High Speed Imaging of Bubble Interface Motion in a Tapered Microgap

The current industrial trend requires development of efficient heat dissipation systems. A tapered microgap on the heater surface provides an efficient pool boiling heat transfer technique in dissipating large heat fluxes. This study is focused on capturing the high-speed images of bubble nucleation, growth and expansion processes. The interface velocities are estimated by tracking the interface of the growing bubble. The insight into interface motion will help in estimating the magnitude of the expanding force and predicting the pressure recovery effect during two-phase flow in the gap. The expansion force helps in establishing high flow rates resulting in high heat transfer coefficient (HTC) and critical heat flux (CHF) values. The effect of design parameters such as taper angle and height of the microgap on the bubble growth patterns are evaluated. The results show that the bubbles are nucleated and are then confined in the narrow gap. The tapered configuration propels the leading bubble interface in the flow direction and eventually the entire bubble in that direction. The bubble motion causes liquid to enter from the narrow region of the microgap. This effect, combined with the pressure recovery resulting from the two-phase flow in the expanding section of the microgap provides a bubble pumping mechanism. This configuration results in improving both the critical heat flux and heat transfer coefficient during pool boiling.