CN110926247A - Pulsating heat pipe with gradient wetting surface and preparation method thereof - Google Patents
Pulsating heat pipe with gradient wetting surface and preparation method thereof Download PDFInfo
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- CN110926247A CN110926247A CN201911286518.5A CN201911286518A CN110926247A CN 110926247 A CN110926247 A CN 110926247A CN 201911286518 A CN201911286518 A CN 201911286518A CN 110926247 A CN110926247 A CN 110926247A
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
- F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
- F28D15/0266—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with separate evaporating and condensing chambers connected by at least one conduit; Loop-type heat pipes; with multiple or common evaporating or condensing chambers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
- F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
- F28F21/081—Heat exchange elements made from metals or metal alloys
- F28F21/085—Heat exchange elements made from metals or metal alloys from copper or copper alloys
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Abstract
The invention provides a pulsating heat pipe with a gradient wettability surface and a preparation method thereof. The inner surface of the pulsating heat pipe channel is processed by chemical etching, and the pulsating heat pipe with micro-nano structure gradient change and surface wettability gradient change is formed by controlling the etching time. The wettability of the pulsating heat pipe channel changes in a gradient manner along the length direction of the pulsating heat pipe, and the wettability of the pulsating heat pipe channel is gradually improved from the condensation section to the evaporation section of the pulsating heat pipe. The gradient wettability surface promotes the working medium to move from the end with low wettability to the end with high wettability, and accelerates the reflux speed of the working medium.
Description
Technical Field
The invention relates to the technical field of research of pulsating heat pipes, in particular to a pulsating heat pipe with a gradient wettability surface and a preparation method thereof, which can be applied to the technical fields of high-efficiency heat dissipation of electronic elements, industrial waste heat recovery, process heat exchange and the like.
Background
With the development of very large scale integrated circuits, local heat flux is gradually increased, and electronic components are gradually miniaturized and integrated, so that a new efficient heat dissipation technology is required. The pulsating heat pipe is a heat pipe with high integration level, the hydraulic diameter range is 0.5-5mm, but with the further reduction of the size of the pulsating heat pipe, the evaporation section is easy to burn out, and the problem of the evaporation section of the pulsating heat pipe needs to be solved for the development of integration and miniaturization of the pulsating heat pipe.
The pulsating heat pipe couples two heat transfer modes of phase change heat transfer and convection heat transfer of the working medium, and has high effective heat conductivity. The present research result shows that the sensible heat transfer of the liquid bomb oscillation motion is the main heat transfer mode of the pulsating heat pipe, the pressure difference generated by the phase change heat transfer is the driving force of the liquid bomb oscillation motion, when the evaporation section of the pulsating heat pipe has no working medium backflow and the phenomenon of 'dry out', the liquid bomb oscillation motion can be driven without pressure, and the heat transfer performance of the pulsating heat pipe is deteriorated. Therefore, the invention provides the gradient wetting surface pulsating heat pipe, promotes the working medium to flow back to the evaporation section of the pulsating heat pipe by utilizing the capillary action of the gradient wetting surface, and provides a new thought and an efficient scheme for the problem that the pulsating heat pipe is easy to burn out and the development of an efficient integrated pulsating heat pipe.
Disclosure of Invention
According to the technical problem that the evaporation section of the pulsating heat pipe is easy to burn out, the pulsating heat pipe with the gradient wettability surface and the preparation method thereof are provided. The invention mainly drives the working medium to directionally move to the evaporation section through the gradient wettability surface, thereby solving the problem of 'dry burning' of the evaporation section, improving the heat transfer capacity of the pulsating heat pipe, and obviously improving the starting and heat load bearing capacity of the pulsating heat pipe.
The technical means adopted by the invention are as follows:
a pulsating heat pipe with a gradient wetting surface comprises a condensation section, a heat insulation section and an evaporation section, wherein the inner surface of the pulsating heat pipe is provided with the gradient wetting surface which is uniformly changed from the condensation section to the evaporation section. Wherein, the uniform change refers to that the wetting property of the gradient wetting surface is gradually increased from the condensation section to the evaporation section.
Further, the surface roughness of the gradient wetting surface is gradually increased from the condensation section to the evaporation section; the gradient wetting surface is formed by a chemical etching technology; the gradient wetting surface is provided with a micro-nano structure which is a micro-scale or nano-scale rough structure; oxidizing the surface of the red copper pulsating heat pipe by a chemical etching method, and generating the micro-nano structure of metal hydroxide or metal oxide with continuously and uniformly changed structure along the direction of the channel on the inner surface of the channel by controlling the etching time, wherein the surface of the obtained micro-nano structure is the wetting surface with the gradient wettability.
Further, the wettability of the gradient wetting surface is characterized by a static contact angle, the static contact angle from the evaporation section to the condensation section is uniformly decreased from 80 degrees to 20 degrees-0 degrees, the etching time or the type and concentration of the etching liquid are controlled, and the decreasing amplitude of the static contact angle is adjusted between 10 degrees/cm and 20 degrees/cm. Wherein, the uniform decreasing to 20 degrees to 0 degrees refers to the uniform decreasing to one of the angle values in the range of 20 degrees to 0 degrees.
Further, the inner surface of the pulsating heat pipe channel is processed by chemical etching, and the pulsating heat pipe with micro-nano structure gradient change and surface wettability gradient change is formed by controlling the etching time. The wettability of the pulsating heat pipe channel changes in a gradient manner along the length direction of the pulsating heat pipe, and the wettability of the pulsating heat pipe channel is gradually improved from the condensation section to the evaporation section of the pulsating heat pipe. The gradient wetting surface promotes the working medium to move from the end with low wetting property to the end with high wetting property, namely the capillary force of the gradient wetting surface drives the working medium to directionally move to the evaporation section, so that the reflux speed of the working medium is accelerated, the problems that the working medium of the pulsating heat pipe or the pulsating heat pipe with low bent pipe number is not easy to reflux, the evaporation section is dried and the like are solved, and the heat transfer performance of the pulsating heat pipe and the capacity of bearing heat load are improved through the gradient wetting surface.
Furthermore, the heat transfer performance of the gradient wetting surface pulsating heat pipe is closely related to the wetting gradient, the input power, the liquid filling rate and the performance of a working medium, the capillary suction capacity can be increased by adjusting the gradient surface static contact angle decreasing amplitude, the working medium backflow is increased, and the heat transfer performance of the pulsating heat pipe is improved.
Furthermore, the number of bent pipes of the pulsating heat pipe is more than or equal to 4; the included angle between the operation direction of the pulsating heat pipe and the horizontal direction is 0-90 degrees; the base material of the pulsating heat pipe is red copper.
Furthermore, the volume liquid filling rate range of the working medium in the pulsating heat pipe is 30-80%.
Furthermore, the working medium of the pulsating heat pipe is one of deionized water, ethanol or acetone, or a combination of more than one of the deionized water, the ethanol and the acetone.
Furthermore, the working temperature range of the pulsating heat pipe is 30-100 ℃, and the working temperature refers to the working temperature of the evaporation section of the pulsating heat pipe.
Further, the hydraulic diameter of the pulsating heat pipe is 0.5mm-3 mm; the shape of the channel in the pulsating heat pipe is rectangular, square, trapezoid or triangular.
The invention also provides a preparation method of the pulsating heat pipe with the gradient wetting surface, which comprises the following steps:
step one, pretreatment: the red copper plate type pulsating heat pipe is soaked in 1mol/L dilute sulfuric acid for 30min, then is washed by a large amount of deionized water and is dried by nitrogen for standby;
step two, preparing a gradient wetting surface: under the regulation of normal temperature or water bath heating, the cleaned pulsating heat pipe is vertically placed in a beaker in the direction that an evaporation section of the pulsating heat pipe is positioned at the bottom; preparing an etching solution, wherein the etching solution is a mixed solution prepared from an alkaline metal hydroxide solution and a persulfate solution according to a certain volume ratio, and the volume ratio is 1: 1; dropwise adding the prepared etching solution into a beaker, controlling the titration speed according to the length of the pulsating heat pipe, wherein the time of the pulsating heat pipe from the evaporation section to the condensation section for oxidation etching is linearly changed, and the etching time of the evaporation section is ensured to be 15-30 minutes;
step three, cleaning and drying: and washing the etched pulsating heat pipe by using a large amount of deionized water, then placing the pulsating heat pipe in a drying oven at 60 ℃, and drying for 15min to form the gradient wetting surface pulsating heat pipe with gradually enhanced wettability from the condensation section to the evaporation section.
Further, the alkali metal hydroxide in the alkali metal hydroxide solution is potassium hydroxide or sodium hydroxide, and the persulfate in the persulfate solution is ammonium persulfate, potassium persulfate or sodium persulfate; the concentration range of the alkaline metal hydroxide solution is 0.5-1mol/L, and the concentration range of the persulfate solution is 0.02-0.1 mol/L.
Further, in the second step, the preparation method of the etching solution comprises: firstly, respectively preparing an alkaline metal hydroxide solution and an ammonium persulfate solution according to the specified concentration, and then mixing the two solutions according to the volume ratio of 1:1 to prepare the etching solution.
Compared with the prior art, the invention has the following advantages:
1. according to the pulsating heat pipe with the gradient wettability surface and the preparation method thereof, the working medium is driven by the gradient wettability surface to move directionally to the evaporation section of the pulsating heat pipe, so that the problem of 'dry burning' of the evaporation section of the pulsating heat pipe is solved, and the heat transfer capacity and the capacity of bearing heat load of the pulsating heat pipe are obviously improved.
2. According to the pulsating heat pipe with the gradient wettability surface and the preparation method thereof, provided by the invention, more vaporization cores are provided on the micro-nano structure surface of the evaporation section, the starting temperature or starting time of the pulsating heat pipe is reduced, and the starting performance of the pulsating heat pipe is improved.
3. According to the pulsating heat pipe with the gradient wettability surface and the preparation method thereof, the contact angle of the working medium at the evaporation section is close to 0 degree, the working medium completely wets the evaporation section of the pulsating heat pipe, and the pulsating heat pipe is in a stable operation stage, so that thin film evaporation is formed, and the heat transfer coefficient of the evaporation section is obviously improved.
In conclusion, the technical scheme of the invention can solve the problem that the evaporation section of the pulsating heat pipe is easy to burn dry in the prior art. The hydraulic diameter of the channel of the pulsating heat pipe is reduced, and the highly integrated and miniaturized pulsating heat pipe is prepared and applied to the fields of heat dissipation and cooling of microelectronic chips under high heat flux and the like.
Based on the reason, the invention can be widely popularized in the fields of microelectronic chip heat dissipation and cooling, industrial waste heat recovery, process heat exchange and the like under high heat flux.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic diagram of a gradient wetted surface pulsating heat pipe of the present invention.
FIG. 2 is a photograph of a static contact angle test of a gradient wetting surface according to the present invention.
FIG. 3 shows the static contact angle values of the pulsating heat pipe along the length direction from the evaporator end to the condenser end.
FIG. 4 is a scanning electron microscope image of the pulsating heat pipe from the evaporation section to the condensation section along the length direction.
FIG. 5 is a schematic diagram of the operation of the pulsating heat pipe made of red copper according to the present invention.
FIG. 6 is a schematic diagram of the operation of the gradient wetting surface pulsating heat pipe of the present invention.
FIG. 7 is a comparison graph of thermal resistances of a red copper pulsating heat pipe and a gradient wetting surface pulsating heat pipe with a liquid filling rate of 50% in the present invention.
FIG. 8 is a heat transfer enhancement efficiency diagram of a pulsating heat pipe with a 50% liquid filling rate gradient wetted surface according to the present invention.
FIG. 9 is a comparison graph of thermal resistances of a red copper pulsating heat pipe with a liquid filling rate of 70% and a gradient wetting surface pulsating heat pipe in the present invention.
FIG. 10 is a heat transfer enhancement efficiency diagram of a pulsating heat pipe with 70% liquid filling rate gradient wetted surface according to the present invention.
In the figure: 1. a liquid phase; 2. a gas phase.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate. Any specific values in all examples shown and discussed herein are to be construed as exemplary only and not as limiting. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.
In the description of the present invention, it is to be understood that the orientation or positional relationship indicated by the directional terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal" and "top, bottom", etc., are generally based on the orientation or positional relationship shown in the drawings, and are used for convenience of description and simplicity of description only, and in the absence of any contrary indication, these directional terms are not intended to indicate and imply that the device or element so referred to must have a particular orientation or be constructed and operated in a particular orientation, and therefore should not be considered as limiting the scope of the present invention: the terms "inner and outer" refer to the inner and outer relative to the profile of the respective component itself.
Spatially relative terms, such as "above … …," "above … …," "above … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial relationship to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, devices described as "above" or "on" other devices or configurations would then be oriented "below" or "under" the other devices or configurations. Thus, the exemplary term "above … …" can include both an orientation of "above … …" and "below … …". The device may be otherwise variously oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
It should be noted that the terms "first", "second", and the like are used to define the components, and are only used for convenience of distinguishing the corresponding components, and the terms have no special meanings unless otherwise stated, and therefore, the scope of the present invention should not be construed as being limited.
As shown in FIG. 1, the invention provides a pulsating heat pipe with a gradient wetting surface, which comprises a condensation section, a heat insulation section and an evaporation section, wherein the inner surface of the pulsating heat pipe is provided with the gradient wetting surface which is uniformly changed from the condensation section to the evaporation section. Wherein, the uniform change refers to that the wetting property of the gradient wetting surface is gradually increased from the condensation section to the evaporation section. The inner surface of the pulsating heat pipe channel is linearly changed from the evaporation section to the condensation section in wettability and roughness, a sodium hydroxide solution and an ammonium persulfate solution are selected as etching solutions, the roughness of the surface is related to the etching time, the surface roughness is controlled by controlling the etching time, a hydrophilic gradient surface with a contact angle continuously changed from the evaporation section to the condensation section from 0-80 degrees is prepared, a gradient wetting surface is introduced to drive a working medium to move directionally to the evaporation section of the pulsating heat pipe, the problem that the evaporation section of the pulsating heat pipe or the pulsating heat pipe with less bent pipes is easy to burn out and has no backflow is solved, and the heat transfer performance and the heat load bearing capacity of the pulsating heat pipe are improved.
The surface roughness of the gradient wetting surface is gradually improved from the condensation section to the evaporation section; the gradient wetting surface is formed by a chemical etching technology, and is provided with a micro-nano structure which is a micro-scale or nano-scale rough structure; oxidizing the surface of the red copper pulsating heat pipe by a chemical etching method, and generating the micro-nano structure of metal hydroxide or metal oxide with continuously and uniformly changed structure along the direction of the channel on the inner surface of the channel by controlling the etching time, wherein the obtained micro-nano structure surface is the wetting surface with the gradient wettability.
The wettability of the gradient wetting surface is characterized by a static contact angle, the static contact angle from an evaporation section to a condensation section is uniformly reduced from 80 degrees to 20 degrees-0 degrees, the etching time or the type and concentration of etching liquid are controlled, and the reduced amplitude of the static contact angle is adjusted between 10 degrees/cm and 20 degrees/cm. Wherein, the uniform decreasing to 20 degrees to 0 degrees refers to the uniform decreasing to one of the angle values in the range of 20 degrees to 0 degrees.
The inner surface of the pulsating heat pipe channel is processed by chemical etching, and the pulsating heat pipe with micro-nano structure gradient change and surface wettability gradient change is formed by controlling the etching time. The wettability of the pulsating heat pipe channel changes in a gradient manner along the length direction of the pulsating heat pipe, and the wettability of the pulsating heat pipe channel is gradually improved from the condensation section to the evaporation section of the pulsating heat pipe. The gradient wetting surface promotes the working medium to move from the end with low wetting property to the end with high wetting property, namely the capillary force of the gradient wetting surface drives the working medium to directionally move to the evaporation section, so that the reflux speed of the working medium is accelerated, the problems that the working medium of the pulsating heat pipe or the pulsating heat pipe with low bent pipe number is not easy to reflux, the evaporation section is dried and the like are solved, and the heat transfer performance of the pulsating heat pipe and the capacity of bearing heat load are improved through the gradient wetting surface.
The heat transfer performance of the gradient wetting surface pulsating heat pipe is closely related to the wetting gradient, the input power, the liquid filling rate and the performance of a working medium, the capillary suction capacity can be increased by adjusting the gradient surface static contact angle decreasing amplitude, the working medium backflow is increased, and the heat transfer performance of the pulsating heat pipe is improved.
The number of the bent pipes of the pulsating heat pipe is more than or equal to 4; the included angle between the operation direction of the pulsating heat pipe and the horizontal direction is 0-90 degrees; the base material of the pulsating heat pipe is red copper, and the channel of the pulsating heat pipe is machined in a machining mode.
The volume liquid filling rate range of the working medium in the pulsating heat pipe is 30-80%.
The working medium of the pulsating heat pipe is one or a combination of more than one of deionized water, ethanol or acetone.
The working temperature range of the pulsating heat pipe is 30-100 ℃, and the working temperature refers to the working temperature of the evaporation section of the pulsating heat pipe.
The hydraulic diameter of the pulsating heat pipe is 0.5mm-3 mm; the shape of the channel in the pulsating heat pipe is rectangular, square, trapezoid or triangular.
The invention also provides a preparation method of the pulsating heat pipe with the gradient wetting surface, which comprises the following steps:
step one, pretreatment: the red copper plate type pulsating heat pipe is soaked in 1mol/L dilute sulfuric acid for 30min, then is washed by a large amount of deionized water and is dried by nitrogen for standby;
step two, preparing a gradient wetting surface: under the regulation of normal temperature or water bath heating, the cleaned pulsating heat pipe is vertically placed in a beaker in the direction that an evaporation section of the pulsating heat pipe is positioned at the bottom; preparing an etching solution, wherein the etching solution is a mixed solution prepared from an alkaline metal hydroxide solution and a persulfate solution according to a certain volume ratio, and the volume ratio is 1: 1; dropwise adding the prepared etching solution into a beaker, controlling the titration speed according to the length of the pulsating heat pipe, wherein the time of the pulsating heat pipe from the evaporation section to the condensation section for oxidation etching is linearly changed, and the etching time of the evaporation section is ensured to be 15-30 minutes;
step three, cleaning and drying: and washing the etched pulsating heat pipe by using a large amount of deionized water, then placing the pulsating heat pipe in a drying oven at 60 ℃, and drying for 15min to form the gradient wetting surface pulsating heat pipe with gradually enhanced wettability from the condensation section to the evaporation section.
The alkaline metal hydroxide in the alkaline metal hydroxide solution includes but is not limited to potassium hydroxide and sodium hydroxide, and the persulfate in the persulfate solution includes but is not limited to ammonium persulfate, potassium persulfate and sodium persulfate; the concentration range of the alkaline metal hydroxide solution is 0.5-1mol/L, and the concentration range of the persulfate solution is 0.02-0.1 mol/L.
In the second step, the preparation method of the etching solution comprises the following steps: firstly, respectively preparing an alkaline metal hydroxide solution and an ammonium persulfate solution according to the specified concentration, and then mixing the two solutions according to the volume ratio of 1:1 to prepare the etching solution.
Example 1
The wetting property of the gradient wetting surface is characterized by a static contact angle, the static contact angle is characterized by a contact angle measuring instrument, and the surface appearance is characterized by a scanning electron microscope picture, wherein the contact angle measuring instrument selects OCAH200 of Germany, and the scanning electron microscope selects Quanta 450 of the Netherlands.
As shown in FIGS. 2-4, in this embodiment, the base material of the pulsating heat pipe is red copper, the total length of the channel of the pulsating heat pipe is 107mm, and the etching solution is 1.5mol/L NaOH solution and 0.06mol/L (NH) solution at a volume ratio of 1:14)2S2O8The mixed solution of the solution is vertically placed in a beaker with the evaporation section of the pulsating heat pipe downward, the etching solution is dropwise added at room temperature, the titration time is 15 minutes, namely the etching time of the evaporation section of the pulsating heat pipe is about 15 minutes, and a gradient surface with gradually reduced wettability from the evaporation section to the condensation section is prepared. Fig. 2 is a static contact angle measurement picture from the evaporation section to different positions of the condensation section, the volume of a liquid drop is selected to be 3 muL during contact angle measurement, fig. 3 is a contact angle value from the evaporation section to different positions of the condensation section, and it can be seen from fig. 3 that the contact angle of the gradient wetting surface is changed linearly, the minimum value of the contact angle is close to 0 degrees, and the maximum value of the contact angle is 83.8 degrees. Fig. 4 is scanning electron microscope pictures of different positions, and the position is the distance from the bottommost of the evaporation section of the pulsating heat pipe in the picture, and as can be seen from fig. 4, the surface roughness is in gradient change, the surface roughness is gradually reduced from the evaporation section to the condensation section of the pulsating heat pipe, the etching solution enables the red copper surface to form a nano grass structure, the etching time is gradually reduced from the evaporation section to the condensation section, and the nano grass structure on the surface of the pulsating heat pipe is gradually changed from dense to sparse. A gradient wetting surface pulsating heat pipe with a uniformly changing contact angle from 0 degrees to 80 degrees is prepared.
Example 2
As shown in fig. 5 and fig. 6, fig. 5 is a schematic diagram of the red copper pulsating heat pipe in steady-state operation, and fig. 6 is a schematic diagram of the gradient wetting surface pulsating heat pipe in steady-state operation. In this embodiment, the basic experimental conditions of the red copper pulsating heat pipe and the gradient wetted surface pulsating heat pipe are the same, that is, the base material of the two pulsating heat pipes is red copper, the number of the bent pipes is 6, and the included angle between the operation direction and the horizontal direction is 0 °, that is, the operation directions of the two pulsating heat pipes are the horizontal direction. The cross sections of the two pulsating heat pipe channels are square, and the hydraulic diameter of the channels is 3 mm. The working medium of the two pulsating heat pipes is deionized water, and the liquid filling rate is 50%. When the gradient wetting surface pulsating heat pipe operates, the working temperature of the evaporation section is 47-96 ℃. When the heating power is 340W, no liquid flows back to the evaporation section of the red copper pulsating heat pipe, the working medium liquid phase 1 is gathered at the condensation section and the heat insulation section of the pulsating heat pipe, the liquid is boundless, and the evaporation section is burnt out. The gradient wetting surface pulsating heat pipe under the same operation condition has the advantages that the contact angle of the surface of the pulsating heat pipe from an evaporation section to a condensation section is uniformly changed from 0 degree to 80 degrees, when the heating power is 340W, the liquid phase 1 flows back at the evaporation section of the gradient wetting surface pulsating heat pipe, the problem of 'drying' of the evaporation section of the red copper pulsating heat pipe under the same operation condition is solved, and a working medium is driven to oscillate in a pulsating heat pipe channel by the pressure difference generated by the evaporation of the liquid phase 1 at the evaporation section and the condensation of the gas phase 2 at the condensation section.
Example 3
As shown in fig. 7 and 8, fig. 7 is a comparison graph of thermal resistances of the red copper pulsating heat pipe and the gradient wetting surface pulsating heat pipe under different heating powers, and fig. 8 is a comparison graph of heat transfer enhancement efficiency of the gradient wetting surface pulsating heat pipe with the red copper pulsating heat pipe. The basic experimental conditions of the red copper pulsating heat pipe and the gradient wetting surface pulsating heat pipe are consistent, namely the base materials of the two pulsating heat pipes are red copper, the number of the bent pipes is 6, the included angle between the operation direction and the horizontal direction is 0 degree, namely the operation directions of the two pulsating heat pipes are the horizontal direction. The cross sections of the two pulsating heat pipe channels are square, and the hydraulic diameter of the channels is 3 mm. The working medium of the two pulsating heat pipes is deionized water, and the liquid filling rate is 50%. When the gradient wetting surface pulsating heat pipe operates, the working temperature of the evaporation section is 47-96 ℃. Starting heating power from 100W, after the pulsating heat pipe stably runs for 20 minutes, increasing the heating power by 40W each time until the average temperature of the evaporation section of the pulsating heat pipe reaches 100 ℃, and defining the heat transfer enhancement efficiency as follows:
as can be seen from fig. 7, in the horizontal heating direction, the heat transfer performance of the red copper pulsating heat pipe of the 6-bend pipe is poor, the visual experiment result also shows that the evaporation section of the red copper pulsating heat pipe is burnt out, almost no working medium flows back to the evaporation section, the heat transfer performance of the gradient wetting surface pulsating heat pipe under the same operation condition is remarkably improved, the thermal resistance of the pulsating heat pipe is reduced along with the increase of the heating power, and the visual experiment shows that the working medium flows back at the evaporation section of the gradient wetting surface pulsating heat pipe, and the liquid bomb oscillates in the passage of the pulsating heat pipe. As can be seen from FIG. 8, when the liquid filling rate is 50%, the heat transfer performance of the gradient wetting surface pulsating heat pipe is improved by 10% -35% compared with that of the red copper pulsating heat pipe under the same operation condition.
Example 4
As shown in fig. 9 and 10, fig. 9 is a comparison graph of thermal resistances of the red copper pulsating heat pipe and the gradient wetting surface pulsating heat pipe under different heating powers, and fig. 10 is a comparison graph of heat transfer enhancement efficiency of the gradient wetting surface pulsating heat pipe with the red copper pulsating heat pipe. The basic experimental conditions of the red copper pulsating heat pipe and the gradient wetting surface pulsating heat pipe are consistent, namely the base materials of the two pulsating heat pipes are red copper, the number of the bent pipes is 6, the included angle between the operation direction and the horizontal direction is 0 degree, namely the operation directions of the two pulsating heat pipes are the horizontal direction. The cross sections of the two pulsating heat pipe channels are square, and the hydraulic diameter of the channels is 3 mm. The working medium of the two pulsating heat pipes is deionized water, and the liquid filling rate of the two pulsating heat pipes is 70%. When the gradient wetting surface pulsating heat pipe operates, the working temperature of the evaporation section is 45-94 ℃. As can be seen from fig. 9 and 10, compared with the red copper pulsating heat pipe, the heat transfer performance of the gradient wetting surface pulsating heat pipe is significantly improved, and the heat transfer performance is improved by 5% -25%. The gradient wetting surface pulsating heat pipe drives the working medium to directionally move to the evaporation section, and the problem of 'dry burning' of the evaporation section in the horizontal heating direction of the 6-elbow pulsating heat pipe with less elbows is solved.
The embodiment of the present invention is not limited by the above examples, wherein the decreasing amplitude of the contact angle of the gradient surface can be controlled by controlling the etching time or the type and concentration of the etching solution.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A pulsating heat pipe with a gradient wetting surface, comprising a condensation section, a heat insulation section and an evaporation section, characterized in that the inner surface of the pulsating heat pipe has a gradient wetting surface that varies uniformly from the condensation section to the evaporation section.
2. A pulsating heat pipe having a gradient wetting surface as defined in claim 1 wherein said gradient wetting surface gradually increases in surface roughness from a condenser section to an evaporator section; the gradient wetting surface is formed by a chemical etching technology; the gradient wetting surface is provided with a micro-nano structure which is a micro-scale or nano-scale rough structure; oxidizing the surface of the red copper pulsating heat pipe by a chemical etching method, and generating the micro-nano structure of metal hydroxide or metal oxide with continuously and uniformly changed structure along the direction of the channel on the inner surface of the channel by controlling the etching time, wherein the surface of the obtained micro-nano structure is the wetting surface with the gradient wettability.
3. A pulsating heat pipe having a gradient wetting surface as defined in claim 1 or 2 wherein the wettability of said gradient wetting surface is characterized by a static contact angle, said static contact angle from the condensing section to the evaporating section decreases uniformly from 80 ° to 20 ° -0 °, the etching time or the type and concentration of the etching liquid is controlled, said decreasing magnitude of the static contact angle being adjusted between 10 °/cm-20 °/cm.
4. A pulsating heat pipe having a gradient wetting surface as defined in claim 1 wherein the number of bends of said pulsating heat pipe is greater than or equal to 4; the included angle between the operation direction of the pulsating heat pipe and the horizontal direction is 0-90 degrees; the base material of the pulsating heat pipe is red copper.
5. A pulsating heat pipe with gradient wetted surface as defined in claim 1 or 4 wherein the volumetric filling rate of the working medium in said pulsating heat pipe is in the range of 30% -80%.
6. The pulsating heat pipe with a gradient wetted surface of claim 5, wherein working medium of said pulsating heat pipe is one or a combination of more than one of deionized water, ethanol or acetone.
7. A pulsating heat pipe having a gradient wetted surface as defined in claim 1 or 4, wherein said pulsating heat pipe has an operating temperature in the range of 30 ℃ to 100 ℃, said operating temperature being the operating temperature of the evaporator section of the pulsating heat pipe.
8. A pulsating heat pipe having a gradient wetting surface as defined in claim 7, wherein said pulsating heat pipe has a hydraulic diameter of 0.5mm to 3 mm; the shape of the channel in the pulsating heat pipe is rectangular, square, trapezoid or triangular.
9. A method for preparing a pulsating heat pipe with a gradient wetting surface as defined in any of claims 1-8, comprising the steps of:
step one, pretreatment: the red copper plate type pulsating heat pipe is soaked in 1mol/L dilute sulfuric acid for 30min, then is washed by a large amount of deionized water and is dried by nitrogen for standby;
step two, preparing a gradient wetting surface: under the regulation of normal temperature or water bath heating, the cleaned pulsating heat pipe is vertically placed in a beaker in the direction that an evaporation section of the pulsating heat pipe is positioned at the bottom; preparing an etching solution, wherein the etching solution is a mixed solution prepared from an alkaline metal hydroxide solution and a persulfate solution according to a certain volume ratio, and the volume ratio is 1: 1; dropwise adding the prepared etching solution into a beaker, controlling the titration speed according to the length of the pulsating heat pipe, wherein the time of the pulsating heat pipe from the evaporation section to the condensation section for oxidation etching is linearly changed, and the etching time of the evaporation section is ensured to be 15-30 minutes;
step three, cleaning and drying: and washing the etched pulsating heat pipe by using a large amount of deionized water, then placing the pulsating heat pipe in a drying oven at 60 ℃, and drying for 15min to form the gradient wetting surface pulsating heat pipe with gradually enhanced wettability from the condensation section to the evaporation section.
10. A method of forming a pulsating heat pipe having a gradient wetted surface as defined in claim 9, wherein said alkali metal hydroxide in said alkali metal hydroxide solution is potassium hydroxide or sodium hydroxide, and said persulfate solution wherein said persulfate salt is ammonium persulfate, potassium persulfate, or sodium persulfate; the concentration range of the alkaline metal hydroxide solution is 0.5-1mol/L, and the concentration range of the persulfate solution is 0.02-0.1 mol/L.
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