多孔泡沫材料强化传热特性及场协同分析

实际生产生活中使用到的多孔泡沫材料通常都是非均质的,文章建立了多孔泡沫材料均质与非均质模型,结合场协同理论,从速度与温度梯度矢量的协同关系出发,分析了多孔泡沫材料内部单相流体对流强化换热的物理机制,研究了孔隙率、孔密度以及空气流速对流体顺流方向协同性能的影响。研究表明:场协同原理适用于分析多孔泡沫材料的强化传热机制;多孔泡沫材料孔隙中心与骨架后缘处的协同程度最好,骨架侧缘协同程度最差(协同角接近90°);非均质多孔泡沫材料孔壁附近协同程度较差,相同条件下全场平均场协同角比均质泡沫大;多孔泡沫材料越均匀全场协同情况越好,在相同流速、孔隙率和孔密度下,均质泡沫材料全场平均协同角余弦值可达非均质泡沫的1.2倍。计算结果表明,空气流速为3m/s时,孔隙率为0.8、0.85和0.9的多孔泡沫材料强化传热强度分别是普通平直翅片的3.3倍、1.9倍和1.2倍。该研究对新型散热器设计具有指导意义。

Heat Transfer Enhancement of Porous Foams and Analysis with Field Synergy Principle

The porous foams used in practical production applications are usually non-uniform foams. In this paper, uniform and non-uniform heat transfer models of porous foams were established to study the effects of porosity, pore density and air flow ve-locity on the synergy performance of velocity and temperature gradient in the downstream.The field synergy principle was employed to analyze the heat transfer enhancement mechanism in a rectangle channel inserted with porous foam under single phase convective heat transfer condition. The results suggest that the field synergy principle can be applied to analyze the convective heat transfer of porous foams. The synergistic degree was better at the center of the pore than the posterior edge of the skeleton. The synergistic degree was the worst at the edge of the skeleton, where the synergetic angle was about 90°. In other words, the porous foam improved the coordination between the velocity and temperature gradient for connective heat transfer in the channel and remarkably enhanced the heat transfer. Non-uniform porous foam had poor degree of coordination near the wall and the average synergetic angle of whole field was larger than that of uniform porous foams. The more uniform the better the synergistic condition of the porous foam, it was also found that the strength of uniform porous foam heat transfer enhancement was more than 1.2 times of non-uniform porous foam at the same velocity, pore density and porosity. The calculated results showed that the enhanced heat transfer intensities of the porous foams with porosities of 0.8,0.85 and 0.9 were 3.3,1.9 and 1.2 times that of the ordinary straight fin heat exchanger at the speed of 3 m/s,which has a guiding significant for the design of new heat exchanger.