Effect of frequency on heat transfer due to oscillating water flow in open-cell metal foam: An experimental study

•Experimental heat transfer due to oscillating water flow in metal foam is presented.•Flow frequency: 0.116–0.696 Hz; displacements: 1.5, 1.9 and 2.2 pipe diameters.•For short displacements, steady flow produced more heat transfer.•Dependence on kinetic Reynolds number may be universal for porous media.

Heat transfer due to oscillating water flow in open-cell aluminum-foam pipe subjected to constant wall heat flux was investigated experimentally. The foam had 20 pores per inch and a porosity of 87.6%. Three flow displacements 1.5, 1.9 and 2.2 pipe diameters, at kinetic Reynolds numbers in the range 1873–9366 were applied. Higher flow displacement and higher frequency generally produced higher heat transfer rates and led to lower and more uniform wall temperature. The flow displacement had the most profound influence on heat transfer. A correlation was obtained for the time- and length-average Nusselt number as a function of non-dimensional flow displacement and kinetic Reynolds number. The dependence on kinetic Reynolds number might be universal for oscillating heat transfer in porous media. Steady-state heat transfer experiments were also conducted in the same porous medium and test facility. Oscillating flow was seen to produce lower rates of heat transfer compared to steady flow. This unexpected finding was explained. The current results were compared to other studies from the literature employing oscillating air and water flows in various kinds of porous media. Some agreements and disagreements were stated and discussed.