Void Fraction Variations in a Fractal-Like Branching MicroChannel Network

摘要

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 μm into a 38.1 mm diameter silicon disk. A Pyrex~® 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 μm to 400 μm 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 glmin at a fixed inlet fluid temperature of 88℃. 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.