Numerical Simulation Of Heat Transfer Enhancement In Porous Foam Metal Based On Macro And Pore Scale Model

Heat exchange and transfer is one of the most common phenomena of energy flow and itis the base for many industrial production areas, such as metal melting, electric products,chemical metallurgy, refrigeration, aviation, nuclear power reactors and so on. Improving theefficiency of heat exchange and transfer and reducing the heat loss during transmission are ofgreat significance to our country’s green manufacture, energy conservation and environmentprotection. This paper discusses the porous foam metal heat transfer enhancement technology,which has drawn great attention in recent years. The porous foam metal has large specificsurface area, high heat conductivity and unordered skeleton space distribution, so this materialcan be used as a good heat transfer enhancement medium. On the one hand, a high specificsurface area will increase the heat exchange area, especially when the skeleton is of high heatconductivity, aluminum metal foams, copper metal foams, for example. On the other hand, theunordered skeleton space distribution can achieve the effect of flow destabilization, reductionof the thickness of the heat transfer layer and enhancement of the heat transfer throughpromotion of the mixture between the boundary layer flow and the core region flow.The effects of the porous foam copper on the flow heat transfer enhancement under airand water are concluded from the heat transfer enhancement experiment by newly-designedexperimental system, from which the permeability coefficient and the inertial resistancecoefficient under different working media are obtained. The experiment results show that thefoam copper has a better air permeability than water permeability. The flow resistance of therunner inserted with foam copper increases as the flow velocity speeds up. Higher cell densityhas higher flow resistance, so the foam copper of higher cell density will result in morepressure drop. As for heat transfer, the average wall temperature decreases and the convectiveheat transfer coefficient, Nusselt number, increase as the flow velocity speeds up. Higher celldensity foam copper material has a better heat transfer performance, especially when theworking medium is air. As for the integrated evaluation of heat transfer enhancementcoefficient, both experiment materials are below1.0and air synthetic evaluation is higherthan that of water synthetic evaluation. In conclusion, the heat transfer can be enhanced byfoam copper but at the same time, flow resistance rises and what’s more, this rate of flow resistance’s increase exceeds that of heat transfer enhancement, thus decreases the integratedperformance of flow heat transfer enhancement.The numerical simulation research of the porous foam copper flow heat transfer is alsocarried out in this paper. It’s a key procedure to set up the foam pore structure in the porescale simulation. The software Surface Evolver is utilized to build the foam pore structure.The effects of the key parameters, such as porosity, cell density on the flow resistancecharacteristic and the convective heat transfer coefficient under air and water, are studied inpore scale simulation. The pore scale simulation results show that under the same porosity,unit pressure drop, flow resistance coefficient, and convective heat transfer coefficient allincrease with the increasing of the cell density. Under the same cell density, unit pressure dropand flow resistance coefficient decrease with the increasing of the porosity. Porosity has noobvious effects on the convective heat transfer coefficient under air and for water, there is nosimple monotonic relationship between the porosity and the convective heat transfercoefficient. Among the range of the porosity selected in the simulation, the foam porosityequaling to0.90is of the highest convective heat transfer coefficient with the same celldensity and flow velocity.This paper puts forward the idea of the connection between the macro scale and the porescale simulation and establishes the UDF subprogram to realize this connection. The papersets the boundary conditions and area property in the macro scale simulation under the base ofthe real experimental physical conditions and updating the interface convective heat transfercoefficient through the UDF subprogram. There is a good trend consistency between themacro scale simulation results and the experimental results but a great difference in their realnumerical values, especially in the case of high flow velocity.