KC-19-C006 -- Three-Dimensional Computations for Forced Convection of Air in Offset-Strip Fin Channels: Effects of Fin Offset Length

Offset-strip plate-fin compact heat exchangers are widely used in applications such as automobile radiators, electronic cooling devices, and HVAC heat exchangers. Higher heat transfer coefficient, compared to plain plate-fin, is obtained from the periodic disruption of the thermal boundary layer and the downstream fluid mixing. Air-flows (Pr = 0.71) in offset-strip plate-fin channels with the boundary surfaces subject to uniform temperature are investigated experimentally and computationally, and the associated Fanning friction factor f and Colburn factor j are obtained. The results characterize the rather distinct flow behavior in laminar and turbulent regions. The effects of offset length to hydraulic diameter ratio (0.3 < L/Dh < 3) are examined parametrically and are found to be the primary geometry variable influencing the performance. The enhancement in heat transfer rates under constant pressure drop condition is seen to be 2.5 -- 3 times that for plain plate-fins with the smallest offset length ratio.