Lateral motion of bubbles from surfaces with mini ratchet topography modifications during pool boiling- experiments and preliminary model

A means to passively effect liquid motion parallel to the surface through surface modifications is presented. The geometry considered is that of repeated array of silicon ratchets with reentrant cavities located on the shallow face of each ratchet. The surface is heated on the bottom side using a thin-film serpentine heater. Experiments were performed using deionized water at atmospheric pressures and subcoolings of 5°C and 20°C. High-speed videos were used to resolve bubble behavior near the surface. A preferential non-vertical bubble growth and departure direction was observed for both subcooling conditions. Tracking of bubbles was accomplished using a custom algorithm, which resolved instantaneous component of velocity of bubbles parallel to the surface in excess of 600 mm/s immediately following departure in the high subcooling condition. Mean horizontal component of velocities of bubbles farther from the surface, which were tracking the liquid velocity, were resolved in the range of 25 and 35 mm/s. A semi-empirical model based on bubble growth is presented to predict the observed liquid velocities.