Experimental investigation of pulsating flow structures and heat transfer characteristics in sinusoidal channels

摘要

In the present work, hydrodynamics and heat transfer characteristics in the sinusoidal channel are investigated experimentally for both steady and pulsating flow conditions. The experiments for heat transfer investigations were performed under a constant heat flux in the range of Strouhal number, St 0.11 <= St <= 2.07for the Reynolds number, in the range of 4 x 10(3) <= Re <= 7 x 10(3). After seeing the improvement of heat transfer with employing pulsation to the working fluid the hydrodynamics of pulsating flow was analyzed by considering the pulsating flow characteristics such as the time-averaged streamlines topology, (Psi), streamwise velocity distribution, < u >, cross-streamwise velocity distribution, < v >, and turbulent Reynolds stress, (u'v') over bar /U-2 using instantaneous flow data measured by the Particle image velocimetry (PIV) system. The results revealed that pulsating flow is highly effective for the lower turbulent flow case in the sinusoidal channel. As the Reynolds number increases, the effect of Strouhal number, St becomes less effective. There is an optimum Strouhal number,St value for different Reynolds numbers, Re to reach the maximum enhancement compared to steady flow cases.. The entrainment between the core flow and recirculating flow enhances the heat transfer rates in a steady flow. But the pulsating flow forces the recirculating flow zones in the diverging-converging section of the channel wave to exchange the flud from the core flow region further and that is an additional mechanism to upgrade the rate of heat transfer comparing to the steady flow cases.