Thermodynamic analysis of microchannel heat sink with cylindrical ribs and cavities

Heat transfer improvement in microchannel heat sink (MCHS) has been a challenge, because it increases the power requirements for the fluid flow. In the present study, MCHS with different wall, geometric, and design configurations of cylindrical ribs and cavities are simulated to investigate their effect on thermal and hydrodynamic performance of MCHS using a laminar flow having Reynolds number in the range from 100 to 1000. The wall configurations include; base wall cylindrical ribs (BWCR), side wall cylindrical ribs (SWCR), and all wall cylindrical ribs (AWCR). Moreover, the geometric configurations involve different AWCR cases having rib spacings (Sfr) of 0.4 mm, 0.8 mm, 1.2 mm, and 0.4mm staggered arrangement. Furthermore, the design configurations include; AWCR, all wall cylindrical cavities (AWCC), and all wall cylindrical ribs and cavities (AWCRC) with constant Sfr=0.4 mm. The performance of various channels with flow disruptors is analyzed in terms of friction factor (f) and Nusselt number and then compared with smooth channel in terms of thermal enhancement factor (η). Based on the first law of thermodynamics, thermal resistance (Rth) is used to investigate the resistance of any configuration to flow of heat comparing at same pumping power. Moreover, the second law of thermodynamics is applied to quantify the rate of entropy generation (Sgen) and transport efficiency (ηt) for MCHS. The results show that although the MCHS with all wall ribs has a lower value of η than the base wall and side wall ribs; however, it has the maximum value of ηt and minimum value of Rth and Sgen; thus, indicating that η is not the only performance criteria for the selection of MCHS.