Study On Heat Transfer Enhancement And Flow Characteristics In Porous Foams

With the rapid development of electronic technology,it is very common to see a microchip with millions of components.The international technology road map for semiconductors reported that the heat flux of chips rose from 330W·cm-2 in 2007 to 520W·cm-2 in 2011,as a result,looking for the appropriate electronic cooling technology and materials becomes more and more concerned at the moment.Recent years a variety of heat transfer enhancement technologies have been widely used in all fields to improve the heat transfer efficiency,save raw material and reduce energy consumption.Under this prospect,metal foams are one of the most promising candidates for replacing the core components of traditional heat exchangers,because metal foam exchangers not only improve the heat transfer efficiency but also allow equipment to be smaller and lighter due to its complex internal structure.For heat exchanger design purpose,metal foam has been greatly limited due to incomplete of the proper characterization and quantification of transport and thermal properties.In this paper,study the porous foams in order to be used as compact radiator material.The flow and heat transfer performance in a rectangle channel inserted with metal foam was studied by experiment and numerical simulation,and a comparison was made with the ordinary fin radiator.Then the convective heat transfer criterion of the foam was obtained by multiple regression method.On the basis of this,a new foam model with stochastic distribution of pore size is established by considering the heterogeneity of the actual foam material to study the flow and heat transfer enhancement performance.After that,a scheme of “secondary enhanced heat transfer” is proposed to reduce the flow resistance and improve heat transfer performance at the same time.Finally,the physical mechanism of the heat transfer inside the foam is discussed with synergy field principle.The main research results and conclusions of this paper as follows:The heat transfer performance of the foam studied was better than that of the ordinary fin radiator.In the experimental flow rate,the surface heat transfer coefficient of the foam was 3 times of that of the ordinary fin radiator.The flow resistance of the foam is obviously larger than that of the ordinary fin radiator.Then the permeability,inertia coefficient and friction factor of the foam were calculated.The porosity uniformity is used to describe the flow and heat transfer performance of non-uniform porous foams.It was found that the larger the pore uniformity,the smaller the flow resistance and the better the heat transfer enhancement."Secondary enhanced heat transfer" of the porous foams by slotting method can effectively reduce the pressure gradient of about 29% or more.At lower flow rates,the heat transfer enhancement performance of slotted foam is not obvious or even weakened.But at higher flow rates,the heat transfer performance of slotted foam is better than that of non-slotted foam,and a small flow resistance is obtained at the same time.After that,the heat transfer performance was evaluated by PEC index.The effects of structural parameters such as porosity,pore density,porosity uniformity and slotting depth on the heat transfer enhancement performance were analyzed from the angle of velocity and temperature gradient vector.And have a try to use the field synergy principle to analyze heat transfer enhancement performance of porous foams.