Boiling in Microchannel with application to Electronic Cooling

The design of next-generation nanoscale integrated circuits requires effective cooling for reliable operation. As the device operating frequency increases, heat dissipation will increase, primarily concentrated at one or more hot spots and accompanied by large heat flux transients. The very large heat flux transients will cause degradation in device reliability and may eventually lead to device failure. Due to poor thermal transport properties of air, the traditional heat sinks will not suffice at largescale integration levels. Microchannel heat sinks have emerged as a promising cooling technique, where higher efficiency results from a large surface area to volume ratio.

Microchannel with integrated micro-heater (left), ) for flow boiling experiments(middle), Obtained flow regime map(right)

In order to understand the flow and heat transfer behaviour, detailed experimental study involving flow boiling of water in microchannel has been conducted in the lab. The work aims to study different aspects of the problem such as pressure drop, heat transfer coefficient, pressure instability, and void fraction. Flow visualization has also been performed. Experiments have been conducted in silicon microchannels with trapezoidal or rectangular cross-section of hydraulic diameter 45-140 micrometer, and a microheater fabricated on the reverse side of the silicon wafer to provide well controlled and metered input power (see figure). For the first time, a flow regime map is obtained for such systems. There are several novel aspects of this study. For example, effect of microchannel aspect ratio on pressure drop is studied for the first time. Some guidelines for choosing the operating point with desired constraints have been proposed. Ways to reduce instability have also been explored. Development of flow regime map and flow visualization technique is not available in the literature currently. Pressure drop data near CHF condition have been presented. The results are interesting from both fundamental and electronic cooling point of view.

References

  1. Kumar, N., Agrawal, A., Singh, S.G., and Sridharan, A., "On bubble dynamics during flow boiling in microchannel," Journal of Energy, Heat and Mass Transfer, Vol. 37, pp. 57-64, 2015.

  2. Duryodhan, V.S., Singh, S.G., and Agrawal, A., "Boiling flow through diverging microchannel," Sadhana, Vol. 38, pp. 1067-1082, 2013.

  3. Agrawal, A., Duryodhan, V.S., and Singh, S.G., "Pressure drop measurements with boiling in diverging microchannel," Frontiers in Heat and Mass Transfer, Vol. 3, 013005 (1-7), 2012. (Invited article)

  4. Bhide, R.R., Singh, S.G., Duryodhan, V.S., Sridharan, A., and Agrawal, A., "Onset of nucleate boiling and critical heat flux with boiling water in microchannel," International Journal of Microscale and Nanoscale Thermal and Fluid Transport Phenomena, Vol. 4 (1), 2012.

  5. Agrawal, A., and Singh, S.G. "A review of state-of-the-art on flow boiling of water in microchannel," International Journal of Microscale and Nanoscale Thermal and Fluid Transport Phenomena, Vol. 2, pp. 1-39, 2011. (Invited review)

  6. Bhide, R.R., Singh, S.G., Sridharan, A., and Agrawal, A., "An active control strategy for reduction of pressure instabilities during flow boiling microchannel," Journal of Micromechanics and Microengineering, Vol. 21, 035021, 2011.

  7. Singh, S.G., Agrawal, A., and Duttagupta, S.P., "Reliable MOSFET operation using two-phase microfluidics in presence of high heat flux transients," Journal of Micromechanics and Microengineering, Vol. 21, 105002, 2011.

  8. Singh, S.G., Duttagupta, S.P., and Agrawal, A., "In-situ impact analysis of very high heat flux transients on non-linear p-n diode characteristics and mitigation using on-chip single-phase and two-phase microfluidics," Journal of Microelectromechanical Systems, Vol. 18(6), pp. 1208-1219, 2009.

  9. Singh, S.G., Jain, A., Sridharan, A., Duttagupta, S.P., and Agrawal, A., "Flow map and measurement of void fraction and heat transfer coefficient using image analysis technique for flow boiling of water in silicon microchannel," Journal of Micromechanics and Microengineering Vol. 19, 075004, 2009.

  10. Bhide, R.R., Singh, S.G., Sridharan, A., Duttagupta, S.P., and Agrawal, A., "Pressure drop and heat transfer characteristics of boiling water in sub-hundred micron channel," Experimental Thermal and Fluid Science, Vol. 33, pp. 963-975, 2009.

  11. Singh, S.G., Bhide, R.R., Duttagupta, S.P., Puranik, B.P., and Agrawal, A., "Two-phase flow pressure drop characteristics in trapezoidal silicon microchannels," IEEE Transactions on Components and Packaging Technologies, Vol. 32 (4), pp. 887-900, 2009.

  12. Singh, S.G., Kulkarni, A., Duttagupta, S.P., Puranik, B.P., and Agrawal, A., "Impact of aspect ratio on flow boiling of water in rectangular microchannels," Experimental Thermal and Fluid Science, Vol. 33, pp. 153-160, 2008.