This work leverages the extensive microfabrication and flow-visualization infrastructures at Stanford to develop new experiments around fundamental questions in two-phase microfluidics. The experiments feature fluorescent imaging of fluid trajectories and phase distributions as well as distributed solid-state sensors for temperature and pressure. The work is supported by simulations of conjugate conduction and convection using reduced-dimensional models accounting for flow regimes, with the ultimate goal of yielding robust simulation tools for industry. Our first application has been towards electronics cooling, specifically two-phase micro heat exchangers. Our contributions to modeling [a] and metrology [b-e] have illustrated the potential applications of two-phase microfluidic cooling to 3D circuit technology. We developed a prototype for a closed-loop microchannel cooling system [f] that led to a startup company, Cooligy. More recently, we have extended this work to the study of two-phase flow regimes and related design challenges for hydrogen and oxygen delivery microchannels in PEM fuel cells [g,h]. Our future research on two-phase microfluidics will feature more contributions relevant to fuel cells given the substantial corporate funding we have in this area, as well as continued modeling relevant to heat sinks.
Figure 1: Schematic of the geometry and simulated flow field that is
used for determining bubble contact angles and departure geometries for
two phase microchannel flows.
a. Koo et al., 2005, “Integrated Microchannel Cooling for Three-Dimensional Circuit Architectures,” ASME Journal of Heat Transfer, Vol. 127, pp. 49-58. pdf
b. Wang et al., 2004, “Micromachined Jets for Liquid Impingement Cooling of VLSI Chips,” JMEMS, Vol. 13, pp. 833-842.
c. Zhang et al., 2003, “Phase Change Phenomena in Silicon Microchannels,” International Journal of Heat and Mass Transfer, Vol. 48, pp.1572-1582
d. Zhang et al., 2002, "Measurements and Modeling of Two-Phase Flow in Microchannels with Nearly-Constant Heat Flux Boundary Conditions," JMEMS, Vol. 11, pp. 12-19.
e. Zhang et al., 2003, Book: Silicon Microchannel Heat Sinks—Theories and Phenomena, Springer-Verlag Microtechnology and MEMS Series, ISBN 3-540-40181-4.
f. Goodson et al., 2002, “Electroosmotic Microchannel Cooling System for Microprocessors,” Technical Brief, Electronics Cooling, Vol. 8, pp. 46-47, see also IEEE Proceedings on Components, Packaging, and Manufacturing Technology, Vol. 25, pp. 347-355.
g. Hidrovo et al., “Two-Phase Microfluidics for Semiconductor Circuits and Fuel Cells,” Heat Transfer Engineering, in press.
h. Steinbrenner et al., “Measurement and Modeling of Liquid Film Thickness Evolution in Stratified Two-Phase Microchannel Flows” submitted to Applied Thermal Engineering.