Method for selecting and developing efficient working medium of pulsating heat pipe

Abstract

The method for selecting and developing the efficient working medium of the pulsating heat pipe comprises the following steps that a heat transfer model of the pulsating heat pipe in an evaporation section is established and used for calculating the heat transfer rate of the evaporation section of the pulsating heat pipe; obtaining a pulsating heat pipe working medium quality factor calculation formula based on the pulsating heat pipe evaporation section heat transfer rate; the pulsating heat pipes of the same size are adopted, and the quality factors of different working media are calculated based on a working medium quality factor formula; the calculation results of the quality factors of different working media are sequenced, the working medium with the maximum working medium quality factor value in the same temperature zone is selected as the optimal working medium of the pulsating heat pipe, and the quality factors of the optimal working medium are improved by adjusting thermophysical parameters such as the heat conductivity coefficient, the constant pressure specific heat capacity and the surface tension of the optimal working medium of the pulsating heat pipe; and development of a new efficient working medium of the pulsating heat pipe is achieved. According to the method, a researcher can priori select a more efficient pulsating heat pipe working medium before an experimental test, and the test cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of high - efficiency heat dissipation and cooling of pulsating heat pipes, and relates to a method for selecting and developing high - efficiency working fluids for pulsating heat pipes. Background Art

[0002] A pulsating heat pipe is an efficient heat transfer element that can be used under conditions of small space and high heat flux density. A typical tubular pulsating heat pipe is made by bending a capillary into a serpentine shape, evacuating the inside of the tube, and filling it with a certain amount of working fluid. The working fluid in the capillary is discrete into randomly distributed and spaced liquid plugs and gas plugs under the action of surface tension. It uses the pressure difference generated by the temperature difference between the hot and cold ends as the driving force for the movement of the working fluid, and conducts heat transfer through both sensible heat and latent heat. Compared with capillary heat pipes, it has the remarkable feature of strong heat transfer ability.

[0003] The working fluid is one of the most important factors affecting the heat transfer performance of pulsating heat pipes, which directly determines the temperature range and performance of pulsating heat pipes. The working fluid mainly affects the heat transfer characteristics of pulsating heat pipes through changes in thermophysical properties. At present, researchers mainly select working fluids through experimental testing methods. Experimental testing not only requires a large amount of manpower and material resources, but also may not necessarily find the optimal working fluid. In addition, due to the lack of relevant method guidance, it also obviously hinders the development of high - efficiency working fluids for pulsating heat pipes. The lack of a method applicable to the prediction and selection of high - efficiency pulsating heat pipe working fluids has become a bottleneck hindering the development of high - efficiency pulsating heat pipes and related product development. Summary of the Invention

[0004] In order to solve the problem that the prior art lacks a method for selecting high - efficiency working fluids for pulsating heat pipes, the technical solution adopted by the present invention is as follows:

[0005] A method for selecting and developing high - efficiency working fluids for pulsating heat pipes, comprising the following steps:

[0006] Establish a heat transfer model for the evaporation section of the pulsating heat pipe to calculate the heat transfer rate of the evaporation section of the pulsating heat pipe;

[0007] Based on the heat transfer rate of the evaporation section of the pulsating heat pipe, obtain a calculation formula for the quality factor of the pulsating heat pipe working fluid;

[0008] Calculate the quality factors of different working fluids based on the quality factor formula of the working fluid;

[0009] Sort the calculation results of the quality factors of different working fluids, and select the working fluid with the largest quality factor value under the same temperature range as the preferred working fluid for the pulsating heat pipe;

[0010] By adjusting the thermophysical parameters such as the thermal conductivity, specific heat capacity at constant pressure, and surface tension of the preferred working fluid of the pulsating heat pipe, improve the quality factor of the preferred working fluid to achieve the development of new high - efficiency working fluids for pulsating heat pipes.

[0011] Furthermore, by adjusting the thermal property parameters such as the thermal conductivity, specific heat, and surface tension of the preferred working fluid of the pulsating heat pipe, it is achieved by adding nanoparticles, surfactants, and adding mixed fluids to the preferred working fluid. Furthermore, the expression of the heat transfer rate in the heat transfer model of the evaporation section of the pulsating heat pipe is as follows:

[0012] Q in = h tp A e (T e - T sat )

[0013] In the formula: where h tp represents the heat transfer coefficient of the evaporation section, A is the evaporation section area of the pulsating heat pipe, T e and T sat respectively represent the wall temperature of the evaporation section of the pulsating heat pipe and the saturation temperature of the working fluid in the pipe;

[0014] The heat transfer coefficient of the evaporation section is as follows:

[0015]

[0016] In the formula: λ l represents the thermal conductivity of the liquid working fluid, σ is the liquid surface tension of the working fluid, ρ l and ρ g respectively represent the liquid density and gas density of the working fluid, μ l is the liquid dynamic viscosity of the working fluid, h fg is the latent heat of vaporization, q is the heat flux density, D h is the pipe diameter of the pulsating heat pipe.

[0017] Furthermore, the process of obtaining the calculation formula of the quality factor of the working fluid of the pulsating heat pipe based on the heat transfer rate formula of the evaporation section of the pulsating heat pipe is as follows:

[0018] According to the Clapeyron equation and the ideal gas state equation, satisfies the following formula:

[0019]

[0020] where: v g and v l represent the specific volume of gas and liquid in the saturated state;

[0021] The specific heat c p satisfies the following formula:

[0022]

[0023] The volume expansion coefficient αv Satisfy the following formula:

[0024]

[0025] When the working fluid changes from saturated liquid to saturated gas, it satisfies the following formula:

[0026]

[0027] The flow velocity of the working fluid in the pulsating heat pipe satisfies the following formula:

[0028]

[0029] Where: β and x0 represent the proportion of latent heat in the heat transfer rate and the mass fraction of the liquid phase at the inlet of the evaporation section;

[0030] Combining the above formulas, the heat transfer rate in the heat transfer model of the evaporation section of the pulsating heat pipe satisfies the following formula:

[0031]

[0032] The expression of the quality factor of the working fluid of the pulsating heat pipe satisfies the following formula.

[0033]

[0034] A device for selecting and developing an efficient working fluid for a pulsating heat pipe, comprising:

[0035] Heat transfer model module: used to establish the heat transfer model of the pulsating heat pipe in the evaporation section and calculate the heat transfer rate of the evaporation section of the pulsating heat pipe;

[0036] Working fluid quality factor calculation formula module: used to obtain the calculation formula of the working fluid quality factor of the pulsating heat pipe based on the heat transfer rate of the evaporation section of the pulsating heat pipe;

[0037] Working fluid quality factor calculation module: calculate different working fluid quality factors based on the working fluid quality factor formula;

[0038] Optimal working fluid sorting module: sort the calculation results of different working fluid quality factors, and select the working fluid with the largest working fluid quality factor value in the same temperature range as the optimal working fluid of the pulsating heat pipe;

[0039] Adjustment module: By adjusting the thermal property parameters such as the thermal conductivity, specific heat capacity at constant pressure, and surface tension of the optimal working fluid of the pulsating heat pipe, improve the quality factor of the optimal working fluid and realize the development of a new efficient working fluid for the pulsating heat pipe. A readable storage medium stores program modules, and the program modules can be run in a processor to implement the method described in any one of the above.

[0040] A method for selecting and developing high-efficiency working fluids for pulsating heat pipes provided by the present invention is used to guide the selection and development of high-efficiency working fluids for pulsating heat pipes. The present invention is mainly based on the heat transfer mechanism of pulsating heat pipes. By establishing a heat transfer model in the evaporation section of the pulsating heat pipe, the heat transfer rate in the evaporation section of the pulsating heat pipe is obtained, and further the thermophysical property parameters of the working fluid are extracted and used as a comprehensive parameter to measure the heat transfer ability of the working fluid for the pulsating heat pipe, that is, the quality factor of the working fluid for the pulsating heat pipe. Based on the quality factor of the working fluid for the pulsating heat pipe, the preferred working fluid in a certain temperature range is selected, and by adjusting the thermophysical property parameters such as the thermal conductivity, specific heat capacity at constant pressure, and surface tension of the preferred working fluid for the pulsating heat pipe, the quality factor of the preferred working fluid is improved, and new high-efficiency working fluids for pulsating heat pipes are developed. Compared with the prior art, the present invention has the following advantages:

[0041] 1. The method for selecting and developing high-efficiency working fluids for pulsating heat pipes provided by the present invention provides a guide for the selection and development of high-efficiency working fluids for pulsating heat pipes.

[0042] 2. The method for selecting and developing high-efficiency working fluids for pulsating heat pipes provided by the present invention enables researchers to select more efficient working fluids for pulsating heat pipes a priori before experimental testing, reducing the testing cost.

[0043] 3. The method for selecting and developing high-efficiency working fluids for pulsating heat pipes provided by the present invention comprehensively considers the influence of many thermophysical properties in the heat transfer process of pulsating heat pipes.

[0044] In summary, applying the technical solution of the present invention solves the problem in the prior art of lacking a guide for the selection and development method of high-efficiency working fluids for pulsating heat pipes.

[0045] For the above reasons, the present invention can be widely promoted in the fields of aviation, military industry, etc. where pulsating heat pipes are used for heat transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0047] Figure 1 is the flow chart of this method;

[0048] Figure 2 is the thermal resistance diagram of the copper pulsating heat pipe filled with acetone, ethanol, and deionized water in the present invention under different heating powers with a working inclination angle of 90° and a bottom heating mode.

[0049] Figure 3 is the quality factor diagram of acetone, ethanol, and deionized water in the present invention.

[0050] Figure 4 This is the thermal resistance diagram of the high-temperature pulsating heat pipe filled with potassium, rubidium, and cesium in the present invention at a working inclination angle of 90° and different heating powers in the bottom heating mode.

[0051] Figure 5 This is the figure of the quality factor of alkali metals sodium, potassium, rubidium, and cesium in the present invention.

[0052] Figure 6 This is the figure of the quality factor of conventional working fluids in the present invention. Detailed implementation manners

[0053] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0054] To make the objectives, 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 only a part of the embodiments of the present invention, rather than all the embodiments. The description of at least one exemplary embodiment below is actually only illustrative and in no way restrictive of the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0055] Figure 1 This is the flowchart of the method;

[0056] A method for selecting and developing an efficient working fluid for a pulsating heat pipe, characterized by comprising the following steps:

[0057] Establish a heat transfer model in the evaporation section of the pulsating heat pipe for calculating the heat transfer rate in the evaporation section of the pulsating heat pipe;

[0058] Based on the heat transfer rate in the evaporation section of the pulsating heat pipe, obtain the calculation formula for the quality factor of the working fluid of the pulsating heat pipe;

[0059] Use pulsating heat pipes of the same size to calculate the quality factors of different working fluids based on the quality factor formula of the working fluid;

[0060] Sort the calculation results of the quality factors of different working fluids, and select the working fluid with the largest quality factor value of the working fluid in the same temperature range as the preferred working fluid of the pulsating heat pipe;

[0061] By adjusting the thermal physical properties such as the thermal conductivity, specific heat capacity at constant pressure, and surface tension of the preferred working fluid of the pulsating heat pipe, improve the quality factor of the preferred working fluid, and realize the development of a new efficient working fluid for the pulsating heat pipe.

[0062] Further: The adjustment of the thermal physical properties such as the thermal conductivity, specific heat, and surface tension of the preferred working fluid of the pulsating heat pipe is achieved by adding nanoparticles, surfactants, and other fluids to the preferred working fluid.

[0063] The nanoparticles include, but are not limited to: alumina, copper oxide, titanium dioxide, silicon dioxide, etc., metal nanoparticles such as copper, gold, silver, etc., and carbon-based nanomaterials such as diamond, graphene oxide, carbon nanotubes, any one or several of them;

[0064] The surfactants include, but are not limited to: sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), fatty alcohol polyoxyethylene ether (AEO-9), sodium stearate (SLS), any one or several of them;

[0065] The mixed fluid includes binary and multi-component mixed fluids.

[0066] The binary mixed fluid includes one or several of water and HFE-7100, water and methanol, pentane and methanol. The multi-component mixed fluid includes multi-component fluids composed of nanofluids and self-wetting fluids, as well as mixed nanofluids, etc. The heat transfer model of the pulsating heat pipe in the evaporation section is as follows: Assuming that the inner wall of the pipe is smooth, that is, there is no capillary structure on the inner surface, and the working fluid is described by the ideal gas state equation when in the gas phase, the working process of the working fluid in the evaporation section of the pulsating heat pipe is regarded as flow boiling heat transfer.

[0067] Further: The expression of the heat transfer rate in the heat transfer model of the pulsating heat pipe in the evaporation section is as follows:

[0068] Q in =h tp A e (T e -T sat )

[0069] In the formula: where h tp represents the heat transfer coefficient of the evaporation section, A is the evaporation section area of the pulsating heat pipe, and T e and T sat represent the wall temperature of the evaporation section of the pulsating heat pipe and the saturation temperature of the working fluid in the pipe.

[0070] The heat transfer coefficient of the evaporation section is as follows:

[0071]

[0072] In the formula: λ l represents the thermal conductivity of the working fluid in the liquid state, σ is the surface tension of the working fluid, ρ l and ρ g respectively represent the liquid density and gas density of the working fluid, μl is the liquid dynamic viscosity of the working fluid, h fg is the latent heat of vaporization, q is the heat flux density, D h is the diameter of the pulsating heat pipe.

[0073] Furthermore, the process of obtaining the calculation formula for the quality factor of the pulsating heat pipe working fluid based on the heat transfer rate in the evaporation section of the pulsating heat pipe is as follows:

[0074] According to the Clapeyron equation and the ideal gas state equation, satisfies the following formula:

[0075]

[0076] where: v g and v l represent the specific volume of the gas and the specific volume of the liquid in the saturated state;

[0077] The specific heat c p satisfies the following formula:

[0078]

[0079] The volume expansion coefficient α v satisfies the following formula:

[0080]

[0081] When the working fluid changes from a saturated liquid to a saturated gas, it satisfies the following formula:

[0082]

[0083] The flow velocity of the working fluid satisfies the following formula:

[0084]

[0085] In the formula: β and x0 represent the proportion of latent heat in the heat transfer rate and the mass fraction of the liquid phase at the inlet of the evaporation section;

[0086] Combining the above formulas, the heat transfer rate in the heat transfer model of the evaporation section of the pulsating heat pipe satisfies the following formula:

[0087]

[0088] The expression of the quality factor of the pulsating heat pipe working fluid satisfies the following formula.

[0089]

[0090] The working fluid of the pulsating heat pipe includes low-temperature, medium-temperature, and high-temperature working fluids.

[0091] Low-temperature working fluid pulsating heat pipe: The working temperature range is 200 - 550K, and the working medium can be refrigerant, ammonia, alcohol, acetone, water, and organic substances, etc.

[0092] Medium-temperature working fluid pulsating heat pipe: The working temperature range is 550 - 750K, and the working media are Therminol, naphthalene, mercury, etc.

[0093] High-temperature working fluid pulsating heat pipe: The working temperature is above 750K, and the working media are liquid metals such as potassium, sodium, lithium, lead, silver and their alloys.

[0094] A device for selecting and developing high-efficiency working fluids for pulsating heat pipes, comprising:

[0095] Heat transfer model module: Used to establish the heat transfer model of the pulsating heat pipe in the evaporation section and calculate the heat transfer rate of the evaporation section of the pulsating heat pipe;

[0096] Working fluid quality factor calculation formula module: Used to obtain the calculation formula of the working fluid quality factor of the pulsating heat pipe based on the heat transfer rate of the evaporation section of the pulsating heat pipe;

[0097] Working fluid quality factor calculation module: Calculate the quality factors of different working fluids based on the working fluid quality factor formula;

[0098] Preferred working fluid sorting module: Sort the calculation results of the quality factors of different working fluids, and select the working fluid with the largest working fluid quality factor value in the same temperature range as the preferred working fluid of the pulsating heat pipe;

[0099] Adjustment module: By adjusting the thermal physical properties such as the thermal conductivity, specific heat capacity at constant pressure, and surface tension of the preferred working fluid of the pulsating heat pipe, improve the quality factor of the preferred working fluid and realize the development of new high-efficiency working fluids for pulsating heat pipes. A readable storage medium stores program modules, and the program modules can be run in a processor to implement the method described in any one of the above.

[0100] Example 1

[0101] In this example, a copper pulsating heat pipe with 6 elbows was fabricated. The inner diameter of the copper tube is 2mm, the outer diameter is 3mm, and acetone, ethanol, and deionized water are used as working fluids, with a filling ratio of 50%. Under the bottom heating mode, the heat transfer performance of the three pulsating heat pipes at a working inclination of 90° was tested. The heat transfer performance of the pulsating heat pipe is represented by thermal resistance, as Figure 2 shown. Figure 2 The figure shows the quality factor diagrams of the three working fluids.

[0102] From Figure 2 it can be seen that the order of the thermal resistance magnitudes of the three working fluids is: ethanol > deionized water > acetone. At Figure 3The acetone curve is at the top, deionized water is next, and ethanol is at the bottom. The quality factor is consistent with the experimental thermal resistance results, indicating that for these three working fluids, the pulsating heat pipe filled with acetone has better heat transfer performance under the same pulsating heat pipe size and test conditions.

[0103] Example 2

[0104] In this example, a high-temperature pulsating heat pipe with 6 elbows was fabricated. The shell was made of 310s stainless steel, with an inner diameter of 3.5 mm and an outer diameter of 6 mm. Alkali metals sodium, potassium, rubidium, and cesium were used as working fluids, and the filling ratio was 50%. Under the bottom heating mode, the heat transfer performance of four pulsating heat pipes was tested at a working inclination angle of 90°. The heat transfer performance of the pulsating heat pipe was represented by thermal resistance.

[0105] During the test, we found that the pulsating heat pipe filled with sodium did not start successfully, had the worst heat transfer performance, and the largest thermal resistance. The thermal resistance of the high-temperature pulsating heat pipes filled with potassium, rubidium, and cesium varied with the heating power as Figure 4 shown. Figure 5 It is a quality factor diagram of four alkali metals.

[0106] From Figure 4 and Figure 5 it can be seen that the thermal resistance order of the four high-temperature pulsating heat pipes is consistent with the quality factor. The quality factors of rubidium and cesium are higher than those of sodium and potassium, and the heat transfer performance of the high-temperature pulsating heat pipe with sodium as the working fluid is much lower than that of the other three working fluids.

[0107] Example 3

[0108] In this example, the quality factors of conventional working fluids were calculated and plotted using the proposed quality factor, as Figure 6 shown, including R134a, R245fa, R113, R152a, R22, acetone, ethanol, ammonia, and deionized water, to facilitate the selection of working fluids for pulsating heat pipes.

[0109] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for selecting and developing an efficient working fluid for a pulsating heat pipe, characterized in that: Including the following steps: Establish a heat transfer model of the pulsating heat pipe in the evaporation section to calculate the heat transfer rate of the pulsating heat pipe evaporation section; Based on the heat transfer rate of the pulsating heat pipe evaporation section, obtain the calculation formula for the quality factor of the pulsating heat pipe working fluid; Calculate the quality factors of different working fluids based on the working fluid quality factor formula; Sort the calculation results of the quality factors of different working fluids, and select the working fluid with the largest quality factor value in the same temperature range as the preferred working fluid of the pulsating heat pipe; By adjusting the thermal property parameters such as the thermal conductivity, specific heat at constant pressure, and surface tension of the preferred working fluid of the pulsating heat pipe, improve the quality factor of the preferred working fluid and achieve the development of a new high-efficiency working fluid for the pulsating heat pipe.

2. A method for selecting and developing an efficient working fluid for a pulsating heat pipe according to claim 1, characterized in that: The adjustment of the thermal property parameters such as the thermal conductivity, specific heat, and surface tension of the preferred working fluid of the pulsating heat pipe is achieved by adding nanoparticles, surfactants, and adding mixed fluids to the preferred working fluid.

3. A method for selecting and developing an efficient working fluid for a pulsating heat pipe according to claim 1, characterized in that: The expression of the heat transfer rate in the heat transfer model of the pulsating heat pipe evaporation section is as follows: Q in = h tp A e (T e - T sat ) In the formula: where h tp represents the heat transfer coefficient of the evaporation section, A is the area of the evaporation section of the pulsating heat pipe, T e and T sat respectively represent the wall temperature of the evaporation section of the pulsating heat pipe and the saturation temperature of the working fluid inside the pipe; The heat transfer coefficient of the evaporation section is as follows: Where: λ l represents the thermal conductivity of the working fluid in the liquid state, σ is the surface tension of the working fluid, ρ l and ρ g represent the liquid density and gas density of the working fluid respectively, μ l is the liquid dynamic viscosity of the working fluid, h fg is the latent heat of vaporization, q is the heat flux density, D h is the diameter of the pulsating heat pipe.

4. A method for selecting and developing an efficient working fluid for a pulsating heat pipe according to claim 1, characterized in that: The process of obtaining the calculation formula for the quality factor of the pulsating heat pipe working fluid based on the heat transfer rate formula of the pulsating heat pipe in the evaporation section is as follows: According to the Clapeyron equation and the ideal gas state equation, the following formula is satisfied: where: v g and v l represent the specific volume of the gas and the specific volume of the liquid in the saturated state; Specific heat c p Satisfies the following formula: Coefficient of volume expansion α v Satisfies the following formula: When the working fluid changes from a saturated liquid to a saturated gas, the following formula is satisfied: The flow velocity of the working fluid in the pulsating heat pipe satisfies the following formula: Where: β and x0 represent the latent heat ratio in the heat transfer rate and the mass fraction of the liquid phase at the evaporation section inlet; Combining the above formulas, the heat transfer rate in the heat transfer model of the pulsating heat pipe evaporation section satisfies the following formula: The expression of the quality factor of the pulsating heat pipe working fluid satisfies the following formula:

5. A device for selecting and developing an efficient working fluid for a pulsating heat pipe, characterized in that: Including Heat transfer model module: used to establish a heat transfer model of the pulsating heat pipe in the evaporation section to calculate the heat transfer rate of the pulsating heat pipe evaporation section; Working fluid quality factor calculation formula module: used to obtain the calculation formula for the quality factor of the pulsating heat pipe working fluid based on the heat transfer rate of the pulsating heat pipe evaporation section; Working fluid quality factor calculation module: calculate the quality factors of different working fluids based on the working fluid quality factor formula; Preferred working fluid sorting module: sort the calculation results of the quality factors of different working fluids, and select the working fluid with the largest quality factor value in the same temperature range as the preferred working fluid of the pulsating heat pipe; Adjustment module: by adjusting the thermal property parameters such as the thermal conductivity, specific heat at constant pressure, and surface tension of the preferred working fluid of the pulsating heat pipe, improve the quality factor of the preferred working fluid and achieve the development of a new high-efficiency working fluid for the pulsating heat pipe.

6. A readable storage medium storing program modules, characterized in that, The program module running in the processor can implement the method according to any one of claims 1-4.

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