Experimental heat transfer analysis of open cell hollow ligament metal foam at low Reynolds number

Abstract

Paper deals with the evaluation of the heat transfer characteristic of metal foam. The novelty of work lies in the use of metal foam with hollow ligaments made by metallic deposition method and evaluation conducted in the conditions of low Reynolds number based on the mean pore diameter. The low flow velocity of the heat transfer medium has been chosen with intent to include the operating conditions of the devices utilizing metal foams in the thus defined conditions such as electronics cooling, low flow rate heat exchangers or solar thermal applications. The evaluation was carried out on two samples of a copper metal foam with a pore density of 10 and 20 PPI (pores per inch) by comparing the Nusselt number at four values of volumetric flow rate of the heat transfer medium (from 1.4 × 10−5 to 3.5 × 10−5 m3·s−1) and at four values of the used heat flux (from 200 to 575 W) on the authors designed and manufactured measuring apparatus. The resulting Nusselt number comparison showed an approximately double increase for the same Reynolds number in a sample with a pore density of 20 PPI, compared to a sample of 10 PPI. The given correlation of the Nusselt number numerically quantifies the effect of the Reynolds number based on the mean pore diameter on its total value and hence on the overall efficiency of the heat transfer process. Presented results have a considerable application potential, especially due to the small number of published works dealing with research of metal foams of a similar type and conducted with such defined flow conditions.