Heat transfer enhancement through pitch ratio optimization of butterfly inserts in minichannel heat sinks

Thermohydraulic characteristics of square minichannel heat sinks (MHS) with butterfly inserts are computa-tionally studied for Reynolds numbers between 200-900 for two hydraulic diameters (Dh) of 2 mm and 2.6 mm and varied pitch distances (P). The present investigation examines the effect of pitch ratio (P* = P/Dh) of butterfly inserts on overall thermal performance of MHS to discern its optimal value for the best possible overall performance. Since inserts result in a concurrent rise in both pressure drop and heat transfer rate, this overall thermohydraulic performance is measured using Performance Evaluation Criteria (PEC), which incorporates the simultaneous effects of change in hydraulic and thermal performance. In the present study, PEC values for all analyzed configurations are found to be above unity, which indicates the adequacy and efficacy of the employed butterfly inserts. The study also corroborates the literature-reported finding that the pitch ratio of butterfly inserts significantly alters the thermohydraulics of MHS. Heat transfer performance is found to improve drastically when pitch ratio is reduced from 5 to 1.5, showing a Nusselt number enhancement of 29.57% to 78.47% for Dh = 2 mm and 27.73% to 63.47% for Dh = 2.6 mm for the tested range of Reynolds numbers. However, further reduction in pitch ratio is found to deteriorate the thermohydraulic performance of these inserts. The highest PEC value is obtained for P* = 1.5 for both the studied hydraulic diameters, leading to the conclusion that P* = 1.5 is the optimal pitch ratio of butterfly inserts when employed within rectangular MHS.