Characteristics of Microlayer Thickness Formed During Boiling in Microgaps

Experiments were performed to measure the thickness of the liquid film formed by growing flattened bubbles in microgaps with laser extinction method for gap sizes of 0.5, 0.3 and 0.15mm. Water, ethanol and toluene were used as working fluids. High-speed camera was also taken to measure the bubble growth process simultaneously. It was confirmed that the gap size and bubble forefront velocity determined the initial microlayer thickness. The variation trend of the microlayer thickness relative to the velocity of interface was divided into two regions: region I where the velocity is small and the thickness increases linearly with increasing velocity; region II where the thickness almost constant or decreased slightly. Furthermore, the non-dimensional correlation for investigating the effects of test materials and gap sizes on micro-layer thickness was presented. With result analysis, the boundaries of the two regions were at Weber number of 80 approximately. And at the region where Weber number was smaller than 80 the thickness of mirolayer was thinner for the liquid whose surface tension coefficient is relatively large. But for the region where Weber number was bigger than 80, the smaller kinematic viscosity of liquid is, the thinner thickness of microlayer became.