Effects of structural parameters on fluid flow and heat transfer characteristics in microchannel with offset zigzag grooves in sidewall

With the rapid development of large data center, the required power consumption increases sharply. The thermal management of that accounts for about 33% of energy consumption. Single phase liquid convection heat transfer of microchannel heat sink has been thought as one of the most promising methods. For energy efficient cooling, optimized microchannel structures is one important approach. Hence, the novel offset zigzag microchannnel is proposed and optimized for inlet Reynolds number ranging from 200-800 in this paper. The heat sink is composed of 30 parallel channels, and basic structure parameters of rectangular channel are width of 0.1 mm, depth of 0.3 mm, length of 5 mm and pitch of 0.2 mm. The numerical model considers entrance effect, viscous heating and the temperature-dependent thermal-physical properties. In order to study the influence of geometry on flow and heat transfer characteristics, two non-dimensional variables are defined, such as the length ratio of zigzag length to channel length (alpha) and the length ratio of zigzag expansion to zigzag length (gamma). Results indicate the zigzag channel can effectively prevent the rise of heat surface temperature along the flow direction and increase the minimum temperature, which improves the temperature distribution uniformity. Under Re-in = 650 and alpha = 0.04, the minimum temperature increases from 309.9 K to 310.1 K and maximum temperature decreases from 324.02 K to 318.91 K. For 0.04 <= alpha < 0.1 and alpha < 0.04 of Re-in < 500, the thermal characteristic is enhanced and the flow resistance also is reduced. Compared with rectangle channel, the maximum temperature and pressure drop of zigzag channel with alpha = 0.04 of Re-in = 650 are also reduced from 324.02 K to 318.76 K and 29.81 kPa to 26.75 kPa, respectively. It can be interpreted that with the decrease of alpha, the porosity and convection heat transfer areas are increased and turbulence intensity of fluid flow is enhanced. The smaller gamma is more favorable for the enhancement of heat transfer except for gamma = 0 due to the fluid stagnation at the bottom of zigzag cavity. However, compared with rectangular microchannel, heat transfer is enhanced for all cases and flow resistance is decreased besides gamma = 0.1 of Re-in > 500. For gamma = 0 of Re-in = 650, the maximum temperature and pressure drop are reduced from 324.02 K to 318.01 K and 298.81 kPa to 27.91 kPa, respectively. The overall thermal performance is measured with total thermal resistance vs pumping power. The best performance of offset zigzag microchannel is found at alpha = 0.04 and gamma = 0.1. For Re-in = 800, the maximum temperature of heat surface is decreased 5.65 K, the minimum increased 0.36 K, and pumping power is decreased 1.4%. And thermal resistance is reduced by 17.4% at the P-p = 0.167 W. (C) 2016 Elsevier Ltd. All rights reserved.