Boiling heat transfer and two-phase flow of water in a single shallow microchannel with a uniform or diverging cross section

TLDR

The study compares boiling heat transfer and two‑phase flow of water in shallow uniform‑ and diverging‑cross‑section microchannels with a 0.183° divergence. Experiments were performed on 20‑µm‑deep microchannels with a 33.3‑µm hydraulic diameter to examine how geometry influences boiling, and empirical convective‑boiling correlations were derived for each geometry. Slug bubbles grew exponentially in both geometries, but the diverging channel achieved superior boiling heat transfer because of more stable two‑phase flow; it also exhibited a higher single‑phase pressure drop, while two‑phase pressure drops were similar at equal heat flux.

Abstract

The present work investigates and compares boiling heat transfer and two-phase flow of water in a single shallow uniform-cross-section microchannel and a diverging one with a diverging angle of 0.183°. Both types of microchannel are with a depth of about 20 µm and a mean hydraulic diameter of about 33.3 µm. Experiments are conducted to study the effect of channel geometry on boiling heat transfer in the microchannel. It is found that the slug bubbles tend to grow exponentially in the present shallow microchannels, uniform-cross section or diverging. The results reveal that the diverging microchannel presents better performance in boiling heat transfer than that of the uniform-cross-section one, primarily due to more stable two-phase flow in the diverging microchannel. Empirical correlations based on convective boiling are developed, respectively, for both types of microchannel. For the same mass flow rate, the diverging microchannel presents a higher single-phase flow pressure drop, while the two-phase flow in both types of channel shows approximately the same pressure drop for boiling at the same heat flux.