Horizontal chain coalescence of bubbles in saturated pool boiling on a thin foil

Wall temperatures were measured by high-speed IR thermography during the sequential chain coalescence of bubbles from four nucleation sites in 4 ms to form a single large hovering bubble during pool boiling of water at atmospheric pressure on an electrically-heated titanium foil 25 μm thick. Interactions between bubbles before and during coalescence were significantly affected by asymmetries in bubble growth rate or size, and by the thermal response of the thin wall to previous heat transfer. Liquid was redistributed over the contact area of a coalesced bubble, maintaining heat transfer. Outward movement of the shared wall contact line at the instant of horizontal coalescence of two attached bubbles caused localized increases in wall heat flux but continuing oscillations following coalescence and during declining coalescence between an attached bubble and a detached bubble did not affect the wall heat flux in these studies. During the contraction of the contact area leading to detachment, there was a reduction in heat flux at the contact line and sometimes a reversal in heat flux at the contact line.