Evaluation of the Conjugate Heat Transfer of Two Heaters in a Top Inlet Duct

Bruno Resende Rodrigues¹; Carlos Alberto Carrasco Altemani¹

¹ UNICAMP

doi:10.20906/CPS/COB-2015-1872

Resumo

The present work reports an experimental investigation of the conjugate forced convection-conduction cooling of two protruding aluminum heaters mounted on the horizontal wall of a rectangular duct. The heating was obtained by independent electric power dissipation in each heater and the cooling was performed by forced airflow in the duct. Heat transfer from the heaters was mainly by direct forced convection to the airflow at the surfaces in contact with the flow and by conduction to the duct wall at their interface. The conjugate heat transfer from the heaters was described by means of a matrix G+ of dimensionless conjugate coefficients g+ni, which are invariant with the conjugate heat loss from each heater. This was shown by several experimental tests with distinct power dissipation in both heaters. The tests were performed in an apparatus consisting of two symmetrical ducts, each with a top inlet, separated by a common wall, denominated the substrate plate. Two heaters were mounted on each side of the substrate and the conjugate coefficients were evaluated for each heater, using one active heater per duct at a time. In order to explore the effect of the conductive heat losses from the heaters on the conjugate coefficients, two substrate plates were employed in the experimental tests: one was made of aluminum and the other of acrylic. For the acrylic plate, the heaters' conductive losses were comparatively small and thus the convective losses were also evaluated and described by means of the adiabatic heat transfer coefficient, had. This coefficient is invariant with the rate of convective heat loss from each heater to the airflow. The experimental tests were performed under steady state conditions for a range of the Reynolds number based on the hydraulic diameter of the duct from 1,200 to 3,000.

Palavras-chave: invariant descriptors; experimental investigation; conjugate heat transfer