Influences of tip clearance on flow and heat transfer characterstics of open type micro pin fin heat sink

Abstract

Microchannel heat sink without any tip clearance i.e. completely closed microchannels have been focused and widely studied. In the present work, detailed comparative analysis has been performed between open and closed micro pin fin configurations of the heat sink. Keeping the constant channel height of 2.0 mm, three different micro pin fin heat sinks with tip clearance of 0%, 25% and 50% of channel height were fabricated and analyzed. Square cross-section fins are considered and arranged in inline fashion. An additional plain channel (without any pin fin) is also examined for the sake of comparison and completeness of the study. The experiments have been conducted using deionized water as the working fluid and copper as microchannel substrate. Present work aims to recognize the importance of tip clearance and quantify its suitable value that facilitates better heat transfer rate. Numerical predictions further elaborate the physical insight of the coolant flow behavior evolved due to the presence of tip clearance in the heat sink. Findings of the present study indicate that tip clearance of 50% results in lesser heat transfer coefficients due to considerably lower net convective surface area. Whereas, tip clearance of 25% has shown superior thermal performance amongst all the configurations explicitly at Reynolds number more than 350. In addition to the net convective surface area, major factors that promote enhanced heat transfer are dispersed fluid flow behavior in the confined space of tip clearance which propagates thinner boundary layer, three dimensionalities in flow and augmented fluid mixing. Moreover, heat sink with tip clearance has also shown lesser pressure drop compared to closed microchannel due to reduced flow obstructions. It has been concluded that tip clearance may have positive impact on overall thermal performance but up to the certain limit.