Investigation of nanofluid bubble characteristics under non-equilibrium conditions

We report experimental and theoretical investigations of the bubble characteristics during the oscillatory growth period for several nanofluids. The nanoparticles were found to affect liquid–gas and solid surface tensions, which modulated the bubble contact angle, radius of triple line, bubble volume and the dynamics of bubble growth. To increase the accuracy of the Young–Laplace equation predictions during the bubble growth in the oscillatory period, a new method multi-section bubble (MSB) approach was developed. In this method, the bubble was divided into n sections (i.e., n = 1:N) and the Young–Laplace equation was solved for each section individually. As N increases, within each section the effects of inertia force and viscosity become reduced comparing to that of the liquid-gas surface tension. Unlike the conventional Young–Laplace approach (i.e., N = 1), the new approach is able to predict the bubble characteristics reliably in the following cases: (a) the oscillatory period when bubble is fluctuating; (b) the departure period when bubble is stretched upward, right before departure; and (c) the high shear stress condition when gas velocity is relatively high.