CN111059940B - Low-resistance enhanced heat transfer layout structure based on nanometer super-wetting interface - Google Patents
Low-resistance enhanced heat transfer layout structure based on nanometer super-wetting interface Download PDFInfo
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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
- F28D15/0233—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 the conduits having a particular shape, e.g. non-circular cross-section, annular
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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
Abstract
The invention relates to a low-resistance enhanced heat transfer layout structure based on a nanometer super-wetting interface, wherein 11 areas with the same area are arranged along the length direction of the surface, the 1 st area is a 100% super-hydrophobic surface, the 2 nd area is a 10% area super-hydrophilic surface, the 10% area super-hydrophilic surface of the area is rectangular or circular, the 3 rd area is a 20% area super-hydrophilic surface, and the like, and then 10% area super-hydrophilic surfaces are sequentially added to each area until the 11 th area is a 100% super-hydrophilic surface, so that patterned gradient wettability of 100% super-hydrophobic area to 100% super-hydrophilic area is formed. The invention can be used in ultra-compact heat exchangers with low or medium heat flux, and the incorporation and use of surface wettability modification in energy systems has great application potential and profound potential impact.
Description
Technical Field
The invention belongs to the technical field of thermal management, and relates to a low-resistance enhanced heat transfer layout structure based on a nanometer super-wetting interface.
Background
Currently, there is interest in the development of advanced ultra-compact heat exchangers in various industries that are important to the overall efficiency, cost, and compactness of many thermal management and energy systems. Heat exchangers are devices responsible for transferring heat between two or more fluids (liquids or gases) by a combination of conduction, internal/external convection and/or radiation, also known as heat exchangers. The heat exchanger can be used as a heater, a cooler, a condenser, an evaporator, a reboiler and the like, and is widely applied. In the evaporator, the liquid working medium absorbs heat to be gasified; in the condenser, the gas working medium releases heat to be condensed. Aluminum, copper, stainless steel, silicon are widely used in heat exchanger construction, all of which are hydrophilic materials. It is well known that the evaporation or condensation of water or steam on a surface depends to a large extent on the surface properties, i.e. the surface wettability. Whereas in ultra-compact heat exchangers, surface forces may dominate as dimensions are reduced to microscale. Surface wettability, which is generally characterized by contact angle, can be used to control heat transfer and pressure drop.
The problem of "surface wettability" has attracted considerable interest in the last few years, and the number of journal publications in the field of engineering and material science has increased significantly and continuously from 1992 to date, based on the scientific index of introduction (SCI) source. "surface wettability" refers to the degree to which a surface is hydrophilic or hydrophobic, and by careful design, the natural wettability of a surface can be altered to make it more hydrophilic or hydrophobic, and the preparation of hydrophilic, superhydrophilic, hydrophobic, superhydrophobic surfaces has been extensively studied. Most materials of practical interest are neither completely moist nor completely non-moist. Surface properties (hydrophobic or hydrophilic) are typically characterized by measuring the contact angle of a droplet of liquid on a surface. When water is used, a contact angle of less than 90 ° indicates a hydrophilic surface, a contact angle of more than 90 ° indicates a hydrophobic surface, a contact angle of less than 5 ° for a superhydrophilic surface, and a contact angle of more than 150 ° for a superhydrophobic surface. It is well known that surface wettability is controlled by surface chemistry and morphology. The chemical composition determines the surface free energy and also reduces the surface activity. Lower surface energy results in higher hydrophobicity. In addition, surface roughness is a key factor of superhydrophobic surfaces, and roughness is also important for surface hydrophilicity due to two-dimensional or three-dimensional capillary effects, that is, roughness amplifies the wetting behavior of the substrate. Inspired by the surface structure of superhydrophobic organisms in nature, such as lotus leaves and water striders legs, more and more people are concerned about the study of specific surface roughness having a micro (or nano) structure. By combining the layered micro/nanostructures with appropriate materials, various surfaces with superhydrophobicity or superhydrophilicity are synthesized.
At present, surfaces with single wettability are generally adopted in the surfaces of ultra-compact heat exchangers, materials such as aluminum, copper, stainless steel, silicon and the like are taken as main materials, and the materials are hydrophilic materials, so that the advantages of different surface wettabilities are not fully utilized. Surface wettability can be modified and controlled by controlling surface chemistry or physics. Besides the hydrophilic surface, the hydrophobic surface is properly adopted in the evaporator, so that the nucleation density can be increased, and the resistance can be reduced. In the condenser, the hydrophilic material is completely adopted, so that the water is difficult to be effectively drained, the retention amount of condensed water is increased, the pressure drop is increased, the possibility of corrosion is generated, the heat transfer efficiency and the overall performance of the heat exchanger are further reduced, and a place is provided for the biological growth which is possibly harmful to human health.
Disclosure of Invention
The technical problem solved by the invention is as follows: the defects of the prior art are overcome, a low-resistance enhanced heat transfer layout structure based on a nanometer super-wetting interface is provided, and the modification and control of the surface wettability of an object are realized.
The technical scheme of the invention is as follows:
a low-resistance enhanced heat transfer layout structure based on a nanometer super-wetting interface is characterized in that super-hydrophilic and super-hydrophobic area layout with a certain proportion is carried out along a certain direction of the surface of an object to form a wettability gradient and control a motion path of liquid drops on an array surface;
the shape of the layout is rectangular or circular;
11 areas with the same area are arranged along the length direction of the surface, the 1 st area is a 100% super-hydrophobic surface, the 2 nd area is a 10% area super-hydrophilic surface, the 10% area super-hydrophilic surface of the area is rectangular or circular, the 3 rd area is a 20% area super-hydrophilic surface, and the like, and then 10% area super-hydrophilic surfaces are sequentially added to each area until the 11 th area is the 100% super-hydrophilic surface, so that the patterned gradient wettability from 100% super-hydrophobic area to 100% super-hydrophilic area is formed;
the vaporization nucleation density of the super-wetting interface is as follows: when Δ Tw,ONB<ΔTw<At 15 deg., Na＝0.34[1-cos(θ)]ΔTw 2.0When Δ T iswWhen the temperature is more than or equal to 15 ℃, Na＝3.4×10-5[1-cos(θ)]ΔTw 5.3；
Wherein, Delta TwSuperheat of the wall, ONB boiling start, Naθ is the contact angle for the vaporization nucleation density;
when the surface is a superhydrophilic surface, θ is close to 0 °, cos (θ) is close to 1, NaIs small;
when the surface is a superhydrophobic surface, θ is close to 180 °, cos (θ) is close to-1, NaIs significantly increased.
Preferably, in the case where the layout surface is rectangular in shape,
11 regions with the same area are arranged along the length direction of the surface, the 1 st region is a 100% super-hydrophobic surface, the 2 nd region is provided with a 10% region area super-hydrophilic surface, the 10% region area super-hydrophilic surface is rectangular, the length is the same as the length of the region, the width is 10% of the width of the region, and the center point of the super-hydrophilic surface is superposed with the center point of the region; the 3 rd region is provided with a super-hydrophilic surface with the area of 20 percent and consists of 2 rectangular super-hydrophilic surfaces with the area of 10 percent, the length of the 2 super-hydrophilic surfaces is the same as that of the region, the width of the 2 super-hydrophilic surfaces is 10 percent of that of the region, the 2 super-hydrophilic surfaces are symmetrically distributed along the axial center line of the region, and the middle of the 2 super-hydrophilic surfaces is separated by the rectangular super-hydrophobic surface with the area of 10 percent;
and by analogy, sequentially adding 10% of the area of the super-hydrophilic surface to each area until the 11 th area is the 100% super-hydrophilic surface, thereby forming the patterned gradient wettability from 100% of the super-hydrophobic area to 100% of the super-hydrophilic area.
Preferably, in the case where the shape of the layout surface is circular,
11 areas with the same area are arranged along the length direction of the surface, the 1 st area is a 100% super-hydrophobic surface, the 2 nd area is provided with a 10% area super-hydrophilic surface, the 10% area super-hydrophilic surface of the area is circular, and the center point of the super-hydrophilic surface is coincided with the center point of the area; setting a super-hydrophilic surface with 20% of area in the 3 rd region, wherein the center point of the super-hydrophilic surface is coincided with the center point of the region;
by analogy, 10% area of the super-hydrophilic surface is sequentially added to each area, the 6 th area is a 50% super-hydrophilic surface, and the super-hydrophobic area and the super-hydrophilic area of the 7 th, 8 th, 9 th, 10 th and 11 th areas are opposite to the 5 th, 4 th, 3 th, 2 th and 1 th areas respectively.
Preferably, the superhydrophobic areas and the superhydrophilic areas of the 1 st region and the 11 th region, the 2 nd region and the 10 th region, the 3 rd region and the 9 th region, the 4 th region and the 8 th region, and the 5 th region and the 7 th region are opposite to each other.
Preferably, the proportion of the superhydrophilic surface of each region along the length of the surface is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%, respectively, to provide a patterned gradient wettability of 100% superhydrophobic area to 100% superhydrophilic area, and vice versa, a patterned gradient wettability of 100% superhydrophilic area to 100% superhydrophobic area is also possible.
Preferably, the critical heat flow density of the superhydrophilic surface is related to the contact angle by:
wherein q ″)CHFwettingCritical heat flux density, h, related to surface wettabilityfgIs the latent heat of the liquid, ρvIs gas phase density, plIs the density of the liquid phase, σ is the surface tension, g is the acceleration of gravity, θRIs the receding contact angle.
Preferably, the wetting process is related to the interfacial tension of the system, and when the liquid is in equilibrium with falling on a horizontal solid surface, the contact angle formed satisfies the following interfacial tensions:
where θ is the contact angle, σ is the surface tension, s is the solid phase, l is the liquid phase, and v is the gas phase.
Preferably, a rough structure is constructed on the surface, and then an acrylic polymer chain is coated on the surface of the microstructure, so that the super-hydrophobic surface is formed; or modifying the surface with a silane coating to make the surface achieve super-hydrophobic characteristics.
Preferably, the superhydrophilic surface is obtained by photoinitiating superhydrophilic; or increase the surface roughness to make the surface hydrophilic.
Preferably, the surface roughness increases the solid surface energy, characterized by r, cos θ*R cos θ, when the solid surface is smooth, r 1, when r>1, the hydrophilic surface is more hydrophilic, while the hydrophobic surface is more hydrophobic.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention modifies and controls the surface wettability by creating a wettability gradient surface and patterning the wettability;
(2) the invention can predetermine the starting position of surface evaporation or condensation, and promote droplet movement and/or control droplet movement path by creating an adjustable wettability pattern or gradient;
(3) in the evaporation process, the wetting gradient surface is adopted to increase the nucleation density and improve the critical heat flow density, thereby reducing the flow resistance and strengthening the heat exchange effect;
(4) in the condensation process, the wetting gradient surface is adopted to promote the movement of liquid drops and/or control the movement path of the liquid drops, the discharge of condensed water is enhanced, and the overall energy efficiency of the system is improved;
(5) the invention can be used in ultra-compact heat exchangers with low or medium heat flux, and the incorporation and use of surface wettability modification in energy systems has great application potential and profound potential impact.
Drawings
FIG. 1 is a wettability gradient surface for an evaporator of the present invention;
FIG. 2 is a wettability gradient surface for a condenser of the present invention.
Detailed Description
The invention is further illustrated by the following examples.
A low-resistance enhanced heat transfer layout structure based on a nanometer super-wetting interface is characterized in that super-hydrophilic and super-hydrophobic area layout with a certain proportion is carried out along a certain direction of the surface of an object to form a wettability gradient and control a motion path of liquid drops on an array surface;
the shape of the layout is rectangular or circular;
in the case where the layout surface is rectangular in shape,
11 areas with the same area are arranged along the length direction of the surface, the 1 st area is a 100% super-hydrophobic surface (white area), the 2 nd area is provided with a 10% super-hydrophilic surface (dark color part), the 10% super-hydrophilic surface of the area is rectangular, the length is the same as the length of the area, the width is 10% of the width of the area, and the center point of the super-hydrophilic surface is coincided with the center point of the area. The super-hydrophilic surface (dark color part) with 20 percent of area is arranged in the 3 rd area and consists of 2 rectangular super-hydrophilic surfaces with 10 percent of area, the length of the 2 super-hydrophilic surfaces is the same as that of the area, the width of the 2 super-hydrophilic surfaces is 10 percent of the width of the area, the 2 super-hydrophilic surfaces are symmetrically distributed along the axial center line of the area, and the middle of the 2 super-hydrophilic surfaces is separated by the rectangular super-hydrophobic surface with 10 percent of area. By analogy, each region is sequentially increased by 10% area of super-hydrophilic surface (dark portion) thereafter until the 11 th region is 100% super-hydrophilic surface (dark portion), thereby forming a patterned gradient wettability of 100% super-hydrophobic area to 100% super-hydrophilic area. Wherein the super-hydrophobic areas and the super-hydrophilic areas of the 1 st area and the 11 th area, the 2 nd area and the 10 th area, the 3 rd area and the 9 th area, the 4 th area and the 8 th area, and the 5 th area and the 7 th area are opposite to each other. Therefore, the proportion of the superhydrophilic surface (dark portion) of each region in the length direction of the surface is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%, respectively.
The vaporization nucleation density can be predicted by the following correlation: when Δ Tw,ONB<ΔTw<At 15 deg., Na＝0.34[1-cos(θ)]ΔTw 2.0When Δ T iswWhen the temperature is more than or equal to 15 ℃, Na＝3.4×10-5[1-cos(θ)]ΔTw 5.3. Wherein, Delta TwSuperheat of the wall, ONB boiling start, NaFor vaporization nucleation density, θ is the contact angle. When the surface is a superhydrophilic surface, θ is close to 0 °, cos (θ) is close to 1, NaIs small; when the surface is a superhydrophobic surface, θ is close to 180 °, cos (θ) is close to-1, NaIs significantly increased.
The super-hydrophilic surface can improve the critical heat flow density, effectively delay the occurrence of heat transfer deterioration and improve the maximum heat exchange capacity of equipment;
wherein q ″)CHFwettingCritical heat flux density, h, related to surface wettabilityfgIs the latent heat of the liquid, ρvIs gas phase density, plIs the density of the liquid phase, σ is the surface tension, g is the acceleration of gravity, θRIs the receding contact angle.
In the case where the shape of the layout surface is circular,
similar to a rectangle, 11 areas with the same area are arranged along the length direction of the surface, the 1 st area is a 100% super-hydrophobic surface (white area), the 2 nd area is a 10% super-hydrophilic surface (dark part), the 10% super-hydrophilic surface of the area is a circle, and the center point of the super-hydrophilic surface is coincident with the center point of the area. A super-hydrophilic surface (dark portion) of 20% area was provided in the 3 rd region, and the center point of the super-hydrophilic surface was coincident with the center point of the region. By analogy, 10% area of super-hydrophilic surface (dark color part) is sequentially added in each area, the 6 th area is 50% super-hydrophilic surface (dark color part), and the super-hydrophobic area and the super-hydrophilic area of the 7 th, 8 th, 9 th, 10 th and 11 th areas are respectively opposite to the 5 th, 4 th, 3 th, 2 th and 1 th areas. Therefore, the proportion of the superhydrophilic surface (dark portion) of each region along the length of the surface is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%, respectively, thereby forming a patterned gradient wettability of 100% superhydrophobic area to 100% superhydrophilic area. The relationship between the vaporization nucleation density, the critical heat flow density, and the contact angle is the same as that in the case where the layout shape is rectangular.
The wetting process is related to the interfacial tension of the system. A drop of liquid is deposited on a horizontal solid surface, and when equilibrium is reached, the resulting contact angle and the respective interfacial tension correspond to the young's formula:
where θ is the contact angle, σ is the surface tension, s is the solid phase, l is the liquid phase, and v is the gas phase.
The surface of the material with lower surface energy has good hydrophobicity. The low surface energy surface treatment technology mostly adopts a treatment technology similar to a bionic micro-nano material, and most researches are carried out at present to use organic polymers as the first choice material of coated low surface energy substances. For example, a physical and chemical combination method is adopted to build a rough structure on the surface, and then acrylic polymer chains are coated on the surface of the microstructure, so that the super-hydrophobic surface is formed. Or modifying the surface with a silane coating to make the surface super-hydrophobic, etc.
There are two aspects to the preparation of superhydrophilic surfaces, one is photoinitiated superhydrophilic, such as: TiO 22Ultra-hydrophilic surfaces can be obtained by exposure to ultraviolet radiation, and the surface becomes more hydrophilic due to the increased roughness of the surface, such as: the surface on which the nanowires are grown has super-hydrophilicity.
The proportion of the super-hydrophilic surface (dark color part) of each area of the layout surface along the length direction of the surface is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100% respectively, so that the patterned gradient wettability of 100% super-hydrophobic area to 100% super-hydrophilic area is formed. Vice versa, patterned gradient wetability from 100% superhydrophilic area to 100% superhydrophobic area can also be formed.
The surface roughness increases the solid surface energy, characterized by r. cos θ*R cos θ. When the solid surface is smooth, r is 1. When r is>1, the hydrophilic surface is more hydrophilic, while the hydrophobic surface is more hydrophobic.
As shown in fig. 1, the wettability gradient surface for an evaporator has different superhydrophilic/superhydrophobic area ratios along the length direction, the superhydrophobic surface being represented by white and the superhydrophilic surface being represented by dark. The wettability patterns in fig. 1a and 1b are rectangular, fig. 1a is a unit diagram, fig. 1b is an overall diagram, the wettability patterns in fig. 1c and 1d are circular, fig. 1c is a unit diagram, and fig. 1d is an overall diagram.
11 areas with the same area are arranged along the length direction of the surface, the 1 st area is a 100% super-hydrophobic surface (white area), the 2 nd area is provided with a 10% super-hydrophilic surface (dark color part), the 10% super-hydrophilic surface of the area is rectangular, the length is the same as the length of the area, the width is 10% of the width of the area, and the center point of the super-hydrophilic surface is coincided with the center point of the area. The super-hydrophilic surface (dark color part) with 20 percent of area is arranged in the 3 rd area and consists of 2 rectangular super-hydrophilic surfaces with 10 percent of area, the length of the 2 super-hydrophilic surfaces is the same as that of the area, the width of the 2 super-hydrophilic surfaces is 10 percent of the width of the area, the 2 super-hydrophilic surfaces are symmetrically distributed along the axial center line of the area, and the middle of the 2 super-hydrophilic surfaces is separated by the rectangular super-hydrophobic surface with 10 percent of area. By analogy, each region is sequentially increased by 10% area of super-hydrophilic surface (dark portion) thereafter until the 11 th region is 100% super-hydrophilic surface (dark portion), thereby forming a patterned gradient wettability of 100% super-hydrophobic area to 100% super-hydrophilic area. Wherein the super-hydrophobic areas and the super-hydrophilic areas of the 1 st area and the 11 th area, the 2 nd area and the 10 th area, the 3 rd area and the 9 th area, the 4 th area and the 8 th area, and the 5 th area and the 7 th area are opposite to each other. Therefore, the proportion of the superhydrophilic surface (dark portion) of each region in the length direction of the surface is 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%, respectively.
The primary means of modifying the surface chemistry is to apply a coating of a different material to the surface because the interfacial free energy associated with the contact angle of a droplet is altered. Wettability is expressed in terms of contact angle, which is generally determined by the attraction of the droplet molecules to the surface (adsorption) and to each other (cohesion). The equation between contact angle and surface tension can be written as:
where σ is the surface tension (or surface free energy), θ is the static contact angle, and subscripts s, v, and l represent solid, vapor, and liquid, respectively. The chemical composition determines the surface free energy and also reduces the surface activity. Lower surface energy results in higher hydrophobicity. Surfaces such as polytetrafluoroethylene, polyethylene, polypropylene, etc., are low energy surfaces.
The physical properties of the surface are modified mainly by manufacturing micro-nano structures with different scales on the surface to enable the micro-nano structures to have different roughness, and the micro-nano roughness can be used for obviously influencing the wetting behavior and the movement of water drops on the surface by increasing or reducing the solid/liquid contact area. It was observed in experiments that roughness makes hydrophilic surfaces (wetted surfaces) more hydrophilic, while hydrophobic surfaces (non-wetted surfaces) are more hydrophobic. The empirical relationship between the static contact angle of a water droplet and the surface roughness coefficient is:
cosθ*＝r cosθ
in the formula, theta*Is the new apparent contact angle on a rough surface, theta is the contact angle on a smooth surface, and r is the roughness coefficient. The multi-scale graded roughness may also create air pockets near the solid surface. This results in a reduction in the liquid-solid contact area, thereby reducing the flow resistance.
The surface can be widely used in evaporators to play a role in effectively reducing drag and enhancing heat exchange. In the evaporator, low-temperature condensed liquid passes through the evaporator to exchange heat with the outside, and the condensed liquid is gasified to absorb heat to achieve the refrigeration effect. The surface of the evaporator is provided with the surface shown in figure 1, and the fluid flows in from the 100% super-hydrophobic area and flows out from the 100% super-hydrophilic area. In the inlet part, the fluid is in a liquid state, the heat exchange surface is a 100% super-hydrophobic surface, and a laminar flow drag reduction phenomenon exists in a micro-channel which is made of the super-hydrophobic surface and has definite micron-scale roughness, so that the reduction of friction pressure drop in the channel is facilitated. This is because the liquid flows on the superhydrophobic surface, wall slip occurs, which reduces resistance in the flow. With the reduction of the size of the micro-channel in the micro-channel heat exchanger, the interfacial resistance is increased, so that the super-hydrophobic surface with the resistance reduction function is the key for developing the micro-channel heat exchanger.
The super-hydrophobic surface is helpful for forming a gasification core when the temperature reaches the gasification temperature, the phase change can be carried out under a lower superheat degree, latent heat is absorbed, and the heat exchange efficiency is higher. Along with the gradual rise of the temperature of the fluid, the area of the super-hydrophilic surface is gradually increased to form a super-hydrophilic-super-hydrophobic alternate surface, so that the advantages of the super-hydrophobic surface and the super-hydrophilic surface can be fully utilized, the super-hydrophobic surface is utilized for nucleation, the super-hydrophilic surface is utilized for timely supplementing the fluid, and the formation of a large-area air film for deteriorating heat transfer is avoided. A superhydrophilic surface with hydrophobic islands can increase the critical heat flow density by 80%. Along with the gradual increase of the heat absorbed by the fluid, the proportion of the gas-phase components is larger and larger, and the proportion of the super-hydrophilic area is larger and larger at the moment, so that annular flow is formed in the flow channel, and the phenomena of forming a gas film on the surface of the flow channel and drying are avoided.
As shown in fig. 2, the wettability gradient surface for the condenser has different superhydrophilic/superhydrophobic area ratios along the length direction, the superhydrophobic surface is represented by white, the superhydrophilic surface is represented by dark color, and the superhydrophobic surface area ratios are 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% in sequence. The wettability patterns in fig. 2a and 2b are rectangular, fig. 2a is a cell diagram, fig. 2b is an overall diagram, the wettability patterns in fig. 2c and 2d are circular, fig. 2c is a cell diagram, and fig. 2d is an overall diagram.
Like the evaporator, the vapor is converted to a liquid in the condenser, so that the heat of the fluid medium is transferred in a rapid manner. The surface of the condenser is provided with the surface shown in figure 2, and the fluid flows in from the 100% super hydrophilic area and flows out from the 100% super hydrophobic area. In the inlet part, the fluid is in a gas state, the heat exchange surface is a 100% super-hydrophilic surface, the temperature is gradually reduced along with the gradual heat release of the fluid, and the fluid is condensed into liquid drops when reaching the condensation temperature. Along with the further reduction of the temperature of the fluid, the area of the super-hydrophobic surface is gradually increased to form a super-hydrophilic-super-hydrophobic interphase surface, so that the respective advantages of the super-hydrophobic surface and the super-hydrophilic surface can be fully utilized, a liquid channel formed by the super-hydrophilic surface is utilized to discharge condensed liquid, film-shaped condensation is avoided, and the main condensation form is drop-shaped condensation. Along with the gradual increase of the heat released by the fluid, the proportion of the liquid phase component is larger and larger, and the proportion of the super-hydrophobic area is larger and larger at the moment, so that the function of reducing the flow resistance is realized.
The non-uniform wettability is very effective in improving drainage. The super-hydrophobic region has rapid liquid drop mobility, and the super-hydrophilic region promotes the removal of liquid drops in the surrounding super-hydrophobic region and plays a role of a drainage channel. Due to the wettability difference, the tiny water drops spontaneously move from the superhydrophobic area to the superhydrophilic area and coalesce into larger water drops, which make drainage more and easier. Experiments prove that the condensation heat transfer coefficient and the heat flux of the mixed surface are substantially improved, and the heat transfer performance can be improved by 180 to 480 percent compared with the uniform surface.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (10)
1. A low-resistance enhanced heat transfer layout structure based on a nanometer super-wetting interface is characterized in that super-hydrophilic and super-hydrophobic area layout with a certain proportion is carried out along a certain direction of the surface of an object to form a wettability gradient and control the movement path of liquid drops on an array surface;
the shape of the layout is rectangular or circular;
11 areas with the same area are arranged along the length direction of the surface, the 1 st area is a 100% super-hydrophobic surface, the 2 nd area is a 10% area super-hydrophilic surface, the 10% area super-hydrophilic surface of the area is rectangular or circular, the 3 rd area is a 20% area super-hydrophilic surface, and the like, and then 10% area super-hydrophilic surfaces are sequentially added to each area until the 11 th area is the 100% super-hydrophilic surface, so that the patterned gradient wettability from 100% super-hydrophobic area to 100% super-hydrophilic area is formed;
the vaporization nucleation density of the super-wetting interface is as follows: when Δ Tw,ONB<ΔTw<At 15 deg., Na＝0.34[1-cos(θ)]ΔTw 2.0When Δ T iswWhen the temperature is more than or equal to 15 ℃, Na＝3.4×10-5[1-cos(θ)]ΔTw 5.3；
Wherein, Delta TwIs a wall surfaceDegree of superheat, ONB boiling onset, Naθ is the contact angle for the vaporization nucleation density;
when the surface is a superhydrophilic surface, θ is close to 0 °, cos (θ) is close to 1, NaIs small;
when the surface is a superhydrophobic surface, θ is close to 180 °, cos (θ) is close to-1, NaAnd is increased.
2. The low resistance enhanced heat transfer layout structure based on nanometer super-wetting interface as claimed in claim 1, wherein for the case that the layout surface is rectangular in shape,
11 regions with the same area are arranged along the length direction of the surface, the 1 st region is a 100% super-hydrophobic surface, the 2 nd region is provided with a 10% region area super-hydrophilic surface, the 10% region area super-hydrophilic surface is rectangular, the length is the same as the length of the region, the width is 10% of the width of the region, and the center point of the super-hydrophilic surface is superposed with the center point of the region; the 3 rd region is provided with a super-hydrophilic surface with the area of 20 percent and consists of 2 rectangular super-hydrophilic surfaces with the area of 10 percent, the length of the 2 super-hydrophilic surfaces is the same as that of the region, the width of the 2 super-hydrophilic surfaces is 10 percent of that of the region, the 2 super-hydrophilic surfaces are symmetrically distributed along the axial center line of the region, and the middle of the 2 super-hydrophilic surfaces is separated by the rectangular super-hydrophobic surface with the area of 10 percent;
and by analogy, sequentially adding 10% of the area of the super-hydrophilic surface to each area until the 11 th area is the 100% super-hydrophilic surface, thereby forming the patterned gradient wettability from 100% of the super-hydrophobic area to 100% of the super-hydrophilic area.
3. The low resistance enhanced heat transfer layout structure based on nanometer super-wetting interface as claimed in claim 1, wherein for the case that the layout surface is circular in shape,
11 areas with the same area are arranged along the length direction of the surface, the 1 st area is a 100% super-hydrophobic surface, the 2 nd area is provided with a 10% area super-hydrophilic surface, the 10% area super-hydrophilic surface of the area is circular, and the center point of the super-hydrophilic surface is coincided with the center point of the area; setting a super-hydrophilic surface with 20% of area in the 3 rd region, wherein the center point of the super-hydrophilic surface is coincided with the center point of the region;
by analogy, 10% area of the super-hydrophilic surface is sequentially added to each area, the 6 th area is a 50% super-hydrophilic surface, and the super-hydrophobic area and the super-hydrophilic area of the 7 th, 8 th, 9 th, 10 th and 11 th areas are opposite to the 5 th, 4 th, 3 th, 2 th and 1 th areas respectively.
4. The low resistance enhanced heat transfer layout structure based on nanometer super wetting interface as claimed in claim 2 or 3, wherein the super hydrophobic area and super hydrophilic area of the 1 st region and the 11 th region, the 2 nd region and the 10 th region, the 3 rd region and the 9 th region, the 4 th region and the 8 th region, and the 5 th region and the 7 th region are opposite to each other.
5. The low resistance enhanced heat transfer layout structure based on the nanometer super-wetting interface as claimed in claim 2 or 3, wherein the proportion of the super-hydrophilic surface of each region along the length direction of the surface is respectively 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%, so as to form a patterned gradient wettability of 100% super-hydrophobic area to 100% super-hydrophilic area, and vice versa, so as to form a patterned gradient wettability of 100% super-hydrophilic area to 100% super-hydrophobic area.
6. The low resistance enhanced heat transfer layout structure based on the nanometer super-wetting interface as claimed in claim 2 or 3, wherein the relation between the critical heat flow density and the contact angle of the super-hydrophilic surface is as follows:
wherein q ″)CHFwettingCritical heat flux density, h, related to surface wettabilityfgIs the latent heat of the liquid, ρvIs gas phase density, plIs the density of the liquid phase, σ is the surface tension, g is the acceleration of gravity, θRIs the receding contact angle.
7. The low resistance enhanced heat transfer layout structure based on the nanometer super-wetting interface as claimed in claim 2 or 3, wherein the wetting process is related to the interfacial tension of the system, and when the liquid falls on the horizontal solid surface and is in equilibrium, the contact angle formed and each interfacial tension satisfy the following conditions:
where θ is the contact angle, σ is the surface tension, s is the solid phase, l is the liquid phase, and v is the gas phase.
8. The low-resistance enhanced heat transfer layout structure based on the nano-super-wetting interface as claimed in claim 1, wherein a rough structure is constructed on the surface, and then acrylic polymer chains are coated on the surface of the micro-structure, so as to form a super-hydrophobic surface; or modifying the surface with a silane coating to make the surface achieve super-hydrophobic characteristics.
9. The low-resistance enhanced heat transfer layout structure based on the nano-super-wetting interface as claimed in claim 1, wherein the super-hydrophilic surface is obtained by photo-induced super-hydrophilicity; or increase the surface roughness to make the surface hydrophilic.
10. The low resistance enhanced heat transfer layout based on nano-sized super-wetting interface as claimed in claim 9 wherein the surface roughness increases the solid surface energy as characterized by r, cos θ*When the solid surface is smooth, r is 1, and when r is rcos θ>1, the hydrophilic surface is more hydrophilic, while the hydrophobic surface is more hydrophobic.
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