| With the development of social economy,energy consumption is increasing.Develop waste heat recovery technology and design efficient and compact heat exchanger are of great significance to improve the utilization rate of industrial energy and implement the basic national policy of energy conservation and emission reduction.Threedimensional(3-D)finned flat tube is a kind of enhanced heat exchange elements with superior performance,which has the advantages of both three-dimensional finned tubes and flat tubes,and is very suitable for the design of compact heat exchanger.This paper takes three-dimensional finned flat tubes as objects,based on the Taguchi method,the influences of fin structure parameters on the flow and heat transfer characteristics of the three-dimensional finned flat tube were studied firstly,and the main effect and contribution ratio of different fin parameters on flow and heat transfer performance were obtained,which can provide guidance for the design and optimization of the threedimensional finned flat tube.At the same time,the optimization of fin structure parameters combination is carried out based on the comprehensive thermal hydraulic performance,and the optimal structural parameters combination within the study range were obtained.Then,based on the optimal three-dimensional finned flat tube,the flow and heat transfer characteristics of three-dimensional finned flat tube bundles with different tube bundle arrangement and tube pitches were studied,the effects of transversal tube pitch and longitudinal tube pitch on the convective heat transfer performance of the three-dimensional finned flat tube bundle were obtained,which could provide a basis for the selection of the tube arrangement of the three-dimensional finned flat tube heat exchanger.Finally,a simplified numerical model has been developed which is capable of predicting the macroscopic behaviour of three-dimensional finned flat tube bundles based on porous media approach,as well as the use of distributed flow resistance and heat source,and the numerical model has achieved good calculation results.The main research contents and conclusions are as follows:(1)The flow and heat transfer performance of three-dimensional finned flat tube with various fin structural parameters were studied based on Taguchi method,the results showed that fin height and axial fin pitch have significant influences on the heat transfer and flow resistance,followed by fin thickness,while fin width and circular fin pitch have less effect.Predictive correlations were developed for the Nusselt number and friction factor by multiply linear regression.The comprehensive heat transfer performance of the three-dimensional flat tube is more than 2 times that of the smooth flat tube,fin height and axial fin pitch have great influences on the comprehensive heat transfer performance of the three-dimensional finned flat tube.Based on the comprehensive heat transfer performance,the optimal structural parameters combination within the study range was obtained with a fin height of 5 mm,fin thickness of 0.4 mm,fin width of 4 mm,axial fin pitch of 1 mm and circular fin pitch of 1 mm.(2)The flow and heat transfer characteristics of three-dimensional finned flat tube bundles with different tube arrangement and tube pitches were studied,the results showed the heat transfer performence of the 3-D finned flat tube bundle is nuch better than the smooth flat tube bundle,but also higher flow resistance.The transverse tube pitch significantly affects the flow and heat transfer performance of staggered 3-D finned flat tube bundle,the increase of the transverse tube pitch degrades the heat transfer performance and reduces the flow resistance,the changing extent can reach 32%～41%and 73%～78%,respectively.The transverse tube pitch has limited influences on the flow and heat transfer performance of staggered 3-D finned flat tube bundle,the differences of heat transfer and flow performance bettwen different longitudinal tube pitch are within3.5% and 3%,respectively.The staggered tube bundle with smaller transverse tube pitch has poor comprehensive heat transfer performance in lower Re,but with the increase of Re,the tube bundle with smaller transverse tube pitch shows better comprehensive heat transfer performance.The longitudinal tube pitch has limited influences on the comprehensive heat transfer performance of staggered 3-D finned flat tube bundle.Parameters corresponding to transversal tube pitch and longitudinal tube pitch can significantly affect the flow and heat transfer performance of inline 3-D finned flat tube bundle,the increase of transversal decrease the heat transfer performance but the flow resistance performance is improved,and the variation degree can reach 49% ～ 55% and84% ～ 87%,respectively.With the increase of longitudinal tube pitch,the flow resistance and the heat transfer performance of inline 3-D finned flat tube bundle both increase.The comprehensive heat transfer performance of inline 3-D finned flat tube bundle decreases with the increase of transverse tube pitch,while increases with the increase of longitudinal tube spitch,but the degree of change is not obvious when the tube pitch is large.(3)Numerical model was constructed based on the porous media theory,as well as the distributed flow resistance and heat source which were set up through the prediction correlations of flow and heat transfer of 3-D finned flat tube bundle.The model obtained good calculation results while greatly reduced the calculation amount.For the staggered3-D finned flat tube bundle,the relative deviation between the outlet temperature calculated by the porous model and the full model is less than 1.5%,and the relative deviations of pressure drop is less than 15%,the average relative deviation of pressure drop is 5%.For the inline 3-D finned flat tube bundle,the relative deviation of fluid outlet temperature calculated by the two methods is less than 1.2%,and the maximum and average relative deviations of pressure drop are 11.5% and 5.1%,respectively. |
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