A CO2 spiral coil heat transfer performance detection device and method thereof

Abstract

The present invention belongs to the technical field of CO2 heat transfer detection equipment, and relates to a CO2 spiral coil heat exchange performance detection device and method thereof, including a CO2 gas cylinder, a fluid energy storage and pressure stabilization system, a high-temperature water bath heat exchanger, a low-temperature water bath heat exchanger, a geothermal water simulation system, a coil convective heat transfer test device, and a low-pressure recovery tank; the output end of the CO2 gas cylinder is connected to the fluid energy storage and pressure stabilization system, the output end of the fluid energy storage and pressure stabilization system is connected in parallel with the high-temperature water bath heat exchanger and the low-temperature water bath heat exchanger, the output ends of the high-temperature and low-temperature water bath heat exchangers are respectively connected to the coil input ends of the coil convective heat transfer test device, the geothermal water simulation system is connected in parallel inside the coil convective heat transfer test device, and the coil output end of the coil convective heat transfer test device is connected to the low-pressure recovery tank; this device realizes the stable output of high-pressure liquid CO2 and the constant pressure difference rapid flow control of CO2, can realize the coil heat exchange simulation experiment of geothermal water and CO2, and is helpful for the integrated research of geothermal utilization, carbon utilization and carbon emission reduction.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 heat transfer detection equipment, and relates to an experimental device and method for testing the heat transfer characteristics between supercritical CO2 inside and outside a spiral coil and geothermal water, with energy storage gas as the pressure stabilizing source. In particular, it relates to a CO2 spiral coil heat exchange performance detection device and its method, which can be used to meet the R & D requirements of scientific research institutions and industrial production for CO2 heat transfer performance detection and application in binary geothermal exploitation. The experimental raw materials are recycled, which is green and low-consumption. Background Art

[0002] Geothermal energy has the advantages of large reserves, wide distribution, clean and environmental protection, etc., and will play an indispensable role in replacing traditional fossil fuel energy. However, the geothermal resources in China are mainly medium- and low-temperature geothermal resources below 150°C, and the utilization efficiency of conventional steam turbines is too low. The binary cycle power generation is an ideal way to utilize medium- and low-temperature geothermal resources. At present, the organic Rankine (ORC) cycle power generation is widely used. Its principle is to use organic matter with a lower boiling point to absorb the heat of geothermal water and transform it into high-temperature and high-pressure steam, and then drive a turbine to do work and generate electricity. Compared with traditional organic matter working fluids, supercritical CO2 does not undergo a phase change when it absorbs heat and then reduces pressure to drive a turbine to do work, thus reducing the equipment complexity and improving the geothermal energy utilization rate. The supercritical CO2 thermal cycle has great application potential in the fields of the fourth-generation advanced nuclear energy system, solar thermal power generation, and coal-fired power generation. Therefore, the binary cycle power generation using supercritical CO2 - geothermal water is an effective way to utilize medium- and low-temperature geothermal resources. The prerequisite for the binary cycle power generation using supercritical CO2 - geothermal water is to determine the heat exchange performance of the CO2 spiral coil through simulation experiments.

[0003] In the existing patented technologies, a Chinese patent with the publication number CN102411863B discloses a teaching experiment device for measuring the convective heat transfer coefficients on two opposite sides of a microtube. A micro-injection pump is connected to the inlet of a detachable mixer through connecting pipe fittings. An air storage tank is connected to the other inlet of the detachable mixer through connecting pipe fittings. The outlet of the detachable mixer is sequentially connected to a glass connecting pipe, a micrometer-grade stainless steel pipe, a flow pattern viewer, and one end of a connecting pipe fitting. An adiabatic black cavity is provided outside the micrometer-grade stainless steel pipe. Thermocouples are provided at the inlet end and the outlet end of the stainless steel pipe. At the same time, heating wires are also connected and are connected to a power-adjustable heating unit. An on-line infrared thermal detector is provided at the corresponding position of the stainless steel pipe. The thermocouples are connected to a computer through a data acquisition unit. The on-line infrared thermal detector, the power-adjustable heating unit, and the computer are connected. A Chinese patent with the publication number CN109709134A discloses a wellbore self-circulation heat exchange experiment device and method. The experimental device includes a heat exchange system, an injection-production system, a heating and insulation system, a data acquisition system, etc. The heat exchange system is used to simulate the wellbore in a geothermal reservoir and provide a flow channel for the heat exchange between the heat-carrying fluid and the geothermal reservoir. The injection-production system is used to inject the low-temperature heat-carrying fluid into the heat exchange system through a booster pump and collect the produced hot fluid and cool and store it. The heating and insulation system is used to heat and insulate the wellbore and the sand-filled cylinder, create a high-temperature environment of the geothermal reservoir, and simulate a stable heat source supply. The data acquisition system is used to monitor and record the temperature and pressure data at key positions such as the heat exchange system, the injection-production system, and the heating and insulation system.

[0004] In the current experimental simulation study on the heat transfer performance of the supercritical CO2-geothermal water binary cycle power generation, the following problems are encountered: (1) When the geothermal water circulates to the ground, the pressure decreases, and the gas dissolved in it will precipitate, and the geothermal water becomes a gas-liquid mixed phase; (2) Due to the large compression ratio of CO2 and the critical pressure of 7.38 MPa, it is difficult to boost the pressure and stabilize the pressure of CO2 during indoor experiments; (3) The spiral coil can increase the heat transfer efficiency and easily meet the requirements of the supercritical pressure of CO2. However, when supercritical CO2 flows in the heated spiral coil, it will be affected by multiple effects such as centrifugal force, buoyancy force, and secondary flow, and experience drastic changes in physical properties near the pseudo-critical temperature, and the heat transfer and flow mechanism is very complex. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings existing in the prior art, aiming at the problems such as the difficulty in boosting the pressure and stabilizing the pressure of CO2, the inconvenience in simulating the gas-liquid mixed phase, and the difficulty in detecting the heat transfer performance in the current experimental simulation of the heat transfer performance of the supercritical CO2-geothermal water binary cycle power generation. Using the energy storage gas as the pressure stabilizing source and taking into account the enhanced heat transfer characteristics of the spiral coil, a CO2 spiral coil heat transfer performance detection device and method are designed to test the heat transfer characteristics between supercritical CO2 inside and outside the spiral coil and geothermal water.

[0006] To achieve the above object, a CO2 spiral coil heat transfer performance detection device involved in the present invention has a main structure including a CO2 gas cylinder, a fluid energy storage and pressure stabilization system, a high-temperature water bath heat exchanger, a low-temperature water bath heat exchanger, a geothermal water simulation system, a coil convective heat transfer test device, an electromagnetic overflow valve, and a low-pressure recovery tank; the output end of the CO2 gas cylinder is connected to the fluid energy storage and pressure stabilization system, and the CO2 gas cylinder drives the fluid energy storage and pressure stabilization system to achieve the output of CO2 fluid with a stabilized pressure in the range of 30 MPa - 50 MPa; the output end of the fluid energy storage and pressure stabilization system is connected in parallel with the high-temperature water bath heat exchanger and the low-temperature water bath heat exchanger, and the output of the CO2 fluid with a constant temperature is further achieved through the high-temperature water bath heat exchanger or the low-temperature water bath heat exchanger; the output ends of the high-temperature water bath heat exchanger and the low-temperature water bath heat exchanger are respectively connected to the coil input ends of the coil convective heat transfer test device, and the geothermal water simulation system is connected in parallel inside the cavity of the coil convective heat transfer test device, and the geothermal water simulation system realizes the simulation of the two-phase flow state of geothermal water on the ground; the coil output end of the coil convective heat transfer test device, the electromagnetic overflow valve, and the low-pressure recovery tank are connected in sequence; the constant-pressure difference flow of CO2 in the coil in the coil convective heat transfer test device 17 and the flow of gas-liquid two-phase fluid in the outer cavity of the coil can simulate the coil convective heat transfer process between CO2 and geothermal water.

[0007] The CO2 gas cylinder described in the present invention is composed of 10 - 15 national standard CO2 gas cylinders with a volume of 40 L and a pressure of 6 MPa - 7 MPa. The CO2 gas cylinder serves as the source of CO2 gas; the output end of the CO2 gas cylinder is connected with a first gas cylinder branch pipe and a second gas cylinder branch pipe. A first pre-pump stop valve is arranged at the front of the first gas cylinder branch pipe, a first gas-liquid booster pump is arranged at the rear of the first gas cylinder branch pipe, the rear side of the first gas-liquid booster pump is connected to a high-pressure stop valve, and the pipeline at the rear side of the high-pressure stop valve is communicated with the high-pressure cavity inside the fluid energy storage and pressure stabilization system; a low-pressure stop valve is arranged at the rear side of the second gas cylinder branch pipe, and the pipeline at the rear side of the low-pressure stop valve is communicated with the low-pressure cavity inside the fluid energy storage and pressure stabilization system.

[0008] The fluid energy storage and pressure stabilizing system described in the present invention includes a high-pressure chamber, a housing, a low-pressure chamber, and a piston. The housing has a convex-shaped structure. The high-pressure chamber and the low-pressure chamber are arranged inside the housing. The volume of the high-pressure chamber is 80 - 100 L, and the volume of the high-pressure chamber is smaller than that of the low-pressure chamber. The upper high-pressure chamber and the lower low-pressure chamber form a convex-shaped cavity. A piston is installed in the cavity. The piston is composed of a thick column at the lower part and a thin column at the upper part, forming an inverted "T"-shaped piston structure. The area ratio of the thick column to the driving surface of the thin column of the piston is 10:1 - 15:1. The piston pressurizes and stabilizes the output of the high-pressure chamber at 30 MPa - 50 MPa. First, the CO2 gas cylinder fills the high-pressure chamber with liquid CO2 under the action of the first gas-liquid booster pump, and then the remaining gaseous CO2 in the CO2 gas cylinder with a pressure of 3 MPa acts on the low-pressure chamber. The upper part of the low-pressure chamber is connected to the ventilation cut-off valve installed outside the housing. The upper side of the high-pressure chamber is respectively connected to the first temperature and pressure sensor and the first safety valve installed on the upper side of the housing. The high-pressure chamber is connected to the outside through a liquid transmission pipe. The rear end of the liquid transmission pipe is connected in parallel with a first liquid transmission branch pipe and a second liquid transmission branch pipe. A pressure reducing valve is installed on the first liquid transmission branch pipe, and the rear end of the pressure reducing valve is connected to an infusion cut-off valve. The rear end of the infusion cut-off valve is connected in parallel with a first infusion branch pipe and a second infusion branch pipe.

[0009] A high-temperature cut-off valve is installed on the first infusion branch pipe described in the present invention. The second temperature and pressure sensor is installed at the rear end of the output side of the high-temperature cut-off valve. The first infusion branch pipe is connected to the input end of the spiral coil installed inside the high-temperature water bath heat exchanger. The output end of the spiral coil of the high-temperature water bath heat exchanger is connected to the fluid transmission pipe. The high-temperature water bath heat exchanger is equipped with a heater and circulating water, and the high-temperature water bath heat exchanger is used to raise the temperature of the fluid in the spiral coil to a maximum of 100 °C.

[0010] A low-temperature cut-off valve is installed on the second infusion branch pipe described in the present invention. The third temperature and pressure sensor is installed at the rear end of the output side of the low-temperature cut-off valve. The second infusion branch pipe is connected to the input end of the infusion spiral coil installed inside the low-temperature water bath heat exchanger. The output end of the infusion spiral coil of the low-temperature water bath heat exchanger is connected to the fluid transmission pipe. The low-temperature water bath heat exchanger is equipped with a refrigerator and a 50% concentration of ethylene glycol solution, which is used to lower the temperature of the fluid in the spiral coil to a minimum of -20 °C. A return cut-off valve is installed on the second liquid transmission branch pipe. The rear side of the return cut-off valve is connected to the second gas-liquid booster pump. The second liquid transmission branch pipe is connected to the output end of the recovery spiral coil installed inside the low-temperature water bath heat exchanger. The input end of the recovery spiral coil of the low-temperature water bath heat exchanger is connected to the fluid recovery pipe.

[0011] A fifth temperature and pressure sensor is provided at the rear side of the fluid transfer pipe described in the present invention. The output end of the fluid transfer pipe is connected to the input end of the heat exchange spiral coil in the coil convective heat transfer test device. The outside of the convective heat transfer test device is grounded to a hot water simulation system. The output end of the heat exchange spiral coil in the coil convective heat transfer test device is connected to a heat exchange output pipe. A seventh temperature and pressure sensor is installed on the heat exchange output pipe. A third mass flowmeter is connected to the rear side of the seventh temperature and pressure sensor. An electromagnetic overflow valve is connected to the rear side of the third mass flowmeter. The electromagnetic overflow valve is used to control the CO2 fluid pressure at the outlet of the coil convective heat transfer test device to achieve a pressure control of 6 MPa - 40 MPa. The rear end of the electromagnetic overflow valve is connected to a low-pressure recovery tank with a volume of 400 L - 600 L. The low-pressure recovery tank is used to recover CO2 with a pressure of 3 MPa - 6 MPa. An eighth temperature and pressure sensor and a second safety valve are installed on the upper side of the low-pressure recovery tank. The lower side of the low-pressure recovery tank is connected to the rear end of the fluid recovery pipe. A recovery stop valve is installed on the fluid recovery pipe.

[0012] The hot water simulation system described in the present invention mainly includes: a gas-liquid mixer, a gas heating circulation device, a liquid heating circulation device, and a gas-liquid separator. The input end of the gas-liquid separator is connected to the cavity of the coil convective heat transfer test device. A sixth temperature and pressure sensor is provided between the input end of the gas-liquid separator and the coil convective heat transfer test device. The gas-liquid separator is used to separate gas-liquid two phases. The gas output end of the gas-liquid separator is connected to the input end of the gas heating circulation device. The gas heating circulation device is used to generate heated and recyclable air. The liquid output end of the gas-liquid separator is connected to the input end of the liquid heating circulation device. The liquid heating circulation device is used to generate heated and recyclable water. The output end of the gas heating circulation device is connected to a first mass flowmeter. A gas stop valve is connected to the front side of the first mass flowmeter. The output end of the gas stop valve is connected to the input end of the gas-liquid mixer. The output end of the liquid heating circulation device is connected to a second mass flowmeter. A liquid stop valve is connected to the front side of the second mass flowmeter. The output end of the liquid stop valve is connected to the input end of the gas-liquid mixer. The gas-liquid mixer modulates the heated air and water into a gas-liquid two-phase fluid. The output end of the gas-liquid mixer is connected to the cavity of the coil convective heat transfer test device. The gas-liquid mixer inputs the gas-liquid two-phase fluid into the cavity of the coil convective heat transfer test device. The coil convective heat transfer test device is used to achieve the heat exchange process between the CO2 fluid with modulated temperature and pressure and the gas-liquid two-phase fluid. The CO2 fluid is inside the heat exchange spiral coil, and the gas-liquid two-phase fluid is outside the heat exchange spiral coil.

[0013] The temperature and pressure sensor described in the present invention uses a temperature and pressure integrated sensor, which is used to monitor the temperature and pressure of the fluid in the pipeline; the safety valve is used to prevent excessive pressure caused by operation errors; the pressure reducing valve is used to control the CO2 fluid pressure at the inlet of the coiled tube convective heat transfer test device to achieve pressure control of 6 MPa - 50 MPa; the mass flowmeter is used to monitor the mass flow rate of the pipeline fluid.

[0014] The opening and closing of the globe valve, gas-liquid booster pump, temperature and pressure integrated sensor, fluid energy storage and pressure stabilizing system, safety valve, pressure reducing valve, high-temperature water bath heat exchanger, low-temperature water bath heat exchanger, mass flowmeter, geothermal water simulation system, coiled tube convective heat transfer test device, and electromagnetic overflow valve described in the present invention can be manually controlled or electrically connected to a controller for automatic control.

[0015] The specific steps for the CO2 spiral coil heat transfer performance detection device involved in this embodiment to simulate the convective heat transfer of the CO2 spiral coil and detect the heat transfer performance data are as follows:

[0016] (1) Open the first stop valve before the pump and the high-pressure stop valve, and inject the liquid CO2 in the CO2 gas cylinder into the high-pressure chamber 5 through the first gas-liquid booster pump;

[0017] (2) Close the first stop valve before the pump and the high-pressure stop valve, open the vent stop valve and the low-pressure stop valve, connect the low-pressure chamber to the gaseous CO2 at 3 MPa in the CO2 gas cylinder, and use the piston to achieve pressurization and stable pressure output of 30 MPa - 50 MPa for the high-pressure chamber;

[0018] (3) Open the gas stop valve and the liquid stop valve, and start the gas heating circulation device, liquid heating circulation device, and gas-liquid separator to realize the circulation of the gas-liquid two-phase fluid at a constant temperature in the coiled tube convective heat transfer test device;

[0019] (4) Set the outlet pressure of the pressure reducing valve and the inlet pressure of the electromagnetic overflow valve to realize the flow of CO2 with a constant pressure difference in the coiled tube of the coiled tube convective heat transfer test device;

[0020] (5) Open the infusion stop valve and the high-temperature stop valve or the infusion stop valve and the low-temperature stop valve, and further realize the output of the CO2 fluid at a constant temperature and pressure through the high-temperature water bath heat exchanger or the low-temperature water bath heat exchanger;

[0021] (6) Monitor and record the changes in the CO2 temperature, flow rate at the inlet and outlet of the heat transfer spiral coil in the coiled tube convective heat transfer test device and the temperature and flow rate of the gas-liquid two-phase fluid outside the heat transfer spiral coil through the temperature and pressure integrated sensor and the mass flowmeter, and calculate the heat transfer coefficient and resistance coefficient of the fluid by back-calculating the measured parameters;

[0022] After the experiment, close the infusion stop valve and the high-temperature stop valve, or the infusion stop valve and the low-temperature stop valve. Then, turn off the gas heating circulation device, the liquid heating circulation device, the gas stop valve, and the liquid stop valve. Open the recovery stop valve, start the second gas-liquid booster pump, cool and liquefy and boost the gaseous CO2 in the low-pressure recovery tank through the low-temperature water bath heat exchanger, and then inject it into the high-pressure chamber. Then, close the recovery stop valve and the second gas-liquid booster pump to prepare for the next set of experiments.

[0023] Compared with the prior art, the main structure of the CO2 spiral coil heat transfer performance detection device and method designed by the present invention is reasonable and has the following effects: (1) Overcome the problems of high CO2 compression ratio, difficult pressurization, and large and expensive pressurization equipment. By using highly compressible gaseous CO2 and a variable-area piston to drive liquid CO2, approximate constant-pressure output of high-pressure liquid CO2 is achieved; (2) Through the combination of a pressure reducing valve and an electromagnetic overflow valve, rapid flow control with a constant pressure difference for CO2 in the coil can be formed; (3) Through the modulation of gas-liquid two-phase flow and CO2 at different temperatures and flow rates, simulation experiments on the coil heat transfer between geothermal water and CO2 can be realized, which is helpful for the integrated research of geothermal utilization, carbon utilization, and carbon emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic block diagram of the structural principle of the vertical sectional view of the CO2 spiral coil heat transfer performance detection device involved in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be further described below through embodiments in conjunction with the drawings.

[0026] Embodiment 1:

[0027] A CO2 spiral coil heat transfer performance detection device involved in this embodiment, as Figure 1As shown in the figure, the main structure includes a CO2 gas cylinder 1, a fluid energy storage and pressure stabilizing system, a high-temperature water bath heat exchanger 11, a low-temperature water bath heat exchanger 12, a geothermal water simulation system, a coil convective heat transfer test device 17, an electromagnetic overflow valve 19, and a low-pressure recovery tank 20; the output end of the CO2 gas cylinder 1 is connected to the fluid energy storage and pressure stabilizing system, and the CO2 gas cylinder 1 drives the fluid energy storage and pressure stabilizing system to achieve the output of CO2 fluid with a stable pressure in the range of 30 MPa - 50 MPa; the output end of the fluid energy storage and pressure stabilizing system is connected in parallel with the high-temperature water bath heat exchanger 11 and the low-temperature water bath heat exchanger 12, and the output of the constant-temperature CO2 fluid is further achieved through the high-temperature water bath heat exchanger 11 or the low-temperature water bath heat exchanger 12; the output ends of the high-temperature water bath heat exchanger 11 and the low-temperature water bath heat exchanger 12 are respectively connected to the coil input end of the coil convective heat transfer test device 17, and the geothermal water simulation system is connected in parallel inside the cavity of the coil convective heat transfer test device 17, and the geothermal water simulation system realizes the simulation of the two-phase flow state of geothermal water on the ground; the coil output end, the electromagnetic overflow valve 19, and the low-pressure recovery tank 20 of the coil convective heat transfer test device 17 are connected in sequence; the constant-pressure difference flow of CO2 in the coil of the coil convective heat transfer test device 17 and the gas-liquid two-phase flow in the outer cavity can simulate the coil convective heat transfer process between CO2 and geothermal water.

[0028] The CO2 gas cylinder 1 involved in this embodiment is composed of 10 - 15 national standard CO2 gas cylinders with a volume of 40 L and a pressure of 6 MPa - 7 MPa. The CO2 gas cylinder 1 serves as the source of CO2 gas; the output end of the CO2 gas cylinder 1 is connected with a first gas cylinder branch pipe 1-1 and a second gas cylinder branch pipe 1-2. A first pre-pump stop valve 2-1 is arranged at the front of the first gas cylinder branch pipe 1-1, a first gas-liquid booster pump 3-1 is arranged at the rear of the first gas cylinder branch pipe 1-1, the rear side of the first gas-liquid booster pump 3-1 is connected to a high-pressure stop valve 2-2, and the pipeline at the rear side of the high-pressure stop valve 2-2 is communicated with the high-pressure cavity 5 inside the fluid energy storage and pressure stabilizing system; a low-pressure stop valve 2-4 is arranged at the rear side of the second gas cylinder branch pipe 1-2, and the pipeline at the rear side of the low-pressure stop valve 2-4 is communicated with the low-pressure cavity 7 inside the fluid energy storage and pressure stabilizing system.

[0029] The fluid energy storage and pressure stabilizing system involved in this embodiment includes a high-pressure chamber 5, a housing 6, a low-pressure chamber 7, and a piston 9. The housing 6 has a convex-shaped structure. Inside the housing 6, there are a high-pressure chamber 5 and a low-pressure chamber 7. The volume of the high-pressure chamber 5 is 80 - 100L, and the volume of the high-pressure chamber 5 is smaller than that of the low-pressure chamber 7. The upper high-pressure chamber 5 and the lower low-pressure chamber 7 form a convex-shaped cavity. Inside the cavity, there is a piston 9 installed. The piston 9 is composed of a thick column at the lower part and a thin column at the upper part, forming an inverted "T"-shaped piston structure. The area ratio of the thick column to the driving surface of the thin column of the piston 9 is 10:1 - 15:1. The piston 9 performs pressurization and stable pressure output of 30MPa - 50MPa on the high-pressure chamber 5. First, the CO2 gas cylinder 1 fills the high-pressure chamber 5 with liquid CO2 under the action of the first gas-liquid booster pump 3-1, and then the remaining gaseous CO2 with a pressure of about 3MPa in the CO2 gas cylinder 1 acts on the low-pressure chamber 7. The upper part of the low-pressure chamber 7 is connected to the air vent shut-off valve 2-3 installed outside the housing 6. The upper side of the high-pressure chamber 5 is respectively connected to the first temperature and pressure sensor 4-1 and the first safety valve 8-1 installed on the upper side of the housing 6. The high-pressure chamber 5 is connected to the outside through a liquid transfer pipe 5-1. The rear end of the liquid transfer pipe 5-1 is connected in parallel with a first liquid transfer branch pipe 5-2 and a second liquid transfer branch pipe 5-3. A pressure reducing valve 10 is installed on the first liquid transfer branch pipe 5-2. The rear end of the pressure reducing valve 10 is connected to an infusion shut-off valve 2-5. The rear end of the infusion shut-off valve 2-5 is connected in parallel with a first infusion branch pipe 11-1 and a second infusion branch pipe 12-1.

[0030] On the first infusion branch pipe 11-1 involved in this embodiment, there is a high-temperature shut-off valve 2-7 installed. The rear end of the output side of the high-temperature shut-off valve 2-7 is installed with a second temperature and pressure sensor 4-2. The first infusion branch pipe 11-1 is connected to the input end of the spiral coil installed inside the high-temperature water bath heat exchanger 11. The output end of the spiral coil of the high-temperature water bath heat exchanger 11 is connected to the fluid transfer pipe 11-2. Inside the high-temperature water bath heat exchanger 11, there are a heater and circulating water. The high-temperature water bath heat exchanger 11 is used to raise the temperature of the fluid inside the spiral coil to a maximum of 100°C.

[0031] On the second infusion branch pipe 12-1 involved in this embodiment, there is a low-temperature shut-off valve 2-8 installed. The rear end of the output side of the low-temperature shut-off valve 2-8 is installed with a third temperature and pressure sensor 4-3. The second infusion branch pipe 12-1 is connected to the input end of the infusion spiral coil installed inside the low-temperature water bath heat exchanger 12. The output end of the infusion spiral coil of the low-temperature water bath heat exchanger 12 is connected to the fluid transfer pipe 11-2. Inside the low-temperature water bath heat exchanger 12, there is a refrigerator and a 50% concentration of ethylene glycol solution, which is used to lower the temperature of the fluid inside the spiral coil to a minimum of -20°C. On the second liquid transfer branch pipe 5-3, there is a reflux cut-off valve 2-6 installed. The rear side of the reflux cut-off valve 2-6 is connected to the second gas-liquid booster pump 3-2. The second liquid transfer branch pipe 5-3 is connected to the output end of the recovery spiral coil installed inside the low-temperature water bath heat exchanger 12. The input end of the recovery spiral coil of the low-temperature water bath heat exchanger 12 is connected to the fluid recovery pipe 12-2.

[0032] A fifth temperature and pressure sensor 4-5 is provided at the rear side of the fluid transfer pipe 11-2 involved in this embodiment. The output end of the fluid transfer pipe 11-2 is communicated with the input end of the heat exchange spiral coil in the coil convective heat transfer test device 17. The coil convective heat transfer test device 17 is externally connected to a ground hot water simulation system. The output end of the heat exchange spiral coil in the coil convective heat transfer test device 17 is connected to a heat exchange output pipe. A seventh temperature and pressure sensor 4-7 is installed on the heat exchange output pipe. A third mass flowmeter 13-3 is connected to the rear side of the seventh temperature and pressure sensor 4-7. An electromagnetic overflow valve 19 is connected to the rear side of the third mass flowmeter 13-3. The electromagnetic overflow valve 19 is used to control the CO2 fluid pressure at the outlet of the coil convective heat transfer test device 17 to achieve pressure control of 6 MPa - 40 MPa; the rear end of the electromagnetic overflow valve 19 is connected to a low-pressure recovery tank 20. The volume of the low-pressure recovery tank 20 is between 400 L and 600 L. The low-pressure recovery tank 20 is used to recover CO2 with a pressure of 3 MPa - 6 MPa; an eighth temperature and pressure sensor 4-8 and a second safety valve 8-2 are installed on the upper side of the low-pressure recovery tank 20. The lower side of the low-pressure recovery tank 20 is communicated with the rear end of the fluid recovery pipe 12-2. A recovery stop valve 2-11 is installed on the fluid recovery pipe 12-2.

[0033] The geothermal water simulation system involved in this embodiment mainly includes: a gas-liquid mixer 14, a gas heating and circulating device 15, a liquid heating and circulating device 16, and a gas-liquid separator 18. The input end of the gas-liquid separator 18 is communicated with the cavity of the coiled tube convective heat transfer test device 17. A sixth temperature and pressure sensor 4-6 is arranged between the input end of the gas-liquid separator 18 and the coiled tube convective heat transfer test device 17. The gas-liquid separator 18 is used to separate the gas-liquid two-phase; the gas output end of the gas-liquid separator 18 is communicated with the input end of the gas heating and circulating device 15, and the gas heating and circulating device 15 is used to generate heated and circulable air. The liquid output end of the gas-liquid separator 18 is communicated with the input end of the liquid heating and circulating device 16, and the liquid heating and circulating device 16 is used to generate heated and circulable water; the output end of the gas heating and circulating device 15 is connected with a first mass flowmeter 13-1. A gas stop valve 2-9 is connected to the front side of the first mass flowmeter 13-1, and the output end of the gas stop valve 2-9 is communicated with the input end of the gas-liquid mixer 14; the output end of the liquid heating and circulating device 16 is connected with a second mass flowmeter 13-2. A liquid stop valve 2-10 is connected to the front side of the second mass flowmeter 13-2, and the output end of the liquid stop valve 2-10 is communicated with the input end of the gas-liquid mixer 14; the gas-liquid mixer 14 modulates the heated air and water into a gas-liquid two-phase fluid, and the output end of the gas-liquid mixer 14 is communicated with the cavity of the coiled tube convective heat transfer test device 17; the gas-liquid mixer 14 inputs the gas-liquid two-phase fluid into the cavity of the coiled tube convective heat transfer test device 17; the coiled tube convective heat transfer test device 17 is used to realize the heat exchange process between the CO2 fluid with modulated temperature and pressure and the gas-liquid two-phase fluid. The CO2 fluid is inside the heat exchange coiled tube, and the gas-liquid two-phase fluid is outside the heat exchange coiled tube.

[0034] The temperature and pressure sensor involved in this embodiment adopts a temperature and pressure integrated sensor, which is used to monitor the temperature and pressure of the fluid in the pipeline; the safety valve is used to prevent excessive pressure under operating errors; the pressure reducing valve 10 is used to control the pressure of the CO2 fluid at the inlet of the coiled tube convective heat transfer test device 17 to realize the pressure control of 6 MPa - 50 MPa; the mass flowmeter is used to monitor the mass flow rate of the pipeline fluid.

[0035] The opening and closing of the stop valve, gas-liquid booster pump, temperature and pressure integrated sensor, fluid energy storage and pressure stabilizing system, safety valve, pressure reducing valve 10, high-temperature water bath heat exchanger 11, low-temperature water bath heat exchanger 12, mass flowmeter, geothermal water simulation system, coiled tube convective heat transfer test device 17, and electromagnetic overflow valve 19 involved in this embodiment can be manually controlled or automatically controlled by being electrically connected to the controller.

[0036] The specific steps for the CO2 coiled tube heat transfer performance detection device involved in this embodiment to simulate the convective heat transfer of the CO2 coiled tube and detect the heat transfer performance data are as follows:

[0037] (1)Open the first pump front stop valve 2-1 and the high-pressure stop valve 2-2, and inject the liquid CO2 in the CO2 gas cylinder 1 into the high-pressure chamber 5 through the first gas-liquid booster pump 3-1;

[0038] (2)Close the first pump front stop valve 2-1 and the high-pressure stop valve 2-2, open the ventilation stop valve 2-3 and the low-pressure stop valve 2-4, connect the low-pressure chamber 7 with the gaseous CO2 in the CO2 gas cylinder 1 at about 3 MPa, and realize the pressurization and steady-state output of 30 MPa - 50 MPa to the high-pressure chamber 5 through the piston 9;

[0039] (3)Open the gas stop valve 2-9 and the liquid stop valve 2-10, start the gas heating circulation device 15, the liquid heating circulation device 16 and the gas-liquid separator 14, and realize the circulation of the gas-liquid two-phase fluid at a constant temperature in the coiled tube convective heat transfer test device 17;

[0040] (4)Set the outlet pressure of the pressure reducing valve 10 and the inlet pressure of the electromagnetic overflow valve 19 to realize the CO2 flow with a constant pressure difference in the coiled tube of the coiled tube convective heat transfer test device 17;

[0041] (5)Open the infusion stop valve 2-5 and the high-temperature stop valve 2-7 or the infusion stop valve 2-5 and the low-temperature stop valve 2-8, and further realize the output of the CO2 fluid at a constant temperature and pressure through the high-temperature water bath heat exchanger 11 or the low-temperature water bath heat exchanger 12;

[0042] (6)Monitor and record the changes in the CO2 temperature, flow rate at the inlet and outlet of the heat exchange coiled tube in the coiled tube convective heat transfer test device 17 and the temperature and flow rate of the gas-liquid two-phase fluid outside the heat exchange coiled tube through the temperature and pressure integrated sensor and the mass flow meter, and calculate the heat transfer coefficient and resistance coefficient of the fluid by inverse calculation of the measured parameters;

[0043] (7)After the experiment, close the infusion stop valve 2-5 and the high-temperature stop valve 2-7 or the infusion stop valve 2-5 and the low-temperature stop valve 2-8, close the gas heating circulation device 15, the liquid heating circulation device 16, the gas stop valve 2-9 and the liquid stop valve 2-10, open the recovery stop valve 2-11, start the second gas-liquid booster pump 3-2, cool and liquefy and pressurize the gaseous CO2 in the low-pressure recovery tank 20 through the low-temperature water bath heat exchanger 12 and inject it back into the high-pressure chamber 5, and then close the recovery stop valve 2-11 and the second gas-liquid booster pump 3-2 to prepare for the next group of experiments.

[0044] The working principle of the CO2 coiled tube heat transfer performance detection device involved in this embodiment is as follows:

[0045] When CO2 is in a liquid state, it has low compressibility and high viscosity, which is conducive to pressurization by a gas-liquid booster pump. Therefore, the initial liquid CO2 in the CO2 gas cylinder 1 can be quickly pressurized by the first gas-liquid booster pump 3-1. When CO2 is in a gaseous state, it has strong compressibility, more than 15 times that of liquid CO2. Therefore, the remaining gaseous CO2 in the gas cylinder 1 after pressurization can be used as a pressure stabilizing source with little pressure change. The gaseous CO2 can drive the variable area piston 9 to achieve an approximately constant pressure output of the liquid CO2 in the high-pressure chamber 5. The pressure reducing valve 10 can control the constant pressure at the outlet of the pressure reducing valve 10, and the electromagnetic overflow valve 19 can control the constant pressure at the inlet of the electromagnetic overflow valve 19. The combination of the two can control the constant fluid pressure at both ends of the coil in the coil convective heat transfer test device 17, so as to achieve a constant pressure difference flow of CO2 in the coil. The gas heating and circulation device 15 can heat and circulate the air, and the liquid heating and circulation device gas-liquid mixer 14 can heat and circulate the water. The heated air and water can be mixed into a high-temperature gas-liquid two-phase flow through the gas-liquid mixer 14, which can simulate the two-phase flow state of geothermal water on the ground. The constant pressure difference flow of CO2 in the coil in the coil convective heat transfer test device 17 and the gas-liquid two-phase flow outside the coil can simulate the coil convective heat transfer process between CO2 and geothermal water.

Claims

1. A CO2 spiral coil heat exchange performance detection device, characterized in that: It includes a CO2 gas cylinder, a fluid energy storage and pressure stabilization system, a high-temperature water bath heat exchanger, a low-temperature water bath heat exchanger, a geothermal water simulation system, a coiled tube convective heat transfer test device, an electromagnetic overflow valve, and a low-pressure recovery tank; the output end of the CO2 gas cylinder is connected to the fluid energy storage and pressure stabilization system, and the CO2 gas cylinder drives the fluid energy storage and pressure stabilization system to achieve the output of CO2 fluid with a stable pressure in the range of 30 MPa - 50 MPa; the output ends of the fluid energy storage and pressure stabilization system are connected in parallel with the high-temperature water bath heat exchanger and the low-temperature water bath heat exchanger, and the high-temperature water bath heat exchanger or the low-temperature water bath heat exchanger is further used to achieve the output of CO2 fluid with a constant temperature; the output ends of the high-temperature water bath heat exchanger and the low-temperature water bath heat exchanger are respectively connected to the coiled tube input end of the coiled tube convective heat transfer test device, and the geothermal water simulation system is connected in parallel inside the cavity of the coiled tube convective heat transfer test device, and the geothermal water simulation system realizes the simulation of the two-phase flow state of geothermal water on the ground; the coiled tube output end, the electromagnetic overflow valve, and the low-pressure recovery tank of the coiled tube convective heat transfer test device are connected in sequence; the constant-pressure difference flow of CO2 in the coiled tube and the gas-liquid two-phase flow in the outer cavity of the coiled tube in the coiled tube convective heat transfer test device can simulate the coiled tube convective heat transfer process between CO2 and geothermal water; The CO2 gas cylinder is composed of 10 - 15 national standard CO2 gas cylinders with a volume of 40 L and a pressure of 6 MPa - 7 MPa, and the CO2 gas cylinder serves as the source of CO2 gas; the output end of the CO2 gas cylinder is connected with a first gas cylinder branch pipe and a second gas cylinder branch pipe. A first pre-pump stop valve is arranged at the front of the first gas cylinder branch pipe, a first gas-liquid booster pump is arranged at the rear of the first gas cylinder branch pipe, the rear side of the first gas-liquid booster pump is connected to a high-pressure stop valve, and the pipeline at the rear side of the high-pressure stop valve is communicated with the high-pressure cavity inside the fluid energy storage and pressure stabilization system; a low-pressure stop valve is arranged at the rear side of the second gas cylinder branch pipe, and the pipeline at the rear side of the low-pressure stop valve is communicated with the low-pressure cavity inside the fluid energy storage and pressure stabilization system; The fluid energy storage and pressure stabilization system includes a high-pressure cavity, a shell, a low-pressure cavity, and a piston. The shell has a convex structure. The high-pressure cavity and the low-pressure cavity are arranged inside the shell. The volume of the high-pressure cavity is 80 - 100 L, and the volume of the high-pressure cavity is smaller than that of the low-pressure cavity. The upper high-pressure cavity and the lower low-pressure cavity form a convex-shaped cavity. A piston is installed inside the cavity. The piston is composed of a thick column at the lower part and a thin column at the upper part to form an inverted "T"-shaped piston structure. The area ratio of the thick column to the driving surface of the thin column of the piston is 10:1 - 15:

1. The piston pressurizes and stabilizes the output of the high-pressure cavity at 30 MPa - 50 MPa; first, the CO2 gas cylinder fills the high-pressure cavity with liquid CO2 under the action of the first gas-liquid booster pump, and then the remaining gaseous CO2 with a pressure of 3 MPa in the CO2 gas cylinder acts on the low-pressure cavity; the upper part of the low-pressure cavity is communicated with the ventilation stop valve installed outside the shell; the upper side of the high-pressure cavity is respectively connected to the first temperature and pressure sensor and the first safety valve installed on the upper side of the shell. The high-pressure cavity is connected to the outside through a liquid transfer pipe. The rear end of the liquid transfer pipe is connected in parallel with a first liquid transfer branch pipe and a second liquid transfer branch pipe. A pressure reducing valve is installed on the first liquid transfer branch pipe, the rear end of the pressure reducing valve is connected to an infusion stop valve, and the rear end of the infusion stop valve is connected in parallel with a first infusion branch pipe and a second infusion branch pipe.

2. The CO2 spiral coil heat transfer performance detection device according to claim 1, wherein: A high-temperature cut-off valve is installed on the first infusion branch pipe. A second temperature and pressure sensor is installed at the rear end of the output side of the high-temperature cut-off valve. The input end of the spiral coil installed inside the high-temperature water bath heat exchanger is connected to the first infusion branch pipe. The output end of the spiral coil of the high-temperature water bath heat exchanger is connected to the fluid transmission pipe; a heater and circulating water are installed in the high-temperature water bath heat exchanger, and the high-temperature water bath heat exchanger is used to raise the temperature of the fluid in the spiral coil to a maximum of 100°C.

3. The CO2 spiral coil heat exchange performance detection device according to claim 2, characterized in that: A low-temperature cut-off valve is installed on the second infusion branch pipe. A third temperature and pressure sensor is installed at the rear end of the output side of the low-temperature cut-off valve. The input end of the infusion spiral coil installed inside the low-temperature water bath heat exchanger is connected to the second infusion branch pipe. The output end of the infusion spiral coil of the low-temperature water bath heat exchanger is connected to the fluid transmission pipe; a refrigerator and 50% concentration of ethylene glycol solution are installed in the low-temperature water bath heat exchanger, which is used to lower the temperature of the fluid in the spiral coil to a minimum of -20°C; a reflux cut-off valve is installed on the second liquid transfer branch pipe. The rear side of the reflux cut-off valve is connected to the second gas-liquid booster pump. The second liquid transfer branch pipe is connected to the output end of the recovery spiral coil installed inside the low-temperature water bath heat exchanger. The input end of the recovery spiral coil of the low-temperature water bath heat exchanger is connected to the fluid recovery pipe.

4. The CO2 spiral coil heat exchange performance detection device according to claim 3, characterized in that: A fifth temperature and pressure sensor is arranged at the rear side of the fluid transmission pipe. The output end of the fluid transmission pipe is communicated with the input end of the heat exchange spiral coil in the coil convective heat transfer test device. The coil convective heat transfer test device is externally grounded to the hot water simulation system. The output end of the heat exchange spiral coil in the coil convective heat transfer test device is connected to the heat exchange output pipe. A seventh temperature and pressure sensor is installed on the heat exchange output pipe. The rear side of the seventh temperature and pressure sensor is connected to a third mass flowmeter. The rear side of the third mass flowmeter is connected to an electromagnetic overflow valve. The electromagnetic overflow valve is used to control the CO2 fluid pressure at the outlet of the coil convective heat transfer test device to achieve pressure control of 6 MPa - 40 MPa; the rear end of the electromagnetic overflow valve is connected to the low-pressure recovery tank. The volume of the low-pressure recovery tank is between 400 L and 600 L. The low-pressure recovery tank is used to recover CO2 with a pressure of 3 MPa - 6 MPa; an eighth temperature and pressure sensor and a second safety valve are installed on the upper side of the low-pressure recovery tank. The lower side of the low-pressure recovery tank is communicated with the rear end of the fluid recovery pipe. A recovery cut-off valve is installed on the fluid recovery pipe.

5. The CO2 spiral coil heat transfer performance detection device according to claim 4, characterized in that: The geothermal water simulation system mainly includes: a gas-liquid mixer, a gas heating circulation device, a liquid heating circulation device, and a gas-liquid separator. The input end of the gas-liquid separator is communicated with the cavity of the coiled tube convective heat transfer test device. A sixth temperature and pressure sensor is arranged between the input end of the gas-liquid separator and the coiled tube convective heat transfer test device. The gas-liquid separator is used to separate gas-liquid two phases. The gas output end of the gas-liquid separator is communicated with the input end of the gas heating circulation device. The gas heating circulation device is used to generate heated and recyclable air. The liquid output end of the gas-liquid separator is communicated with the input end of the liquid heating circulation device. The liquid heating circulation device is used to generate heated and recyclable water. The output end of the gas heating circulation device is connected with a first mass flowmeter. A gas stop valve is connected to the front side of the first mass flowmeter. The output end of the gas stop valve is communicated with the input end of the gas-liquid mixer. The output end of the liquid heating circulation device is connected with a second mass flowmeter. A liquid stop valve is connected to the front side of the second mass flowmeter. The output end of the liquid stop valve is communicated with the input end of the gas-liquid mixer. The gas-liquid mixer modulates the heated air and water into a gas-liquid two-phase fluid. The output end of the gas-liquid mixer is communicated with the cavity of the coiled tube convective heat transfer test device. The gas-liquid mixer inputs the gas-liquid two-phase fluid into the cavity of the coiled tube convective heat transfer test device. The coiled tube convective heat transfer test device is used to realize the heat exchange process between the CO2 fluid with modulated temperature and pressure and the gas-liquid two-phase fluid. The CO2 fluid is inside the heat exchange coiled tube, and the gas-liquid two-phase fluid is outside the heat exchange coiled tube.

6. The CO2 spiral coil heat exchange performance detection device according to claim 5, characterized in that: The temperature and pressure sensor adopts a temperature and pressure integrated sensor, which is used to monitor the temperature and pressure of the fluid in the pipeline. The safety valve is used to prevent excessive pressure under operating errors. The pressure reducing valve is used to control the pressure of the CO2 fluid at the inlet of the coiled tube convective heat transfer test device to achieve pressure control of 6 MPa - 50 MPa. The mass flowmeter is used to monitor the mass flow rate of the pipeline fluid.

7. The CO2 spiral coil heat transfer performance detection device according to claim 6, wherein: The opening and closing of the stop valve, gas-liquid booster pump, temperature and pressure integrated sensor, fluid energy storage and pressure stabilizing system, safety valve, pressure reducing valve, high-temperature water bath heat exchanger, low-temperature water bath heat exchanger, mass flowmeter, geothermal water simulation system, coiled tube convective heat transfer test device, and electromagnetic overflow valve can be manually controlled or connected to the controller for automated control through electrical information.

8. A method for simulating the convective heat transfer and detecting the heat transfer performance data of a CO2 spiral coil by using the CO2 spiral coil heat transfer performance detection device according to claim 7, characterized in that: The specific steps are as follows: (1) Open the first pre-pump stop valve and the high-pressure stop valve, and inject the liquid CO2 in the CO2 gas cylinder into the high-pressure chamber through the first gas-liquid booster pump; (2) Close the first pre-pump stop valve and the high-pressure stop valve, open the ventilation stop valve and the low-pressure stop valve, connect the low-pressure chamber with the gaseous CO2 at 3 MPa in the CO2 gas cylinder, and realize the pressurization and steady-state output of 30 MPa - 50 MPa for the high-pressure chamber through the piston; (3) Open the gas stop valve and the liquid stop valve, start the gas heating circulation device, the liquid heating circulation device, and the gas-liquid separator, and realize the circulation of the gas-liquid two-phase fluid at a constant temperature in the coiled tube convective heat transfer test device; (4)Set the outlet pressure of the pressure reducing valve and the inlet pressure of the electromagnetic overflow valve to achieve the CO2 flow with a constant pressure difference inside the coil in the coil convective heat transfer test device; (5)Open the infusion stop valve and the high-temperature stop valve or the infusion stop valve and the low-temperature stop valve to further achieve the output of the CO2 fluid with a constant temperature and pressure through the high-temperature water bath heat exchanger or the low-temperature water bath heat exchanger; (6)Monitor and record the changes in the CO2 temperature, flow rate at the inlet and outlet of the heat exchange spiral coil in the coil convective heat transfer test device, and the temperature and flow rate of the gas-liquid two-phase fluid outside the heat exchange spiral coil through the temperature and pressure integrated sensor and the mass flowmeter, and calculate the heat transfer coefficient and resistance coefficient of the fluid by back-calculating the measured parameters; (7)After the experiment, close the infusion stop valve and the high-temperature stop valve or the infusion stop valve and the low-temperature stop valve, close the gas heating circulation device, the liquid heating circulation device, the gas stop valve and the liquid stop valve, open the recovery stop valve, start the second gas-liquid booster pump, cool and liquefy and boost the gaseous CO2 in the low-pressure recovery tank through the low-temperature water bath heat exchanger and inject it into the high-pressure chamber, and then close the recovery stop valve and the second gas-liquid booster pump to prepare for the next group of experiments.

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