Pool boiling heat transfer on ultra-light porous metal foam surfaces

Experiments were conducted to study pool boiling heat transfer on ultra-light porous metal foam surfaces, with deionized water as working fluid. The metal foams have pore densities from 30 to 60ppi (pores per inch) and thickness from 2.0 to 5.0mm. The effects of heat flux, surface superheat, liquid temperature and characteristic parameters of metal foam on pool boiling heat transfer were investigated. It is found that metal foam surfaces can significantly enhance pool boiling heat transfer and lower the surface superheat at the boiling incipience. Pore density and thickness exists an optimal value to strengthen boiling heat transfer. The boiling heat transfer coefficient on the metal foam surfaces is about 2~3 times of those on the plain surfaces. The significant reasons are due to the distinct nature of high porosity and multi-scale pore sizes of metal foams. The larger pores help to release the created vapor while the smaller pores help to suck the liquid toward the heater surface, decreasing the shear stress at the vapor-liquid interface for the counter-current flow.