Numerical Prediction of Effect of Oxide Characteristics on Heterogeneous Nucleation of Bubbles in Aluminium Foaming

Abstract

Effects of oxide wettability, oxide surface cavities and cavity surface area-to-volume ratio on heterogeneous nucleation of bubbles in hydrogen supersaturated liquid aluminium foam precursor were studied. Increase in cavity surface area-to-volume ratio, oxide contact angle and cavity sharpness led to increase in cavity nucleation rate of bubbles. Oxides with lower contact angles required sharper cavities for nucleation to occur. A characteristic cavity angle exists for given oxide contact angle to make bubble nucleation feasible. A suitable combination of oxide contact angle and cavity angle were selected to estimate heterogeneous nucleation rates for different cavity surface areas and combined with bubble growth analysis to arrive at final bubble size distribution. The mean bubble size predicted numerically compared favourably with experimental observation on cell size of the foam.