Tapered shrinkage and gradual expansion type heat pipe and method

Abstract

The invention belongs to but not limited to the technical field of heat pipes, and discloses a gradually-shrunk and gradually-expanded heat pipe which comprises a pipe wall, a wick tightly attached to the interior of the pipe wall, and a steam cavity structure of the heat pipe formed in the wick. The steam cavity can be divided into three sections along the axial heat pipe, namely an evaporation section, a heat insulation section and a condensation section in sequence from left to right; the evaporation section is of a divergent structure, and the inclination angle is theta 1; the heat insulation section is of a parallel structure; the condensation section is of a gradually-shrunk structure, and the inclination angle is theta 2. The sound velocity limit of the heat pipe is improved, and the starting power of the heat pipe is improved at the initial starting stage. The effective length of the condensation section of the heat pipe is increased, so that the heat transfer performance of the heat pipe can be improved.

Description

Technical Field

[0001] The present invention belongs to, but is not limited to, the technical field of heat pipes, and particularly relates to a tapered and flared heat pipe and method. Background Art

[0002] As a passive heat transfer element, heat pipes are widely used in electronic devices, industrial equipment, aerospace and other fields due to their high heat transfer characteristics. Heat pipes with liquid metal as the working medium have an operating temperature above 450°C and are also known as high-temperature heat pipes. In deep space and deep sea exploration, reactors with high-temperature heat pipes as the core energy transfer equipment have attracted extensive attention due to their solid state, high inherent safety, simple structure, easy modular transportation and expansion, etc. Improving the heat transfer power and heat transfer stability of heat pipes is crucial for the miniaturized design and safe operation of reactors.

[0003] Although heat pipes have good heat transfer performance, the load cannot be increased without limit. Heat pipes are affected by various limit constraints during startup and operation, including the capillary pressure limit of the wick, the boiling limit of the working liquid, the sonic velocity limit of vapor flow, the entrainment limit of high-speed vapor flow on the reflux liquid, and the viscous limit of vapor flow.

[0004] At present, the optimization research of heat pipes is too single, mostly concentrated on the optimization of the wick in order to improve the capillary limit of the working medium and reduce the flow resistance. However, at the initial stage of startup, the sonic velocity limit existing in the heat pipe limits the startup speed of the working medium, and there is little research on the optimization of the sonic velocity limit.

[0005] In addition, the effective length of the condensation section also limits the heat transfer performance of the heat pipe. When the high-temperature vapor moves to the condensation section, as the gas liquefies, the gas mass flow rate decreases and the flow velocity decreases. When the viscous limit is reached, the gas cannot continue to advance, and the distance advanced at this time is the effective length of the condensation section of the heat pipe. The longer the effective length, the larger the effective heat conduction area available for the condensation section, and the higher the heat transfer efficiency of the heat pipe. Therefore, increasing the effective length of the condensation section is also an effective method to improve the heat transfer performance of the heat pipe.

[0006] In view of the above analysis, reasonable means are adopted to optimize the sonic velocity limit and viscous limit existing in the heat pipe during startup, so as to increase the startup power of the heat pipe at the initial stage of startup, optimize the viscous limit, increase the effective length of the condensation section of the heat pipe, and improve the heat transfer performance of the heat pipe. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the present invention provides a tapered and flared heat pipe.

[0008] The present invention is implemented as follows. A tapered and flared heat pipe includes a pipe wall, and a wick is disposed inside the pipe wall in close contact. A steam cavity structure of the heat pipe is formed inside the wick;

[0009] The steam chamber can be axially divided into three sections, which are an evaporation section, an adiabatic section, and a condensation section from left to right; the evaporation section is a divergent structure with an inclination angle of θ 1 ; the adiabatic section is a parallel structure; the condensation section is a convergent structure with an inclination angle of θ 2 .

[0010] Furthermore, the material of the pipe wall can be glass, copper, stainless steel, nickel-chromium alloy, etc.

[0011] Furthermore, the wick can be a wire mesh wick, a groove wick, a sintered structure wick, etc.

[0012] Furthermore, the material of the wick can be copper wire mesh, stainless steel wire mesh, ceramic particle sintering, etc.

[0013] Combined with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by the present invention are as follows:

[0014] In order to overcome the limit problems encountered by the heat pipe during startup, the present invention provides a design idea for the heat pipe, and specifically optimizes the sonic limit and viscous limit problems encountered by the heat pipe during startup. The specific solution is to design the evaporation section of the heat pipe as a divergent pipe structure and the condensation section of the heat pipe as a convergent pipe structure. No specific adjustment is made to other structures.

[0015] At the evaporation section, with the input of external heat, the liquid working fluid in the evaporation section is heated and vaporized. As the total amount of gas increases, the mass flow rate of the working fluid in the steam chamber of the evaporation section increases. In a traditional heat pipe with a constant diameter, the gas will be continuously accelerated until the flow velocity reaches the maximum value after reaching the adiabatic section. Once the sonic limit is encountered, it is equivalent to forming a flow "blockage" at the outlet of the evaporation section. At this time, even if the temperature of the cold source in the condensation section is continuously reduced, the axial heat flow of the heat pipe will no longer increase. By designing the evaporation section of the heat pipe with a divergent structure, as the steam flows, the flow area of the steam gradually increases and the steam flow velocity decreases, objectively delaying the reaching of the sonic limit, thereby increasing the sonic limit of the heat pipe and increasing the startup power of the heat pipe in the initial stage of startup.

[0016] At the condensation section, as the working fluid condenses, the steam flow velocity decreases. By designing the condensation section of the heat pipe with a convergent structure, the flow area can be effectively reduced, thereby increasing the steam flow velocity in the condensation section, enabling the steam to move a longer distance and delaying the arrival of the viscous limit. Furthermore, the effective length of the condensation section of the heat pipe is increased, thereby improving the heat transfer performance of the heat pipe.

[0017] Currently, the optimization design of heat pipes is still limited to conventional cylindrical heat pipes. Even for special-shaped heat pipes, they are optimized and adjusted according to actual needs. There is no research on the ultimate impact of the configuration itself on the heat pipe and its heat transfer capacity, and at the same time, the discussion on the sonic limit and viscous limit is also insufficient. The tapered and flared heat pipe design adopted in the present invention enriches the considerations for the design of heat pipes and can effectively overcome the troubles caused by the sonic limit in principle. Brief Description of the Drawings

[0018] Figure 1 is the axial view of the tapered and flared heat pipe provided by the embodiment of the present invention;

[0019] Figure 2 is the axial sectional view of the tapered and flared heat pipe provided by the embodiment of the present invention;

[0020] In the figure: 1, pipe wall; 2, wick; 3, vapor chamber; 31, evaporation section; 32, adiabatic section; 33, condensation section. Detailed Embodiments

[0021] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] The present invention uses an inclined gradient structure to optimize the design of traditional heat pipes. The pipe wall 1 of the heat pipe can be made of materials such as glass, copper, stainless steel, nickel-chromium alloy, etc. to adapt to different temperature conditions. The heat pipe contains a wick 2 inside, which can be of types such as metal mesh, groove structure or sintered material according to needs, and its material can include copper mesh, stainless steel mesh or ceramic particle sintering, etc. The vapor chamber 3 inside the heat pipe is close to vacuum in the initial state and is gradually filled with gaseous working medium as the working medium evaporates during operation to maintain a saturated pressure state.

[0023] Axially, the heat pipe is divided into an evaporation section, an adiabatic section and a condensation section. In the evaporation section, an external heat source heats the heat pipe to evaporate the internal working medium to form a gaseous flow. The equal-diameter design of traditional heat pipes is prone to reach the sonic limit due to high flow velocity, restricting the flow of the working medium. The present invention adopts a flared structure with an inclination angle θ 1 so that the diameter of the evaporation section gradually increases along the flow direction. According to the law of conservation of mass, at the same mass flow rate, the increase in the flow cross-sectional area will reduce the steam flow velocity, thus effectively preventing the sonic limit phenomenon caused by too high flow velocity.

[0024] After the gaseous working medium is heated in the evaporation section, due to the pressure difference, it flows towards the adiabatic section of the heat pipe. The pipe wall of this part is insulated from the outside world to avoid energy loss caused by external interference. During this process, the flow velocity of the working medium remains basically constant and is not affected by the external environmental temperature, providing a stable gas flow input to the condensation section and ensuring the uniformity of heat transfer.

[0025] In the condensation section, the gaseous working medium releases heat when it is cooled and gradually condenses into a liquid. In a traditional straight pipe structure, the gas may stop flowing at the front end of the condensation section due to the decrease in flow velocity, forming a viscous limit, making part of the condensation section unable to be effectively utilized. The present invention designs a tapered structure with an inclination angle θ 2 By reducing the flow cross-sectional area, the gas flow velocity is forced to increase, thereby extending the flow distance of the working medium and increasing the effective heat transfer length of the condensation section.

[0026] To adapt to different heat flux density conditions, the present invention further adopts a shape memory alloy (such as Ni-Ti alloy) to dynamically adjust the inclination angles θ 1 and θ 2 of the evaporation section and the condensation section. Under high heat flux density, the internal pressure and temperature of the heat pipe increase, and the shape memory alloy causes the inclination angle of the evaporation section to increase, resulting in an increase in the flow cross-sectional area, a decrease in the flow velocity, and an inhibition of the sonic limit phenomenon. Under low heat flux density, the temperature inside the heat pipe decreases, and the shape memory alloy causes the inclination angle of the condensation section to increase, reducing the flow cross-sectional area, increasing the flow velocity, and inhibiting the viscous limit phenomenon, thereby enhancing the adaptability of the heat pipe under different working conditions.

[0027] The present invention further proposes a dynamic proportional formula for the angles and lengths of the gradually expanding evaporation section and the gradually contracting condensation section and the total length of the heat pipe, and establishes a mathematical model in combination with the working medium flow velocity and phase change efficiency. This model is used to optimize the flow and heat transfer processes inside the heat pipe, ensure uniform steam distribution, and improve the heat transfer efficiency. At the same time, through geometric optimization, the internal flow characteristics of the heat pipe are further improved, and the overall performance and stability are enhanced.

[0028] As Figure 1 shown, an embodiment of the present invention provides a tapered and expanded heat pipe. The tapered and expanded heat pipe includes a pipe wall 1, and a wick 2 is disposed inside the pipe wall 1 in close contact. A steam cavity 3 structure of the heat pipe is formed inside the wick 2;

[0029] As Figure 2 shown, the steam cavity 3 can be axially divided into three sections, which are an evaporation section 31, an adiabatic section 32, and a condensation section 33 in sequence from left to right; the evaporation section 31 is a gradually expanding structure with an inclination angle of θ 1 ; the adiabatic section 32 is a parallel structure; the condensation section 33 is a gradually contracting structure with an inclination angle of θ 2 .

[0030] The materials of the heat pipe wall 1 provided by the embodiments of the present invention include glass, copper, stainless steel, nickel-chromium alloy, etc. from low temperature to high temperature. The wick 2 can be divided into wire mesh wicks, groove wicks, sintered structure wicks, etc. from the structure; the wick 2 can be divided into copper wire mesh, stainless steel wire mesh, ceramic particle sintering, etc. from the materials. The structure of the steam chamber 3 of the heat pipe is in a state close to vacuum at the initial working condition. As the working fluid evaporates, the steam chamber is gradually filled with the gaseous working fluid and is in a saturated pressure state.

[0031] Axially, the heat pipe can be divided into three sections, and the leftmost one is the evaporation section 31. In the evaporation section 31, the heat pipe absorbs heat from the outside and heats the working fluid inside the pipe. According to the operating temperature of the heat pipe, the working fluid can be ammonia, water, sodium-potassium alloy, potassium, sodium, lithium, etc. from low temperature to high temperature. After the working fluid is heated and vaporized, it accumulates in the evaporation section. Subsequently, the pressure in the evaporation section increases, and the gaseous working fluid flows from the evaporation section to the condensation section under the action of the pressure difference. Axially, affected by the evaporation, the quantity of the working fluid continuously increases from the evaporation section to the adiabatic section 32. The present invention designs the traditional straight heat pipe with equal diameter into a structure of the evaporation section 31 with an inclination angle of θ 1 , and the specific structure is as Figure 2 shown. According to the law of conservation of mass, under the condition of consistent mass flow rate, the larger the flow area, the smaller the flow velocity. Therefore, the existence of the inclination angle reduces the flow velocity, so that the sonic speed limit is not easily reached inside the pipe.

[0032] The middle section is the adiabatic section 32 of the heat pipe. The heat pipe is adiabatic to the outside in the adiabatic section 32. Therefore, the velocity of the working fluid is basically unchanged in the adiabatic section 32. When the steam reaches the rightmost side, the heat pipe wall is connected to the external heat sink, and the gaseous working fluid releases energy and transfers it to the wick and the pipe wall, and finally releases the energy to the external heat sink. The temperature of the gaseous working fluid decreases. When its temperature reaches the saturation temperature corresponding to the pressure, the gas begins to liquefy, so that the quantity of the working fluid in the steam chamber of the condensation section decreases. With the density and flow area unchanged, the flow velocity of the working fluid decreases. When the flow velocity decreases to 0, the gaseous working fluid does not continue to advance forward. At this time, the viscous limit of the heat pipe is reached. The viscous limit makes the condensation section 33 not fully utilized, and the steam may stop flowing before reaching the end of the condensation section. This will cause an obvious temperature drop near the end of the condensation section 33. The present invention designs the condensation section 33 of the heat pipe into a tapered structure. After the gaseous working fluid with the same mass flow rate flows through, due to the narrowing of the flow cross-section, the gas flow velocity increases, so that the working fluid can move to a farther distance and the effective length of the condensation section 33 is increased. The inclination angle of the condensation section 33 is θ 2 , where θ 1 and θ 2 are not limited by specific angle requirements, which is related to the usage scenario of the heat pipe.

[0033] In terms of mechanical strength, the tapered and flared structure improves the axial redundancy of the heat pipe. When the heat pipe undergoes axial deformation due to thermal stress, the tapered and flared structure can release the axial thermal stress through the deformation of the heat pipe.

[0034] The present invention can be applied to the design and use of heat pipe reactors, effectively improving the start-up characteristics of heat pipe reactors. In addition, in other scenarios of heat pipe use, if there are no rigid requirements for the outer shape of the heat pipe at the heat end and the cold end, the present invention can be adapted for use.

[0035] Based on the common knowledge that under the same flow rate condition, the larger the flow area, the lower the flow velocity of the working fluid, the present invention optimizes the heat pipe structure. In the evaporation section, a flared design is used to increase the cross-sectional flow area of the heat pipe, thereby reducing the steam flow velocity inside the pipe. In the condensation section, a tapered design is used to reduce the cross-sectional flow area of the heat pipe, thereby increasing the steam flow velocity of the heat pipe. The aim is to overcome the sonic limit encountered at the outlet of the evaporation section and the viscous limit encountered at the end of the flow in the condensation section, thereby optimizing the heat transfer efficiency of the heat pipe and improving the performance of the heat pipe.

[0036] In the description of the present invention, unless otherwise specified, "a plurality of" means two or more; the orientation or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0037] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A gradually contracting and expanding heat pipe, characterized in that: The heat pipe comprises a pipe wall, a liquid wick and a steam chamber, wherein the heat pipe comprises an evaporation section, an insulation section and a condensation section along the axial direction, wherein: The evaporation section is an inclined gradually expanding structure with an inclination angle of θ1; The condensation section is an inclined tapered structure with an inclination angle of θ2; The steam chamber is in a near-vacuum state under the initial operating condition and is filled with saturated gaseous working fluid during operation; The liquid absorption core is arranged on the inner side of the tube wall and penetrates the evaporation section, the heat insulation section and the condensation section along the axial direction.

2. The heat pipe according to claim 1, characterized in that The material of the tube wall is selected from at least one of glass, copper, stainless steel and nickel-chromium alloy.

3. The heat pipe according to claim 1, characterized in that The structure of the absorbent core is selected from a metal wire mesh absorbent core, a groove absorbent core or a sintered structure absorbent core, and the material of the absorbent core is selected from a copper wire mesh, a stainless steel wire mesh or a ceramic particle sintered material.

4. The heat pipe according to claim 1, characterized in that The inclined gradually expanding structure of the evaporation section gradually increases the flow cross-sectional area of ​​the evaporation section along the flow direction, and the inclined gradually contracting structure of the condensation section gradually decreases the flow cross-sectional area of ​​the condensation section along the flow direction.

5. The heat pipe according to claim 1, characterized in that The heat pipe uses a shape memory alloy to adjust the inclination angle θ1 of the evaporation section and the inclination angle θ2 of the condensation section, and the shape memory alloy is selected from Ni-Ti alloy.

6. The heat pipe according to claim 1, characterized in that The ratio of the inclination angle θ1 of the evaporation section to the inclination angle θ2 of the condensation section is dynamically set according to a mathematical model of the total length of the heat pipe and the flow rate of the working medium.

7. A method for optimizing a gradually contracting and expanding heat pipe, characterized in that: The following steps are involved: A gradually expanding structure is designed in the evaporation section of the heat pipe, and an inclination angle θ1 is set to increase the flow cross section of the evaporation section, so that the flow velocity of the working fluid is reduced after evaporation; Maintaining a parallel structure in the heat pipe insulation section allows the gaseous working medium to flow evenly along the axial direction without heat exchange and maintain a stable pressure; A tapered structure is designed in the condensation section of the heat pipe, and an inclination angle θ2 is set to reduce the flow cross section of the condensation section, increase the flow rate of the gaseous working medium, and ensure that the gas fully flows to the end of the condensation section; Based on the heat pipe usage scenario, adjust the value range of θ1 and θ2 to optimize heat transfer efficiency and stability.

8. The method according to claim 7, characterized in that The evaporation section of the heat pipe reduces the working medium flow rate through a gradual expansion structure to prevent reaching the sonic limit, ensure uniform distribution of steam, and optimize the pressure difference from the evaporation section to the condensation section.

9. The method according to claim 7, characterized in that: The condensation section of the heat pipe increases the working medium flow rate through a tapered structure to overcome the viscosity limit, so that the gaseous working medium can fully flow to the end of the condensation section, thereby increasing the effective heat transfer length of the condensation section.

10. The method according to claim 7, characterized in that In terms of mechanical stress optimization, the gradually contracting and expanding structure can improve the axial redundancy of the heat pipe, so that when the heat pipe produces axial deformation under the action of thermal stress, the risk of structural damage can be reduced through the buffering effect of the inclination angle.

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