Visualization research on confined bubble growth feature and heat transfer characteristic in ultra-shallow micro channel

Visualization study on flow boiling in ultra-shallow (aspect ratio = 0.2) micro channels have been conducted under various operating conditions. The confined bubble behaviors are explored in detail with high-quality photos. Different from the traditional classifications on the growth process of the confined bubbles, an interesting but rationally new dividing criterion is proposed here, which is based on not only the objective bubble dynamics, but also the variations of the heat transfer mechanism. Two innovative definitions turning point and transition stage are put forward for the first time, and their features are studied more thoroughly. In addition, the influences of the operating conditions on the bubble dynamics and the heat transfer characteristics have been summarized. The enhancement of heat transfer in ultra-shallow micro channels requires more harsh terms to be achieved, which brings about the risk of Departure from Nucleate Boiling (DNB) and Premature Critical Heat Flux (PCHF), dramatically reducing the heat transfer capability. Contents in present work help fill the gaps in the experimental research on the micro channels with extreme aspect ratios, and further guide the related utilization. (C) 2016 Elsevier Ltd. All rights reserved.