Numerical Equivalent Method Of Heat Exchanger Based On Flow And Heat Transfer Characteristics Of Representative Unit

With the development of vehicle heat exchanger toward compact and miniaturization,the cross-scale problem of heat exchanger is becoming more obvious.During the technical design stage of compact and miniaturized heat exchanger,especially for the new type of heat exchanger,there is no large amount of experimental data to predict the flow and heat transfer performance of heat exchanger at the design stage.In addition,if the detailed model of heat exchanger is used for numerical simulation,it will consume a lot of computational resources and time.Therefore,whether to establish a numerical equivalent method of heat exchanger witch does not rely on the experiments,has high prediction accuracy and fast calculation will greatly affect the time of design and optimization of heat exchanger.In this paper,an equivalent calculation method based on the flow and heat transfer characteristics of representative unit was proposed with the aim of "independent of experiment" and "high accuracy".Based on the flow and heat transfer theory of fin unit,this method established the mapping relation between micro and macro scale of heat exchanger,and this relation was used to calculate the overall performance of heat exchanger.Finally,the method is compared and verified with the experimental data of different types of heat exchanger.Firstly,based on the flow and heat transfer process of fin unit of heat exchanger,the internal flow in heat exchanger is simplified as the flow in porous media,the flow resistance is described by the parameter of porous medium.And the heat transfer performance of fin unit is described in the form of thermal resistance with simplification.The mapping relation between micro and macro scale of heat exchanger is established by combining flow and heat transfer parameters with “dual cell” mesh structure,at last,a complete equivalent calculation process was obtained.In order to verify the prediction accuracy of the equivalent method,a numerical simulation study is carried out using a vehicle oil cooler.By the numerical simulation of oil cool using representative unit,simplified flow and heat transfer parameters are obtained,and the overall model of oil cooler is established according to its mapping relation.The calculation results show that the equivalent method could accurately predict the performance of whole oil cooler in a wide working condition range.Considering all working conditions,the prediction error of heat transfer is about 2.3%,and the maximum error is less than 15%,which verifies the accuracy of this method.Finally,the applicability of the equivalent method is studied.Through the equivalent calculation of different types of heat exchanger,the applicability and calculation error of the equivalent method are analyzed.The results show that the prediction error of the method for different types of heat exchanger is mostly within±10%,which proves that the equivalent method has good applicability for oil cooler,intercooler and water cooler.In addition,the heat exchanger with closed import and export pipelines has higher calculation accuracy,and the heat exchanger with single flow direction has higher convenience.