Heat Transfer Engineering, Vol.28, No.10, 806-816, 2007
Void fraction variations in a fractal-like branching microchannel network
Based on predictions of lower pressure drop penalties in fractal- like branching channels compared to parallel channels, an experimental investigation of two- phase void fraction variations was performed. The flow network, mimicking flow networks found in nature, was designed with a self- similar bifurcating channel configuration and etched 150 mu m into a 38.1 mm diameter silicon disk. A Pyrex (R) cover was anodically bonded to the silicon disk to allow for flow visualization. The length and width scale ratios between channels on either side of a bifurcation are fixed. The channel widths range in size from 100 mu m to 400 mu m over a total channel length of approximately 17 mm. Experimental results of flow boiling are presented for a heater energy input power of 66 W and an inlet water flow rate of 45 g/min at a fixed inlet fluid temperature of 88 degrees C. High- speed, high-resolution imaging was used to visualize the flow and quantify void fraction values in several channels within a branching structure. Both time- averaged and instantaneous two- dimensional void fraction data are presented, showing a correlation between channels at the same bifurcation level and between channels at different bifurcation levels.