module in a one-way communication manner. The pipeline minimization and parameter input module is connected to the wall temperature iterative solution module in a one-way communication manner. The wall temperature iterative solution module is connected to the refrigerant state and heat exchange calculation module in a one-way communication manner. The refrigerant state and heat exchange calculation module is connected to the along-process parameter traversal module in a one-way communication manner.

[0149] Working principle of the present invention: When in use, in the present invention, by establishing a dryness prediction model, relevant parameters of the dryness prediction model in the unit are obtained, the dryness prediction model is converted into the dryness change in the evaporator tube under different refrigerant mass flow rates, and the optimal refrigerant mass flow rate is selected, so that the ammonia liquid circulation ratio of the ammonia refrigeration system is lower than 1.2, ensuring the safe operation of the ammonia system while saving costs, and obtaining the dryness change of the evaporator pipeline under different loads, different evaporation temperatures, different heat exchange temperature differences, and different liquid supply methods of the ammonia refrigeration cold storage through the dryness prediction model, with the ammonia liquid circulation ratio of the ammonia refrigeration system being lower than 1.2 as the goal, obtaining the optimal refrigerant mass flow under different load conditions, adjusting the control valve until the mass flow rate is close to the optimal refrigerant mass flow rate, thereby obtaining the optimal opening under different loads, and storing the data in the cloud management platform. When the cold storage load changes, the cold storage system obtains the optimal opening of the control valve at this time from the cloud management platform according to the load change, adjusts the control valve, and accurately controls the refrigerant mass flow rate.

[0150] The above are only preferred specific implementation modes of the present invention; however, the protection scope of the present invention is not limited thereto; any technician familiar with the technical field within the technical scope disclosed by the present invention; any equivalent replacement or change based on the technical solution and improved concept of the present invention shall be covered within the protection scope of the present invention.

Claims

1. A refrigeration liquid supply valve control method based on an evaporator tube dryness prediction model, characterized in that: The following steps are involved: Step 1: Use the microelement method to divide the pipeline into several microelement segments, and input the pipeline structure parameters, air temperature t air , natural convection heat transfer coefficient of air on the pipe surface h air , the temperature of the refrigerant at the pipe inlet t e and dryness x e , and refrigerant mass flow rate G; Step 2: Preset wall temperature t w0 , using the air side physical parameters to calculate the heat flux density q, and then get the heat transfer coefficient h TP and the total heat transfer coefficient K, based on which the heat transfer Q is calculated, and the actual wall temperature t is inferred through the heat balance principle w and iteratively adjust with the preset value until the accurate wall temperature t is obtained w ; Step 3: Based on the accurate wall temperature t w , calculate the heat flux density q and heat transfer coefficient h again TP and the total heat transfer coefficient K, and then the heat exchange Q, the refrigerant outlet enthalpy h0 and the outlet dryness x0 are obtained; Step 4: Use the outlet parameters of the current micro-element segment as the inlet parameters of the next micro-element segment, traverse the entire pipeline, obtain the refrigerant dryness distribution along the pipeline and the evaporator heat exchange, and select the refrigerant mass flow rate with an outlet dryness in the range of 0.98-1; Step 5: According to the matching characteristics of the dryness prediction model, the mass flow corresponding to the outlet dryness close to 0.98 is taken as the target, and the control valve opening is initially set to 50%. The control valve is adjusted by the step method until the mass flow is close to the optimal value, thereby determining the optimal control valve opening under different loads.

2. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to claim 1 is characterized in that: The outlet enthalpy and outlet dryness of the previous micro-element pipe segment are used as the inlet parameters of the next micro-element pipe segment for calculation. The input parameters of the dryness prediction model are the air temperature outside the pipe, the natural convection heat transfer coefficient of the air outside the pipe, the refrigerant temperature at the pipe inlet, and the mass flow rate of the refrigerant in the pipe. The output parameters of the dryness prediction model are the outlet dryness, cooling capacity, and pipe outlet wall temperature of each micro-element pipe segment.

3. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to claim 1 is characterized in that: The heat flux q is calculated by the following formula: q=h air (t w0- t air ); The two-phase flow heat transfer coefficient on the inner surface of the evaporator tube is an important indicator for determining the outlet dryness and outlet enthalpy of the micro-element tube, which is expressed as: h TP =ψh f ; Among them, h f is the forced convection heat transfer coefficient in the tube, ψ is h TP With h f ratio.

4. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to claim 3 is characterized in that: For the forced convection heat transfer coefficient in the tube, the most widely used correlation Ditus-Belt is used: Among them, G is the mass flow rate, x is the dryness, D is the inner diameter of the evaporation tube, μ f is the dynamic viscosity, Pr is the Prandtl number, k f is the thermal conductivity of the liquid; When there is two-phase flow in the tube, the heat transfer is calculated using the Shah Chart recommended relationship. First, three dimensionless numbers are calculated: Convective heat transfer parameters: Where x is the dryness, ρ g is the gas phase density, ρ f is the liquid density; Boiling heat transfer parameters: Where q″ is the heat flux, G is the mass flow rate, H fg is the latent heat of vaporization; Floating Point Number: Where G is the mass flow rate, ρ f is the liquid density, g is the acceleration due to gravity, and D is the inner diameter of the evaporation tube.

5. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to claim 4 is characterized in that: Based on the above calculation results, the specific process of calculating the parameter ψ is as follows: When N>1.0: At this time, ψ=max{ψ nb ,ψ cb }; When 0.1 <N≤1.0:ψ bε =FB0 0.5 exp(2.74N -0.15 ); When N≤0.1: ψ bε =FB0 0.5 exp(2.74N -0.1 ); At this time, ψ=max{ψ bε ,ψ cb }; The calculation formula of F in the above formula is:

6. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to claim 5 is characterized in that: The total heat transfer coefficient of the evaporation micro-element tube section is expressed as: Where d0 is the outer diameter of the evaporation tube, d e is the inner diameter of the evaporator tube, and λ is the thermal conductivity of the evaporator tube.

7. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to claim 6 is characterized in that: The heat transfer of the micro-element pipe section is expressed as: φ=KA0(t f0 -t fe ); Where A0 is the outer area of ​​the pipe section, t f0 is the air temperature outside the evaporator tube, t fe is the refrigerant temperature in the evaporator tube.

8. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to claim 7 is characterized in that: The outlet enthalpy of the microelement pipe section is expressed as: Among them, φ is the heat transfer of the micro-element pipe section, G is the mass flow rate, A is the cross-sectional area of ​​the pipe section, and h e is the inlet enthalpy of the pipe section; The outlet dryness of the micro-element pipe section is expressed as: Wherein, h' is the enthalpy of the saturated liquid phase under the inlet conditions, and h" is the enthalpy of the saturated gas phase under the inlet conditions.

9. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to claim 8 is characterized in that: The heat transfer model of ammonia refrigerant flowing in the evaporator tube is established by using the microelement method. The length of the pipeline microelement is used as the calculation cycle step, and the outlet thermal properties of the previous microelement are used as the inlet thermal properties of the next microelement. Each microelement tube follows the principle of energy conservation. The following model is established according to the heat exchange conditions: Q=KA0Δt=KA0(t w- t air )=m(h0-h e ); Among them, Q is the heat exchange amount, A0 is the outer area of ​​the tube section, Δt is the temperature difference between the fluid inside and outside the evaporator tube, m is the mass flow rate of the refrigerant, h0 is the outlet enthalpy of the tube section, and h e is the inlet enthalpy of the pipe section; Based on the confirmed heat transfer Q, the actual wall temperature is inferred through the heat balance formula:

10. The refrigeration liquid supply valve control method based on the evaporator tube dryness prediction model according to any one of claims 1 to 9, characterized in that: It is applied to the refrigeration liquid supply valve control system based on the evaporator tube dryness prediction model, including cloud management platform, data acquisition module, pipeline microelementization and parameter input module, wall temperature iterative solution module, refrigerant state and heat exchange calculation module, along-the-process parameter traversal module and control valve opening optimization module; The data acquisition module collects ambient temperature data, control valve inlet and outlet pressure difference data, evaporator pipeline temperature data and refrigerant temperature data; The pipeline microelementization and parameter input module divides the pipeline into multiple microelement segments by microelement method, and inputs pipeline structure, air temperature, heat transfer coefficient, refrigerant inlet state and mass flow rate; The wall temperature iterative solution module solves the accurate wall temperature through an iterative method; The refrigerant state and heat exchange calculation module calculates the heat exchange and the refrigerant outlet enthalpy and outlet dryness based on the accurate wall temperature; The parameter traversal module along the pipeline obtains the refrigerant dryness distribution along the pipeline and the heat exchange of the evaporator, and selects the mass flow with appropriate outlet dryness; The control valve opening optimization module sets the target flow rate according to the dryness-mass flow rate characteristics, the initial control valve opening is 50%, and the control valve opening is adjusted step by step to the optimum to determine the optimal control valve opening under different loads.

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