CN109974513B

CN109974513B - Micro-scale cooperative surface structure for enhancing boiling heat exchange

Info

Publication number: CN109974513B
Application number: CN201910241520.4A
Authority: CN
Inventors: 吕继组; 白敏丽; 高林松
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2019-03-28
Filing date: 2019-03-28
Publication date: 2020-05-19
Anticipated expiration: 2039-03-28
Also published as: CN109974513A

Abstract

The invention belongs to the technical field of enhanced heat transfer, and relates to a micro-scale cooperative surface structure for enhancing boiling heat transfer, which comprises a large groove, a small groove, a connecting groove, a micro rib, a base surface and a super-hydrophobic coating; the base surface of the enhanced boiling heat exchange structure forms a cooperative scale surface through mechanical cutting, structural electroplating or laser burning; the base surface is divided by ribs to form a large groove, a small groove and a connecting groove. The micro-scale cooperative structure surface can generate capillary force, so that liquid can reach a vaporization core point more quickly, the requirement of a boiling heat exchange vaporization process on the scale can be met under the condition of different superheat degrees, the connection grooves between the large grooves and the small grooves enable liquid among the grooves to interact, steam is discharged more easily, and further boiling heat transfer is enhanced.

Description

Micro-scale cooperative surface structure for enhancing boiling heat exchange

Technical Field

The invention belongs to the technical field of enhanced heat transfer, and designs a micro-scale cooperative surface structure capable of regulating and controlling a bubble growth process.

Background

Among the many challenges that continue to meet the growth of global energy demand in a sustainable manner, improving phase change heat transfer has been the forefront of engineering research for decades. The high heat transfer rate associated with phase change heat transfer is critical to energy and industrial applications, but phase change heat transfer has the problem of low heat exchange efficiency under the condition of low heat density. And the micro-nano related technologies can enable the surface size structure to be from molecular to centimeter magnitude, and the technologies can obtain a silicon-based surface, a sintered structure and a polymerized coating. Different structured surfaces can in practical cases influence the multiphase conversion process. Boiling heat transfer refers to a vaporization process performed in a form of generating bubbles in liquid, and the latent heat of vaporization of substances is huge, so that the boiling heat transfer has high heat flow density, and a cooling surface has a high-efficiency cooling effect. The work on the improvement of boiling heat exchange surfaces has evolved from traditional surface structures (such as ribbed structures, etc.) to current microstructured surfaces. The hydrophobic surface coating can effectively reduce the initial boiling point of the surface and can generate more vaporization cores, thereby enhancing the heat transfer effect of the boiling surface. However, at high heat flux densities, larger structural dimensions are required to meet the bubble spill requirements. The single-scale microstructure surface can not overcome the boiling heat transfer process, and the root cause of thermodynamic non-equilibrium vapor bubble growth is as follows: single scale surface structures cannot coordinate the different requirements of vapor escape and liquid intake for pore size. And the different scales are mutually coordinated to jointly promote the process of boiling heat transfer, so that the requirements of different stages of boiling heat transfer on different scales are met. Therefore, the surfaces of the cooperative structures with different scales can meet the requirement of the boiling heat transfer vapor bubble characteristics, so that the boiling heat transfer capacity can be greatly improved.

Disclosure of Invention

The invention aims to overcome the defect of a single microstructure and provides a micro-scale cooperative surface structure.

The technical scheme of the invention is as follows:

a micro-scale cooperative surface structure for enhancing boiling heat transfer comprises a large groove 1, a small groove 2, a connecting groove 3, a micro rib 4, a base surface 5 and a super-hydrophobic coating 6; the surface of the base surface 5 of the enhanced boiling heat exchange structure is formed into a cooperative scale surface through mechanical cutting, structural electroplating or laser burning; the surface of the base surface 5 is divided by micro ribs 4 to form a large groove 1, a small groove 2 and a connecting groove 3;

the large grooves 1 and the small grooves 2 are arranged in a staggered manner, the large grooves 1 and the small grooves 2 are formed by a plurality of micro ribs which are uniformly arranged at intervals, and the width L3 of each micro rib is 50-100 mu m; the groove width L1 of the small groove 2 is 50-100 μm, and the groove depth H of the small groove 2 is 200-300 μm; the groove width L2 of the large groove 1 is 400-700 μm; the small grooves 2 form a super-hydrophobic coating 6 in a chemical and mechanical mode;

the connecting grooves 3 are arranged in the same row of micro ribs, and the distances among the micro ribs are the same; the length L4 of the micro rib is 500-800 μm, and the groove width L5 of the connecting groove 3 is 150-250 μm.

The invention has the beneficial effects that: two micron-scale cooperative micro-groove structures are manufactured on the surface of the nickel substrate, and micro-grooves of two scales are communicated with each other in a mode of connecting holes. The bottom of the small groove is coated with a super-hydrophobic coating, so that the vaporization core effect is generated in the small groove, and the vapor bubbles grow and are separated in the large groove under the synergistic effect of the large groove and the small groove. Under the condition of low heat flow density of the cooperative surface, the super-hydrophobic coating at the bottom of the small groove can reduce the superheat degree of initial boiling, the vaporization core is mainly generated in the small groove, but the growth of vapor bubbles is limited in the small groove, but the capillary pressure generated in the small groove can enable the groove to be filled with liquid rapidly, so that the separation of the vapor bubbles in the groove is promoted, and the boiling heat exchange effect is enhanced. Under the condition of high heat flow density, the growth process of the vapor bubble is changed, the vaporization core is generated in the small groove and grows and separates in the large groove in the form of the connecting hole, and the large groove does not limit the growth process of the vapor bubble. And under the effect of the connecting groove, the capillary pressure generated in the small groove can ensure that the large groove is quickly filled with liquid and has sufficient superheated liquid, the separation diameter of the vapor bubble is reduced, the growth time is shortened, and therefore the boiling heat exchange effect is enhanced. Therefore, the micro-scale cooperative structure can achieve the effect of generating capillary force, so that the liquid can reach the vaporization core point more quickly; the connecting groove between the big groove and the small groove enables the big groove to be filled with liquid quickly, and the effect of boiling heat transfer is enhanced.

Drawings

FIG. 1 is a schematic three-dimensional view of a micro-scale cooperative surface structure for enhancing boiling heat exchange;

FIG. 2 is a structural feature of a macro groove and a micro groove;

FIG. 3 is a structural feature of the connecting slot;

in the figure: 1, a large groove; 2, small grooves; 3, connecting grooves; 4 micro-ribs; 5 base surface; 6 super-hydrophobic coating.

Detailed Description

The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions.

As shown in fig. 1 to 3, a micro-scale cooperative structure for surface enhanced boiling heat transfer comprises a large groove 1, a small groove 2, a connecting groove 3, a micro-rib 4, a base surface 5 and a super-hydrophobic coating 6; the surface of the base surface 5 of the reinforced boiling structure forms a cooperative scale surface through mechanical cutting, structural electroplating or laser burning; the surface of the base surface 5 is divided by micro ribs 4 to form a large groove 1, a small groove 2 and a connecting groove 3;

The material of the base surface 5 comprises metal and inorganic non-metal materials.

The super-hydrophobic coating 6 is a low surface energy material of fluorine-containing polymer.

The large groove 1 and the small groove 2 are made of metal and inorganic non-metal materials and are made of the same material as the base surface 5.

The method for enhancing boiling of the surface structure activates vaporization cores with different structure sizes under the condition of different heat flux densities. In the case where the heat flux density is small and the vaporization core is generated in the hydrophobic surface of the bottom of the small groove 2, the diameter of the vapor bubble increases with the increase of the heat flux density, and the growth of the vapor bubble is restricted in the small groove 2. At higher heat flux density, the vaporization core of the connecting slot 3 is activated, and as the diameter of the vapor bubble increases, the vapor bubble grows and detaches into the large slot 1. The superheated liquid in the large tank 1 can accelerate the growth and the separation of the vapor bubbles, thereby achieving the effect of enhancing boiling. At high heat flux density, the vaporization core in vat 1 is activated, causing the bubble escape diameter to be larger and the bubble escape frequency to be faster due to the sufficient liquid in vat 1. The micro-scale cooperative structure surface is a hydrophilic surface, and can meet the requirement of boiling heat exchange on capillary pressure. But also can meet the requirement of the vapor bubble on the structure size in a larger range, thereby being capable of strengthening boiling heat transfer.

The specific working process of the invention is as follows:

under the condition of pool boiling heat exchange, after the boiling heat exchange surface is heated and heated, the surface of the super-hydrophobic coating 6 at the bottom of the small groove 2 starts to generate bubbles under the condition of a small superheat degree. The hydrophobic surface material can reduce the initial boiling temperature of the surface, so that a vaporization core is generated under a lower superheat degree, at the moment, the vapor bubbles are mainly generated in the small grooves 2, and the microstructure also has a certain hydrophilic function, so that the growth of the vapor bubbles can be accelerated, the vapor bubbles can be promoted to be rapidly separated from the surface, and the effect of enhancing the boiling heat exchange of the low superheat degree is achieved. As the heating power increases, the bubble detachment diameter increases, since the surface tension of water decreases with increasing temperature, resulting in a larger diameter at which the bubbles detach. At the moment, the width of the inner groove of the small groove 2 is small, so that the increase of the steam bubble is limited, but the vaporization core near the connecting groove 3 is activated, the steam bubble grows and separates towards the direction of the large groove 1 along with the increase of the diameter of the steam bubble, and the large groove 1 is provided with enough superheated liquid without limiting the growth of the steam bubble, so that the separation of the steam bubble can be accelerated, and the effect of enhancing boiling heat transfer is achieved. Due to the capillary pressure generated in the small groove 2, the cavity generated in the large groove 1 after the bubble is removed can be quickly filled with liquid to prepare for the growth and the removal of the next bubble. At high heat flux density, the vaporization core in the large tank 1 is activated and since bubble growth is not limited by the tank width, the diameter of the bubble increases and carries more latent heat of vaporization. Meanwhile, the capillary pressure generated in the small groove 2 can enable liquid to flow to the large groove 1 from the connecting groove, so that sufficient liquid is ensured in the large groove 1, the frequency of bubble separation is accelerated, and the boiling heat exchange effect is enhanced. Because the micro-scale cooperative surface structure has hydrophilicity, the critical heat flux density can be delayed. The surface of the structure can meet the requirements of liquid suction and vapor bubble separation on the structure size in a larger heat flow density area, and the effect of enhancing boiling heat transfer is achieved.

Claims

1. A micro-scale cooperative structure for enhancing boiling heat exchange is characterized in that the micro-scale cooperative structure for enhancing boiling heat exchange surface comprises: the water-repellent coating comprises a large groove (1), a small groove (2), a connecting groove (3), ribs (4), a base surface (5) and a super-hydrophobic coating (6); the surface of the base surface (5) of the enhanced boiling heat exchange structure is formed into a cooperative scale surface through mechanical cutting, structural electroplating or laser burning; a large groove (1), a small groove (2) and a connecting groove (3) are formed on the surface of the base surface (5) through division of a rib (4);

the large grooves (1) and the small grooves (2) are arranged in a staggered manner, the large grooves (1) and the small grooves (2) are formed by a plurality of micro-scale ribs which are uniformly arranged at intervals, and the width L3 of each rib is 50-100 mu m; the groove width L1 of the small groove (2) is 50-100 μm, and the groove depth H of the small groove (2) is 200-300 μm; the groove width L2 of the large groove (1) is 400-700 μm; the small grooves (2) form a super-hydrophobic coating (6) in a chemical and mechanical mode;

the connecting grooves (3) are the same row of ribs, and the distances among the ribs are the same; the length L4 of the rib is 500-800 μm, and the groove width L5 of the connecting groove (3) is 150-250 μm.

2. The micro-scale cooperative structure for enhancing boiling heat transfer of claim 1, wherein the materials of the macro grooves (1), the micro grooves (2) and the base surface (5) comprise metal and inorganic non-metal materials, and the materials of the macro grooves (1) and the micro grooves (2) are the same as or different from the materials of the base surface (5).

3. The micro-scale cooperative structure for enhancing boiling heat transfer according to claim 1 or 2, wherein the super-hydrophobic coating (6) is a low surface energy material of fluoropolymer.