An Experimental Study of Passive and Active Heat Transfer Enhancement in Microchannels

An experimental study on single-phase heat transfer and fluid flow downstream a single microscale pillar in a microchannel was conducted. A secondary jet flow was issued from slits formed along the pillar. A comparison of the thermal performances of a plain microchannel, a microchannel with a pillar, and a microchannel with a jet issued from a pillar was performed to elucidate the merits of this heat transfer enhancement technique. It was found that the presence of a pillar upstream the heater enhanced the heat transfer; the addition of jet flow issued from a pillar further enhanced the heat transfer. At a Reynolds number of 730, an improvement of spatially averaged Nusselt number of 80% was achieved due to the combined effect of the pillar and the jet compared with the corresponding plain channel. Micro particle image velocimetry (μPIV) measurements provided planar velocity fields at two planes along the channel height, and allowed flow structure visualization. Turbulent kinetic energy (TKE) was used to measure flow mixing and to quantify the hydrodynamic effect of the jet. It was shown that the TKE is closely related to the Nusselt number.