Heat transfer in porous media of steel balls under oscillating flow

In this paper, heat transfer in porous media under oscillating water flow has been studied experimentally. A total of 54 sets of heat transfer experiments, each representing a different frequency, flow displacement length and heat input, have been conducted for two different porous media of steel balls. Cycle averaged local Nusselt numbers are obtained by measuring the bulk temperatures at the inlet cross sections and the center of the porous medium. It is observed that the local Nusselt number based on time averaged wall and bulk temperatures increases by frequency and maximum fluid displacement, and depends on the axial direction with increasing frequency. The variation of spaced-cycle averaged Nusselt numbers based on the averaged surface and bulk temperatures are introduced for different frequencies and flow displacements. The space-cycle averaged Nusselt number increases by kinetic Reynolds number and non-dimensional fluid displacement. The averaged Nusselt number for a certain porous medium can be correlated with kinetic Reynolds number and non-dimensional fluid displacement. Then, a more general Nusselt number correlation independent from the porous medium type and fluid properties is proposed. It is also shown that the Nusselt correlation which is a function of A _o and ReωDa is in good agreement with experimental data.