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.