Study On Heat Transfer Enhancement And Flow Resistance Characteristics Of Porous Foams

With the rapid development of electronic technology, the electronic devices arebecoming smaller, lightweight, compact, and efficient increasing, which generated moreheat. However, the traditional metal heat sinks have difficult to meet the requirements.The porous foams, as a novel functional material, have high specific surface area, highporosity, high conductivity and low density, so that the porous foams can be used as thecore component material of radiator which is light and with high thermal conductivity,especially in aerospace, military and electronics engineering for which the weightshould be much concerned.In this paper, research work for the resistance and heat transfer characteristics ofthe porous foam as a lightweight high thermal radiator core component was taken. Anexperimental table about the heat dispersion of porous foam radiator was built, theexperiments were taken on two porous foam samples, and the results were comparedwith the traditional flat radiator. According to the geometric structure of the porousfoam, homogeneous and heterogeneous geometric model of porous foam wereestablished, the flow and convective heat transfer process in the porous foam weresimulated, and the influence of the porous foam geometry parameters on the flowresistance and heat transfer characteristics were discussed. In the last chapter, thesynergistic properties of the porous foam flow field and temperature field was analyzedbased on the field synergy principle of convective heat transfer. So, the main contentsand results obtained of this paper including the follow:The performance of the two copper foam radiator were superior to the straight finheat sink which was selected in the test, the heat transfer coefficient of copper radiatoris1.6to1.9times to the straight fin heat sink within the experimental range of flowrates.Reynolds number based on the permeability was defined, and the relationshipbetween the friction factor and Reynolds number of the porous foams used in theexperiment were obtained. That is f=1/Rek+c, for the porosity equal to0.946,0.957, thedimensionless ineratial coefficient c are0.03448and0.02806.The permeability and inertial coefficient of porous foams have nothing to do withthe properties of fluid. With the guide of Ergun equation, dimensionless permeabilityand dimensionless ineratial coefficient based on an equivalent particle diameter were defined, and the correlation between the dimensionless permeability, dimensionlessineratial coefficient and structural parameters was received. The heat transfer coefficientwas calculated based on contact surface, the criterion equation of the convective heattransfer of porous metal foams were obtained.Form the numerical results, the thermal resistance of heat transfer and pumpingpower were calculated and analysis. The results showed that the “critical velocity” wasexisted. The integrated performance evaluation indicator PEC was used in this paper toevaluate the enhanced heat transfer performance of porous metal foams, and the resultsshowed the porous foams with low porosity and high pore density are easier to get abetter overall heat transfer performance.A random parameter of pore uniformity was proposed in order to studyperformance of heterogeneous porous foam and analyze the influence of poreuniformity on the characteristic of porous foams. The numerical results ofheterogeneous porous foams showed that with the decrease of pore uniformity, all thepermeability, thermal performance and overall heat transfer permeability were gotworse, that is to say, the much random of pore structure, the much worse of theperformance. The correlations for dimensionless permeability, dimensionless inertialcoefficient with the structural paremeter and Nusselt criteria were proposed consideredthe influence of pore uniformity.In the last, the average synergy angle was calculated with field synergy principlebased on the numerical results in this paper. The synergistic properties of the flow fieldand temperature gradient in porous foams was analyzed, and the effects of structuralparameters, such as porosity, pore density and pore uniformity were all discussed, theresults demonstrated the importance and feasibility of field synergy principle in theconvective heat transfer of porous foams.