Design method of dynamic critical tube diameter of pulsating heat pipe in horizontal state

Abstract

This invention provides a dynamic critical diameter design method for a pulsating heat pipe in a horizontal state. The steps are as follows: Step 1, establish a first model, a second model, and a third model; Step 2, combining the first, second, and third models, and without considering the heat conduction of the pipe wall and working fluid, obtain a fourth model according to the law of conservation of mass in a gas-liquid stratification state; Step 3, establish a fifth model; Step 4, establish a sixth model based on the fifth model; Step 5, establish a seventh model, which is the critical vapor velocity for the transition from gas-liquid stratification to intermittent flow in the horizontal pulsating heat pipe obtained from the sixth model; Step 6, determine the minimum input power for the transition from gas-liquid stratification to intermittent flow in the pulsating heat pipe based on the fourth and seventh models, and obtain the dynamic critical diameter of the pulsating heat pipe in a horizontal state by combining the working fluid properties, filling ratio, and gas-liquid channel cross-sectional area. This invention expands the application scope of pulsating heat pipes.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation technology for high-power and high-heat-flux-density components. More specifically, it relates to a dynamic critical diameter design method for a pulsating heat pipe in a horizontal state, and proposes a dynamic critical diameter for the pulsating heat pipe in a horizontal state. Background Technology

[0002] A pulsating heat pipe is a highly efficient heat transfer element with advantages such as simple structure, wide applicability, and strong heat transfer performance. Pulsating heat pipes are generally made of bent metal tubes in a serpentine shape. After the tube is evacuated, a certain volume fraction of working fluid is filled in. Under the influence of surface tension, gravity, and flow resistance, the liquid working fluid forms randomly distributed gas and liquid plugs within the tube. Part of the working fluid evaporates or condenses at either the evaporation or condensation end of the pulsating heat pipe, creating a pressure difference between the hot and cold sections, driving the working fluid to flow within the tube, thereby achieving efficient heat transfer.

[0003] The diameter of a pulsating heat pipe has a significant impact on its heat transfer performance. The maximum diameter of a pulsating heat pipe that ensures the liquid plug can remain suspended in the gas plug at the operating temperature is called the critical diameter. Existing critical diameter design methods only consider the effects of static factors and do not account for the dynamic conditions during actual operation. Experiments have shown that pulsating heat pipes exceeding the critical diameter can still operate under certain conditions with heat input at the heating end. The maximum diameter that ensures the operation of a supercritical pulsating heat pipe is defined as the dynamic critical diameter.

[0004] There is a need to propose a new design method for pulsating heat pipes with diameters exceeding the critical diameter, i.e., supercritical pulsating heat pipes, to achieve better operating conditions and heat transfer performance, thus overcoming the limitations of existing technology research. Summary of the Invention

[0005] To address the issue that existing pulsating heat pipe diameter design only considers static forces, this invention provides a dynamic critical diameter design method for pulsating heat pipes in horizontal conditions. This invention primarily obtains a fourth model by establishing a first, second, and third model; and a seventh model by establishing a fifth and sixth model. The fourth and seventh models determine the minimum input power required for the transition from gas-liquid stratification to intermittent flow within the pulsating heat pipe. By combining these models with the working fluid properties, filling ratio, and gas-liquid channel cross-sectional area, the dynamic critical diameter of the pulsating heat pipe in horizontal conditions is obtained.

[0006] The technical means employed in this invention are as follows:

[0007] A method for designing the dynamic critical diameter of a pulsating heat pipe in a horizontal state, comprising:

[0008] Step 1: Establish the first model, the second model, and the third model. The first model is the heat absorption model of the working fluid in the pulsating heat pipe when the input heat fails to enable the pulsating heat pipe to work normally. The second model is the mass flow rate of the gaseous working fluid that undergoes phase change per unit time. The third model is the mass flow rate of the liquid working fluid that undergoes phase change in the pulsating heat pipe. The first model, the second model, and the third model are obtained from the parameters of the working fluid in the pipe in the state of gas-liquid stratification before operation. The parameters include the average flow velocity of the gas-liquid working fluid in the pulsating heat pipe, the density of the gas-liquid working fluid, and the cross-sectional area of ​​the gas-liquid working fluid channel.

[0009] Step 2: Combining the first model, the second model, and the third model, without considering the heat conduction of the pipe wall and the working fluid, in the gas-liquid stratification state, according to the law of conservation of mass, the fourth model is obtained. The fourth model is the flow velocity of the gas working fluid relative to the liquid working fluid before the pulsating heat pipe is working.

[0010] Step 3: Establish the fifth model, which is the liquid level height under gas-liquid stratification. It is obtained by using the cross-sectional area of ​​the gaseous working fluid channel and the cross-sectional area of ​​the liquid working fluid channel, expressed by the liquid filling rate of the working fluid, based on geometric relationships.

[0011] Step 4: Establish a sixth model based on the fifth model. The sixth model is the critical velocity for the growth of the liquid surface wave crest. This model is the vapor velocity that allows the liquid surface wave crest to grow to contact the upper wall of the pipe when the flow pattern changes due to the pressure difference between two infinite plates without considering the heat conduction of the pipe wall and the working fluid.

[0012] Step 5: Establish the seventh model, which is the critical vapor velocity for the transition from gas-liquid stratification to intermittent flow in a horizontally pulsating heat pipe, obtained from the sixth model.

[0013] Step 6: Determine the minimum input power required for the gas-liquid stratification flow pattern to transform into intermittent flow in the pulsating heat pipe based on the fourth and seventh models. Then, combine the working fluid properties, filling rate, and gas-liquid channel cross-sectional area to obtain the dynamic critical pipe diameter of the pulsating heat pipe under horizontal conditions.

[0014] Furthermore, the first model satisfies the following formula:

[0015]

[0016] In the formula: q is the power input to the evaporation section (W); h lv The latent heat of vaporization of the working fluid at the temperature when the pulsating heat pipe is not in operation (J / kg); The mass flow rate (kg / s) of the gaseous working fluid undergoing phase change;

[0017] The second and third models satisfy the following formulas respectively:

[0018]

[0019]

[0020] In the formula: A represents the average flow velocity (m / s) of the gaseous working fluid within the pulsating heat pipe. v The cross-sectional area of ​​the gaseous working fluid channel (m²) 2 );ρ v The density (kg / m³) of the gaseous working fluid at this temperature before the pulsating heat pipe operates. 3 ); The mass flow rate (kg / s) of the liquid working fluid undergoing phase change within the pulsating heat pipe; A represents the average flow velocity (m / s) of the liquid working fluid inside the pipe. l The cross-sectional area of ​​the liquid working fluid channel (m²) 2 );ρ l The density of the liquid working fluid at this temperature before the pulsating heat pipe starts operating (kg / m³) 3 ).

[0021] Furthermore, the fourth model satisfies the following formula:

[0022]

[0023]

[0024] In the formula: u v The velocity (m / s) of vapor relative to the liquid working fluid before the pulsating heat pipe is operational.

[0025] Furthermore, the cross-sectional areas of the gaseous working fluid channel and the liquid working fluid channel are expressed by the filling ratio, and respectively satisfy the following formulas:

[0026]

[0027]

[0028]

[0029]

[0030] Where: h l Φ represents the liquid level height (m); D represents the diameter of the pulsating heat pipe (m); and Φ represents the filling rate (%).

[0031] Furthermore, the sixth model satisfies the following formula:

[0032]

[0033] in,

[0034]

[0035]

[0036] Where: u is the critical vapor velocity (m / s) for the transition from gas-liquid stratified flow to intermittent flow; C2 is a dimensionless number; A v ' is the cross-sectional area (m²) of the gas channel at the wave crest. 2 g is the acceleration due to gravity (N / kg).

[0037] Furthermore, the minimum input power required for the gas-liquid stratified flow pattern to transition to intermittent flow within the pulsating heat pipe satisfies the following formula:

[0038]

[0039] The dynamic critical diameter of the pulsating heat pipe in the horizontal state satisfies the following formula:

[0040]

[0041] In the formula: q min The minimum input power (W) required for the transition from stratified gas-liquid flow to intermittent flow within a pulsating heat pipe; D cr The dynamic critical pipe diameter (m) under horizontal conditions.

[0042] The present invention also discloses a supercritical diameter pulsating heat pipe, which is obtained by the above-mentioned dynamic critical diameter design method of pulsating heat pipe in horizontal state.

[0043] Furthermore, the volumetric filling rate of the working fluid inside the pulsating heat pipe ranges from 30% to 70%.

[0044] Furthermore, the working fluid is in a gas-liquid stratified state after being filled into the pulsating heat pipe, and the working fluid is a single working fluid or a mixture of working fluids.

[0045] Furthermore, the single working medium is a liquid metal or a non-liquid metal; the mixed working medium is a mixture of liquid metal and non-liquid metal.

[0046] Compared with the prior art, the present invention has the following advantages:

[0047] 1. The dynamic critical diameter design method for pulsating heat pipes under horizontal conditions provided by this invention results in a larger range of critical diameters for pulsating heat pipes compared to existing design methods, and can ensure better heat transfer performance and heat transfer limit between the critical diameter and the dynamic critical diameter.

[0048] 2. The dynamic critical diameter design method for pulsating heat pipes in horizontal state provided by this invention comprehensively considers dynamic and static factors such as the physical properties of the working fluid in gas-liquid stratification state, the latent heat of vaporization of the liquid working fluid during phase change, the cross-sectional area of ​​the gas channel and the cross-sectional area of ​​the liquid channel, the filling rate of the working fluid, the liquid level height when the flow pattern changes, and the minimum input power to cause the flow pattern change, thus expanding the application range of pulsating heat pipes.

[0049] 3. The dynamic critical diameter design method for pulsating heat pipes in horizontal state provided by this invention offers a new design method for using larger diameter pipes in industry.

[0050] In summary, the technical solution of this invention can solve the problem that the critical diameter of pulsating heat pipes in the prior art only considers static factors, and expands the range of critical diameters.

[0051] Based on the above reasons, this invention can be widely promoted in fields such as aviation and military where pulsed heat pipes are used for heat transfer. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a schematic diagram of the formation process of the pulsating heat pipe liquid plug in the visualization experiment of this invention.

[0054] Figure 2 This is a schematic diagram of point A in the present invention. In Figure (a), the working fluid in the heating section rapidly boils and vaporizes at time t = 0 s, and small-diameter bubbles are formed. Figures (b) and (c) show the superposition of the fluctuations in the working fluid surface and the fluctuations caused by the bursting of bubbles in the endothermic section at times t = 0.005 s and t = 0.085 s, respectively. Figure (d) shows the process of the growth of liquid surface peaks and the formation of liquid bridges in the tube, eventually forming a liquid plug.

[0055] Figure 3 This is a schematic diagram of the flow analysis of the working fluid in the pulsating heat pipe of the present invention in a stratified state after heat input and before the formation of a liquid plug. In the diagram, Figure (a) is a schematic diagram of the flow analysis, Figures (b) and (c) show that the cross-sectional area of ​​the gas channel and the cross-sectional area of ​​the liquid channel at point B in Figure (a) are functions of the liquid filling rate, and Figure (d) shows that the liquid height at point C in Figure (a) is a function of the stress on the liquid.

[0056] Figure 4This is a schematic diagram showing the growth of liquid surface peaks due to pressure difference in a pulsating heat pipe under horizontal conditions in this invention.

[0057] Figure 5 This is a schematic diagram comparing the experimental pipe diameter and dynamic pipe diameter with water and anhydrous ethanol as the working fluids in the horizontal state of the present invention, with a diameter of 6 mm. Figure (a) shows a schematic diagram comparing the experimental pipe diameter and dynamic critical pipe diameter when the working fluid is water, and Figure (b) shows a schematic diagram comparing the experimental pipe diameter and dynamic critical pipe diameter when the working fluid is anhydrous ethanol.

[0058] Figure 6 Figure 1 shows the theoretical calculation results of the dynamic critical tube diameter of the pulsating heat pipe when the working fluid is water and anhydrous ethanol in this invention. Figure 2 shows the calculation results of the tube diameter from 0 mm to 10 mm when the working fluid is water and the liquid filling rate is 30%, 50%, and 70%; Figure 3 shows the calculation results of the tube diameter from 0 mm to 10 mm when the working fluid is anhydrous ethanol and the liquid filling rate is 30%, 50%, and 70%; Figure 4 shows the calculation results of the tube diameter from 5 mm to 7 mm when the working fluid is water and the operating temperature is from 20°C to 60°C; Figure 5 shows the calculation results of the tube diameter from 5 mm to 7 mm when the working fluid is water and the operating temperature is from 20°C to 60°C. Figure 6 shows the calculation results of the tube diameter from 5 mm to 7 mm when the working fluid is anhydrous ethanol and the operating temperature is from 20°C to 60°C. Detailed Implementation

[0059] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0062] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0063] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0064] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0065] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0066] This invention provides a dynamic critical diameter design method for a pulsating heat pipe in a horizontal state, comprising the following steps: Step 1: Establishing a working fluid heat absorption model when the input heat fails to enable the pulsating heat pipe to operate normally; Step 2: Without considering the heat conduction of the pipe wall and the working fluid, obtaining the gas flow velocity relative to the liquid in a gas-liquid stratification state according to the law of conservation of mass, and the cross-sectional area of ​​the gas-liquid channel can be represented by the liquid filling ratio; Step 3: Without considering the heat conduction of the pipe wall and the working fluid, establishing a model of the flow pattern change caused by the pressure difference between two infinite plates, obtaining the critical velocity that causes the liquid surface wave crest to grow; Step 4: Based on the critical velocity obtained from the model of two infinite plates in the previous step, extending to the critical velocity of the gas-liquid stratification flow pattern to intermittent flow in the horizontal pulsating heat pipe, and obtaining the dynamic critical diameter of the pulsating heat pipe under horizontal conditions based on the above-mentioned relative gas-liquid velocity, working fluid physical properties, liquid filling ratio, and gas-liquid channel cross-sectional area.

[0067] Specifically, the dynamic critical diameter design method for the pulsating heat pipe in the horizontal state includes the following steps:

[0068] Step 1: Establish a heat absorption model for the working fluid when the input heat fails to enable the pulsating heat pipe to operate normally, i.e., the first model; establish the second and third models. The second model is the mass flow rate of the gaseous working fluid undergoing phase change per unit time, and the third model is the mass flow rate of the liquid working fluid undergoing phase change within the pulsating heat pipe. The first, second, and third models are obtained from the parameters of the working fluid in a gas-liquid stratified state within the pipe before operation. The parameters include the working fluid density, liquid cross-sectional area, and gas density of the pulsating heat pipe.

[0069] Step 2: Combining the first, second, and third models, without considering the heat conduction of the pipe wall and working fluid, when the working fluid is in a gas-liquid stratification state within the pulsating heat pipe, all heat is transferred to the heat release end through the phase change of the working fluid. According to the laws of conservation of mass and energy, the flow velocity of the gas working fluid relative to the liquid working fluid can be obtained, i.e., the fourth model. Based on geometric relationships, the conversion between the cross-sectional areas of the gas channel and the liquid channel can be expressed by the working fluid filling rate, thereby obtaining the liquid level height in the gas-liquid stratification state, i.e., the fifth model.

[0070] Step 3: Based on the liquid level height under the gas-liquid stratification state obtained in Step 2, assume that between two infinite plates, due to the pressure difference caused by the sufficiently large gas velocity, the wave crest grows to contact the upper wall of the pipe, causing the flow pattern to change, and obtain the critical velocity range, which is the sixth model of the critical velocity for the growth of the liquid surface wave crest.

[0071] Step 4: Based on the critical gas velocity range between the two infinite plates obtained in Step 3, extend it to the horizontal pulsating heat pipe. Combine the liquid level and pipe diameter to derive the critical velocity for the transition from gas-liquid stratified flow to intermittent flow (i.e., the seventh model). Substitute the physical properties of the gas and liquid working fluid, the cross-sectional area of ​​the gas and liquid phases, the heating power, and the liquid filling rate into the pulsating heat pipe to determine the dynamic critical pipe diameter of the pulsating heat pipe in the horizontal state.

[0072] Preferably, before the pulsating heat pipe is put into operation, the heat conduction between the pipe wall and the working fluid is not considered. The heat input at the heat absorption end is completely transferred to the heat release end by the phase change of the working fluid. Therefore, the first model satisfies the following formula:

[0073]

[0074] In the formula: q is the power input to the evaporation section (W); h lv The latent heat of vaporization of the working fluid at the temperature when the pulsating heat pipe is not in operation (J / kg); The mass flow rate (kg / s) of the gaseous working fluid undergoing phase change; A represents the average flow velocity (m / s) of the gaseous working fluid within the pulsating heat pipe. v The cross-sectional area of ​​the gaseous working fluid channel (m²) 2 );ρ vThe density (kg / m³) of the gaseous working fluid at this temperature before the pulsating heat pipe operates. 3 ).

[0075] According to the law of conservation of mass, the following formula is also satisfied:

[0076]

[0077]

[0078]

[0079] In the formula: The mass flow rate (kg / s) of the liquid working fluid undergoing phase change within the pulsating heat pipe; A represents the average flow velocity (m / s) of the liquid working fluid inside the pipe. l The cross-sectional area of ​​the liquid working fluid channel (m²) 2 );ρ l The density of the liquid working fluid at this temperature before the pulsating heat pipe starts operating (kg / m³) 3 ).

[0080] Preferably, the vapor flow rate relative to the liquid working fluid before the pulsating heat pipe operates satisfies the following formula:

[0081]

[0082] In the formula: u v The velocity (m / s) of vapor relative to the liquid working fluid before the pulsating heat pipe is operational.

[0083] Preferably, when the working fluid exhibits a gas-liquid stratification state within the pulsating heat pipe, the conversion between the cross-sectional areas of the gas channel and the liquid channel can be expressed by the working fluid filling ratio based on geometric relationships, as shown in the following formula:

[0084]

[0085]

[0086]

[0087] In the formula: h l Φ represents the liquid level height (m); D represents the diameter of the pulsating heat pipe (m); and Φ represents the filling rate (%).

[0088] Preferably, the vapor velocity at which the liquid surface crest grows to contact the pipe wall satisfies the following formula:

[0089]

[0090] in,

[0091]

[0092]

[0093] Where: u is the critical vapor velocity (m / s) for the transition from gas-liquid stratified flow to intermittent flow; C2 is a dimensionless number; A v ' is the cross-sectional area (m²) of the gas channel at the wave crest. 2 g is the acceleration due to gravity (N / kg).

[0094] Preferably, the gas-liquid relative velocity u mentioned above is used. v The minimum input power required for the manifold transition satisfies the following formula:

[0095]

[0096] Therefore, under horizontal conditions, the dynamic critical diameter of a pulsating heat pipe satisfies the following formula:

[0097]

[0098] In the formula: q min The minimum input power (W) required for the transition from stratified gas-liquid flow to intermittent flow within a pulsating heat pipe; D cr The dynamic critical pipe diameter (m) under horizontal conditions.

[0099] Example 1

[0100] like Figure 1 , Figure 2 The diagram illustrates the formation process of a liquid plug in a supercritical diameter pulsating heat pipe during a visualization experiment. With the input of heat, the working fluid in the heating section rapidly boils and vaporizes, accompanied by the formation of small-diameter bubbles, as shown in the image. Figure 2 As shown in (a), the vapor generated by rapid evaporation flows at high speed from the endothermic end to the exothermic end, causing fluctuations on the working fluid surface. These fluctuations are superimposed on the surface fluctuations generated by the bursting of bubbles at the endothermic end, as shown in (a). Figure 2 As shown in (b) and (c). From Figure 2 As can be seen from (d), due to the high-speed flow of steam, a low pressure is formed at the crest. Under the action of the pressure difference, the crest continues to grow and eventually forms a liquid bridge after contacting the upper wall of the pipe, and finally forms a liquid plug.

[0101] like Figure 3 The diagram shows a flow analysis of the working fluid in a stratified state inside a pulsating heat pipe after heat input and before the formation of a liquid plug. Figures (b) and (c) show cross-sectional views inside the pulsating heat pipe, where h... l The cross-sectional area of ​​the gas channel and the cross-sectional area of ​​the liquid channel are functions of the filling rate. Through geometric relationships, the cross-sectional area of ​​the gas-liquid two-phase channel can be expressed by the filling rate of the working fluid.

[0102] like Figure 4 The diagram illustrates the growth of liquid surface crests in a pulsating heat pipe under horizontal conditions due to pressure difference. When high-speed vapor flows through the liquid surface crests, a low pressure is created at the crests, causing the crest height to continuously increase under the pressure difference until it contacts the pipe wall, at which point the flow pattern changes.

[0103] Example 2

[0104] In this embodiment, the operating conditions are as follows: water and anhydrous ethanol are used as working fluids in a horizontal state, with filling rates of 50% and 70% respectively, and the operating temperature is 20°C. Figure 5 (a) indicates that the working medium is water. Figure 5 (b) indicates that the working fluid is anhydrous ethanol. After substituting the geometric parameters of the pulsating heat pipe, the input power at startup, and the working fluid properties corresponding to the hot and cold end temperatures into the formula, the dynamic critical pipe diameter value can be obtained and compared with the experimental pipe diameter in the visualization experiment.

[0105] Example 3

[0106] In this embodiment, the operating conditions are as follows: when the working fluid is water and anhydrous ethanol, the starting temperature difference of the pulsating heat pipe is 60°C, the liquid filling rate is 30%, 50%, and 70%, and the pipe diameter varies from 0 to 10 mm.

[0107] In MATLAB software, by substituting the physical properties of the working fluid, start-up temperature difference, filling rate, and pulsating heat pipe diameter parameters under this operating condition into the formula for the minimum input power to achieve flow pattern transformation, the theoretical calculation results of the pulsating heat pipe start-up power and its schematic diagram are obtained, as follows: Figure 6 As shown in (a) and (b), where (a) represents the working medium as water and (b) represents the working medium as anhydrous ethanol.

[0108] Example 4

[0109] In this embodiment, the operating conditions are as follows: when the working fluid is water and anhydrous ethanol, the starting temperature difference of the pulsating heat pipe is 60°C, and the pipe diameters are 5mm, 5.5mm, 6mm, 6.5mm, and 7mm, respectively, with the operating temperature ranging from 20°C to 60°C.

[0110] In MATLAB software, the physical properties of the working fluid, the start-up temperature difference, the pipe diameter, and the operating temperature under this condition are substituted into the minimum input power formula to obtain the theoretical calculation results of the pulsating heat pipe start-up power and its schematic diagram, as follows: Figure 6 Figures (c) and (d) are shown, where (c) represents the working medium as water and (d) represents the working medium as anhydrous ethanol.

[0111] In summary, pulsating heat pipes can still operate even when their diameter exceeds the critical diameter, and they exhibit excellent heat transfer performance.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for dynamic critical tube diameter design of pulsating heat pipes in horizontal orientation, characterized by, include: Step 1: Establish the first model, the second model, and the third model. The first model is the heat absorption model of the working fluid in the pulsating heat pipe when the input heat fails to enable the pulsating heat pipe to work normally. The second model is the mass flow rate of the gaseous working fluid that undergoes phase change per unit time. The third model is the mass flow rate of the liquid working fluid that undergoes phase change in the pulsating heat pipe. The first model, the second model, and the third model are obtained from the parameters of the working fluid in the pipe in the state of gas-liquid stratification before operation. The parameters include the average flow velocity of the gas-liquid working fluid in the pulsating heat pipe, the density of the gas-liquid working fluid, and the cross-sectional area of ​​the gas-liquid working fluid channel. Step 2: Combining the first model, the second model, and the third model, without considering the heat conduction of the pipe wall and the working fluid, in the gas-liquid stratification state, according to the law of conservation of mass, the fourth model is obtained. The fourth model is the flow velocity of the gas working fluid relative to the liquid working fluid before the pulsating heat pipe is working. Step 3: Establish the fifth model, which is the liquid level height under gas-liquid stratification. It is obtained by using the cross-sectional area of ​​the gaseous working fluid channel and the cross-sectional area of ​​the liquid working fluid channel, expressed by the liquid filling rate of the working fluid, based on geometric relationships. Step 4: Establish a sixth model based on the fifth model. The sixth model is the critical velocity for the growth of the liquid surface wave crest. This model is the vapor velocity that allows the liquid surface wave crest to grow to contact the upper wall of the pipe when the flow pattern changes due to the pressure difference between two infinite plates without considering the heat conduction of the pipe wall and the working fluid. Step 5: Establish the seventh model, which is the critical vapor velocity for the transition from gas-liquid stratification to intermittent flow in a horizontally pulsating heat pipe, obtained from the sixth model. Step 6: Determine the minimum input power required for the gas-liquid stratification flow pattern to transform into intermittent flow in the pulsating heat pipe based on the fourth and seventh models. Combine the working fluid properties, filling rate, and gas-liquid channel cross-sectional area to obtain the dynamic critical pipe diameter of the pulsating heat pipe under horizontal conditions.

2. The method of determining the dynamic threshold diameter of a pulsating heat pipe in horizontal state according to claim 1, wherein, The first model satisfies the following formula: ； In the formula: q is the power input to the evaporation section (W); is the latent heat of vaporization of the working fluid at the temperature at which the pulsating heat pipe is not operating (J / kg); is the mass flow rate of the gaseous working fluid undergoing a phase change (kg / s); The second and third models satisfy the following formulas respectively: ； ； In the formula: The average flow velocity (m / s) of the gaseous working fluid in the pulsating heat pipe. The cross-sectional area of ​​the gaseous working fluid channel (m²) 2 ); The density of the gaseous working fluid at this temperature before the pulsating heat pipe operates (kg / m³) 3 ); The mass flow rate (kg / s) of the liquid working fluid undergoing phase change within the pulsating heat pipe. The average flow velocity of the liquid working fluid in the pipe (m / s). The cross-sectional area of ​​the liquid working fluid channel (m²) 2 ); The density of the liquid working fluid at this temperature before the pulsating heat pipe starts operating (kg / m³) 3 ).

3. The dynamic critical diameter design method for a pulsating heat pipe in a horizontal state according to claim 2, characterized in that, The fourth model satisfies the following formula: ； ； In the formula: u v is the flow velocity of the vapor phase relative to the liquid working fluid (m / s) before the pulsating heat pipe is operated.

4. The method of claim 3, wherein, The cross-sectional areas of the gaseous working fluid channel and the liquid working fluid channel are represented by the filling ratio, and respectively satisfy the following formulas: ； ； ； ； In the formula: The liquid level height is in meters (m). The diameter of the pulsating heat pipe (m); The filling rate is % (%).

5. The dynamic critical diameter design method for a pulsating heat pipe in a horizontal state according to claim 4, characterized in that, The sixth model satisfies the following formula: ； in, ； ； In the formula: The critical vapor velocity (m / s) for the transition from gas-liquid stratified flow to intermittent flow. C 2 is a dimensionless number; The cross-sectional area (m²) of the gas channel at the wave crest 2 ); The acceleration due to gravity (N / kg).

6. The dynamic critical diameter design method for a pulsating heat pipe in a horizontal state according to claim 5, characterized in that, The minimum input power required for the transition from gas-liquid stratification to intermittent flow within the pulsating heat pipe satisfies the following formula: ； The dynamic critical diameter of the pulsating heat pipe in the horizontal state satisfies the following formula: ； In the formula: The minimum input power (W) for the transition from gas-liquid stratification to intermittent flow in a pulsating heat pipe; The dynamic critical pipe diameter (m) under horizontal conditions.

7. A supercritical diameter pulsating heat pipe, characterized in that, The supercritical diameter pulsating heat pipe is obtained by the dynamic critical diameter design method of the pulsating heat pipe in the horizontal state as described in any one of claims 1-6.

8. The supercritical diameter pulsating heat pipe according to claim 7, characterized in that, The volumetric filling rate of the working fluid inside the pulsating heat pipe is in the range of 30%≤Ф≤70%.

9. The supercritical diameter pulsating heat pipe according to claim 8, characterized in that, The working fluid is in a gas-liquid stratified state after being filled into the pulsating heat pipe, and the working fluid is a single working fluid or a mixture of working fluids.

10. The supercritical diameter pulsating heat pipe according to claim 9, characterized in that, The single working medium is either liquid metal or non-liquid metal; the mixed working medium is a mixture of liquid metal and non-liquid metal.

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