Experimental study of natural convective heat transfer in horizontally-positioned cellular metal foams with open cells

Experimental study of air natural convective heat transfer in horizontally-positioned copper metallic foams with open cells was conducted. The effects of porosity and pore density on the total thermal resistance of the foam sample were quantified. It is found that the porous surface can enhance the natural convection and reduce the thermal resistance by about 20% in comparison with a smooth surface. The surface area density and mass flow rate in natural convection are affected by porosity and pore density simultaneously. When the porosity is relative small (ε = 0.9), there exits a critical value of the Gr number (turning point) for two pore densities (400 m^-1 and 1600 m^-1). When the Gr number is less than this critical value, the foam with a higher pore density has the lower total thermal resistance, whereas when the Gr number exceeds the turning point value, the opposite holds. If the porosity is increased to ε = 0.95, the foam with a higher pore density has the lower thermal resistance in the whole experimental range. For the two pore densities studied (800 m^-1 and 1600 m^-1), the foam with a lower porosity (from 0.95 to 0.9) has the lower thermal resistance and the decrease is more obvious for the case of 1600 m^-1 than the case of 800 m^-1.