Flow and Heat Transfer in a 2-D Channel Partially Filled With Porous Medium

Graphite foam, developed by the Oak Ridge National Laboratory, has shown excellent thermal properties and has potential applications for compact heat exchangers. The flow and heat transfer characteristics of a 2-D channel partially filled with graphite foam as the porous medium are determined. A steady, incompressible and constant-property water flow is modeled using the commercial software COMSOL^â. Flow is uniform at the inlet and the base of the foam is subjected to a constant heat flux boundary condition. The permeability( 7x10^-8 to 1.4x10^-6 m²)and the dimensionless height of the porous block are varied. Heat fluxes of 1x10⁵ and 3x10⁵ W/m² are considered for Reynolds numbers of 1000 and 2000.

For the range of parameters considered in this study, the results show that

(1) The friction factor decreases with increase in Reynolds number and permeability. It increases almost exponentially at moderate to higher values of dimensionless block height.

(2) The Nusselt number increases with Reynolds number, permeability and dimensionless block height.

(3) The maximum surface temperature of the heater decreases with increasing Reynolds number and dimensionless block height. It decreases with increasing permeability for both Reynolds number and heat flux cases considered.

(4) A dimensionless parameter effectiveness is introduced and it increases linearly with heat flux and decreases rapidly with increase in Reynolds number. For example, when Reynolds numberis doubled effectiveness is shown to drop by a factor of about eight.

(5) For the two values of heat fluxes and for all permeability values considered in this study, the maximum effectiveness is found to occur at h_p/H = 0.15 and 0.10 for Re_Dh=1000 and 2000, respectively.