Numerical Simulation Of Heat Transfer And Flow Resistance Characteristics Of Serrated Fin-tube Bundles

The serrated fin-tube developed on the basis of continuous finned tubes have been widely used in heat exchange equipment such as waste heat boilers and strong oil air coolers.The effect of fin teeth on the performance of annular finned tube bundles and spiral finned tube bundles The comparative study of finned tubes is still insufficient,which limits the wider application of this type of finned tubes.In this paper,the Nusselt number（Nu）and the Euler number（Eu）are used to characterize the heat transfer characteristics and flow resistance characteristics respectively by numerical simulation method.In-depth study of characteristics and flow resistance characteristics,and three kinds of heat exchanger comprehensive performance evaluation indicators(j/f factor,j/f^1/2factor,j/f^1/3factor)are used to compare and analyze the comprehensive performance of each tube bundle.The main research contents and conclusions are as follows:（1）The effect of fin toothing on the characteristics of helical continuous and annular continuous finned tube bundles was comparatively studied.Through comparison,it is found that the effect of fin toothing on the characteristics of spiral continuous and annular continuous finned tube bundles has the same trend.The Nu of the two types of fin tube bundles is slightly increased,and the Eu will also increase,however,when the Reynolds number（Re）is low,,the treatment has little effect on Eu,and the effect is more obvious when the Re is high,increasing the tooth density has a positive effect on strengthening heat transfer but increase the flow resistance,compared with the continuous finned tube bundle,the fin toothing will lead to the decrease of the j/f factor and the increase of the j/f^1/2and j/f^1/3factors.The main difference is that under the same conditions,the enhanced heat transfer effect of the helical finned tube bundle with fin teeth is better,but the increase in flow resistance is larger,and the effect of fin teeth on the comprehensive performance of the annular finned tube bundle is better.（2）The effects of structural parameters such as the bottom width between the teeth,the top width between the teeth and the depth of the teeth on the performance of the bundles are studied respectively.The research results show that increasing the bottom width,the top width and the depth of the teeth can increase the Nu of the fin side,however,the bottom width and the top width between the teeth have little influence on it,and the heat transfer enhancement effect of increasing the depth of the teeth is more obvious,increasing the bottom width,the top width and the depth of teeth will increase Eu,especially when the depth is close to the height of the fin,Eu has a larger increase.Using different heat exchanger comprehensive performance evaluation indicators will have different results,but mostly increasing the bottom width,the top width and the depth of the teeth will reduce the comprehensive performance of the tube bundle,especially the comprehensive performance of the tube bundle with the depth of the teeth close to the fin height is significantly reduced.（3）A processing method for staggered bending of serrated finned tubes with teeth is proposed,and the influence of the bending angle on the performance of finned tube bundles is studied.The results show that increasing the angle can enhance the heat transfer,but the flow resistance also increases more,strengthening the heat transfer effect cannot make up for the adverse effect of the increased flow resistance on the overall performance.Mostly,the bending treatment will reduce the comprehensive performance,when only the j/f^1/3factor is used as the evaluation index,the comprehensive performance is slightly improved,about 5.3%.