A columnar fin falling film evaporation heat exchange tube

Abstract

The invention discloses a columnar fin falling film evaporation heat exchange tube, on the outer surface of which rectangular columnar fins are evenly arranged, and the gaps between adjacent columnar fins form axial and circumferential grooves, forming a flow network that is conducive to the uniform distribution of liquid; in order to prevent splashing and changing the surface morphology caused by liquid from an upper row of heat exchange tubes dripping onto the surface of a lower row of heat exchange tubes, the top of the columnar fin is designed as an inclined surface; a plurality of micro-oblique grooves are arranged at the bottom of the circumferential groove, thereby improving the wetting angle, and the combined effect of the micro-oblique grooves at the bottom of the groove and the oblique top of the columnar fin increases the hydrophobicity of the surface, so that its state reaches the Cassie state of a rough surface; not only the flow resistance of the liquid is reduced, the spreading performance of the liquid is improved, and the thickness of the liquid film is thinned, but also a composite boundary composed of solid, liquid and vapor can be formed, the number of gasification cores is increased, and the evaporation heat transfer coefficient is increased.

Description

Technical Field

[0001] The invention relates to a columnar fin falling film evaporation heat exchange tube, belonging to the technical field of heat exchangers, and is particularly suitable for falling film evaporators, including absorbers in absorption heat pump systems. Background Art

[0002] At present, falling film evaporators are widely used in evaporators in central air-conditioning systems, including evaporators and absorbers of lithium bromide absorption heat pumps. The specific working method is: the refrigerant passes through the spray device on the top, spraying the refrigerant onto the horizontally arranged heat exchange tubes, and part of the liquid generates steam by heat exchange with the hot fluid in the heat exchange tubes, and the other part of the unevaporated liquid will drip radially along the heat exchange tubes onto the tubes arranged below. Since the liquid sprayed by the sprayer and the liquid dripping from the high heat exchange tubes are basically in the shape of drops or columns, the local liquid film thickness at the dripping point is greater than that at other places. Therefore, in order to make the liquid film on the surface of the heat exchange tube uniform and prevent drying, the liquid on the surface of the heat exchange tube needs to have a path and ability to flow axially. Although the conventionally used spiral fins can greatly increase the heat exchange area, the protruding radial fins block the axial flow of the liquid. When the liquid film is unevenly distributed, it cannot meet the requirements of the liquid flowing along the axial direction. Once local drying occurs, the effective evaporation heat exchange area is greatly reduced. In order to solve this problem, a Chinese utility model patent with the authorization announcement number CN 201034434 Y proposed a pockmarked tube. Specifically, multiple notches are radially processed along the outer edge of the fin on the axially extended spiral fin to form circumferential teeth, so as to manufacture multiple prism-shaped fins and flow paths along the axial and radial directions. Under the action of capillary force, the sprayed liquid on the surface of the heat exchange tube is quickly and evenly diffused. Experiments show that the heat exchange efficiency of this type of tube is improved. However, during use, it is found that there is room for improving the performance of this type of heat exchange tube. In a falling film evaporator, liquid is generally supplied to the heat exchange tube by a spray device at the top and a heat exchange tube at a high position continuously dripping liquid. However, when the dripping liquid at a high position hits the surface of the heat exchange tube below, splashing occurs. These splashed liquids either drip directly to the bottom of the heat exchanger through the gaps between the heat exchange tubes and cannot participate in evaporation, or are randomly carried away by the steam, resulting in uneven local liquid distribution, which will seriously affect the heat exchange efficiency of the evaporator; or even rush out of the evaporator to endanger the safety of the connected equipment. Summary of the invention

[0003] The object of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide a falling film evaporation heat exchange tube with inclined top columnar fins.

[0004] The technical solution provided by the present invention is as follows: a columnar fin falling film evaporation heat exchange tube, which includes a light section and an evaporation surface section. The evaporation surface section is a heat exchange surface. The evaporation surface section includes a heat exchange tube body and fins arranged on the outer surface of the heat exchange tube body and distributed in a spiral shape along the axis of the heat exchange tube. It is characterized in that the fins are composed of evenly arranged rectangular columnar fins, the top surface of the rectangular columnar fins is an inclined surface, and the inclined surface faces the axial direction of the heat exchange tube; the axial gap between adjacent rectangular columnar fins forms an axial groove, and the circumferential gap between adjacent rectangular columnar fins forms a circumferential groove 7), the axial grooves and the circumferential grooves form an alternating mesh groove, and a plurality of evenly distributed micro-oblique grooves are provided at the bottom of the circumferential groove, and the two ends of the micro-oblique grooves extend to the roots of the rectangular columnar fins.

[0005] Furthermore, the normal section perpendicular to the micro-oblique groove is a triangle.

[0006] Furthermore, the angle between the micro-slanted groove and the axis of the heat exchange tube body is 20-60°; the depth of the micro-slanted groove is 0.03-0.10 mm, the width of the upper opening is 0.03-0.3 mm, and 60-100 micro-slanted grooves are arranged along the circumferential direction of the heat exchange tube body.

[0007] Furthermore, the angle between the micro-slanted groove and the axis of the heat exchange tube body is 45°, the depth of the micro-slanted groove is 0.05 mm, the width of the upper opening is 0.15 mm, and 70 micro-slanted grooves are arranged along the circumferential direction of the heat exchange tube body.

[0008] Furthermore, the inner surface of the heat exchange tube is provided with 8-40 triangular grooves 5 with a helical angle of 20-60° and a depth of 0.10-0.45 mm.

[0009] Furthermore, the rectangular columnar fins have an angle of 30-45° with the direction of gravity.

[0010] Furthermore, the rectangular columnar fins are provided with 144 per inch along the axial direction.

[0011] Furthermore, the height of the rectangular columnar fin is 0.15-0.5 mm; the aspect ratio of the columnar cross section is (1.1-4):1.

[0012] Furthermore, the height of the rectangular columnar fin is 0.35 mm, the length of the columnar section is 0.57 mm, and the width is 0.45 mm.

[0013] Furthermore, 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.

[0014] The beneficial effects of the present invention are:

[0015] 1. In the falling film evaporator, the liquid on the surface of the heat exchange tube is provided by the liquid dripping from the upper heat exchange tube. The collision of the dripping liquid with the solid plane causes the liquid to break and rebound to form liquid splash. In addition, the results of numerical calculations show that the steam velocity between the heat exchange tubes can reach more than 10m / s, and the splashing liquid is immediately carried by the steam after leaving the solid surface; since the flow of steam between the heat exchange tubes in the evaporator is not uniform, the flow of the splashing droplets carried by the steam and the adhesion to the surface of the heat exchange tube are random, which will aggravate the uneven distribution of the liquid; sometimes the splashing liquid drips directly to the bottom of the heat exchanger through the gap between the heat exchange tubes without contacting the heat exchange tubes, reducing the steam production. The droplets entrained in the steam cannot be discharged from the evaporator, otherwise it will cause harm to the next-level equipment, that is, the compressor. In summary, how to reduce the splashing of liquid, or even eliminate the splashing of liquid, will be an important way to improve the heat exchange efficiency. In addition to the initial velocity of the liquid, that is, the kinetic energy of the impact on the wall, the splash of the liquid is 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: perpendicular to the wall and along the wall. Obviously, the inclined surface can weaken the kinetic energy of the rebound, thereby reducing the probability of the droplet rebounding. In the experiment, it was found through high-speed photography that as the impact angle decreases, the critical speed (the droplet speed that produces splashing) increases, until the impact angle decreases to 30°, and the droplet speed continues to increase, and there will be no splashing. At the same time, as the impact angle decreases, the flow speed of the liquid film on the inclined surface gradually increases, and the thickness of the liquid film on the surface is significantly reduced.

[0016] Second, when the top of the rectangular columnar fin is an inclined surface, the breakage and splashing of the liquid dripping from a high place are eliminated, so more liquid flows into the groove at the root along the columnar fin. The thickness of the liquid film is the main factor affecting the evaporation heat transfer process. In order to avoid the liquid forming a thick film in the groove, the present invention optimizes the hydrophilic and hydrophobic properties of the solid surface by regulating and controlling. The specific method is to set a plurality of micro-bevel grooves at the bottom of the radial groove, and the two ends of the micro-bevel grooves extend to the root of the columnar fin, and the angle with the axis of the heat exchange tube is 45°. According to experimental observation and testing, it is found that the surface with multiple micro-bevel grooves 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 its surface and the liquid is about 80°; however, when multiple micro-bevel grooves are set on its surface, the surface contact angle changes to 105--135°. As we all know, 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-slope grooves, the surface changes from hydrophilic to hydrophobic. When the hydrophobic surface is formed at the bottom of the groove, the liquid often forms beads or strips 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-slope grooves, and air exists in it. At this time, a composite boundary composed of solid-liquid-gas is formed on the surface, which 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.

[0017] Third, the advantage of the rectangular columnar fin is that the processing mold is simple and convenient to manufacture, which is convenient for processing the inclined top of the fin and the micro-inclined groove on the bottom surface of the groove.

[0018] In addition, while enhancing the evaporation heat transfer efficiency on the outside of the heat exchange tube, the present invention sets spiral triangular grooves on the inner surface of the heat exchange tube to improve the convection heat transfer coefficient inside the tube. According to experiments, the evaporation heat transfer coefficient outside the tube of the present invention is more than 40% higher than that of the light tube; and about 10% higher than that of a pitted tube proposed in the Chinese utility model patent with the authorization announcement number CN 201034434 Y. At the same time, the spread diameter of the droplets on the surface of the heat exchange tube of the present invention is more than 13% higher than that of a pitted tube proposed in the Chinese utility model patent with the authorization announcement number CN 201034434 Y. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the present invention;

[0020] Figure 2 It is a longitudinal cross-sectional schematic diagram of the evaporation surface section of the present invention;

[0021] Figure 3Schematic diagram of the cross section of the evaporation surface section of the present invention

[0022] Figure 4 is a cross-sectional view of a rectangular columnar fin of the present invention;

[0023] Figure 5 is a normal cross-sectional view of the micro-oblique groove of the present invention;

[0024] Figure 6 It is a comparison chart of heat exchange experimental data between the present invention, the light tube type falling film evaporator tube and the conventional micro columnar falling film evaporator heat exchange tube.

[0025] Explanation of symbols in the figure:

[0026] Evaporation heat transfer coefficient of the light tube falling film evaporator (calculated according to the experimental correlation formula);

[0027] - - -Heat transfer coefficient of conventional micro-columnar falling film evaporation heat exchange tube (calculated according to the experimental correlation formula);

[0028] Heat transfer coefficient test points of the columnar fin falling film evaporation heat exchange tube of the present invention. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings:

[0030] like Figure 1-Figure 6 As shown, a columnar fin falling film evaporation heat exchange tube is The pipe fitting includes a light section 1 and an evaporation surface section. The evaporation surface section is a heat exchange surface. The evaporation surface section includes a heat exchange tube body and fins arranged on the outer surface of the heat exchange tube body and distributed in a spiral shape along the axis of the heat exchange tube. The fins are composed of evenly arranged rectangular columnar fins 2. There are 144 rectangular columnar fins 2 per inch along the axial direction. 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 length of the columnar section of the rectangular columnar fin 2 is preferably 0.57mm and the width is 0.45mm. The top surface 3 of the rectangular columnar fin 2 is an inclined surface, and the angle with the gravity direction is 30-45 degrees, and the inclined surface faces the axial direction of the heat exchange tube. The axial gap between adjacent rectangular columnar fins 2 forms an axial groove 6, and the circumferential gap between adjacent rectangular columnar fins 2 forms a circumferential groove 7. The axial groove 6 and the circumferential groove 7 form a mesh groove that is staggered in the axial and circumferential directions. The width of the axial groove 6 is 0.1-1.0 mm, and the width of the circumferential groove 7 is 0.3-0.8 mm. A plurality of evenly distributed micro-slanted grooves 4 are provided at the bottom of the circumferential groove 7. Both ends of the micro-slanted grooves 4 extend to the root of the rectangular columnar fin 2. The normal section perpendicular to the micro-slanted grooves 4 is a triangle. The angle between the micro-slanted grooves 4 and the axis of the heat exchange tube body is 20-60° (preferably 45°); the depth of the micro-slanted grooves 4 is 0.03-0.10 mm (preferably 0.05 mm), the upper opening width is 0.03-0.3 mm (preferably 0.15 mm), and 60-100 (preferably 70) grooves are provided 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 grooves 5 with a helical angle of 20-60° (preferably 43°) and a depth of 0.10-0.45 mm (preferably 0.3 mm).

[0031] It should be understood that the parts not elaborated in detail in this specification belong to the prior art. The above embodiments are only descriptions of the preferred implementation methods of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made by ordinary engineers and technicians in this field to the technical solution of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A columnar fin falling film evaporation heat exchange tube, comprising a light section (1) and an evaporation surface section, wherein the evaporation surface section is a heat exchange surface, and the evaporation surface section comprises a heat exchange tube body, and fins arranged on the outer surface of the heat exchange tube body and distributed in a spiral shape along the axis of the heat exchange tube, characterized in that The fins are composed of rectangular columnar fins (2) arranged evenly, the top surface (3) of the rectangular columnar fins (2) is an inclined surface, the inclined surface faces the axial direction of the heat exchange tube, and the angle between the inclined surface and the gravity direction is 30-45 degrees; the axial gap between adjacent rectangular columnar fins (2) forms an axial groove (6), the circumferential gap between adjacent rectangular columnar fins (2) forms a circumferential groove (7), the axial groove (6) and the circumferential groove (7) form a staggered mesh groove, and the bottom of the circumferential groove (7) is provided with a plurality of evenly distributed micro-oblique grooves (4), and the two ends of the micro-oblique groove (4) extend to the root of the rectangular columnar fin (2); Wherein, the inclined surface is used to receive liquid dripping from above, and the width of the axial groove (6) is 0.1-1.0 mm.

2. The columnar fin falling film evaporation heat exchange tube according to claim 1, characterized in that The normal section perpendicular to the micro-oblique groove (4) is a triangle.

3. The columnar fin falling film evaporation heat exchange tube according to claim 2, characterized in that The angle between the micro-slanted groove (4) and the axis of the heat exchange tube body is 20-60°; the depth of the micro-slanted groove (4) is 0.03-0.10 mm, the width of the upper opening is 0.03-0.3 mm, and 60-100 micro-slanted grooves (4) are arranged along the circumferential direction of the heat exchange tube body.

4. The columnar fin falling film evaporation heat exchange tube according to claim 3, characterized in that The angle between the micro-slanted groove (4) and the axis of the heat exchange tube body is 45°, the depth of the micro-slanted groove (4) is 0.05 mm, the width of the upper opening is 0.15 mm, and 70 micro-slanted grooves (4) are arranged along the circumferential direction of the heat exchange tube body.

5. The columnar fin falling film evaporation heat exchange tube according to claim 1, characterized in that The inner surface of the heat exchange tube is provided with 8-40 triangular grooves with a spiral angle of 20-60 degrees and a depth of 0.10-0.45 mm.

6. The columnar fin falling film evaporation heat exchange tube according to claim 1, characterized in that The rectangular columnar fins (2) are provided with 144 pieces per inch along the axial direction.

7. A columnar fin falling film evaporation heat exchange tube according to claim 1 or 6, characterized in that The height of the rectangular columnar fin (2) is 0.15-0.5 mm; the length-to-width ratio of the columnar cross section is (1.1-4):

1.

8. The columnar fin falling film evaporation heat exchange tube according to claim 1, characterized in that The rectangular columnar fin (2) has a height of 0.35 mm, a length of 0.57 mm and a width of 0.45 mm in the columnar section.

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