Abstract:

The convection heat transfer for natural flow of air over an isothermal vertical surface embedded with porous metal foam was theoretically studied using boundary-layer theory and local thermal equilibrium assumption. The conservation equations were simplified by analyzing the order of magnitude of each term and then solved by using integration method. It was shown that the develop of fluid boundary-layer thickness with metal foam was much faster than that of plain vertical surface because of disturbances induced by metal foam. The fluid boundary-layer thickness grew faster with larger porosity and higher pore density(porosity 0.9—0.95 and pore density 5—40 PPI).The flow velocity of air reached the maximum quickly and kept almost constant. The heat transfer in porous aluminum with 0.9 porosity and pore density 5 PPI was enhanced more than 9 times compared with that of plain vertical surface. However，with further increase in porosity and pore density，the develop of fluid boundary-layer thickness was too fast，which made heat transfer worse.

摘要：

应用边界层理论和局部热平衡传热模型，建立控制方程组,理论分析了多孔泡沫金属中等温竖壁面空气自然对流的传热特性。采用数量级分析法简化控制方程组，再进行积分求解。结果表明：多孔泡沫金属对自然对流具有强烈的扰动作用，使边界层发展很快，其厚度远大于光壁面时的边界层厚度，在等温竖壁面条件下本文所选的参数范围内(孔隙率0.9～0.95，孔密度5～40PPI)，孔隙率越大、PPI越大，边界层也越厚；空气流速很快达到最大值，且此后的速度峰值几乎维持不变；自然对流传热的强化效果非常明显，相比光壁面，加入孔隙率0.9、孔密度5 PPI的多孔泡沫铝后其强化倍数达9以上,但孔隙率、孔密度增大时，流体边界层厚度增长过快，会使得传热恶化。