Heat Transfer and Pressure Drop of Lotus-Type Porous Metals

Metal foams are of interest for heat transfer applications because of their high surface-to-volume ratio and high convective heat transfer coefficients. However, conventional open-cell foams have high pressure drop and low net thermal conductivity in the direction normal to a heated surface due to the fully random structure. This paper examines heat transfer elements made by stacking thin layers of lotus metal which have many small pores aligned in the flow direction. The reduction in randomness reduces the pressure drop and increases the thermal conduction compared to conventional metal foams. Experimental results are presented for the heat transfer performance of two types of lotus metal fins, one with a deterministic pattern of machined holes and one with a random hole pattern made by a continuous casting technique. The layer spacing, the hole diameter, the porosity, and the flow Reynolds number were all varied. The measurements show that spacing between fin layers and the relative alignment of pores in successive fins can have a substantial effect on the heat transfer performance.