System and method for measuring convective heat transfer coefficient in low-temperature fluid pipe

Abstract

The invention relates to the technical field of convective heat transfer coefficient measurement, in particular to a system and a method for measuring a convective heat transfer coefficient in a low-temperature fluid pipe. The system comprises a convective heat transfer coefficient measuring device, the measuring device comprises a first middle pipeline, two first heating electrodes and a plurality of first temperature sensors, and the two first heating electrodes are arranged at the two ends of the first middle pipeline; the plurality of first temperature sensors are used for measuring the wall surface temperature of the first middle pipeline between the two first heating electrodes; based on the mass flow of the low-temperature fluid flowing through the first middle pipeline, the change function of the specific heat of the low-temperature fluid along with the temperature, the length of the first middle pipeline between the two first heating electrodes, the inner diameter of the first middle pipeline, the heating power of the two first heating electrodes and the wall surface temperature measured by the multiple first temperature sensors, the temperature of the low-temperature fluid is measured. And the convective heat transfer coefficient in the low-temperature fluid pipe is determined. According to the scheme, the convective heat transfer coefficient of low-temperature fluid such as liquid hydrogen can be effectively measured.

Description

Technical Field

[0001] The invention relates to the technical field of convective heat transfer coefficient measurement, and in particular to a system and method for measuring the convective heat transfer coefficient in a cryogenic fluid tube. Background Art

[0002] In the engineering field, thermophysical property measurements are crucial, especially when it comes to optimizing heat exchangers, cooling systems, and thermal management equipment. Accurately measuring the convective heat transfer coefficient of cryogenic fluids (usually fluids with a saturation temperature below 120K at normal pressure are called cryogenic fluids, such as liquid hydrogen, liquid helium, liquid nitrogen, etc.) in tubes helps engineers adjust the design to ensure optimal heat transfer performance and energy efficiency. In addition, accurate local convective heat transfer coefficient data is essential for verifying calculation models.

[0003] The density of hydrogen at room temperature and pressure is very low. Safe and efficient storage of hydrogen is the key to long-distance transportation and large-scale application of hydrogen. The main current hydrogen storage methods include high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, and solid material hydrogen storage. Among them, low-temperature liquid hydrogen storage has the advantages of high storage-to-weight ratio, low storage and transportation pressure, and high safety in use. It has good application prospects in aerospace, energy, chemical industry, and medicine. However, the temperature of liquid hydrogen is extremely low, and the boiling point under normal pressure is about 20.37 K. The temperature difference with the external environment is usually more than 200K. The storage, transportation, filling, and vaporization of liquid hydrogen are all accompanied by flow heat exchange.

[0004] Therefore, there is an urgent need to provide a system and method for measuring the convective heat transfer coefficient in a cryogenic fluid tube to effectively measure the convective heat transfer coefficient of cryogenic fluids such as liquid hydrogen. Summary of the invention

[0005] The embodiment of the present invention provides a system and method for measuring the convective heat transfer coefficient in a cryogenic fluid tube, which can effectively realize the measurement of the convective heat transfer coefficient of cryogenic fluids such as liquid hydrogen.

[0006] In a first aspect, an embodiment of the present invention provides a system for measuring a convective heat transfer coefficient in a cryogenic fluid pipe, comprising a device for measuring a convective heat transfer coefficient, wherein the device comprises a measuring area, wherein a first intermediate pipeline, two first heating electrodes and a plurality of first temperature sensors are arranged in the measuring area, wherein the two first heating electrodes are arranged at both ends of the first intermediate pipeline, and the plurality of first temperature sensors are used to measure a wall temperature of the first intermediate pipeline between the two first heating electrodes; The convective heat transfer coefficient in the cryogenic fluid tube is determined based on the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline, the function of the change of the specific heat of the cryogenic fluid with temperature, the length of the first intermediate pipeline between the two first heating electrodes, the inner diameter of the first intermediate pipeline, the heating power of the two first heating electrodes, and the wall temperature measured by multiple first temperature sensors.

[0007] In a second aspect, an embodiment of the present invention provides a method for measuring the convective heat transfer coefficient in a cryogenic fluid pipe, which is applied to the system described in the above embodiment, comprising: Acquire the mass flow rate of the low-temperature fluid flowing through the first intermediate pipeline, the heating power of the two first heating electrodes, and the wall temperature measured by the plurality of first temperature sensors; The convective heat transfer coefficient in the cryogenic fluid tube is determined based on the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline, the function of the change of the specific heat of the cryogenic fluid with temperature, the length of the first intermediate pipeline between the two first heating electrodes, the inner diameter of the first intermediate pipeline, the heating power of the two first heating electrodes, and the wall temperature measured by multiple first temperature sensors.

[0008] The embodiment of the present invention provides a system and method for measuring the convective heat transfer coefficient in a cryogenic fluid tube. By setting a first intermediate pipeline, two first heating electrodes and a plurality of first temperature sensors in the measurement area, the convective heat transfer coefficient in the cryogenic fluid tube can be determined based on the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline, the function of the change of the specific heat of the cryogenic fluid with temperature, the length of the first intermediate pipeline between the two first heating electrodes, the inner diameter of the first intermediate pipeline, the heating power of the two first heating electrodes and the wall temperature measured by the plurality of first temperature sensors. Therefore, the above technical solution can effectively realize the measurement of the convective heat transfer coefficient of cryogenic fluids such as liquid hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0010] Figure 1 It is a structural schematic diagram of a measuring device in a system for measuring a convective heat transfer coefficient of a cryogenic fluid in a tube provided by an embodiment of the present invention; Figure 2 yes Figure 1 A schematic diagram of the structure of the measuring area in the measuring device shown; Figure 3 yes Figure 1 A schematic diagram of the structure of the end cover in the measuring device shown; Figure 4 yes Figure 1 A schematic diagram of the structure of the pipe support in the measuring device shown; Figure 5 It is a schematic diagram of the structure of a system for measuring the convective heat transfer coefficient of a cryogenic fluid in a tube provided by an embodiment of the present invention.

[0011] Reference numerals: 10- measuring device; 20- Dewar; 30- weight sensor; 40- helium cylinder; 50- flow regulating valve; 11-first intermediate pipeline; 12-first heating electrode; 13-first temperature sensor; 21 - second intermediate pipeline; 22 - second heating electrode; 23 - mixer; 24 - second temperature sensor; 25 - pressure sensor; 31- spiral coil; 32- third temperature sensor; 41-tank body; 42-end cover; 43-pipeline support; 44-vacuum port; 45-vacuum pump; 431 - insulation ring; 432 - support ring; 433 - support rod; 434 - fixing bracket. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0013] like Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a system for measuring the convective heat transfer coefficient in a cryogenic fluid pipe, including a convective heat transfer coefficient measuring device 10, the measuring device 10 including a measuring area, a first intermediate pipeline 11, two first heating electrodes 12 and a plurality of first temperature sensors 13 are arranged in the measuring area, the two first heating electrodes 12 are arranged at both ends of the first intermediate pipeline 11, and the plurality of first temperature sensors 13 are used to measure the wall temperature of the first intermediate pipeline 11 between the two first heating electrodes 12; The convective heat transfer coefficient in the cryogenic fluid tube is determined based on the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline 11, the function of the change of the specific heat of the cryogenic fluid with temperature, the length of the first intermediate pipeline 11 between the two first heating electrodes 12, the inner diameter of the first intermediate pipeline 11, the heating power of the two first heating electrodes 12, and the wall temperature measured by multiple first temperature sensors 13.

[0014] In this embodiment, by arranging the first intermediate pipeline 11, two first heating electrodes 12 and a plurality of first temperature sensors 13 in the measurement area, the convective heat transfer coefficient in the cryogenic fluid pipe can be determined based on the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline 11, the function of the change of the specific heat of the cryogenic fluid with the temperature, the length of the first intermediate pipeline 11 between the two first heating electrodes 12, the inner diameter of the first intermediate pipeline 11, the heating power of the two first heating electrodes 12 and the wall temperature measured by the plurality of first temperature sensors 13. Therefore, the above technical solution can effectively realize the measurement of the convective heat transfer coefficient of cryogenic fluids such as liquid hydrogen.

[0015] In some implementations, the first temperature sensor 13 may be a thermocouple, or other types of temperature sensors, which are not specifically limited herein.

[0016] In some embodiments, the cryogenic fluid may be liquid hydrogen, liquid helium, liquid nitrogen, etc., which are not specifically limited herein.

[0017] In one embodiment of the present invention, the convective heat transfer coefficient is determined by the following formula: In the formula, h (x) represents the convective heat transfer coefficient, q represents the heat flux density of the tube wall, T w (x) represents the wall temperature measured by the first temperature sensors 13, x represents the positions of the plurality of first temperature sensors 13, x =0 represents the position of the first heating electrode 12 arranged along the flow direction of the low-temperature fluid, T f (x) represents the local effective temperature of the fluid, P represents the heating power of the two first heating electrodes 12, D represents the inner diameter of the first intermediate pipeline 11, L represents the length of the first intermediate pipeline 11 between the two first heating electrodes 12, Qrepresents the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline 11, c p (T) represents the function of the change of specific heat of cryogenic fluid with temperature.

[0018] It should be noted that T w (x) The thermal resistance of the tube wall is ignored, and the outer wall temperature is measured experimentally as the inner wall temperature; the heat flux density of the tube wall surface is heated q Considered uniform; T f (x) is estimated by the law of conservation of energy.

[0019] In one embodiment of the present invention, the measuring device 10 also includes a preheating area, which is connected to the measuring area and is located upstream of the measuring area. A second intermediate pipeline 21, two second heating electrodes 22, a mixer 23, a second temperature sensor 24 and a pressure sensor 25 are arranged in the preheating area. The two second heating electrodes 22 are arranged at both ends of the second intermediate pipeline 21. The mixer 23 is connected to the end of the second intermediate pipeline 21. The diameter of the mixer 23 is larger than the diameter of the second intermediate pipeline 21, which is used to improve the uniformity of the temperature of the fluid in the pipe. The second temperature sensor 24 is used to measure the temperature of the fluid in the pipe at the outlet of the mixer 23, and the pressure sensor 25 is used to measure the pressure in the pipe at the outlet of the mixer 23.

[0020] In this embodiment, by providing the mixer 23, the uniformity of the temperature of the fluid in the tube can be improved; by providing the second temperature sensor 24 and the pressure sensor 25, different measurement conditions of the cryogenic fluid (i.e., the inlet temperature and inlet pressure of the measurement area) can be adjusted to achieve the measurement of the convective heat transfer coefficient under different working conditions. Among them, the second heating electrode 22 is used to connect to an external DC power supply, and the current passes through the second intermediate pipeline 21 to preheat the cryogenic fluid in the tube by using the resistance of the second intermediate pipeline 21, so as to adjust the inlet temperature of the cryogenic fluid in the downstream measurement area.

[0021] In one embodiment of the present invention, the measuring device 10 also includes an inlet area and an outlet area. The inlet area is connected to the preheating area and is located upstream of the preheating area. The outlet area is connected to the measuring area and is located downstream of the measuring area. A spiral coil 31 is arranged in the inlet area. The spiral coil 31 is used to absorb the expansion and contraction of the pipeline. A third temperature sensor 25 is arranged in the outlet area. The third temperature sensor 25 is used to measure the temperature of the fluid in the pipe in the outlet area.

[0022] It can be understood that the entrance area, preheating area, measurement area, and exit area are connected in sequence through flanges. To prevent leakage of the first heating electrode 12 in the measurement area and the second heating electrode 22 in the preheating area, the flange gaskets and bolt washers used in the flanges can be made of insulating materials.

[0023] In one embodiment of the present invention, the measuring device 10 further includes a tank body 41, two end caps 42 and two pipe brackets 43. The two end caps 42 are sealed at both ends of the tank body 41, and the two pipe brackets 43 are fixed inside the tank body 41. A measuring area is formed between the two pipe brackets 43. One end cap 42 and one pipe bracket 43 form an inlet area and a preheating area, and the other end cap 42 and the other pipe bracket 43 form an outlet area. A vacuum port 44 is provided on the tank body 41. The vacuum port 44 is used to use an external vacuum pump 45 (see Figure 5 ) The tank body 41 is evacuated.

[0024] In this embodiment, by evacuating the tank body 41, heat leakage of the cryogenic fluid can be reduced; by providing a pipeline support 43, the stability of the pipeline can be ensured.

[0025] It can be understood that an external DC power supply can apply DC power to the first intermediate pipeline 11 through the first heating electrode 12, so as to utilize the inherent resistance of the first intermediate pipeline 11 to achieve uniform heating of the fluid in the pipeline, and the pipeline surface temperature (i.e., the wall temperature) is collected through a thermocouple, and the power line of the first heating electrode 12 and the signal line of the thermocouple can be led out of the tank body 41 through the top cover.

[0026] like Figure 3 As shown, in one embodiment of the present invention, the end cover 42 is formed by stacking a plurality of U-shaped structures connected in sequence, so that the heat leakage from the tank body 41 to the pipeline can be reduced by increasing the heat conduction distance.

[0027] like Figure 4 As shown, in one embodiment of the present invention, the pipeline support 43 includes an insulating ring 431, a support ring 432, a support rod 433 and a fixing bracket 434 which are connected in sequence. The insulating ring 431 is sleeved on the outside of the support ring 432 and abuts against the inner wall of the tank body 41. One end of the support rod 433 is fixed to the inner wall of the support ring 432, and the other end is connected to the fixing bracket 434. The fixing bracket 434 is used to fix the intermediate pipeline through which the cryogenic fluid flows.

[0028] In some embodiments, the insulating ring 431 may be a bakelite ring, and the support ring 432, the support rod 433 and the fixing bracket 434 may be made of metal materials such as stainless steel, which are not specifically limited herein.

[0029] In one embodiment of the present invention, one pipeline support 43 is disposed upstream of the second temperature sensor 24, and the other pipeline support 43 is disposed downstream of the third temperature sensor 25, so that the influence of heat leakage of the pipeline support 43 on the measurement result can be minimized.

[0030] like Figure 5 As shown, in one embodiment of the present invention, the above-mentioned measuring system further includes a dewar 20, a weight sensor 30, a helium cylinder 40 and a flow regulating valve 50. The dewar 20 is used to contain a cryogenic fluid, the weight sensor 30 is used to measure the real-time weight of the dewar 20, the helium cylinder 40 is used to pass into the dewar 20 to cause the cryogenic fluid in the dewar 20 to enter the measuring device 10, and the flow regulating valve 50 is used to control the flow of the cryogenic fluid entering the measuring device 10.

[0031] In this embodiment, by adjusting the flow control valve 50, the flow rate of the cryogenic fluid can be controlled to reach the target value; by setting the weight sensor 30, the total weight of the Dewar 20 can be measured in real time; when the heat exchange state in the measuring device 10 (i.e., the wall temperature of the pipeline) reaches stability (for example, the wall temperature fluctuation within 100s can be specified to be <0.03K), the mass flow rate of the cryogenic fluid can be calculated by the weight change value.

[0032] Of course, a mass flow sensor may also be used to monitor the mass flow of the cryogenic fluid, which will not be described in detail here.

[0033] In addition, an embodiment of the present invention further provides a method for measuring the convective heat transfer coefficient in a cryogenic fluid pipe, which is applied to the system mentioned in any of the above embodiments, comprising: Obtaining the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline 11, the heating power of the two first heating electrodes 12, and the wall temperature measured by the plurality of first temperature sensors 13; The convective heat transfer coefficient in the cryogenic fluid tube is determined based on the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline 11, the function of the change of the specific heat of the cryogenic fluid with temperature, the length of the first intermediate pipeline 11 between the two first heating electrodes 12, the inner diameter of the first intermediate pipeline 11, the heating power of the two first heating electrodes 12, and the wall temperature measured by multiple first temperature sensors 13.

[0034] It can be understood that the method embodiment and system embodiment provided by the present invention are based on the same inventive concept and have the same beneficial effects, and the beneficial effects of the method embodiment will not be elaborated herein.

[0035] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the presence of other identical factors in the process, method, article or device including the elements.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for measuring the convective heat transfer coefficient of a cryogenic fluid in a pipe, characterized in that: A device (10) for measuring a convective heat transfer coefficient is provided, wherein the device (10) comprises a measuring area, wherein a first intermediate pipeline (11), two first heating electrodes (12) and a plurality of first temperature sensors (13) are arranged in the measuring area, wherein the two first heating electrodes (12) are arranged at two ends of the first intermediate pipeline (11), and the plurality of first temperature sensors (13) are used to measure the wall temperature of the first intermediate pipeline (11) located between the two first heating electrodes (12); The convective heat transfer coefficient in the cryogenic fluid tube is determined based on the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline (11), the function of the change of the specific heat of the cryogenic fluid with temperature, the length of the first intermediate pipeline (11) between the two first heating electrodes (12), the inner diameter of the first intermediate pipeline (11), the heating power of the two first heating electrodes (12) and the wall temperature measured by the plurality of first temperature sensors (13).

2. The system according to claim 1, characterized in that The convective heat transfer coefficient is determined by the following formula: In the formula, h (x) represents the convective heat transfer coefficient, q represents the heat flux density of the tube wall, T w ( x ) represents the wall temperature measured by the plurality of first temperature sensors (13), x represents the positions of the plurality of first temperature sensors (13), x =0 represents the position of the first heating electrode (12) arranged along the flow direction of the low-temperature fluid, T f ( x ) represents the local effective temperature of the fluid, P represents the heating power of the two first heating electrodes (12), D represents the inner diameter of the first intermediate pipeline (11), L represents the length of the first intermediate pipeline (11) between the two first heating electrodes (12), Q represents the mass flow rate of the low-temperature fluid flowing through the first intermediate pipeline (11), c p (T) represents the function of the change of specific heat of the cryogenic fluid with temperature.

3. The system according to claim 1, characterized in that The measuring device (10) further comprises a preheating region, the preheating region being connected to the measuring region and being located upstream of the measuring region, the preheating region being provided with a second intermediate pipeline (21), two second heating electrodes (22), a mixer (23), a second temperature sensor (24) and a pressure sensor (25), the two second heating electrodes (22) being provided at both ends of the second intermediate pipeline (21), the mixer (23) being connected to the end of the second intermediate pipeline (21), the diameter of the mixer (23) being larger than the diameter of the second intermediate pipeline (21) and being used to improve the uniformity of the temperature of the fluid in the pipeline, the second temperature sensor (24) being used to measure the temperature of the fluid in the pipeline at the outlet of the mixer (23), and the pressure sensor (25) being used to measure the pressure in the pipeline at the outlet of the mixer (23).

4. The system according to claim 3, characterized in that The measuring device (10) further comprises an inlet area and an outlet area, wherein the inlet area is connected to the preheating area and is located upstream of the preheating area, and the outlet area is connected to the measuring area and is located downstream of the measuring area. A spiral coil (31) is arranged in the inlet area, and the spiral coil (31) is used to absorb the expansion and contraction of the pipeline. A third temperature sensor (25) is arranged in the outlet area, and the third temperature sensor (25) is used to measure the temperature of the fluid in the pipe in the outlet area.

5. The system according to claim 4, characterized in that The measuring device (10) further comprises a tank body (41), two end covers (42) and two pipe supports (43), wherein the two end covers (42) are sealedly arranged at two ends of the tank body (41), the two pipe supports (43) are fixed inside the tank body (41), the measuring area is formed between the two pipe supports (43), one end cover (42) and one pipe support (43) form the inlet area and the preheating area, and the other end cover (42) and the other pipe support (43) form the outlet area, and the tank body (41) is provided with a vacuum port (44), and the vacuum port (44) is used to evacuate the tank body (41) using an external vacuum pump (45).

6. The system according to claim 5, characterized in that The end cover (42) is formed by stacking a plurality of U-shaped structures connected in sequence.

7. The system according to claim 5, characterized in that The pipeline support (43) comprises an insulating ring (431), a support ring (432), a support rod (433) and a fixing bracket (434) which are connected in sequence; the insulating ring (431) is sleeved on the outside of the support ring (432) and abuts against the inner wall of the tank body (41); one end of the support rod (433) is fixed to the inner wall of the support ring (432), and the other end is connected to the fixing bracket (434); the fixing bracket (434) is used to fix the intermediate pipeline flowing through the cryogenic fluid.

8. The system according to claim 5, characterized in that One of the pipeline supports (43) is arranged upstream of the second temperature sensor (24), and the other pipeline support (43) is arranged downstream of the third temperature sensor (25).

9. The system according to any one of claims 1 to 8, characterized in that: The measuring device (10) further comprises a dewar (20), a weight sensor (30), a helium cylinder (40) and a flow regulating valve (50); the dewar (20) is used to contain the cryogenic fluid; the weight sensor (30) is used to measure the real-time weight of the dewar (20); the helium cylinder (40) is used to pass into the dewar (20) to cause the cryogenic fluid in the dewar (20) to enter the measuring device (10); and the flow regulating valve (50) is used to control the flow of the cryogenic fluid entering the measuring device (10).

10. A method for measuring the convective heat transfer coefficient of a cryogenic fluid pipe, characterized in that: A system as claimed in any one of claims 1 to 9, comprising: Acquiring the mass flow rate of the low-temperature fluid flowing through the first intermediate pipeline (11), the heating power of the two first heating electrodes (12), and the wall temperature measured by the plurality of first temperature sensors (13); The convective heat transfer coefficient in the cryogenic fluid tube is determined based on the mass flow rate of the cryogenic fluid flowing through the first intermediate pipeline (11), the function of the change of the specific heat of the cryogenic fluid with temperature, the length of the first intermediate pipeline (11) between the two first heating electrodes (12), the inner diameter of the first intermediate pipeline (11), the heating power of the two first heating electrodes (12) and the wall temperature measured by the plurality of first temperature sensors (13).

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