The effect of fluctuating pressure gradient on the coalescence of Taylor bubble

Abstract

The oscillatory coalescence phenomenon of the Taylor bubble flow subjected to the action of a fluctuating pressure gradient in a pulsating heat pipe was investigated using the front tracking method (FTM). The effects of amplitude and frequency of fluctuating pressure, bubble size, Reynolds number (Re), and Weber number (We) on the bubble coalescence process were studied. The results demonstrated that the lower the pulsation frequency, the longer the period of bubble oscillation, which could provide enough time for bubbles to drain and promoted the coalescence of the bubbles. The larger Euler number (Eu) was, the more easily bubbles coalesced. On the contrary, when Eu was small, the bubbles were slow to coalesce. The size of the top bubble and the bottom bubble had different effects on coalescence. An increase of the length of the top bubble (Lt) was beneficial to bubble coalescence while increasing the length of the bottom bubble (Lb) restrained bubble coalescence. Time required for bubble coalescence increased with the increase of Re and decreased with increasing We.