A method for enhancing heat transfer outside an evaporative cooling coil

Abstract

The present application belongs to the technical field of evaporative heat exchange, and provides a method for enhancing heat transfer outside evaporative cooling coil, comprising: arranging heat exchange tubes in the evaporative coil in a slant array along the air flow direction, so that adjacent heat exchange tubes form a multi-stage "squeezing-dilating" flow path in the main air flow direction; controlling the ratio of the minimum cross-sectional oblique spacing between adjacent heat exchange tubes to the nominal outer diameter of the heat exchange tube, so that the air flow in the coil bundle produces multi-stage speed changes; using the slant array to induce the migration of the boundary layer during the air flow around the heat exchange tube; the "squeezing-dilating" effect induced by the slant array improves the heat transfer coefficient outside the tube; compared with the complex zigzag path of the triangular arrangement, the slant array arrangement reduces the number of air flow zigzag, and the fluid dynamics software CFD simulation verification shows that under the condition of maintaining the same system pressure drop, the air volume can be increased by about 4%.

Description

Technical Field

[0001] This invention belongs to the field of evaporative heat transfer technology, specifically relating to a method for enhancing heat transfer outside an evaporative cooling coil. Background Technology

[0002] The heat transfer section of the evaporative cooling coil consists of a serpentine tube assembly made of bare tubes or finned tubes, housed within a casing constructed of profiles. The bottom of the casing serves as a water tray. Spray water from the tray is pumped to the top of the coil and sprayed onto the outer surface of the serpentine tubes through nozzles, where it exchanges heat with the medium inside the tubes through evaporation. Unevaporated spray water flows back into the water tray. A fan is installed at the top of the evaporative cooling coil, causing air inside the casing to flow upwards through the serpentine tube assembly and exit from the top.

[0003] With the advancement of global energy conservation and carbon reduction policies, the need to reduce the energy consumption of cooling systems is becoming increasingly urgent. Insufficient external heat transfer efficiency is a key factor contributing to the high energy consumption of evaporative cooling systems, thus requiring technological improvements to reduce energy waste.

[0004] Traditional technologies face numerous bottlenecks:

[0005] 1. High heat and mass transfer resistance of liquid film outside the tube: The sprayed liquid on the surface of the tube is prone to form a continuous thick liquid film, which has a high thermal resistance ratio and significantly reduces the heat transfer efficiency. In addition, uneven liquid film flow can easily lead to local liquid accumulation or dry areas, which are even more unfavorable for heat and mass transfer.

[0006] 2. Poor gas-liquid contact effect: Traditional coil arrangement is prone to creating airflow dead zones, resulting in insufficient relative flow velocity between air and spray liquid, and inadequate heat and mass transfer between the gas and liquid phases.

[0007] 3. Structural design limitations: Traditional bare tubes have limited heat exchange area. Adding fins to the outside of the tube can easily cause scaling, leading to equipment corrosion and a significant decrease or even failure of the heat exchange tube performance. Even if straight fins are used, their effect on promoting airflow disturbance and liquid film renewal is weak.

[0008] like Figure 1-3 As shown, there are usually three ways to arrange heat exchange tubes: triangular, square, and concentric circle.

[0009] Advantages and disadvantages of the triangle method:

[0010] Advantages: The tubes are tightly packed, resulting in a large number of heat exchange tubes per unit volume and a large heat exchange area; the airflow is strongly disturbed during circulation, the boundary layer is easily broken, the heat transfer coefficient outside the tubes is high, and the heat transfer efficiency is optimal.

[0011] Disadvantages: The pipe channels are narrow and tortuous, resulting in high fluid flow resistance and high system pressure drop; the channels are prone to dust and scale buildup, making cleaning difficult and maintenance costs high; it is not suitable for fluids containing particles, high viscosity, or prone to scaling.

[0012] Advantages and disadvantages of the square method:

[0013] Advantages: The pipe channels are spacious and straight, resulting in low fluid flow resistance and reduced system pressure. The channels are easy to clean, and scale and ash can be removed by mechanical cleaning or high-pressure flushing, making maintenance convenient.

[0014] Disadvantages: The number of heat exchange tubes per unit volume is less than that of the triangular method, and the heat exchange area is relatively small; the airflow disturbance is weak, the boundary layer is thicker, the heat transfer coefficient outside the tube is lower than that of the triangular method, and the heat transfer efficiency is generally lower.

[0015] Advantages and disadvantages of concentric circle arrangement:

[0016] Advantages: The fluid flows along the annular channel with uniform velocity distribution, avoiding local dead zones and ensuring more thorough gas-liquid contact; the central area can be reserved for the arrangement of spray pipes and maintenance channels, and it is suitable for large or special-shaped heat exchangers.

[0017] Disadvantages: The structure is complex, difficult to process and manufacture, and the cost is higher than the previous two methods; the heat exchange area per unit volume is between the triangular method and the square method, and the heat transfer efficiency is moderate; the annular channel is moderately difficult to clean and is not suitable for high fouling conditions.

[0018] In actual industrial production processes, the triangular arrangement method has the highest heat transfer efficiency and is the most widely used.

[0019] In summary, existing evaporative cooling coils mostly adopt regular and fixed heat exchange tube arrangements, making it difficult to control the airflow pattern and flow separation position. Under low Reynolds number conditions, stable boundary layers and airflow dead zones are easily formed, resulting in insufficient renewal of the liquid film outside the tubes and limited gas-liquid heat and mass transfer. On the other hand, increasing the heat exchange area or changing the tube density often introduces problems such as increased flow resistance, scaling and corrosion, and increased maintenance costs, making it difficult to effectively enhance the heat transfer performance outside the tubes under low energy consumption conditions. Summary of the Invention

[0020] This invention provides a method for enhancing external heat transfer in evaporative cooling coils, which addresses the problems of low external heat transfer efficiency, limited gas-liquid heat and mass transfer, and difficulty in achieving effective external heat transfer enhancement under low energy consumption conditions in the background art.

[0021] The technical solution adopted in this invention is: a method for enhancing heat transfer outside an evaporative cooling coil, comprising:

[0022] The heat exchange tubes in the evaporator coil are arranged in an oblique array along the airflow direction, so that adjacent heat exchange tubes form a multi-stage "squeeze-expansion" flow path in the mainstream airflow direction;

[0023] By controlling the ratio of the minimum oblique spacing of the cross sections between adjacent heat exchange tubes to the nominal outer diameter of the heat exchange tubes, multi-stage velocity changes are generated during the air flow in the coil bundle.

[0024] By using oblique array arrangement to induce the migration of boundary layer during the air flow around the heat exchange tube, the flow separation angle of the air sweeping across the outer surface of the heat exchange tube is delayed compared with the conventional tube arrangement, thereby disrupting the stable laminar boundary layer.

[0025] The coordinated disturbance between the upper heat exchange tube wake and the windward side of the lower heat exchange tube promotes the renewal of the liquid film on the outside of the heat exchange tube, reduces the thick liquid film accumulation area, and improves the gas-liquid heat and mass transfer efficiency.

[0026] Preferably, the minimum oblique spacing of the cross sections between adjacent heat exchange tubes is 0.1-1.5 times the nominal outer diameter of the heat exchange tubes.

[0027] Preferably, the angle between the arrangement direction of the heat exchange tubes on the cross-section and the horizontal direction is 5-85°.

[0028] Preferably, the humid air mass velocity at the minimum cross-section of the evaporator coil is lower than... ·s.

[0029] Preferably, the conventional tube arrangement is such that the heat exchange tubes are arranged in a triangular, square, or concentric circle pattern along the airflow direction. In the oblique array arrangement of the heat exchange tubes, the flow separation angle of the air flowing around the heat exchange tubes lags by 5-80° compared to the conventional triangular arrangement. This configuration is designed to enhance the heat transfer characteristics of the liquid film on the outer wall of the tubes, ensuring that the laminar boundary layer can still maintain efficient heat transfer under low Re numbers.

[0030] Preferably, the Re number satisfies 10 < Re number .

[0031] Preferably, the airflow direction includes vertical flow from bottom to top, vertical flow from top to bottom, horizontal flow, or flow inclined relative to the horizontal direction.

[0032] The beneficial effects of this invention are as follows:

[0033] Compared with existing technologies, this invention significantly improves the external heat transfer efficiency of evaporative cooling coils by using oblique array tube arrangement and flow control technology, under the constraints of "four no increases" (no increase in footprint, no increase in heat exchange area, no increase in pressure drop of medium inside the tube, and no increase in fan energy consumption (air volume)). The specific advantages are as follows:

[0034] 1. Improved heat transfer efficiency: The "compression-expansion" effect induced by the oblique array arrangement improves the heat transfer coefficient outside the tube.

[0035] 2. Pressure Drop and Energy Consumption Optimization: Compared to the complex deflection path of a triangular arrangement, the oblique array layout reduces the number of airflow deflections (e.g., from 16 rows of pipes to 8 deflections). Verified by CFD simulation software, the airflow can be increased by approximately 4% while maintaining the same system pressure drop.

[0036] 3. Enhanced anti-fouling and self-cleaning capabilities: Higher inter-pipe air velocity enhances the turbulence of the liquid film, effectively suppressing stagnant areas in the liquid film, reducing salt deposition and dirt adhesion, extending the operating cycle, and reducing operation and maintenance costs.

[0037] 4. Compact Structure and Maintenance Adaptability: The compactness of the oblique array design is not compromised while maintaining the same footprint and heat exchange area. Compared to a triangular arrangement, the larger spacing between the oblique tubes facilitates cleaning and maintenance of the heat exchange tubes, making it suitable for various evaporative cooling applications, especially significantly improving the high humidity and scaling characteristics of evaporative cooling.

[0038] 5. Precise boundary layer control: By optimizing the oblique spacing By adjusting the flow separation angles (α, γ), the heat transfer characteristics of the liquid film on the outer wall of the tube are enhanced in specific zones. This is achieved at Reynolds numbers (10 < Reynolds number). Under these conditions, it can still maintain efficient heat transfer, breaking through the limitations of traditional laminar flow.

[0039] 6. Enhanced gas-liquid mass transfer: The multi-stage extrusion-expansion flow channel promotes an increase in the relative velocity between air and sprayed water, accelerates the evaporation rate, and thus improves cooling efficiency. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the triangular arrangement of heat exchange tubes in the existing technology.

[0041] Figure 2 This is a schematic diagram of the square arrangement of heat exchange tubes in the prior art;

[0042] Figure 3 This is a schematic diagram of the concentric circle arrangement of heat exchange tubes in the existing technology.

[0043] Figure 4 This is a schematic diagram of the triangular arrangement of evaporative coils in the prior art and a magnified schematic diagram of a local wind field.

[0044] Figure 5 This is a schematic diagram of a square arrangement of evaporative coils in the prior art, and a magnified schematic diagram of a local wind field.

[0045] Figure 6 This is a schematic diagram of the oblique array arrangement of the evaporative coils of the present invention and a partially enlarged schematic diagram of the wind field.

[0046] Figure 7This is a schematic diagram of air separation across the boundary layer of a single tube in the prior art.

[0047] Figure 8 This is a schematic diagram of the separation of the boundary layer of air sweeping across triangularly arranged heat exchange tubes in the prior art.

[0048] Figure 9 This is a schematic diagram illustrating the separation of the boundary layer of the air-swept oblique array heat exchange tubes according to the present invention.

[0049] Figure 10 This is a schematic diagram illustrating the variation of the local Nu number of a constant heat flux wall with the debonding angle in existing technologies.

[0050] Figure 11 This is a schematic diagram illustrating the variation of the local Nu number on the constant heat flux wall surface with the decomposition angle according to the present invention;

[0051] Figure 12 This is a schematic diagram of the existing technology, which features counter-current airflow, triangular arrangement, and water spray impact on the heat exchange tube wall and the formation of water droplets on the tube wall.

[0052] Figure 13 This is a schematic diagram illustrating the counter-current airflow and oblique array arrangement of the present invention, where sprayed water impacts the heat exchange tube wall and generates water droplets on the tube wall. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] A method for enhancing heat transfer outside the evaporative cooling coil includes:

[0055] The heat exchange tubes 1 inside the evaporator coil are arranged in an oblique array along the airflow direction. The angle between the arrangement direction of the heat exchange tubes 1 and the horizontal direction on the cross-section is 5-85°, so that adjacent heat exchange tubes 1 form a multi-stage "compression-expansion" flow path in the mainstream airflow direction. The airflow direction includes vertical flow from bottom to top, vertical flow from top to bottom, horizontal flow, or flow inclined relative to the horizontal direction. That is, this method is not only applicable to counter-flow evaporative cooling, but also to cross-flow, co-flow, and mixed-flow evaporative cooling equipment.

[0056] The ratio of the minimum oblique spacing of the cross-section between adjacent heat exchange tubes 1 to the nominal outer diameter of heat exchange tube 1 is controlled. Specifically, in this example, the minimum oblique spacing of the cross-section between adjacent heat exchange tubes 1 is 0.1-1.5 times the nominal outer diameter of heat exchange tube 1, and the humid air mass velocity at the minimum cross-section of the evaporator coil is controlled to be lower than... This causes multi-level velocity changes in the air as it flows within the coil bundle, creating multi-level disturbance regions inside the bundle and enhancing mass and heat transfer at the gas-liquid interface.

[0057] By inducing boundary layer migration during airflow around heat exchange tubes 1 using a slanted array arrangement, the flow separation angle of air sweeping across the outer surface of heat exchange tubes 1 lags behind that of conventional tube arrangements, thereby disrupting the stable laminar boundary layer. Conventional tube arrangements involve heat exchange tubes 1 arranged in a triangular, square, or concentric circle configuration along the airflow direction. With the slanted array arrangement of heat exchange tubes 1, the flow separation angle of airflow around the heat exchange tubes 1 lags behind that of a conventional triangular arrangement by 5-80°. This configuration achieves zoned enhancement of the liquid film heat transfer characteristics on the outer wall of the tubes, ensuring that the laminar boundary layer maintains efficient heat transfer even at low Reynolds number conditions, with a Reynolds number of 10 < Reynolds number. .

[0058] The coordinated disturbance between the wake of the upper heat exchange tube 1 and the windward side of the lower heat exchange tube 1 promotes the renewal of the outer liquid film of the heat exchange tube 1, reduces the thick liquid film accumulation area, and improves the gas-liquid heat and mass transfer efficiency.

[0059] The following description, in conjunction with the accompanying drawings, further illustrates this scheme.

[0060] like Figure 4 , Figure 5 , Figure 6 As shown in the figure, for ease of explanation, the figure uses the commonly used ф25 tubes and a tube spacing of 50mm as an example, and the specific values ​​such as 48 tubes in a single-pass heat exchanger and 16 tubes in an 8-pass heat exchanger are used as one embodiment for illustration.

[0061] like Figure 5 As shown, this is a typical square arrangement. The airflow disturbance around the square arrangement is weak, the boundary layer is thicker, the heat transfer coefficient outside the tube is lower than that of the triangular method, and the heat transfer efficiency is generally lower. Therefore, this will not be explained further below.

[0062] like Figure 4 As shown, this is a typical triangular arrangement of evaporative cooling coils. The airflow around the coils experiences strong disturbance, the boundary layer is easily broken, the heat transfer coefficient outside the coils is high, and the heat transfer efficiency is optimal. This design further optimizes and innovates upon this generally accepted optimal arrangement, enhancing heat transfer through the liquid film outside the coils.

[0063] like Figure 7The diagram shows the separation of air flowing across the boundary layer K of a single tube. Air flows across the surface of heat exchange tube 1 in a direction perpendicular to the axis of the tube. Besides exhibiting the characteristics of boundary layer K, air flowing across a single tube also experiences flow separation, generating backflow, vortices, and eddy bundles. The separation phenomenon is qualitatively explained below: When air flows past the location of the circular tube, the velocity increases and the pressure decreases due to the reduced flow cross-section; however, in the latter half, the velocity decreases and the pressure rises again due to the increased flow cross-section. At this point, the fluid within the boundary layer K overcomes the pressure increase with its own momentum and flows forward, resulting in a relatively flat velocity distribution. The fluid layer near the wall, due to its low momentum, finds it increasingly difficult to overcome the rising pressure, eventually leading to a velocity gradient of zero at the wall. This results in backflow in the opposite direction to the original flow direction. This turning point is called the starting point of flow separation. From this point, the inner edge of the boundary layer K separates from the wall, a process called flow separation. The angle formed between the starting point of flow separation and the previous stagnation point L is called the flow separation initiation angle. The location of the separation starting point depends on the Reynolds number. Studies have shown that: 10 < Re number ≤ When the boundary layer is laminar, the Reynolds number (Re) on the air side of the evaporator coil is within this range, and delamination occurs at β = 80-85°. The development of the boundary layer K and flow delamination determine the characteristics of heat transfer in an outer circular tube.

[0064] like Figure 10 As shown, when air flows across a circular tube, the local Nu number at the wall of the constant heat flux decreases with increasing angle in the range of 0-80°, due to the continuous thickening of the laminar boundary layer; simultaneously, the local Nu number at the wall of the heat flux increases with increasing Reynolds number. After the air flows past the starting point of the flow separation, it becomes turbulent, and the local Nu number at the wall of the heat flux increases.

[0065] In contrast, such as Figure 8 As shown, in a conventional triangular arrangement, the water and air in the lower part of heat exchange tube 1 achieve convective heat and mass transfer through complete countercurrent contact. The water mainly transfers heat to the air through evaporation supplemented by convective heat transfer, while the air achieves the functions of humidification and heating. However, in the upper part of heat exchange tube 1, dead zones and recirculation of air form in regions G and E, significantly reducing the relative Reynolds number between gas and liquid, and the high humidity of the recirculating air severely restricts mass and heat transfer between the liquid film and air. In this scheme, the countercurrent contact area between the liquid film and air is greatly increased, and dead zones are less likely to form at the top. This utilizes the mass and heat transfer between the liquid film and air, and ultimately improves the outlet humidity and temperature of the air.

[0066] like Figure 4 , Figure 6 As shown, using the same heat exchange area for comparison, to ensure the required airflow for heat exchange, the floor space of the evaporative cooling coil, i.e., the tube bundle width W, remains constant. Assume the average face velocity of the evaporative cooling coil is 3 m / s: (e.g., ...) Figure 4As shown, the minimum lateral spacing between adjacent heat exchange tubes 1 inside the coil is S1=25mm, the number of flow sections is 24, that is, the width of the flow section is 600mm, the average flow velocity of the humid air at the minimum section is 6m / s, and at this time, the Re number on the air side of the evaporative cooling coil is ≈8500.

[0067] like Figure 6 The diagram shows the oblique array tube arrangement method used in this method, with the minimum oblique spacing between adjacent heat exchange tubes 1 inside the coil. With 48 flow sections, each 480mm wide, and an average humid air velocity of 7.65m / s at the minimum section, the Reynolds number (Re) on the air side of the evaporator coil is approximately 10800, enhancing inter-tube turbulence. Furthermore, for comparison, such as... Figure 4 As shown, in this tube arrangement, the minimum longitudinal spacing of adjacent heat exchange tubes 1 inside the coil is... In this case, combined with Figure 7-8 As shown, a "dead zone" forms in the wake region H above heat exchanger tube 1, where humid air is suppressed and cannot be smoothly discharged upwards; however, in this solution, as... Figure 6 As shown, the minimum longitudinal spacing of adjacent heat exchange tubes 1 inside the coil. In this case, due to the increase in the longitudinal spacing of heat exchange tube 1, the wind speed between tubes is high (especially the wind speed in zone D increases), the Re number is large, the degree of turbulence is increased, and the compression of the lower air by the adjacent upper tubes results in a small "dead zone" (the original dead zone in zone E migrates), the suppression of the humid air by the upper heat exchange tube 1 is small, and the humid air is more easily discharged upwards.

[0068] Although the flow cross-sectional width of this method is smaller than that of the traditional triangular arrangement, taking 16 rows of pipes as an example, such as Figure 4 As shown, the air undergoes 16 deflections from bottom to top; as Figure 6 As shown, the air undergoes eight deflections from bottom to top. Figure 6 The oblique array pipe arrangement shown was simulated using CFD software, and compared to... Figure 4 The triangular duct layout shown increases airflow by approximately 4%.

[0069] In contrast, such as Figure 12 The diagram shows a counter-current, triangular arrangement of evaporative coils where sprayed water impacts the wall of heat exchange tube 1 and forms water droplets M. Research indicates that as the sprayed water falls and impacts the upper wall of heat exchange tube 1, a turbulent water film region N is formed. Under the influence of air vortices, the heat transfer coefficient outside the tube on the upper wall is the highest. On the lower wall of heat exchange tube 1, the liquid film gradually gathers into water droplets M along the tube's length and falls to the lower tube wall. Since most of the lower wall of heat exchange tube 1 does not form water droplets, the air... Figure 7The liquid film disturbance at the stagnation point L forms a turbulent region Q of water droplets, resulting in a relatively large average external heat transfer coefficient on the lower wall of heat exchange tube 1. Meanwhile, a stable water film layer P forms on the side wall of heat exchange tube 1, especially before flow separation occurs. The air side also has a stable laminar boundary layer K, where the external heat transfer coefficient on the side wall of heat exchange tube 1 is the lowest, with the minimum heat transfer coefficient occurring at an angle θ≈60°.

[0070] The locally low external heat transfer coefficient significantly affects the overall heat transfer coefficient of heat exchanger tube 1. This method aims to specifically enhance the area with the lowest heat transfer coefficient on the outer wall of heat exchanger tube 1, effectively "filling the valley." For example... Figure 9 , Figure 13 As shown, due to the unique pipe layout of this scheme, the front stagnation point L will shift slightly. Figure 9 The diagram shown illustrates the separation of the boundary layer of the air-swept oblique array heat exchange tubes 1 in this scheme. As previously explained, without increasing the overall pressure drop of the evaporator coil (i.e., without reducing the airflow), the Reynolds number increases due to the increase in the average velocity of the humid air at the minimum cross-section, thus intensifying the turbulence in regions D and E. Due to the migration of the stagnation point L, the flow separation angle in region D changes from β to α, as shown... Figure 10 As shown, due to both the increase in the Reynolds number and the increase in the flow separation angle, the heat transfer coefficients at the original starting point of the flow separation (β=80°) and the original lowest point of the heat transfer coefficient outside the heat exchange tube 1 (θ=60°) are both enhanced, thus increasing the overall heat transfer coefficient outside the tube. Figure 8-9 In the middle, zones D, E, F and G are four regions divided by the cross center line of the heat exchange tube 1.

[0071] like Figure 9 As shown, the airflow in region G becomes turbulent after passing the initiation point of flow separation, and the wake of the lower heat exchange tube 1 further intensifies the turbulence. Due to the presence of the upper heat exchange tube 1, the airflow is obstructed, breaking the original boundary layer in region F, causing the initiation point of flow separation to shift upwards. The flow separation angle changes from β to γ, and the boundary layer thickness at the original initiation point of flow separation (β=80°) is thinner than before. Figure 13 As shown, the air boundary layer thickness is thinner and the Reynolds number is higher at the original lowest point (θ=60°) on the side wall of heat exchanger tube 1. Figure 11 As shown, the heat transfer coefficients in the starting regions of flow separation from region F to region E are enhanced due to both the increase in the Re number and the increase in the flow separation angle.

[0072] Summary: This scheme, through its oblique array tube arrangement, achieves "four no increases" (no increase in footprint, no increase in heat exchange area, no increase in internal medium pressure drop, and no increase in fan energy consumption (air volume)) through innovative structural design. This creates a "continuous compression-expansion" effect during airflow, disrupting the stable laminar boundary layer and causing the starting point of airflow separation to shift, thus altering the boundary layer separation characteristics. This shift in the air boundary layer reshapes the distribution characteristics of the water film on the outer wall of the tube, fundamentally improving liquid film heat transfer efficiency and enhancing external heat transfer.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for enhancing heat transfer outside an evaporative cooling coil, characterized in that, include: The heat exchange tubes in the evaporator coil are arranged in an oblique array along the airflow direction, so that adjacent heat exchange tubes form a multi-stage "compression-expansion" flow path in the mainstream airflow direction; The ratio of the minimum oblique spacing of the cross section between adjacent heat exchange tubes to the nominal outer diameter of the heat exchange tubes is controlled to generate multi-stage velocity changes during the air flow in the coil bundle; the minimum oblique spacing of the cross section between adjacent heat exchange tubes is 0.1-1.5 times the nominal outer diameter of the heat exchange tubes. By using oblique array arrangement to induce the migration of boundary layer during the air flow around the heat exchange tube, the flow separation angle of the air sweeping across the outer surface of the heat exchange tube is delayed compared with the conventional tube arrangement, thereby disrupting the stable laminar boundary layer. By coordinating the disturbance between the upper heat exchange tube wake and the windward side of the lower heat exchange tube, the renewal of the liquid film on the outside of the heat exchange tube is promoted, the thick liquid film accumulation area is reduced, and the gas-liquid heat and mass transfer efficiency is improved. The humid air mass velocity at the minimum cross-section of the evaporator coil is less than 20 kg / m²·s; Conventional tube arrangement involves heat exchange tubes arranged in a triangular, square, or concentric circle pattern along the airflow direction. In the oblique array arrangement of heat exchange tubes, the flow separation angle of air flowing around the heat exchange tubes lags by 5-80° compared to the conventional triangular arrangement. This configuration is designed to enhance the heat transfer characteristics of the liquid film on the outer wall of the tubes, ensuring that the laminar boundary layer can still maintain efficient heat transfer under low Re numbers. The Relative number satisfies 10 < Relative number ≤ 1.5 × 10⁻� 5 ; The angle between the arrangement direction of the heat exchange tubes on the cross-section and the horizontal direction is 5-85°.

2. The method for enhancing heat transfer outside the evaporative cooling coil according to claim 1, characterized in that, The airflow direction includes vertical flow from bottom to top, vertical flow from top to bottom, horizontal flow, or flow inclined relative to the horizontal direction.

Images