阅读说明：本技术 一种水平管内临界热流密度测量系统及调控方法 (Measuring system and regulating method for critical heat flux density in horizontal pipe ) 是由 李冲 罗祖分 方贤德 于 2021-07-12 设计创作，主要内容包括：本发明公开了一种水平管内临界热流密度测量系统及调控方法,系统包括：制冷剂储液罐、电动风扇、加热片、流通管道、球阀开关、变频器、齿轮泵、质量流量计、预热段、数据采集模块、工业计算机、实验段、T型热电偶、通讯线、压力传感器、可视化透管、高速摄像机、制冷剂入口管道、U型冷凝器、冷却水入口管道、冷却水出口管道、制冷剂出口管道、水箱、电磁膨胀阀、液氮罐、水泵及塑料水瓶；本发明的测量系统对于低热流、低质量流速水平管内的临界热流密度现象监控和测量具有系统简单、判定条件可靠、测量精度高的优点；本发明的调控方法具有操作简便、系统稳定性好的优点。(The invention discloses a system for measuring critical heat flux density in a horizontal pipe and a regulation and control method, wherein the system comprises: the system comprises a refrigerant liquid storage tank, an electric fan, a heating plate, a circulation pipeline, a ball valve switch, a frequency converter, a gear pump, a mass flowmeter, a preheating section, a data acquisition module, an industrial computer, an experimental section, a T-shaped thermocouple, a communication line, a pressure sensor, a visual through pipe, a high-speed camera, a refrigerant inlet pipeline, a U-shaped condenser, a cooling water inlet pipeline, a cooling water outlet pipeline, a refrigerant outlet pipeline, a water tank, an electromagnetic expansion valve, a liquid nitrogen tank, a water pump and a plastic water bottle; the measuring system has the advantages of simple system, reliable judging conditions and high measuring precision for monitoring and measuring the critical heat flux density phenomenon in the horizontal pipe with low heat flux and low mass flow rate; the regulation and control method has the advantages of simple and convenient operation and good system stability.)

1. A system for measuring critical heat flux density in a horizontal tube, comprising: the device comprises a refrigerant liquid storage tank (1), an electric fan (2), a heating plate (3), a circulating pipeline (4), a ball valve switch (5), a frequency converter (6), a gear pump (7), a mass flow meter (8), a preheating section (9), a data acquisition module (10), an industrial computer (11), an experimental section (12), a T-shaped thermocouple (13), a communication line (14), a pressure sensor (15), a visual through pipe (16), a high-speed camera (17), a refrigerant inlet pipeline (18), a U-shaped condenser (19), a cooling water inlet pipeline (20), a cooling water outlet pipeline (21), a refrigerant outlet pipeline (22), a water tank (23), an electromagnetic expansion valve (24), a liquid nitrogen tank (25), a water pump (26) and a plastic water bottle (27);

the electric fan (2) is fixed above the outer wall of the refrigerant liquid storage tank (1), the heating sheet (3) is bonded below the outer wall of the refrigerant liquid storage tank (1), and the electric fan (2) and the heating sheet (3) are respectively arranged on two sides of the refrigerant liquid storage tank (1); the refrigerant liquid storage tank (1), the ball valve switch (5), the gear pump (7), the mass flowmeter (8), the preheating section (9), the experiment section (12) and the refrigerant inlet pipeline (18) are connected in pairs through circulation pipelines (4), and the circulation pipelines (4) are screwed and compressed through compression heads; the frequency converter (6) is respectively connected with the gear pump (7) and the data acquisition module (10); the experimental section (12) is provided with a plurality of T-shaped thermocouples (13); the bottom of the pressure sensor (15) is in interference fit with an outlet of the experimental section (12) through a pressure taking hole, and the top of the pressure sensor (15) is connected with the data acquisition module (10) through a communication line (14); the high-speed camera (17) is fixedly arranged above the visual transparent pipe (16); the U-shaped condenser (19) is arranged between the visual permeable pipe (16) and the refrigerant liquid storage tank (1), and four circulation pipelines on the U-shaped condenser (19) are sequentially screwed and compressed with the outlet of the visual permeable pipe (16), the outlet of the water pump (26), the water tank (23) and the top of the refrigerant liquid storage tank (1) through a compression head from left to right; the liquid nitrogen tank (25) is connected with the plastic water bottle (27) through a circulating pipeline (4), and a through pipe at the bottom of the electromagnetic expansion valve (24) is screwed with the circulating pipeline (4) through threads; the bottoms of the water pump (26) and the plastic water bottle (27) are fixedly connected with the ground bottom surface inside the water tank (23);

the industrial computer (11) monitors the system pressure value and flow value through the data acquisition module (10) to adjust the rotating speed of the water pump (26) and the frequency of the frequency converter (7), so that the system pressure and flow are kept at set values.

2. The system for measuring the critical heat flux density in the horizontal pipe according to claim 1, wherein the experimental section (12) comprises a horizontal pipe (121), an insulating tape (123), a resistance wire (124), an insulating tape (125) and an insulating tape (126) from inside to outside in sequence, wherein the insulating tape (123), the insulating tape (125) and the insulating tape (126) are wound and bonded on the previous layer of structure, and the resistance wire (124) is uniformly wound on the insulating tape (123) at a high density and a small interval.

3. The system for measuring the critical heat flow density in the horizontal tube according to claim 2, wherein the horizontal tube (121) of the experimental section (12) is made of copper tube, and the preheating section (9) and the experimental section (12) are identical in composition and structure.

4. The system for measuring the critical heat flux density in the horizontal pipe according to claim 2, wherein the horizontal pipe (121) of the experimental section (12) is made of a steel pipe, and the experimental section (12) further comprises a graphite heat storage sleeve (122) which is sleeved on the outer wall of the horizontal pipe (121) and is in interference fit with the horizontal pipe.

5. The system for measuring critical heat flux density in a horizontal tube according to claim 1, wherein the distance between the T-shaped thermocouples (13) uniformly arranged at two thirds of the experimental section (12) from the inlet of the experimental section (12) is large, and the distance between the T-shaped thermocouples (13) uniformly arranged at the rest of the experimental section (12) is small.

6. The system for measuring the critical heat flow density in the horizontal pipe according to claim 1, wherein the bottom of a T-shaped thermocouple (13) on the experimental section (12) is welded with the horizontal pipe (121), and the top of the T-shaped thermocouple (13) is connected with the data acquisition module (10) through a communication line (14); the data acquisition module (10) is connected with an industrial computer (11) in a plug-in mode through a communication line (14).

7. The system for measuring critical heat flow density in a horizontal tube according to claim 1, wherein the refrigerant and the cooling water flowing through the U-shaped condenser (19) flow in a counter-current manner.

8. The system of claim 1, wherein an electric fan and heating fins on the refrigerant reservoir are used for fine adjustment of system pressure and subcooling.

9. A regulation and control method of a critical heat flux density measurement system in a horizontal pipe is characterized by comprising the following steps: a refrigerant circulation circuit and a cooling water circulation circuit;

the flow of the refrigerant circulating loop is as follows:

the rigidity of the part between the refrigerant liquid storage tank and the ball valve switch is increased and the compressibility space of the part between the refrigerant liquid storage tank and the ball valve switch is reduced by adjusting the opening of the ball valve switch, refrigerant liquid pumped out of the gear pump enters the mass flow meter, is preheated by the preheating section, enters the U-shaped condenser through the visual through pipe after the experiment is completed in the experiment section, is cooled into liquid, enters the gear pump through the refrigerant liquid storage tank, and is pumped out of the gear pump to complete the circulation;

the cooling water circulation loop flow is as follows:

cooling water in the water tank is pumped out by a water pump, flows through a U-shaped condenser to cool the gas-liquid two-phase refrigerant into liquid, and then flows back to the water tank again; when the temperature of the cooling water in the water tank exceeds a certain range, the electromagnetic expansion valve is adjusted to a certain opening degree according to the pressure corresponding to the temperature of the cooling water, so that the liquid nitrogen in the liquid nitrogen tank is injected into the plastic water bottle, tap water in the plastic water bottle is instantly solidified into ice, and heat transfer is carried out between the solidified ice in the plastic water bottle and the cooling water, so that the temperature of the cooling water is kept constant.

10. The method for regulating and controlling the critical heat flux density measuring system in the horizontal pipe according to claim 9, wherein the preheating section and the experimental section generate uniform and stable heat flux by applying direct current to the resistance wire, the data acquisition module sends acquired real-time data to the industrial computer, and when the average temperature value of the thermocouple at the part close to the outlet 1/3 of the experimental section is higher than the average temperature value of the thermocouple at the part close to the front 2/3 of the inlet of the experimental section by 3 ℃ and lasts for more than 6 seconds, the opening degree of the water pump is adjusted by the industrial computer, the rotating speed of the water pump is reduced, and further the pressure of the system is increased.

Technical Field

The invention belongs to the technical field of general thermal equipment, and particularly relates to a system for measuring critical heat flux density in a horizontal pipe and a regulating and controlling method.

Background

The heat exchange coefficient of the boiling heat exchange in the horizontal pipe is usually several times higher than that of a single-phase heat exchange coefficient, so that the heat exchange device has energy-saving benefit and is closely related to the fields of power, space navigation, low-temperature refrigeration and the like, but the boiling heat exchange in the horizontal pipe can generate critical heat flux density. The critical heat flux density is a thermal parameter that must be strictly monitored on the boiling heat exchange surface, and for various heat exchange devices that operate by controlling the heat flux density in the processes of transferring and converting heat energy, once the heat flux density exceeds the critical heat flux density value, the heat exchange coefficient will be rapidly reduced, the wall temperature will rapidly rise, and the device will be burned out most likely. Aiming at the problem that the boiling heat exchange in the horizontal pipe is unstable continuously, how to reduce and inhibit the instability degree of the system is solved; the method aims at solving the problem that most of the judging conditions of the critical heat flow density in the horizontal tube are judged from a qualitative concept, namely, the extremely small heat flow density increase of a heating wall surface causes the great rise of the wall surface temperature under the condition of controlling the heat flow. How to define quantitative determination conditions for critical heat flux density in a horizontal tube under low heat flux and low flow rate; the method aims at the problems of great reduction of pressure and flow fluctuation of an experimental section when critical heat flow density occurs in a system, and inaccurate measured heat flow density value can be caused if the pressure and flow fluctuation of the system cannot be stabilized in time.

Therefore, how to design a system and a method for measuring critical heat flux density in a horizontal tube to reduce the degree of instability in the system and improve the accuracy of measuring the critical heat flux density is a content of intensive research required by various researchers.

Disclosure of Invention

In view of the above-mentioned deficiencies of the prior art, the present invention aims to provide a system and a method for measuring critical heat flux density in a horizontal tube, which not only make the measurement system have the advantages of simple system, reliable determination conditions and high measurement accuracy, but also make the method for regulating and controlling have the advantages of simple operation and good system stability.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the invention discloses a critical heat flux density measuring system in a horizontal pipe, which comprises: the system comprises a refrigerant liquid storage tank, an electric fan, a heating plate, a circulation pipeline, a ball valve switch, a frequency converter, a gear pump, a mass flowmeter, a preheating section, a data acquisition module, an industrial computer, an experimental section, a T-shaped thermocouple, a communication line, a pressure sensor, a visual through pipe, a high-speed camera, a refrigerant inlet pipeline, a U-shaped condenser, a cooling water inlet pipeline, a cooling water outlet pipeline, a refrigerant outlet pipeline, a water tank, an electromagnetic expansion valve, a liquid nitrogen tank, a water pump and a plastic water bottle;

the electric fan is fixed above the outer wall of the refrigerant liquid storage tank, the heating sheet is adhered below the outer wall of the refrigerant liquid storage tank, and the electric fan and the heating sheet are respectively arranged on two sides of the refrigerant liquid storage tank; the refrigerant liquid storage tank, the ball valve switch, the gear pump, the mass flow meter, the preheating section, the experiment section and the refrigerant inlet pipeline are connected in pairs through circulation pipelines, and the circulation pipelines are screwed and compacted through the compacting head; the frequency converter is respectively connected with the gear pump and the data acquisition module; a plurality of T-shaped thermocouples are arranged on the experimental section; the bottom of the pressure sensor is in interference fit with an outlet of the experimental section through a pressure taking hole, and the top of the pressure sensor is connected with the data acquisition module through a communication line; the high-speed camera is fixedly arranged above the visual transparent pipe; the U-shaped condenser is arranged between the visual permeable pipe and the refrigerant liquid storage tank, and four circulation pipelines on the U-shaped condenser are sequentially screwed and compressed with the outlet of the visual permeable pipe, the outlet of the water pump, the water tank and the top of the refrigerant liquid storage tank from left to right through the compression heads; the liquid nitrogen tank is connected with the plastic water bottle through a circulating pipeline, and a through pipe at the bottom of the electromagnetic expansion valve is screwed with the circulating pipeline through threads; the bottoms of the water pump and the plastic water bottle are fixedly connected with the ground bottom surface inside the water tank;

the industrial computer monitors the system pressure value and the flow value through the data acquisition module to adjust the rotating speed of the water pump (used for adjusting the system pressure) and the frequency of the frequency converter (used for adjusting the rotating speed of the gear pump and further adjusting the mass flow), so that the system pressure and the flow are kept at set values.

Furthermore, the experimental section comprises a horizontal pipe, an insulating tape, a resistance wire, an insulating tape and a heat insulation tape from inside to outside in sequence, wherein the insulating tape, the insulating tape and the heat insulation tape are wound and bonded on the upper layer of structure, and the resistance wire is uniformly wound on the insulating tape at a high density and small interval.

Furthermore, the horizontal pipe of the experimental section is a copper pipe, and the preheating section and the experimental section have the same composition structure.

Furthermore, the horizontal pipe of experiment section adopts the steel pipe, and then experiment section still includes graphite heat accumulation sleeve pipe, and its overcoat is in horizontal pipe outer wall, and both interference fit.

Further, the distance between the T-shaped thermocouples uniformly arranged from the inlet of the experimental section to two thirds of the position of the experimental section is large, and the distance between the T-shaped thermocouples uniformly arranged at the rest position of the experimental section is small.

Furthermore, the bottom of the T-shaped thermocouple on the experimental section is welded with the horizontal pipe, and the top of the T-shaped thermocouple is connected with the data acquisition module through a communication line; the data acquisition module is connected with the industrial computer in a plug-in mode through a communication line.

It should be noted that the T-shaped thermocouple is inserted into the wall thickness of the horizontal tube inside the experimental section, and mainly measures the inner wall temperature of the horizontal tube (because the wall thickness is small and the thermal conductivity of the horizontal tube is high, the inner wall temperature is an approximate value here, because the bottom of the thermocouple is not in contact with the inner surface of the horizontal tube).

Further, the refrigerant and the cooling water flowing through the U-shaped condenser flow in a counter-current manner.

Further, an electric fan and a heating plate on the refrigerant liquid storage tank are used for fine adjustment of system pressure and supercooling degree.

When critical heat flow density occurs in the horizontal pipe, the resistance in the experimental section is increased, the pressure drop is increased, the system pressure is reduced, the flow fluctuation is obvious, and in order to ensure the accuracy of measuring the critical heat flow density, the system pressure and the flow are required to be kept near set values; therefore, the industrial computer adjusts the rotating speed of the water pump (used for adjusting the system pressure) and the frequency of the frequency converter (used for adjusting the rotating speed of the gear pump and further adjusting the mass flow) through the system pressure value and the flow value which are monitored and recorded by the data acquisition module, so that the system pressure and the flow are stabilized near set values, and the measuring result of the critical heat flow density is prevented from being influenced due to the fact that the measuring system is unstable greatly.

The invention discloses a regulation and control method of a critical heat flux density measurement system in a horizontal pipe, which is based on the system and comprises the following steps: a refrigerant circulation circuit and a cooling water circulation circuit;

the flow of the refrigerant circulating loop is as follows:

the rigidity of the part between the refrigerant liquid storage tank and the ball valve switch is increased and the compressibility space of the part between the refrigerant liquid storage tank and the ball valve switch is reduced by adjusting the opening of the ball valve switch, refrigerant liquid pumped out of the gear pump enters the mass flow meter, is preheated by the preheating section, enters the U-shaped condenser through the visual through pipe after the experiment is completed in the experiment section, is cooled into liquid, enters the gear pump through the refrigerant liquid storage tank, and is pumped out of the gear pump to complete the circulation;

the cooling water circulation loop flow is as follows:

cooling water in the water tank is pumped out by a water pump, flows through a U-shaped condenser to cool the gas-liquid two-phase refrigerant into liquid, and then flows back to the water tank again; when the temperature of the cooling water in the water tank exceeds a certain range, the electromagnetic expansion valve is adjusted to a certain opening degree according to the pressure corresponding to the temperature of the cooling water, so that the liquid nitrogen in the liquid nitrogen tank is injected into the plastic water bottle, tap water in the plastic water bottle is instantly solidified into ice, and heat transfer is carried out between the solidified ice in the plastic water bottle and the cooling water, so that the temperature of the cooling water is kept constant.

Further, the preheating section and the experimental section generate uniform and stable heat flow by electrifying the resistance wire with direct current, the data acquisition module transmits acquired real-time data to the industrial computer, and when the average temperature value of the thermocouple close to the 1/3 part of the experimental section outlet is higher than the average temperature value of the thermocouple close to the 2/3 part of the experimental section inlet by 3 ℃ and lasts for more than 6 seconds, the opening of the water pump is adjusted by the industrial computer, the rotating speed of the water pump is reduced, and the pressure of the system is further increased.

The invention has the beneficial effects that:

1. the circulation loop in the invention is divided into two parts: a refrigerant circulation circuit and a cooling water circulation circuit. The refrigerant circulating loop mainly comprises a refrigerant liquid storage tank, a ball valve switch, a frequency converter, a gear pump, a mass flowmeter, a preheating section, an experimental section and a condenser; the cooling water loop mainly comprises a water tank, a water pump, a liquid nitrogen tank, an electromagnetic expansion valve and a plastic water bottle. The measuring system is simple and reliable, and the measuring result precision is higher.

2. To reduce the degree of instability of the flow boiling system itself, the following procedure is used: the rigidity of the part between the refrigerant liquid storage tank and the ball valve switch is increased by utilizing a ball valve switch throttling pressurization method, the compressibility space of the part between the refrigerant liquid storage tank and the ball valve switch is reduced, and severe pressure drop type fluctuation is eliminated; secondly, if the horizontal pipe in the experimental section is a steel pipe, the critical heat flux density is measured by a mode of increasing the heat capacity of the pipe wall (externally coating a graphite heat storage sleeve). The heat conductivity coefficient of the steel pipe is lower than that of the copper pipe, namely the axial heat conductivity is also lower, and the instantaneous heat flow received by the fluid working medium in the pipe and the axial temperature difference of the heated pipe are reduced by increasing the heat capacity of the pipe wall, so that the unstable amplitude of the flowing boiling is reduced.

3. Because the influence of gravity leads to the cyclic annular flow liquid film of horizontal pipe inner wall to distribute unevenly, and top liquid film thickness is thinner, and bottom liquid film thickness is thicker, and the influence of experiment section thermal current in addition, critical thermal current phenomenon takes place near experiment section top exit position usually, and the temperature variation near experiment section top exit is violent than other positions, consequently, for the more reliable wall temperature condition of understanding the experiment section, the arrangement of experiment section thermocouple adopts different density evenly distributed.

4. The visual transparent pipe is convenient for an experimenter to observe the gas content of the refrigerant at the outlet of the experimental section and the flow pattern of the two-phase flow, and the high-speed camera is used for recording the evolution process of the two-phase flow pattern in the experimental process.

5. In order to improve the supercooling degree of the refrigerant entering the refrigerant storage tank, the refrigerant and cooling water flowing through the U-shaped condenser flow in a countercurrent mode. In addition, an electric fan and a heating plate on the refrigerant liquid storage tank are used for fine adjustment of system pressure and supercooling degree.

6. Aiming at the critical heat flux density in the horizontal pipe under low heat flux and low flow rate, the judgment conditions are as follows: the thermocouple mean temperature value near the exit 1/3 of the experimental section was 3 ℃ higher than the thermocouple mean temperature value near the front 2/3 of the inlet of the experimental section for more than 6 seconds, with a concomitant decrease in the heat transfer coefficient. When the critical heat flow phenomenon occurs, the pressure drop in the horizontal pipe of the experimental section is increased, the system pressure is reduced, and the opening degree of the gear pump is manually adjusted to be small through the industrial computer, so that the system pressure can be increased.

Drawings

FIG. 1 is a schematic diagram of the system of the present invention;

FIG. 2 is a perspective view showing an internal structure of a water tank in the present invention;

FIG. 3 is a schematic structural diagram of an experimental section in the present invention;

in the figure: the device comprises a refrigerant storage tank 1, an electric fan 2, a heating plate 3, a flow pipeline 4, a ball valve switch 5, a frequency converter 6, a gear pump 7, a mass flow meter 8, a preheating section 9, a data acquisition module 10, an industrial computer 11, an experimental section 12, a T-shaped thermocouple 13, a communication line 14, a pressure sensor 15, a visual through pipe 16, a high-speed camera 17, a refrigerant inlet pipeline 18, a U-shaped condenser 19, a cooling water inlet pipeline 20, a cooling water outlet pipeline 21, a refrigerant outlet pipeline 22, a water tank 23, an electromagnetic expansion valve 24, a liquid nitrogen tank 25, a water pump 26, a plastic water bottle 27, a horizontal pipe 121, a graphite heat storage sleeve 122, an insulating tape 123, a resistance wire 124, an insulating tape 125 and an insulating tape 126.

Detailed Description

In order to facilitate understanding of those skilled in the art, the present invention will be further described with reference to the following examples and drawings, which are not intended to limit the present invention.

Referring to fig. 1 to 3, a system for measuring critical heat flux density in a horizontal tube according to the present invention includes: the system comprises a refrigerant liquid storage tank 1, an electric fan 2, a heating plate 3, a flow pipeline 4, a ball valve switch 5, a frequency converter 6, a gear pump 7, a mass flow meter 8, a preheating section 9, a data acquisition module 10, an industrial computer 11, an experiment section 12, a T-shaped thermocouple 13, a communication line 14, a pressure sensor 15, a visual through pipe 16, a high-speed camera 17, a refrigerant inlet pipeline 18, a U-shaped condenser 19, a cooling water inlet pipeline 20, a cooling water outlet pipeline 21, a refrigerant outlet pipeline 22, a water tank 23, an electromagnetic expansion valve 24, a liquid nitrogen tank 25, a water pump 26 and a plastic water bottle 27;

the electric fan 2 is fixed above the outer wall of the refrigerant liquid storage tank 1, the heating sheet 3 is adhered below the outer wall of the refrigerant liquid storage tank 1, and the electric fan 2 and the heating sheet 3 are respectively arranged at two sides of the refrigerant liquid storage tank 1; the refrigerant liquid storage tank 1, the ball valve switch 5, the gear pump 7, the mass flowmeter 8, the preheating section 9, the experiment section 12 and the refrigerant inlet pipeline 18 are connected in pairs through a circulating pipeline 4, and the circulating pipeline 4 is screwed and compacted through a compaction head; the frequency converter 6 is respectively connected with the gear pump 7 and the data acquisition module 10; a plurality of T-shaped thermocouples 13 are arranged on the experimental section 12; the bottom of the pressure sensor 15 is in interference fit with the outlet of the experimental section 12 through a pressure taking hole, and the top of the pressure sensor 15 is connected with the data acquisition module 10 through a communication line 14; the high-speed camera 17 is fixedly arranged above the visual transparent pipe 16 in an inclined manner; the U-shaped condenser 19 is arranged between the visual permeable pipe 16 and the refrigerant liquid storage tank 1, and four circulation pipelines on the U-shaped condenser 19 are sequentially screwed and compressed with the outlet of the visual permeable pipe 16, the outlet of the water pump 26, the water tank 23 and the top of the refrigerant liquid storage tank 1 from left to right through a compression head; the liquid nitrogen tank 25 is connected with the plastic water bottle 27 through the circulating pipeline 4, and a through pipe at the bottom of the electromagnetic expansion valve 24 is screwed with the circulating pipeline 4 through threads; the bottoms of the water pump 26 and the plastic water bottle 27 are fixedly connected with the ground bottom surface inside the water tank 23;

the industrial computer 11 monitors the system pressure value and the flow value through the data acquisition module 10 to adjust the rotating speed of the water pump 26 (for adjusting the system pressure) and the frequency of the frequency converter 7 (for adjusting the rotating speed of the gear pump, and further adjusting the mass flow), so that the system pressure and the flow are stabilized at set values, and the measurement result of the critical heat flow density is prevented from being influenced by the large instability of the measurement system.

In an example one, the experimental section 12 is sequentially provided with a horizontal tube 121, an insulating tape 123, a resistance wire 124, an insulating tape 125 and an insulating tape 126 from inside to outside, wherein the insulating tape 123, the insulating tape 125 and the insulating tape 126 are wound and bonded on a previous layer of structure, and the resistance wire 124 is uniformly wound on the insulating tape 123 at a high density and a small interval; the horizontal pipe 121 is made of a copper pipe, and the preheating section 9 and the experiment section 12 are identical in composition structure.

In the second example, the experimental section 12 is sequentially provided with a horizontal pipe 121, a graphite heat storage sleeve 122, an insulating tape 123, a resistance wire 124, an insulating tape 125 and an insulating tape 126 from inside to outside; the insulating tape 123, the insulating tape 125 and the heat insulation tape 126 are wound and bonded on the upper layer of structure, and the resistance wire 124 is uniformly wound on the insulating tape 123 at a high density and a small interval; the graphite heat storage sleeve 122 is sleeved on the outer wall of the horizontal pipe 121 and is in interference fit with the horizontal pipe 121; the horizontal pipe 121 is made of a steel pipe, the preheating section 9 is provided with one layer of graphite heat storage sleeve 122 less than the experiment section 12, and other structures and connection modes are the same as those of the copper pipe in the first example.

In addition, the distance between the T-type thermocouples 13 uniformly arranged from the inlet of the experimental section 12 to two thirds of the position of the experimental section 12 is large, and the distance between the T-type thermocouples 13 uniformly arranged at the rest position of the experimental section 12 is small.

The bottom of the T-shaped thermocouple 13 on the experimental section 12 is welded with the horizontal pipe 121, and the top of the T-shaped thermocouple 13 is connected with the data acquisition module 10 through a communication line 14; the data acquisition module 10 is connected with an industrial computer 11 through a communication line 14.

It should be noted that the T-shaped thermocouple 13 is inserted into the wall thickness of the horizontal tube inside the experimental section, and mainly measures the inner wall temperature of the horizontal tube (since the wall thickness is small and the thermal conductivity of the horizontal tube is high, the inner wall temperature is an approximate value here, because the bottom of the thermocouple is not in contact with the inner surface of the horizontal tube).

In a preferred embodiment, the refrigerant and cooling water flowing through the U-shaped condenser 19 flow in a counter-current manner.

And the electric fan and the heating plate on the refrigerant liquid storage tank are used for fine adjustment of system pressure and supercooling degree.

The invention discloses an adjusting method of a critical heat flux density measuring system in a horizontal pipe, which comprises the following steps: a refrigerant circulation circuit and a cooling water circulation circuit;

the flow of the refrigerant circulating loop is as follows:

the rigidity of the part between the refrigerant liquid storage tank and the ball valve switch is increased and the compressibility space of the part between the refrigerant liquid storage tank and the ball valve switch is reduced by adjusting the opening of the ball valve switch, refrigerant liquid pumped out of the gear pump enters the mass flowmeter, is preheated by the preheating section, enters the U-shaped condenser through the visual through pipe after the experiment is completed in the experiment section, is cooled into liquid, enters the gear pump through the refrigerant liquid storage tank, and is pumped out of the gear pump to complete the circulation;

the cooling water circulation loop flow is as follows:

cooling water in the water tank is pumped out by a water pump, flows through a U-shaped condenser to cool the gas-liquid two-phase refrigerant into liquid, and then flows back to the water tank again; in the process of transferring the refrigerant and the cooling water by the U-shaped condenser, the temperature of the cooling water is increased, so that the supercooling degree of the refrigerant flowing into the refrigerant liquid storage tank is reduced, and the instability of the flowing boiling measurement system is increased. Therefore, when the temperature of the cooling water in the water tank exceeds a certain range, the electromagnetic expansion valve is adjusted to a certain opening degree according to the pressure corresponding to the temperature of the cooling water, so that the liquid nitrogen in the liquid nitrogen tank is injected into the plastic water bottle, tap water in the plastic water bottle is instantly solidified into ice, and the cooling water is ensured to be close to a constant temperature through heat transfer between the solidified ice in the plastic water bottle and the cooling water.

The preheating section and the experimental section generate uniform and stable heat flow by electrifying the resistance wires with direct current, so that the use of alternating current is avoided, and the alternating magnetic field of the alternating current can influence the critical heat flow density. The purpose of setting up the preheating section is required entry quality when getting into the experiment section, and in the experiment section, because the influence of gravity, leads to the annular flow liquid film of horizontal pipe inner wall to distribute unevenly, and top liquid film thickness is thinner, and bottom liquid film thickness is thicker, in addition the influence of experiment section thermal current, and critical thermal current phenomenon generally appears at first in the position of being close to experiment section export top. In order to more reliably know the wall temperature condition of the experimental section and measure the critical heat flow density value, the arrangement density of the thermocouples is different according to different parts of the experimental section: the arrangement density of the part 2/3 before the inlet of the experimental section is low, and thermocouples are arranged every 100 mm; the part close to the outlet 1/3 of the experimental section is arranged with higher density, and thermocouples are arranged at intervals of 30 mm. Data obtained by parameter measurement in the experiment are collected through a data acquisition module, built-in signals are used for adjusting and measuring a thermocouple, direct current voltage and current, gear pump flow and water pump rotating speed, and the data are communicated with an industrial computer through a communication line, so that real-time data monitoring and storage are realized. Aiming at the critical heat flux density in the horizontal pipe under low heat flux and low flow rate, the judgment conditions are as follows: the thermocouple mean temperature value near the exit 1/3 of the experimental section was 3 ℃ higher than the thermocouple mean temperature value near the front 2/3 of the inlet of the experimental section for more than 6 seconds, with a concomitant decrease in the heat transfer coefficient. When critical heat flux density occurs, the pressure drop in the horizontal pipe of the experimental section is increased, the system pressure is reduced, the system pressure reduction can aggravate the system instability (the density difference between a gas phase and a liquid phase is increased due to the pressure reduction, and the disturbance of the pressure difference to a liquid film is higher than the high pressure under the low pressure condition), at the moment, the opening of the water pump is manually reduced through the industrial computer, the rotating speed of the water pump can be reduced, and the system pressure is increased. In addition, an electric fan and a heating plate on the refrigerant liquid storage tank are used for fine adjustment of system pressure and supercooling degree.

As shown in fig. 3, because the heat transfer coefficient of the steel tube is lower than that of the copper tube, the heated tube conducts heat axially, which causes dry-up points in the horizontal tube. Therefore, in order to avoid the dry points of the steel pipes during flowing boiling, aggravate the instability degree of the system and influence the measurement value of the critical heat flow density, the graphite heat storage sleeve is added outside the horizontal pipe, and the instantaneous heat flow received by the fluid working medium in the pipe and the axial temperature difference of the heated pipe are reduced by increasing the heat capacity of the pipe wall, so that the unstable amplitude of the flowing boiling is reduced, and the accuracy of measuring the critical heat flow density is improved.

While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.