Enhanced microscale heat transfer in macro geometry: effect of groove orientation and working fluid

• Main Author: Jaishankar, Sunil Shankar
• Other Authors: Ooi Kim Tiow
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/61363
• Institution: Nanyang Technological University

The present era is the age of computing and this revolution is being powered by microchips that are becoming increasingly powerful by the day. This increase in processing power, however, is accompanied by very high heat dissipation in the range of 100 W/cm2. In fact, insufficient cooling for microchips is seen as the single largest stumbling block in producing powerful computers. This project investigates the heat transfer at the microscale level to effectively carry away the heat produced, a phenomenon reported to be effective in the same by Tuckerman and Pease in 1981. This project aims to study the heat transfer performance of microchannels with grooved walls in the attempt to attain passive heat transfer augmentation. In continuation of previous works, the effect of groove geometry, in particular circular pitch and orientation of the grooves, is studied. Experiments and numerical simulations have been performed to deduce pressure drop and thermal characteristics of the microchannel flow with heat supplied at 26.5 and 15.9 W/cm2. In order to create the microchannel, solid cylindrical rods, called inserts, made of stainless steel with conical ends are used in conjunction with external piping. The space in between the insert and the external piping creates the annular microchannel investigated in this study. Grooves are fabricated on the insert surface in order to enhance heat transfer. Numerical simulations were also performed to investigate the effect of using air as the working fluid as against water for the other investigations. Investigations revealed that increasing the circular pitch of the grooves results in a decrease in both total pressure drop and heat transfer coefficient. Increasing the orientation angle of the groove was found to increase the heat transfer coefficient by 16.00% on average while subjected to an acceptable pressure penalty between 12.8 kPa to 143.8 kPa depending on insert and flow rate. Finally, the use of air as the working fluid revealed that water generally performs better than air in terms of heat transfer performance with water having 12% higher Nusselt number at Reynolds number of 1000 and 182% higher Nusselt number at Reynolds number of 5500.