A flow heat transfer experiment system of a CO2 / H2O phase change composite working medium printed circuit board heat exchanger

Abstract

The application belongs to the field of phase change composite working medium printed circuit board heat exchanger, and discloses a CO2 / H2O phase change composite working medium printed circuit board heat exchanger flow heat transfer experiment system, which comprises a carbon dioxide circulating unit, a high-pressure water circulating unit and a cooling water circulating unit which are coupled with each other, and the internal structure of the units and the arrangement mode thereof are improved and designed. Through the application, given adjustable temperature and pressure can be provided for the cold and hot circuits of the printed circuit board heat exchanger to be tested, the flow of different working media can be adjusted and fully mixed in a gas mixer to realize stable and accurate control of the component proportion of the composite working medium; in addition, the experiment system has high testing precision, the working pressure can reach 4 MPa, the application range is wide, the flow and heat transfer performance of the phase change composite working medium of the printed circuit board heat exchanger with different flow channel structures can be tested, and thus the experiment system is suitable for providing data support and technical verification for condenser design.

Description

Technical Field

[0001] This invention belongs to the field of phase change composite working fluid printed circuit board heat exchangers, and more specifically, relates to a flow heat transfer experimental system for a CO2 / H2O phase change composite working fluid printed circuit board heat exchanger. Background Technology

[0002] The semi-closed supercritical Brayton cycle, an advanced thermodynamic cycle system, typically uses natural gas or coal-derived syngas as fuel, and employs the combustion products of carbon dioxide and a small amount of water directly as the working fluid. Due to its clean and efficient heat-to-work conversion characteristics, this cycle technology is considered one of the most promising technological directions in the field of thermal power generation. Among them, the Allam cycle, a representative of semi-closed supercritical Brayton cycle systems, can achieve turbine inlet temperatures of 1100°C–1200°C, a maximum cycle pressure of approximately 30 MPa, and a turbine outlet pressure of approximately 3 MPa. During this cycle, water vapor in the working fluid can be separated from the gas phase after condensation and cooling. The obtained carbon dioxide can directly meet the purity requirements for carbon capture without additional complex processing, thus providing a feasible technical path to achieve net-zero carbon emissions at the system level.

[0003] Given the stringent requirements of semi-closed supercritical carbon dioxide Brayton cycles for system compactness and pressure resistance, printed circuit board heat exchangers (PCHEs), as compact heat exchangers with excellent heat transfer performance and high efficiency, are considered the most promising heat exchange equipment for regenerators, coolers, and waste heat recovery devices in this cycle system. They can withstand a maximum pressure of 60 MPa, a maximum temperature of 900°C, and a heat exchange efficiency of over 90%. Moreover, under the same heat load and pressure drop, the volume of a PCHE is only 1 / 6 to 1 / 4 of that of a traditional shell-and-tube heat exchanger.

[0004] However, further research shows that under the actual operating conditions of the aforementioned cycle, the working fluid is not a single pure carbon dioxide fluid, but a complex of carbon dioxide and water, with the molar fraction of water at the turbine outlet being approximately 3% to 10%. As the heat exchange process proceeds, the water component in the complex is highly susceptible to condensation and phase change as the temperature drops below the dew point, resulting in a complex thermohydraulic process involving both gas-liquid two-phase flow and phase change heat transfer. This heat transfer mechanism involving a composite working fluid with partial component phase change is extremely complex, and its heat transfer coefficient, flow resistance, and gas-liquid distribution characteristics directly determine the thermodynamic design accuracy and operational safety threshold of the printed circuit board heat exchanger.

[0005] Currently, due to the technical difficulties, safety risks, and limitations of measurement methods in constructing experimental rigs for high-temperature, high-pressure composite working fluids, research on the flow and heat transfer characteristics within PCHEs (Printed Circuit Sheets) both domestically and internationally mainly relies on numerical simulation and theoretical analysis. Regarding the local condensation characteristics, two-phase pressure drop evolution, and system dynamic response characteristics of CO2 / H2O composite working fluids in printed circuit board heat exchangers with different etched flow channel structures, existing technologies still lack a dedicated experimental research scheme capable of achieving precise control of component ratios, stable input of operating parameters, and high-precision data acquisition capabilities.

[0006] Accordingly, further research and improvements are urgently needed in this field to better meet the comprehensive performance testing needs of CO2 / H2O composite working fluid printed circuit board heat exchangers in scenarios such as semi-closed supercritical carbon dioxide Brayton cycles. Summary of the Invention

[0007] To address one or more of the above-mentioned deficiencies or improvement needs in the prior art, this invention provides a flow heat transfer experimental system for a CO2 / H2O phase change composite working fluid printed circuit board heat exchanger. By re-studying and redesigning the overall structure, layout, and operating mechanism of the experimental system, it can provide a given adjustable temperature and pressure for the hot and cold circuits of the printed circuit board heat exchanger under test. Furthermore, by adjusting the flow rates of different working fluids and performing thorough mixing, it can achieve stable and precise control of the composite working fluid component ratio, thus effectively solving the technical pain point of the lack of such experimental devices in the prior art. Furthermore, the experimental system of this invention has high testing accuracy, an operating pressure of up to 4MPa, and a wide range of applications. It can conduct flow and heat transfer performance tests on phase change composite working fluids in printed circuit board heat exchangers with different flow channel structures. Therefore, it is particularly suitable for providing data support and technical verification for the design of condensers such as semi-closed supercritical carbon dioxide Brayton cycles.

[0008] To achieve the above objectives, according to the present invention, a flow heat transfer experimental system for a CO2 / H2O phase change composite working fluid printed circuit board heat exchanger is provided, comprising a carbon dioxide circulation unit, a high-pressure water circulation unit, and a cooling water circulation unit coupled to each other, characterized in that: The carbon dioxide circulation unit includes a low-pressure gas storage tank, a compressor, a high-pressure gas storage tank, a gas heater, a gas mixer, a cooler, a primary gas-liquid separator, and a secondary gas-liquid separator. The low-pressure gas storage tank stores pure CO2 at a first atmospheric pressure, and its fluid output is connected to the compressor and then controllably to the gas heater. The high-pressure gas storage tank stores pure CO2 at a second atmospheric pressure, which is higher than the first atmospheric pressure, and its port is connected to the pipeline between the compressor and the gas heater. The fluid output from the gas heater is mixed with fluid from the high-pressure water circulation unit... The fluids of the unit are combined into a composite working fluid in the gas mixer, and the fluid output end of the gas mixer is controllably connected to the hot-side fluid input end of the printed circuit board heat exchanger, which is the object of detection. At the same time, the hot-side fluid output end of the printed circuit board heat exchanger is controllably connected to the hot-side fluid input end of the cooler. In addition, the hot-side fluid output end of the cooler is connected to the gas input end of the first-stage gas-liquid separator, the gas output end of the first-stage gas-liquid separator is connected to the gas input end of the second-stage gas-liquid separator, and the gas output end of the second-stage gas-liquid separator is connected to the fluid recovery end of the low-pressure gas storage tank. The high-pressure water circulation unit includes a high-pressure pump, a high-pressure water buffer tank, and a liquid heater. The high-pressure pump obtains fluid from the low-pressure pump of the cooling water circulation unit, and its fluid output is controllably connected to the liquid heater. The port of the high-pressure water buffer tank is connected to the pipeline between the high-pressure pump and the liquid heater. The liquid heater heats the input fluid, and its output fluid is combined with the fluid from the carbon dioxide circulation unit in the gas mixer to form a composite working fluid. The cooling water circulation unit includes a cooling water tank and a low-pressure pump. The cooling water tank is used to store pure water, and its outlet is connected to the low-pressure pump. The fluid output by the low-pressure pump flows controllably to the cold-side fluid inlet of the printed circuit board heat exchanger, the cold-side fluid inlet of the cooler, and the fluid inlet of the high-pressure pump. The cold-side output fluid of the printed circuit board heat exchanger and the cold-side output fluid of the cooler merge and are connected to the cooling water tank. Furthermore, for the gas heater, a first temperature sensor is provided upstream, and a second temperature sensor is provided downstream; for the liquid heater, a sixth temperature sensor is provided upstream, and a second pressure sensor, a seventh temperature sensor, and a second volumetric flow meter are provided downstream; for the printed circuit board heat exchanger, a third temperature sensor, a first volumetric flow meter, and a first pressure sensor are provided at its hot-side fluid inlet, and a fourth temperature sensor and a differential pressure sensor are provided at its hot-side fluid outlet; simultaneously, an eighth temperature sensor and a third pressure sensor are provided at its cold-side fluid inlet, and a ninth temperature sensor, a fourth pressure sensor, and a third volumetric flow meter are provided at its cold-side fluid outlet; for the secondary gas-liquid separator, a fifth temperature sensor is provided at its gas outlet. In this way, after the above experimental system is started, the ratio of carbon dioxide to water in the composite working fluid can be controlled and the output can be stabilized. At the same time, multiple thermal-hydraulic parameters of the composite working fluid in the printed circuit board heat exchanger can be obtained comprehensively.

[0009] As a further preferred embodiment of the present invention, the above-mentioned experimental system preferably further includes a sampler for sampling the components of the composite working fluid, and then determining the proportion of water vapor in the composite working fluid by a drying and weighing method.

[0010] As a further preferred embodiment of the present invention, the above-mentioned experimental system preferably further includes a data acquisition computer, which is connected to the first to ninth temperature sensors, the first to fourth pressure sensors, the first to third volume flow meters, and the differential pressure sensor, and processes the acquired data.

[0011] As a further preferred embodiment of the present invention, the gas heater and the gas heater are preferably in the form of a pipeline electric heater, and they are controlled by PID according to the set temperature.

[0012] As a further preferred embodiment of the present invention, the liquid output end of the primary gas-liquid separator is connected to the liquid output end of the secondary gas-liquid separator through a pipeline and is connected to the atmosphere through a first drain valve; in addition, a second drain valve is provided at the bottom of the low-pressure gas storage tank and is connected to the atmosphere.

[0013] As a further preferred embodiment of the present invention, a first check valve is provided between the compressor and the high-pressure gas storage tank to prevent backflow of fluid in the high-pressure gas storage tank; in addition, a second check valve is provided downstream of the high-pressure pump to prevent backflow of fluid in the high-pressure water buffer tank.

[0014] As a further preferred embodiment of the present invention, the low-pressure pump and the printed circuit board heat exchanger are connected by a first check valve and a valve G, wherein the upstream lead-out circuit of the first check valve is connected to the upstream of the cooling water tank through a valve H, and the low-pressure pump and the cooler are connected through a valve I, thereby controlling the cold side fluid flow rate of the printed circuit board heat exchanger in a coordinated manner through the valve G and the valve H. In addition, a second check valve is provided upstream of the high-pressure pump, and a valve E connecting to the environment is provided on the pipeline downstream of the fluid output end of the liquid heater. A circuit is led out downstream of the high-pressure water buffer tank and connected to the upstream of the second check valve. This circuit is controlled by valve D.

[0015] As a further preferred embodiment of the present invention, a pipeline is provided between the high-pressure gas storage tank and the gas heater, connecting to the low-pressure gas storage tank, and a valve A is provided on this pipeline; a valve B is provided upstream of the gas heater; in addition, a bypass is provided between the gas mixer and the printed circuit board heat exchanger, connecting to the sampler, and a main route between the gas mixer and the printed circuit board heat exchanger is connected by a valve C; the liquid heater is connected to the gas mixer via a valve F.

[0016] As a further preferred embodiment of the present invention, the above-described experimental system is used in scenarios such as a semi-closed supercritical carbon dioxide Brayton cycle.

[0017] In summary, the technical solutions conceived by this invention have the following main technical advantages compared with the prior art: (1) The experimental system designed in this invention re-studies and designs the overall structure and its arrangement, operating mechanism and other aspects, and can conduct flow and heat transfer performance tests of printed circuit board heat exchangers with different flow channel structures in a way that has high testing accuracy and wide applicability; accordingly, it fills the gap in the prior art of lacking such a dedicated experimental solution, and provides a more reliable experimental verification means for the design verification and optimization of heat exchange equipment; (2) The experimental system designed in this invention has heating and temperature control devices set independently upstream of the gas mixer by the carbon dioxide circulation unit and the high-pressure water circulation unit, and combined with flow regulation means, which can achieve precise control and stable output of the ratio of carbon dioxide and water in the composite working medium; compared with the scheme of directly heating the premixed working medium in the prior art, this invention effectively avoids the interference of the component ratio caused by uneven heating or premature phase change of a single component, and ensures the reproducibility and accuracy of the experimental conditions; (3) The experimental system designed in this invention optimizes the arrangement of complete temperature, pressure and flow measurement points on the hot and cold sides of the printed circuit board heat exchanger under test, and is equipped with a high-precision data acquisition system, which can comprehensively acquire key thermal-hydraulic parameters such as heat transfer coefficient, flow pressure drop and component phase change characteristics of composite working fluid in the heat exchanger; the reasonable arrangement of these measurement points and the comprehensive data acquisition provide sufficient experimental data support for in-depth research on the heat transfer mechanism of multi-component phase change flow in microchannels; (4) The present invention further incorporates a primary and a secondary series gas-liquid separation device after the composite working fluid completes heat exchange. Combined with the cooling effect of the cooler, this device can efficiently separate and discharge water from the composite working fluid, while simultaneously recovering carbon dioxide gas to a low-pressure storage tank for recycling. This design not only reduces carbon dioxide consumption during experimental operation but also avoids the environmental impact caused by direct emission of carbon-containing gases, demonstrating good economic and environmental benefits. (5) The experimental system designed in this invention can flexibly simulate operating conditions under different working parameters by adjusting the temperature, pressure and flow rate settings of each circulation unit. The printed circuit board heat exchanger under test is replaceable and is suitable for comparative studies of the performance of heat exchangers with different microchannel structures. The platform has strong applicability, a wide range of operating parameters, and good scalability and engineering application value. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall composition and coupling method of the experimental system designed according to a preferred embodiment of the present invention; In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1. Low-pressure gas storage tank; 2. Compressor; 3. First check valve; 4. High-pressure gas storage tank; 5. Valve A; 6. Valve B; 7. First temperature sensor; 8. Gas heater; 9. Second temperature sensor; 10. Gas mixer; 11. Sampler; 12. Valve C; 13. First volumetric flow meter; 14. Third temperature sensor; 15. First pressure sensor; 16. Differential pressure sensor; 17. Printed circuit board heat exchanger; 18. Fourth temperature sensor; 19. Cooler; 20. First-stage gas-liquid separator; 21. Second-stage gas-liquid separator; 22. Fifth temperature sensor; 23. First drain valve; 24. Second drain valve; 2 5. Valve I; 26. Cooling water tank; 27. Low-pressure pump; 28. First check valve; 29. ​​Valve G; 30. Eighth temperature sensor; 31. Third pressure sensor; 32. Fourth pressure sensor; 33. Ninth temperature sensor; 34. Third volumetric flow meter; 35. Valve H; 36. Valve D; 37. Second check valve; 38. High-pressure pump; 39. Second check valve; 40. High-pressure water buffer tank; 41. Sixth temperature sensor; 42. Liquid heater; 43. Valve E; 44. Second pressure sensor; 45. Seventh temperature sensor; 46. Second volumetric flow meter; 47. Valve F; 48. Data acquisition computer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] It should be understood that expressions such as "comprising" and "may include" as used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "comprising" and / or "having" may be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or combination thereof, but should not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0022] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] Figure 1 This is a schematic diagram of the overall composition and coupling method of the experimental system designed according to a preferred embodiment of the present invention. The following will be combined with... Figure 1 To explain the invention in more detail.

[0024] like Figure 1 As shown, the experimental system of the present invention mainly includes a carbon dioxide circulation unit, a high-pressure water circulation unit, and a cooling water circulation unit that are coupled to each other. Each of these will be explained in detail below.

[0025] The carbon dioxide cycle unit a includes a low-pressure gas storage tank 1, a compressor 2, a high-pressure gas storage tank 4, a gas heater 8, a gas mixer 10, a cooler 19, a primary gas-liquid separator 20, and a secondary gas-liquid separator 21. The low-pressure gas storage tank 1 stores pure CO2 at a first gas pressure, and its fluid output is connected to the compressor 2, and then controllably connected to the gas heater 8. The high-pressure gas storage tank 4 stores pure CO2 at a second gas pressure, which is higher than the first gas pressure, and its port is connected to the pipeline between the compressor 2 and the gas heater 8. The fluid output from the gas heater 8 is mixed with fluid from the high-pressure water... The fluids of the circulation unit are combined into a composite working fluid in the gas mixer 10, and the fluid output end of the gas mixer 10 is controllably connected to the hot-side fluid input end of the printed circuit board heat exchanger 17, which is the object of detection. At the same time, the hot-side fluid output end of the printed circuit board heat exchanger 17 is controllably connected to the hot-side fluid input end of the cooler 19. In addition, the hot-side fluid output end of the cooler 19 is connected to the gas input end of the first-stage gas-liquid separator 20, the gas output end of the first-stage gas-liquid separator 20 is connected to the gas input end of the second-stage gas-liquid separator 21, and the gas output end of the second-stage gas-liquid separator 21 is connected to the fluid recovery end of the low-pressure gas storage tank 1. The high-pressure water circulation unit b includes a high-pressure pump 38, a high-pressure water buffer tank 40, and a liquid heater 42. The high-pressure pump 38 obtains fluid from the low-pressure pump 27 of the cooling water circulation unit, and its fluid output is controllably connected to the liquid heater 42. The port of the high-pressure water buffer tank 40 is connected to the pipeline between the high-pressure pump 38 and the liquid heater 42. The liquid heater 42 heats the input fluid, and its output fluid is combined with the fluid from the carbon dioxide circulation unit in the gas mixer 10 to form a composite working fluid. The cooling water circulation unit c includes a cooling water tank 26 and a low-pressure pump 27. The cooling water tank 26 is used to store pure water, and its outlet is connected to the low-pressure pump 27. The fluid output by the low-pressure pump 27 flows controllably to the cold-side fluid input end of the printed circuit board heat exchanger 17, the cold-side fluid input end of the cooler 19, and the fluid input end of the high-pressure pump 38. The cold-side output fluid of the printed circuit board heat exchanger 17 and the cold-side output fluid of the cooler 19 merge and are connected to the cooling water tank 26. Furthermore, in order to achieve more accurate and comprehensive testing of the forced flow heat transfer characteristics of the composite working fluid composed of carbon dioxide and water in a printed circuit board heat exchanger, this invention specifically designed the following multiple sensing elements, and obtained the required key test data through their specific settings and working mechanisms; at the same time, multiple sets of valve structures were also designed to ensure the overall system's operational reliability.

[0026] More specifically, for the gas heater 8, a first temperature sensor 7 is provided upstream and a second temperature sensor 9 is provided downstream; for the liquid heater 42, a sixth temperature sensor 41 is provided upstream and a second pressure sensor 44, a seventh temperature sensor 45 and a second volumetric flow meter 46 are provided downstream. For the printed circuit board heat exchanger 17, a third temperature sensor 14, a first volumetric flow meter 13 and a first pressure sensor 15 are provided at its hot side fluid inlet end, and a fourth temperature sensor 18 and a differential pressure sensor 16 are provided at its hot side fluid outlet end. At the same time, an eighth temperature sensor 30 and a third pressure sensor 31 are provided at its cold side fluid inlet end, and a ninth temperature sensor 33, a fourth pressure sensor 32 and a third volumetric flow meter 34 are provided at its cold side fluid outlet end. For the secondary gas-liquid separator 21, a fifth temperature sensor 22 is provided at its gas output end; in this way, after the above experimental system is started, the ratio of carbon dioxide to water in the composite working fluid can be regulated and the output can be stabilized, while the multiple thermal and hydraulic parameters of the composite working fluid in the printed circuit board heat exchanger can be fully obtained.

[0027] According to another preferred embodiment of the present invention, the above-mentioned experimental system preferably further includes a sampler 11, which is used to sample the components of the composite working fluid and then determine the proportion of water vapor in the composite working fluid by a drying and weighing method.

[0028] According to another preferred embodiment of the present invention, the above-mentioned experimental system preferably further includes a data acquisition computer 48, which is connected to the first to ninth temperature sensors, the first to fourth pressure sensors, the first to third volume flow meters, and the differential pressure sensor, and processes the acquired data.

[0029] The following section will provide a more detailed explanation of the multiple sets of valve components that are used in this experimental system.

[0030] See again Figure 1 The liquid output end of the primary gas-liquid separator 20 is connected to the liquid output end of the secondary gas-liquid separator 21 through a pipeline, and is connected to the atmosphere through the first drain valve 23; in addition, the bottom of the low-pressure gas storage tank 1 is provided with a second drain valve 24, which is also connected to the atmosphere. A first check valve 3 is provided between the compressor 2 and the high-pressure gas storage tank 4 to prevent backflow of fluid in the high-pressure gas storage tank 4; in addition, a second check valve 39 is provided downstream of the high-pressure pump 38 to prevent backflow of fluid in the high-pressure water buffer tank 40.

[0031] The low-pressure pump 27 is connected to the printed circuit board heat exchanger 17 by a first check valve 28 and a valve G 29. The upstream lead-out circuit of the first check valve 28 is connected to the upstream of the cooling water tank 26 through a valve H 35. The low-pressure pump 27 is connected to the cooler 19 through a valve I 25. Thus, the cold-side fluid flow rate of the printed circuit board heat exchanger 17 is controlled by the coordinated action of the valve G 29 and the valve H 35. A second check valve 37 is provided upstream of the high-pressure pump 38. A valve E 43 connecting to the environment is provided on the pipeline downstream of the fluid output end of the liquid heater 42. A circuit is led out downstream of the high-pressure water buffer tank 40 and connected to the upstream of the second check valve 37. This circuit is controlled by valve D 36.

[0032] Furthermore, a pipeline is provided between the high-pressure gas storage tank 4 and the gas heater 8, connecting to the low-pressure gas storage tank 1, and a valve A 5 is provided on this pipeline; a valve B 6 is provided upstream of the gas heater 8; in addition, a bypass is provided between the gas mixer 10 and the printed circuit board heat exchanger 17, connecting to the sampler 11, and the main route between the gas mixer 10 and the printed circuit board heat exchanger 17 is connected by valve C 12; the liquid heater 42 is connected to the gas mixer 10 through valve F 47.

[0033] The working process of the above-described experimental system of the present invention will be explained in more detail below.

[0034] Cycle Start-up Phase: Close the shut-off valve, first drain valve 23, second drain valve 24, and valve F47 of high-pressure gas tank 4. Vacuum the carbon dioxide circulation unit a through the shut-off valve port of the low-pressure gas tank. After vacuuming is complete according to the pressure gauges equipped in high-pressure gas tank 4 and low-pressure gas tank 1, use a carbon dioxide cylinder to inject pure carbon dioxide gas into low-pressure gas tank 1 through the shut-off valve until the pressure of the entire carbon dioxide circulation unit is slightly higher than atmospheric pressure. After the system pressure stabilizes, close valve A5 on the return path of high-pressure gas tank 4 and valve B6 on the downstream path. Continuously inject carbon dioxide gas into low-pressure gas tank 1, for example, until the pressure reaches 0.5 MPa. Then start compressor 2 and continuously inject carbon dioxide gas into low-pressure gas tank 1 until the carbon dioxide is forced into high-pressure gas tank 4 until the pressure reaches, for example, 3 MPa. Once the pressure is reached, open valve A 5 on the return path of high-pressure gas storage tank 4. After the return circulation stabilizes, slowly open valve B 6 and continue to inject carbon dioxide gas into low-pressure gas storage tank 1. Adjust valve A on the return branch and valve B on the main branch so that the pressure at the first pressure sensor 15, which is also the inlet pressure on the hot side of the printed circuit board heat exchanger 17, reaches the experimental requirements.

[0035] Carbon dioxide circulation unit a: After gas injection is completed, compressor 2 is kept running to ensure continuous and stable gas circulation. Low-pressure gas storage tank 1 is connected to high-pressure gas storage tank 4 and gas heater 8 via compressor 2. Compressor 2 and high-pressure gas storage tank 4 are connected by a first one-way valve 3 to prevent backflow of carbon dioxide fluid in high-pressure gas storage tank 4. The carbon dioxide fluid from low-pressure gas storage tank 1, after being pressurized by compressor 2, mainly enters the gas heater 8 with adjustable heating power. It is connected to high-pressure gas storage tank 4 between compressor 2 and gas heater 8 for pressure stabilization. A bypass is led out from the pipeline between high-pressure gas storage tank 4 and gas heater 8 and connected to low-pressure gas storage tank 1. This bypass is connected via valve A5 to regulate the pressure in the high-pressure gas storage tank. Gas heater 8 needs to heat the carbon dioxide fluid to a temperature higher than the target experimental inlet temperature required by the hot-side fluid of the heat exchanger.

[0036] A first temperature sensor 7 and a second temperature sensor 9 are respectively arranged upstream and downstream of the gas heater 8 to monitor the input and output temperatures. Based on the input and set temperatures, the heating power of the gas heater 8 is dynamically adjusted via PID control. A valve B 6 is arranged upstream of the gas heater 8 to regulate the overall gas loop flow rate. Downstream of the gas heater 8 is a gas mixer 10, which is connected to the hot-side input port of a printed circuit board heat exchanger 17. A valve C 12 controls whether the fluid bypasses the sampler 11 to determine the component ratio in the composite working fluid. Upstream of the hot side 17 of the printed circuit board heat exchanger is a third temperature sensor 14, a first pressure sensor 15, and a first volumetric flow meter 13. Downstream is a fourth temperature sensor 18 and a differential pressure sensor 16 connected to the upstream inlet first pressure sensor 15. All these sensors are connected to a data acquisition computer 48. The hot-side output port of the printed circuit board heat exchanger 17 is connected to the cooler 19 to ensure complete condensation of water vapor in the working fluid. The cooler 19 is connected sequentially to a primary gas-liquid separator 20 and a secondary gas-liquid separator 21. A fifth temperature sensor 22 is arranged downstream of the secondary gas-liquid separator 21 to monitor the temperature of the working fluid after cooling, preventing icing and blockage. The liquid outputs of the primary and secondary gas-liquid separators 20 and 21 are interconnected to the same first drain valve 23, which discharges the liquid using the system's internal pressure when necessary. After passing through the primary and secondary gas-liquid separators 20 and 21, the fluid returns to the low-pressure storage tank 1 to enter the next cycle. To further prevent unseparated liquid from entering the next cycle, a second drain valve 23 is provided at the bottom of the low-pressure storage tank 1.

[0037] High-pressure water circulation unit b: The high-pressure water circulation is supplied by the low-pressure pump 27 of the cooling water tank 26. The low-pressure pump 27 is connected to the high-pressure pump 38 through the second check valve 37. The output end of the high-pressure pump 38 is connected to the high-pressure water buffer tank 40 and the liquid heater 42. A bypass is led out from the pipeline between the high-pressure water buffer tank 40 and the liquid heater 42, and connected to the upstream of the second check valve 37 through valve D 36 to form a loop. This controls the pressure of the high-pressure water buffer tank 40 to be slightly higher than the pressure of the carbon dioxide side upstream of the gas mixer 10. In addition, a second one-way valve 39 is provided downstream of the high-pressure pump 38 to prevent backflow of fluid in the high-pressure water buffer tank 40. The sixth temperature sensor 41 and the seventh temperature sensor 45 are respectively arranged upstream and downstream of the liquid heater 42 to monitor the input and output temperatures, and adjust the heating power of the liquid heater 42 according to the input temperature and the set temperature through PID control. The liquid heater 42 is connected to the gas mixer 10, through which a second pressure sensor 44 and a second volumetric flow meter 46 are arranged. A bypass is led downstream of the liquid heater 42 and connected to the environment via valve E 43 to discharge air from the high-pressure water circulation unit. All of the above sensors are connected to the data acquisition computer 48.

[0038] Cooling water circulation unit c: The cooling water in the cooling water tank 26 must be pure water, preferably deionized water. The outlet of the cooling water tank 26 is connected to the low-pressure pump 27. The fluid from the outlet of the low-pressure pump 27 flows to the cold-side input of the printed circuit board heat exchanger 17, the cold-side input of the cooler 19, and the input of the high-pressure pump 38 of the high-pressure water circulation unit. The cold-side input of the printed circuit board heat exchanger 17 is equipped with an eighth temperature sensor 30 and a third pressure sensor 31. The output is equipped with a ninth temperature sensor 33, a fourth pressure sensor 32, and a third volumetric flow meter 34. All of these sensors are connected to the data acquisition computer 48. Upstream of the cold-side input of the printed circuit board heat exchanger 17, there is a valve G 29 and a first check valve 28. A bypass is led out upstream of the first check valve 28 and connected to the downstream of the cold-side output of the printed circuit board heat exchanger 17 via valve H 35. The cold-side flow rate of the printed circuit board heat exchanger 17 is controlled by valve G 29 and valve H 35. The fluid from the cold side output end of the cooler merges with the fluid from the cold side output end of the printed circuit board heat exchanger 17 and flows into the cooling water tank 26. A valve I25 is provided upstream of the cold side input end of the cooler to control the flow rate of cooling water in the cooler 19.

[0039] In addition, a heat-insulating device with heating function is arranged around the sampler 11. Before sampling, the sampler needs to be heated to slightly higher than the saturation temperature of the working fluid to prevent water vapor from condensing and accumulating in the sampler. After connecting the bypass and opening the needle valves at both ends of the sampler, the main valve C12 is closed, allowing the working fluid to continuously flow into the sampler 11. After the temperature of the sampler 11 stabilizes for a period of time, the needle valves at both ends of the sampler are closed and the main valve C12 is opened to continue the main circulation. To maintain the temperature of the sampler 11, one end of the sampler 11 is connected to a copper pipe exposed to the atmosphere or cooling water, and the other end is connected to a compressor connected upstream to the atmosphere. The compressor and the sampler 11 are connected by a multi-stage drying device. Initially, the pressure inside the sampler is used to push the working fluid through the copper pipe. The outlet of the copper pipe is connected to a multi-stage drying device. After the pressure inside the sampler drops to the atmospheric level, the valve at the other end is opened and the compressor is turned on to continuously ventilate the sampler for more than 20 minutes. The multi-stage drying device is a section of pipeline containing cotton, desiccant, and molecular sieve. After the ventilation is completed, the contents of the multi-stage drying device after removing the copper tube are weighed, and the change in mass is used to obtain the water content in the sampler. After calculation, the water vapor composition ratio in the composite working fluid is obtained.

[0040] Finally, the pressure and temperature experimental data of the inlet and outlet of the hot and cold side circuit of the printed circuit board heat exchanger 17 are recorded by the sensors at the inlet and outlet of the hot and cold side circuits, respectively. The composition of the composite working fluid is determined by sampling and drying weighing. All the above sensors are connected to the data acquisition computer 48. The data acquisition computer 48 records the data collected by all the above sensors in different categories and generates a data summary table, making the experimental data clear at a glance.

[0041] In summary, the flow heat transfer experimental system designed according to this invention can provide a given adjustable temperature and pressure for the hot and cold circuits of the printed circuit board heat exchanger under test. Furthermore, by adjusting the flow rates of different working fluids and performing thorough mixing, it can achieve stable and precise control of the proportions of the composite working fluid components, thus effectively solving the technical pain point of the lack of such experimental devices in the prior art. This experimental system boasts high testing accuracy, a working pressure of up to 4 MPa, and a wide range of applications. It can conduct flow and heat transfer performance tests on phase change composite working fluids in printed circuit board heat exchangers with different flow channel structures. Therefore, it is particularly suitable for providing data support and technical verification for the design of condensers such as semi-closed supercritical carbon dioxide Brayton cycles, and possesses good practical value and application prospects.

[0042] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A flow heat transfer experimental system for a CO2 / H2O phase change composite working fluid printed circuit board heat exchanger, comprising a carbon dioxide circulation unit, a high-pressure water circulation unit, and a cooling water circulation unit coupled to each other, characterized in that: The carbon dioxide circulation unit includes a low-pressure gas storage tank (1), a compressor (2), a high-pressure gas storage tank (4), a gas heater (8), a gas mixer (10), a cooler (19), a primary gas-liquid separator (20), and a secondary gas-liquid separator (21). The low-pressure gas storage tank (1) stores pure CO2 at a first pressure, and its fluid output is connected to the compressor (2) and then controllably connected to the gas heater (8). The high-pressure gas storage tank (4) stores pure CO2 at a second pressure higher than the first pressure, and its port is connected to the pipeline between the compressor (2) and the gas heater (8). The fluid output from the gas heater (8) is mixed with fluid from the high-pressure water... The fluids of the circulation unit are combined into a composite working fluid in the gas mixer (10), and the fluid output end of the gas mixer (10) is controllably connected to the hot-side fluid input end of the printed circuit board heat exchanger (17) which is the object of detection. At the same time, the hot-side fluid output end of the printed circuit board heat exchanger (17) is controllably connected to the hot-side fluid input end of the cooler (19). In addition, the hot-side fluid output end of the cooler (19) is connected to the gas input end of the first-stage gas-liquid separator (20), the gas output end of the first-stage gas-liquid separator (20) is connected to the gas input end of the second-stage gas-liquid separator (21), and the gas output end of the second-stage gas-liquid separator (21) is connected to the fluid recovery end of the low-pressure gas storage tank (1). The high-pressure water circulation unit includes a high-pressure pump (38), a high-pressure water buffer tank (40), and a liquid heater (42), wherein the high-pressure pump (38) obtains fluid from the low-pressure pump (27) of the cooling water circulation unit, and its fluid output is controllably connected to the liquid heater (42); the port of the high-pressure water buffer tank (40) is connected to the pipeline between the high-pressure pump (38) and the liquid heater (42); the liquid heater (42) heats the input fluid, and its output fluid is combined with the fluid from the carbon dioxide circulation unit in the gas mixer (10) to form a composite working fluid; The cooling water circulation unit includes a cooling water tank (26) and a low-pressure pump (27), wherein the cooling water tank (26) is used to store pure water and its outlet is connected to the low-pressure pump (27); the fluid output by the low-pressure pump (27) flows controllably to the cold-side fluid input end of the printed circuit board heat exchanger (17), the cold-side fluid input end of the cooler (19) and the fluid input end of the high-pressure pump (38); the cold-side output fluid of the printed circuit board heat exchanger (17) and the cold-side output fluid of the cooler (19) merge and are connected to the cooling water tank (26). Furthermore, for the gas heater (8), a first temperature sensor (7) is provided upstream, and a second temperature sensor (9) is provided downstream; for the liquid heater (42), a sixth temperature sensor (41) is provided upstream, and a second pressure sensor (44), a seventh temperature sensor (45), and a second volumetric flow meter (46) are provided downstream; for the printed circuit board heat exchanger (17), a third temperature sensor (14), a first volumetric flow meter (13), and a first pressure sensor (15) are provided at its hot-side fluid input end, and a fourth temperature sensor (18) and a differential pressure sensor (16) are provided at its hot-side fluid output end. At the same time, an eighth temperature sensor (30) and a third pressure sensor (31) are provided at its cold-side fluid input end, and a ninth temperature sensor (33), a fourth pressure sensor (32), and a third volumetric flow meter (34) are provided at its cold-side fluid output end; for the secondary gas-liquid separator (21), a fifth temperature sensor (22) is provided at its gas output end. In this way, after the above experimental system is started, the ratio of carbon dioxide to water in the composite working fluid can be controlled and the output can be stabilized. At the same time, multiple thermal-hydraulic parameters of the composite working fluid in the printed circuit board heat exchanger can be obtained comprehensively.

2. The flow heat transfer experimental system as described in claim 1, characterized in that, The experimental system described above preferably also includes a sampler (11), which is used to sample the components of the composite working medium and then determine the proportion of water vapor in the composite working medium by a drying and weighing method.

3. The flow heat transfer experimental system as described in claim 2, characterized in that, The experimental system described above preferably also includes a data acquisition computer (48), which is connected to the first to ninth temperature sensors, the first to fourth pressure sensors, the first to third volume flow meters, and the differential pressure sensor, and processes the acquired data.

4. The flow heat transfer experimental system as described in any one of claims 1-3, characterized in that, The gas heater (8) and the liquid heater (42) are preferably in the form of pipe-type electric heaters, and they are controlled by PID according to the set temperature.

5. The flow heat transfer experimental system as described in claim 2, characterized in that, The liquid output end of the primary gas-liquid separator (20) is connected to the liquid output end of the secondary gas-liquid separator (21) through a pipeline and is connected to the atmosphere through the first drain valve (23); in addition, the bottom of the low-pressure gas storage tank (1) is provided with a second drain valve (24) and is connected to the atmosphere.

6. The flow heat transfer experimental system as described in claim 5, characterized in that, A first check valve (3) is provided between the compressor (2) and the high-pressure gas storage tank (4) to prevent the fluid in the high-pressure gas storage tank (4) from flowing back; in addition, a second check valve (39) is provided downstream of the high-pressure pump (38) to prevent the fluid in the high-pressure water buffer tank (40) from flowing back.

7. The flow heat transfer experimental system as described in claim 6, characterized in that, The low-pressure pump (27) is connected to the printed circuit board heat exchanger (17) by a first check valve (28) and a valve G (29), wherein the upstream lead-out circuit of the first check valve (28) is connected to the upstream of the cooling water tank (26) through a valve H (35), and the low-pressure pump (27) is connected to the cooler (19) through a valve I (25), thereby the cold side fluid flow of the printed circuit board heat exchanger (17) is controlled by the valve G (29) and the valve H (35). In addition, a second check valve (37) is provided upstream of the high-pressure pump (38), and a valve E (43) connecting to the environment is provided on the pipeline downstream of the fluid output end of the liquid heater (42). A circuit is led out downstream of the high-pressure water buffer tank (40) and connected to the upstream of the second check valve (37). This circuit is controlled by valve D (36).

8. The flow heat transfer experimental system as described in claim 7, characterized in that, A pipeline is provided between the high-pressure gas storage tank (4) and the gas heater (8) to the low-pressure gas storage tank (1), and a valve A (5) is provided on the pipeline; a valve B (6) is provided upstream of the gas heater (8); in addition, a bypass is provided between the gas mixer (10) and the printed circuit board heat exchanger (17) to the sampler (11), and the main route between the gas mixer (10) and the printed circuit board heat exchanger (17) is connected by valve C (12); the liquid heater (42) is connected to the gas mixer (10) through valve F (47).

9. The flow heat transfer experimental system according to any one of claims 1-8, characterized in that, The above experimental system is used in scenarios such as a semi-closed supercritical carbon dioxide Brayton cycle.

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