Thermal transport in microchannels
Abstract
Thermal transport in microchannels is investigated to better understand the fundamentals of fluid flow and heat transfer that occur at the microscale. Pressure drop and heat transfer measurements are obtained to validate the applicability of conventional theory in predicting single-phase fluid flow and heat transfer behavior in microchannels. The results suggest that conventional theory and carefully selected correlations are entirely capable of predicting single-phase transport characteristics in the microchannels considered. To supplement the experimental measurements, a detailed computational fluid dynamics analysis is performed to study the three-dimensional, steady-state, convection-conduction conjugate problem in a microchannel heat sink. Local temperature, heat flux and Nusselt number distributions are obtained. Approximate analytical models are presented to aid in the design and optimization of microchannel heat sinks to satisfy the thermal performance requirement. A graphical method is outlined to assess the suitability of pumps for particular microchannel heat sinks. A non-intrusive diagnostic technique, infrared micro-particle image velocimetry is developed for measuring flow fields within MEMS devices with micron-scale resolution. Experiments conducted demonstrate the efficacy of this technique for flow measurement in silicon-based microdevices. Convective flow boiling in microchannels is studied to advance the understanding of flow boiling and two-phase flow in microchannels. Boiling heat transfer is experimentally characterized. Onset of nucleate boiling is studied with a high-speed imaging system and the heat flux at incipience is measured in a microchannel heat sink under various flow conditions. An analytical model is developed to predict the incipient heat flux as well as the bubble size at the onset of boiling. An investigation of bubble motion and evolution is performed using high-speed photography to reveal the complex bubble dynamics during nucleate boiling in microchannel flows. Convective boiling heat transfer coefficients are measured and compared to predictions from existing correlations proposed for larger channels. While an existing correlation is found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in the microchannels, saturated boiling is not well predicted by the correlations for macro- and mini-channels. A new superposition model is developed to correlate the heat transfer data in the saturated boiling regime in microchannel flows.
Degree
Ph.D.
Advisors
Garimella, Purdue University.
Subject Area
Mechanical engineering
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