CN112033209A - A columnar fin falling film evaporation heat exchange tube - Google Patents

Abstract

The invention discloses a columnar fin falling film evaporation heat exchange tube, wherein rectangular columnar fins are uniformly arranged on the outer surface of the columnar fin, and axial and circumferential grooves are formed in gaps between adjacent columnar fins to form a flow network beneficial to uniform distribution of liquid; in order to prevent the liquid of the upper heat exchange tube from splashing and changing the surface appearance when the liquid of the lower heat exchange tube drops on the surface of the lower heat exchange tube, the top of the columnar fin is designed into an inclined surface; the bottom of the circumferential groove is provided with a plurality of micro chutes, so that the wetting angle is improved, and the comprehensive action of the micro chutes at the bottom of the groove and the inclined tops of the columnar fins increases the hydrophobicity of the surface, so that the state of the groove reaches a Cassie state of a rough surface; not only reducing the flow resistance of the liquid, improving the spreading performance of the liquid, reducing the thickness of the liquid film, but also forming a composite boundary composed of solid, liquid and vapor, improving the number of gasification cores and increasing the evaporation heat exchange coefficient.

Description

A columnar fin falling film evaporation heat exchange tube

technical field

The invention relates to a columnar fin falling film evaporation heat exchange tube, which belongs to the technical field of heat exchangers, and is especially suitable for falling film evaporators, including absorbers in absorption heat pump systems.

Background technique

At present, falling film evaporators are widely used in the evaporators of central air-conditioning systems, including the evaporators and absorbers of lithium bromide absorption heat pumps. On the arranged heat exchange tubes, part of the liquid will generate steam through heat exchange with the hot fluid in the heat exchange tubes, and another part of the unevaporated liquid will drip down the tubes arranged below along the radial direction of the heat exchange tubes. Since the liquid sprayed by the sprinkler and the liquid dripping from the heat exchange tube at high places are basically in the shape of drops or columns, the thickness of the local liquid film at the dripping place is larger than that in other places. Therefore, in order to make the liquid film on the surface of the heat exchange tube uniform , it cannot dry up, and the liquid on the surface of the heat exchange tube needs the path and ability to flow along the axial direction. Although the conventionally used helical fins can greatly increase the heat exchange area, the protruding radial fins block the axial flow of the liquid. If local drying occurs, the effective evaporative heat transfer area will be greatly reduced. In order to solve this problem, the Chinese utility model patent with the authorization announcement number CN 201034434 Y proposes a pitted tube. Specifically, on the axially extending spiral fin, a plurality of The method of forming circumferential teeth by notching, manufactures a plurality of prismatic fins and flow paths along the axial and radial directions, and under the action of capillary force, the spray liquid on the surface of the heat exchange tube is rapidly and uniformly diffused. It shows that the heat exchange efficiency of this tube type is improved. However, in the process of use, it is found that there is room for improving the performance of this type of heat exchange tube. In the falling film evaporator, liquid is generally supplied to the heat exchange tubes by means of the spray device at the top and the heat exchange tubes at high places continuously dripping liquid. However, when the liquid dripping from a high place hits the surface of the heat exchange tube below, there will be splashes. These splashed liquids either drop directly to the bottom of the heat exchanger through the gap between the heat exchange tubes and cannot participate in the evaporation, or are randomly The steam is carried and separated, resulting in uneven local liquid distribution, which will seriously affect the heat exchange efficiency of the evaporator; even rushing out of the evaporator will endanger the safety of connected equipment.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a sloping top columnar fin falling film evaporation heat exchange tube.

The technical solution provided by the present invention is as follows: a columnar fin falling film evaporation heat exchange tube, which includes two parts: a light section and an evaporation surface section, the evaporation surface section is a heat exchange surface, and the evaporation surface section includes a heat exchange tube body, a heat exchange The fins arranged on the outer surface of the heat pipe body in a spiral shape along the axis of the heat exchange pipe are characterized in that the fins are composed of uniformly arranged rectangular columnar fins, the top surface of the rectangular columnar fins is an inclined surface, and the inclined surface faces the exchange Heat pipe axial; axial gaps between adjacent rectangular columnar fins form axial grooves, and circumferential gaps between adjacent rectangular columnar fins form circumferential grooves 7), axial grooves and The circumferential grooves form staggered mesh grooves, a plurality of evenly distributed micro-inclined grooves are arranged at the bottom of the circumferential grooves, and both ends of the micro-inclined grooves extend to the roots of the rectangular columnar fins.

Further, the normal section perpendicular to the micro-chutes is triangular.

Further, the angle between the axis of the micro-inclined groove and the heat exchange tube body is 20° to 60°; the depth of the micro-inclined groove is 0.03-0.10mm, and the upper opening is 0.03-0.3mm wide. 60-100 strips are set in the circumferential direction.

Further, the angle between the axis of the micro-inclined groove and the heat exchange tube body is 45°, the depth of the micro-inclined groove is 0.05mm, the width of the upper opening is 0.15mm, and 70 pieces are arranged along the circumferential direction of the heat exchange pipe body. .

Further, 8-40 triangular channels 5 with a helix angle of 20-60° are arranged on the inner surface of the heat exchange tube, and the depth is 0.10-0.45mm.

Further, the angle between the rectangular columnar fin and the direction of gravity is 30-45°.

Further, there are 144 rectangular columnar fins per inch along the axial direction.

Further, the height of the rectangular columnar fins is 0.15-0.5mm; the length-width ratio of the columnar section is (1.1-4):1.

Further, the height of the rectangular columnar fin is 0.35mm, the length of the columnar section is 0.57mm, and the width is 0.45mm.

Further, the width of the axial groove is 0.1-1.0 mm, and the width of the circumferential groove is 0.3-0.8 mm.

The beneficial effects of the present invention are:

1. In the falling film evaporator, the liquid on the surface of the heat exchange tube is provided by dripping the liquid from the heat exchange tube above. The impact of the dripping liquid on the solid surface produces the fragmentation of the liquid and the rebound of the liquid to form a liquid splash. In addition, the results of numerical calculation show that the steam velocity between the heat exchange tubes can reach more than 10m/s, and the splashed liquid is carried by the steam immediately after leaving the solid surface; due to the flow of steam between the heat exchange tubes in the evaporator, the Non-uniform, so the flow of the splashed droplets carried by the steam and the adhesion of the surface of the heat exchange tube is random, which will aggravate the non-uniformity of the liquid distribution; sometimes the splashed liquid directly drips through the gap between the heat exchange tubes to the The bottom of the heater is not in contact with the heat exchange tubes, reducing the steam production. The liquid droplets entrained in the steam cannot be discharged from the evaporator, otherwise it will cause harm to the equipment of the next stage, namely the compressor. To sum up, how to reduce the liquid splash, or even eliminate the liquid splash, will be an important way to improve the heat exchange efficiency. The splash of the liquid is not only related to the initial velocity of the liquid, that is, the kinetic energy of hitting the wall, but also related to the impact angle of the liquid (impact angle: the angle between the droplet's dripping direction and the surface). When the impact angle is less than 90°, The momentum of the falling droplet can be decomposed into two parts, the momentum perpendicular to the wall and along the wall. Obviously, the inclined surface can weaken the kinetic energy of the rebound, thus reducing the probability of the droplet rebounding. In the experiment, it was found through high-speed photography that with the decrease of the impact angle, the critical speed (the speed of the droplet that produces the splash phenomenon) increases, and when the impact angle decreases to 30°, the speed of the droplet will continue to increase, and it will not. Splashing occurs. At the same time, with the decrease of the impact angle, the flow velocity of the liquid film on the inclined surface gradually increases, and the thickness of the liquid film on the surface decreases significantly.

2. When the top of the rectangular columnar fins is inclined, the breakage and splashing of liquid dripping from a high place are eliminated, so more liquid flows into the grooves at the root along the columnar fins. The thickness of the liquid film is the main factor affecting the evaporation heat transfer process. In order to prevent the liquid from forming a thick film in the groove, the present invention optimizes the hydrophilic and hydrophobic properties of the solid surface. The specific method is to set a plurality of micro-inclined grooves at the bottom of the radial groove. According to experimental observations and tests, it is found that the surface with multiple micro-slopes creates a regular rough surface, which can change the wettability of the surface. The measurement of the smooth surface shows that the contact angle between the surface and the liquid is about 80°; however, when a plurality of micro-slopes are arranged on the surface, the surface contact angle changes to 105--135°. It is well known that when the contact angle is less than 90°, the surface is defined as a hydrophilic surface; and when the contact angle is greater than 90°, it is defined as a hydrophobic surface. Therefore, when the surface is provided with micro-chutes, the surface is changed from hydrophilic to hydrophobic. When a hydrophobic surface is formed at the bottom of the groove, the liquid tends to form a bead or rope shape on it, which reduces the flow resistance, increases the flow speed, and reduces the thickness of the liquid film. On the other hand, when the bottom surface of the groove is covered with liquid, due to the poor wettability of the hydrophobic surface, the liquid cannot completely fill the micro-chutes, and there is air in it. At this time, the surface forms a composite boundary composed of solid-liquid-gas. That is called the Cassie state of the rough surface. The composite boundary can provide more vaporization cores, enhance the boiling heat transfer efficiency, and improve the evaporation heat transfer coefficient.

Third, the advantage of the rectangular columnar fin is that its processing mold is simple and convenient to manufacture, which is convenient for the processing of the inclined top of the fin and the micro inclined groove on the bottom surface of the groove.

In addition, while enhancing the evaporative heat transfer efficiency on the outside of the heat exchange tube, the present invention provides a spiral triangular channel on the inner surface of the heat exchange tube to improve the convective heat transfer coefficient inside the tube. The evaporative heat transfer coefficient of the light pipe is increased by more than 40%; it is about 10% higher than the pockmarked surface pipe proposed in the Chinese utility model patent with the authorization announcement number CN 201034434 Y. At the same time, the spreading diameter of the droplets on the surface of the heat exchange tube of the present invention is increased by more than 13% compared with the spreading diameter of the pockmarked tube surface proposed in the Chinese utility model patent with the authorized announcement number CN 201034434 Y.

Description of drawings

Fig. 1 is the structural representation of the present invention;

Fig. 2 is the longitudinal sectional schematic diagram of the evaporation surface section of the present invention;

Figure 3 is a schematic cross-sectional view of the evaporation surface section of the present invention

4 is a cross-sectional view of a rectangular columnar fin of the present invention;

Fig. 5 is the normal sectional view of the micro-chutes of the present invention;

FIG. 6 is a comparison diagram of the heat exchange experimental data of the present invention, a light pipe type falling film evaporation tube and a conventional miniature columnar type falling film evaporation heat exchange tube.

Description of symbols in the figure:

光管型降膜蒸发管的蒸发换热系数（根据试验关联公式计算）；

Evaporation heat transfer coefficient of the light pipe type falling film evaporation tube (calculated according to the test correlation formula);

- - -Heat transfer coefficient of conventional miniature columnar falling film evaporation heat exchange tubes (calculated according to the test correlation formula);

本发明柱状翅片降膜蒸发换热管的换热系数试验点。

The heat transfer coefficient test point of the columnar fin falling film evaporation heat exchange tube of the present invention.

Detailed ways

The specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings:

的管件，其包括光 段1与蒸发表面段两部分，蒸发表面段为换热表面，蒸发表面段包括换热管管体、换热管本 体外表面设置的沿换热管轴线呈螺旋状分布的翅片，翅片由均匀排列的长方形柱状翅片2 构成，长方形柱状翅片2沿轴向每英寸设有144个，长方形柱状翅片2的高度为0.15—0.5mm （优选0.35mm）；柱状截面的长宽比为（1.1—4）：1，优选长方形柱状翅片2的柱状截面的长为 0.57mm，宽为0.45mm。长方形柱状翅片2的顶面3为倾斜面，与重力方向夹角为30—45度，倾 斜面朝向换热管轴向。相邻的长方形柱状翅片2之间的轴向间隙形成轴向沟槽6，相邻的长 方形柱状翅片2之间的周向间隙形成周向沟槽7，轴向沟槽6和周向沟槽7形成轴向与周向交 错的网状沟槽，轴向沟槽6的宽度为0.1—1.0mm，周向沟槽7的宽度为0.3—0.8mm。周向沟槽 7底部设有均匀分布的多条微斜槽4，微斜槽4的两端延伸至长方形柱状翅片2的根部，垂直 于微斜槽4的法向截面为三角形，微斜槽4与换热管管体的轴线夹角为20~60°（优选45°）；微 斜槽4的深度为0.03—0.10mm（优选0.05mm），上开口宽0.03—0.3mm（优选0.15mm），沿换热 管管体圆周方向上设置60—100条（优选70条）。换热管管体内表面设置螺旋升角为20~60° （优选43°）的8—40条（优选25条）三角形槽道5，深度为0.10—0.45mm（优选0.3mm）。 As shown in Figures 1-6, a columnar fin falling film evaporation heat exchange tube is

The evaporating surface section is the heat exchange surface, and the evaporation surface section includes the heat exchange tube body, and the outer surface of the heat exchange tube body is arranged in a spiral shape along the axis of the heat exchange tube. The fins are composed of evenly arranged rectangular columnar fins 2, the rectangular columnar fins 2 are provided with 144 per inch along the axial direction, and the height of the rectangular columnar fins 2 is 0.15-0.5mm (preferably 0.35mm); The aspect ratio of the columnar section is (1.1-4):1, and the columnar section of the rectangular columnar fin 2 preferably has a length of 0.57 mm and a width of 0.45 mm. The top surface 3 of the rectangular columnar fin 2 is an inclined surface, and the included angle with the direction of gravity is 30-45 degrees, and the inclined surface faces the axial direction of the heat exchange tube. The axial gaps between adjacent rectangular columnar fins 2 form axial grooves 6, and the circumferential gaps between adjacent rectangular columnar fins 2 form circumferential grooves 7. The axial grooves 6 and the circumferential The grooves 7 form mesh grooves with alternating axial and circumferential directions. The width of the axial grooves 6 is 0.1-1.0 mm, and the width of the circumferential grooves 7 is 0.3-0.8 mm. The bottom of the circumferential groove 7 is provided with a plurality of evenly distributed micro-inclined grooves 4, the two ends of the micro-inclined groove 4 extend to the root of the rectangular columnar fin 2, and the normal cross-section perpendicular to the micro-inclined groove 4 is a triangle, and the slightly inclined The included angle between the groove 4 and the axis of the heat exchange tube body is 20-60° (preferably 45°); the depth of the micro-chutes 4 is 0.03-0.10mm (preferably 0.05mm), and the width of the upper opening is 0.03-0.3mm (preferably 0.15mm). mm), 60-100 (preferably 70) are arranged along the circumferential direction of the heat exchange tube body. The inner surface of the heat exchange tube is provided with 8-40 (preferably 25) triangular channels 5 with a helix angle of 20-60° (preferably 43°), and a depth of 0.10-0.45mm (preferably 0.3mm).

It should be understood that the parts not described in detail in this specification belong to the prior art. The above embodiments are only to describe the preferred embodiments of the present invention, but do not limit the scope of the present invention. On the premise of not departing from the design spirit of the present invention, various modifications made by ordinary engineers and technicians in the art to the technical solutions of the present invention and improvements, all should fall within the protection scope determined by the claims of the present invention.

Claims (10)

1. A columnar fin falling-film evaporation heat exchange tube, which comprises two parts, an optical section (1) and an evaporation surface section, the evaporation surface section is a heat exchange surface, and the evaporation surface section includes a heat exchange tube body and a heat exchange tube body The fins arranged on the outer surface and distributed in a spiral shape along the axis of the heat exchange tube are characterized in that the fins are composed of uniformly arranged rectangular columnar fins (2), and the top surface (3) of the rectangular columnar fins (2) is inclined The inclined surface faces the axial direction of the heat exchange tube; the axial gap between the adjacent rectangular columnar fins (2) forms an axial groove (6), and the circumference between the adjacent rectangular columnar fins (2) forms an axial groove (6). Circumferential grooves (7) are formed toward the gap, the axial grooves (6) and the circumferential grooves (7) form staggered mesh grooves, and the bottom of the circumferential grooves (7) is provided with a plurality of evenly distributed The chute (4), the two ends of the micro chute (4) extend to the root of the rectangular columnar fin (2). 2 . The columnar fin falling film evaporation heat exchange tube according to claim 1 , wherein the normal section perpendicular to the micro-chutes ( 4 ) is triangular. 3 . 3. A columnar fin falling film evaporation heat exchange tube according to claim 2, characterized in that the angle between the micro-chutes (4) and the axis of the heat exchange tube body is 20-60°; The depth of the inclined groove (4) is 0.03-0.10mm, the width of the upper opening is 0.03-0.3mm, and 60-100 pieces are arranged along the circumferential direction of the heat exchange tube body. 4. A columnar fin falling film evaporation heat exchange tube according to claim 3, characterized in that the angle between the micro-inclined groove (4) and the axis of the heat exchange tube body is 45°, and the micro-inclined groove (4) is 45°. (4) The depth is 0.05mm, the width of the upper opening is 0.15mm, and 70 pieces are arranged along the circumferential direction of the heat exchange tube body. 5. A columnar fin falling film evaporation heat exchange tube according to claim 1, characterized in that the inner surface of the heat exchange tube tube is provided with 8-40 triangular channels with a helix angle of 20-60° 5. The depth is 0.10-0.45mm. 6 . The columnar fin falling film evaporation heat exchange tube according to claim 1 , wherein the angle between the rectangular columnar fins ( 2 ) and the direction of gravity is 30-45°. 7 . 7 . The columnar fin falling film evaporation heat exchange tube according to claim 1 , wherein the rectangular columnar fins ( 2 ) are provided with 144 pieces per inch along the axial direction. 8 . 8. A columnar fin falling film evaporation heat exchange tube according to claim 1, 6 or 7, characterized in that the height of the rectangular columnar fins (2) is 0.15-0.5mm; The width ratio is (1.1-4):1. 9. A columnar fin falling film evaporation heat exchange tube according to claim 1, characterized in that the height of the rectangular columnar fins (2) is 0.35mm, the length of the columnar section is 0.57mm, and the width is 0.45mm. 10. A columnar fin falling film evaporation heat exchange tube according to claim 1, characterized in that the width of the axial groove (6) is 0.1-1.0 mm, and the width of the circumferential groove (7) is 0.1-1.0 mm. The width is 0.3-0.8mm.

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