Numerical Study of Single-Phase Heat Transfer Performance of a Mini/Micro-Channel Integrated With Multiple Bypass Micro-Nozzles

Abstract

Surface temperature uniformity is an important factor in the thermal management of electronics. The present numerical study investigates the influence of multiple bypass injections on the wall temperature distribution of a single-phase mini/micro-channel. The proposed scheme consists of sending a fraction of the coolant through the inlet of a 0.6 mm deep, 2.5 mm wide, and 25 mm long channel and injecting the remaining coolant through multiple bypass inlets on top of the channel positioned at different axial locations. The study explores four different configurations: the first one being three equispaced bypass micro-nozzles or bypass inlets of uniform diameter (1 mm), the second one being three equispaced bypass micro-nozzles of varying diameter (2 mm, 1 mm, and 0.5 mm), the third one being five equispaced bypass micro-nozzles of varying diameter (2 mm, 1 mm, 0.5 mm, 0.25 mm, and 0.125 mm), and the fourth one being five bypass micro-nozzles, but with three equispaced bypass inlets of varying diameter (2 mm, 1 mm, and 0.5 mm), and the last two bypass inlets of the same diameter as that of the third inlet (0.5 mm). Water is considered as the coolant in the study and the simulations are carried out for two mass fluxes of 465 kg/m2s and 930 kg/m2s and two heat fluxes of 25 kW/m2 and 125 kW/m2. The thermal performance of the channel is evaluated for bypass percentages of 25%, 50%, and 75%, with the Reynolds number varying from 150 to 900 at the primary channel inlet and at the secondary channel inlet, and the range of the nozzle Reynolds number varying from 10 to 707. The fourth configuration results in a near uniform wall temperature distribution, with 82–89% reduction in the wall temperature nonuniformity compared with the no-bypass case. The reductions for the third, second and first configurations are 65–71%, 53–76%, and 54–74%, respectively. The third configuration results in an average heat transfer coefficient enhancement of up to 49%. On the whole, the improvement in the wall temperature uniformity is higher than the increase in the pressure drop, and the increase in the channel heat transfer coefficient is higher than pressure drop for some cases.