| Wind tunnel heat exchanger as an important part of the wind tunnel plays a role in reducing the wind tunnel air temperature to maintain the stable operation of the wind tunnel,wind tunnel heat exchanger also affects the wind tunnel resistance loss.The design of a heat exchanger with good heat transfer performance and low drop loss is of great significance.A multi-channel transverse finned flat tube heat exchanger is proposed and its heat transfer and flow characteristics are investigated using a combination of experimental and numerical methods and its optimum structural parameters are obtained through optimal design with a view to playing an important role in the wind tunnel.Firstly,the heat transfer and flow performance of the multi-channel transverse finned flat tube heat exchanger are studied through experiments.The multi-channel transverse finned flat tube heat exchanger with a size of 768×420×154mm and a 810×440×280mm circular tube finned heat exchanger are selected.For the finned heat exchanger,the following conclusions are obtained through experimental comparison:at the same flow rate,the air resistance of the multi-channel transverse finned flat tube heat exchanger is much lower than that of the circular tube finned heat exchanger.When the wind speed is 4 m/s,the pressure drop per unit length of the flat tube heat exchanger is 441.56 Pa/m,while that of the circular tube finned heat exchanger is 1933.04 Pa/m.When the Reynolds number is greater than 2×104,heat capacity of the multi-channel transverse finned flat tube heat exchanger exceeds that of the circular tube finned heat exchanger and the comprehensive performance index is up to 2.58 times that of the round tube fin heat exchanger.Secondly,the establishment of multi-channel transverse finned flat tube exchanger unit heat transfer model size 174.0×4.4×17.5mm.Flat tube and circulation length of 190mm elliptical tube for comparison,windward surface arc diameter of 10mm flat tube and 9.5mm diameter round tube comparison,6 flow channels and a single flow channel comparison,streamlined arc windward surface and rectangular right angle windward surface comparison.The following conclusions are obtained through numerical simulation:（1）at wind speed of 1.8m/s,the elliptical tube Eu is 2.39times of the flat tube Eu;at wind speed of 0.5m/s,the pressure drop of the round tube is 2.45 times of the pressure drop of the flat tube;at wind speed of 1.8m/s,the calculated value of h/△p of the flat tube is 2.18 times of the elliptical tube;at speed of 2m/s,the heat exchange of the flat tube is 2.77W greater than that of the round tube（2）the total heat exchange area of the multiple flow channels The heat exchange area is 0.001m2larger than the total heat exchange area of single runner and the heat transfer effect is improved.When the water flow rate is 1m/s,the heat exchange of multi-flow channel is 25.35%larger than that of single-flow channel;when the water flow rate is 5m/s,the resistance loss of multi-channel channel is only 1.85%higher than that of single-flow channel and the effect of resistance loss brought by increasing the number of flow channels can be ignored.（3）When the wind speed is 15m/s,the heat transfer coefficient of the circular windward side is 1.21%higher than the heat transfer coefficient of the rectangular windward side;when the wind speed is20m/s,the pressure drop of the rectangular windward side is 7.32%greater than the pressure drop of the circular windward side.The pressure loss and heat transfer effect of the heat transfer model of the multi-channel transverse finned flat tube exchanger unit are studied by numerical simulation when the fin thickness is 0.1-0.5mm,the fin height is 4.0-12.0mm and the fin spacing is 2.4-4.0mm respectively.（2）At a wind speed of 2m/s,the heat transfer rate of 2mm fin height is 2.32 times that of 4mm fin height;at a wind speed of 5m/s,the pressure drop increases from 4mm to 6mm by 4.193 Pa.（3）At a wind speed of 10m/s,the heat transfer rate of 4mm fin pitch is greater than that of 2.4mm.Then the equations of j and f factors were fitted by regression analysis and passed the confidence test with a confidence level higher than 95%,and the objective function j/f1/3 was established.height 4.00mm.Finally,the multi-channel transverse finned flat tube heat exchanger with 0.35mm fin thickness,2.00mm fin spacing and 4.00mm fin height was applied to the 10.5m×10.5m square section wind tunnel project and compared with the elliptical tube finned heat exchanger for heat transfer effect and flow pressure drop.The total pressure drop of the multi-channel transverse finned flat tube heat exchanger is 831 Pa.The total pressure drop of the elliptical tube finned heat exchanger is 2.14times the total pressure drop of the multi-channel transverse finned flat tube heat exchanger.The h/△p value of the multi-channel transverse finned flat tube heat exchanger is 56.55%higher than the average elliptical finned heat exchanger. |
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