Lee Poh Seng, PhD

Assistant Professor of Mechanical Engineering

National University of Singapore

The ever-increasing power consumption of electronics coupled with the shrinking dimensions of devices has pushed the conventional air cooling solution to its physical limits. As such, there is an urgent need for the development of advanced thermal management techniques for the next generation of electronics, among which micro-channel heat sinks is one of the most effective. Despite its potential as a highly efficient compact cooling solution, significant temperature variations across the chip can still persist since the heat transfer performance deteriorates in the flow direction in conventional micro-channel as the boundary-layer thickens and the coolant heats up. This talk presents a novel heat transfer enhancement scheme that is recently proposed; where miniature oblique fins are employed in contrast to the continuous fins in the conventional settings. The breakage of continuous fin into oblique sections causes the thermal boundary layers to be re-initialized at the leading edge of each oblique fin and reduces the boundary-layer thickness. This regeneration of the entrance effect causes the flow to be always in a developing state thus resulting in better heat transfer. In addition, the presence of the smaller oblique channels causes a fraction of the flow to branch into the adjacent main channels. The secondary flows thus created improve fluid mixing which serves to further enhance the heat transfer. Simulation and experimental investigations demonstrated that the combination of the entrance and secondary flow effect from oblique fins results in a much improved heat transfer performance against the conventional configuration. The average heat transfer coefficient, h_ave, for the silicon microchannel heat sink (120µm channel width and 375µm channel depth) using water as working fluid can increase as much as 80%, from 25,000W/m²K to 45,000W/m²K which matched the performance for flow boiling but without the need of a complex flow loop and no flow instabilities that typically came along with two-phase systems. Interestingly, there is only little or negligible pressure drop penalty associated with this heat transfer enhancement scheme. Besides, the heat sink design is applicable for hotspot mitigation and air-cooled heat sink.

Dr Lee Poh Seng did his Bachelor and Masters of Engineering with the Department of Mechanical Engineering at the National University of Singapore in 1999 and 2001 respectively. He then proceeded to pursue a PhD with the Cooling Technologies Research Center at Purdue University, West Lafayette, Indiana, USA working with Professor Suresh Garimella on thermal transport in microchannels (both single and two-phase). He is currently an Assistant Professor with the Department of Mechanical Engineering at the National University of Singapore. His current research interests include micro-fluidics, microscale heat transfer, hybrid solar energy harvesting systems and internal combustion engine fueled by biofuels and fuel blends.