Experimental Investigation of Cavity Induced Two Phase Flow in Silicon Microchannels
Type of DegreeThesis
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Modern developments in microelectronics manufacturing and architecture continue to lead to reductions in feature sizes on microprocessor chips. The demand for faster and more powerful systems has approached the limits of conventional passive and active electronics cooling schemes. Future high-powered electronics require new and innovative heat removal methods. The research study presented in this thesis is conducted in order to better understand two-phase heat transfer in a microchannel heat sink using FC-72 as the test fluid. This study will cover the design, fabrication and testing of several silicon microchannel test sections. The test section consists of an (1cm x 1cm) array of nineteen parallel microchannels etched into silicon with the following hydraulic diameters: 253 and 356µm. The base of each channel contains two arrangements of re-entrant type cavities spaced evenly along the length. One arrangement has been fabricated with 2 cavities per channel and the other with 6 cavities per channel. Each cavity, measuring 20 microns in mouth size, is used to promote controlled nucleation activity in the base of the channels. The experimental results presented include the bulk fluid temperature and pressure at the inlet and outlet, axial in-channel temperature measurements, and flow visualization taken through high-speed imaging. The results also include the comparison of several existing heat transfer correlations with the current studies data and evaluation of transient two-phase instabilities. It was found that the two-phase heat transfer coefficients reaching values of 10,000 W/m2-k, that were calculated in this study, agreed well with macrochannel scale heat transfer correlations. Cavities were used to successfully eliminate instabilities during saturated exit conditions. Also the dominant frequencies of the two-phase instabilities were found to range from 8-14 Hz causing the in-channel temperatures to fluctuate as much as 4oC.