Experimental And Numerical Investigations On Fluid Flow And Heat Transfer In Rectangular Microchannels With Longitudinal Vortex Generators

Heat transfer and fluid flow in rectangular micochannel with longitudinal vortex generators (LVGs) were performed by using DI water as the working fluid at the Reynolds number of 170-1200. LVGs were fabricated by micro process along the stream-wise direction in rectangular microchannel with hydraulic diameter of 187.5μm and aspect ratio of 0.067 for different number of pairs and angles of attack. Critical Reynolds number (600-720) was found to be at a much smaller value by adding LVGs than the one without (²300). In the present work, it was found that rectangular microchannels with LVGs would improve heat transfer performance (9-21% higher for those with laminar flow and 39-90% for those with turbulent flow) compared with smooth rectangular microchannel, while encountering larger pressure drop (34-83% for laminar flow and 61-169% for turbulent flow); G6 channel (with three pairs of LVGs at angles of attack of 30°, 150°, and 30°) had the best overall heat transfer performance (0.30 for laminar flow and 0.66 for turbulent flow), expressed in terms of the ratio of heat transfer enhancement to increase in pressure drop (Φ_Nu /Φ_f). For the numerical simulation part, heat transfer and fluid flow investigations were carried out on the channel type of G1 (5×30°). The numerical results indicated that heat transfer was enhanced in the wake region behind the LVGs which played important role on the interactions among heated wall, fluid in the lower layer of the channel and fluid in the higher layer of the channel. In the wake region, two dimensional transverse and three dimensional longitudinal vortices were found at the same time; the transverse vortices affect the heat transfer enhancement to some extent and can improve the heat exchange between fluid and side walls for the reason that the side walls of microchannel are also heated at the constant temperature; while, the longitudinal vortices are strengthened with the increase of mass flow rate in the inlet of microchannel. In addition, it was found that at the constant mass flow rate, longitudinal vortices demonstrated different intensity at the different heights of microchannel.