TECHNICAL PAPER Prediction of Bubble Size Distribution in Aluminium Foam as a Function of %Titanium Hydride Addition S.N. Sahu 1 • A.A. Gokhale 2 • Anurag Mehra 3 Received: 28 September 2016 / Accepted: 25 November 2016 Ó The Indian Institute of Metals - IIM 2016 Abstract Foaming of liquid aluminium by addition of foaming agent (TiH 2 particles) is numerically simulated using population balance equations. Phenomena such as hydrogen release by the TiH 2 particles, heterogeneous nucleation of bubbles in oxide surface cavities, and diffu- sion based bubble growth are modelled. A simple mass transfer coefficient, which varies inversely with the bubble size is used to estimate the bubble growth rate. Simulation is performed to study the effect of TiH 2 content on the final bubble size distribution, total number of bubbles and average bubble size. In general, the average properties of the predicted distributions are close to the experimental values, whereas the spread in the bubble size is observed to be considerably narrower for the predicted values. The deviation in the spread of the distributions is attributed to the inverse bubble size dependent growth rate and non- inclusion of bubble coalescence in the model. Keywords Aluminium foam  Nucleation  Growth  Population balance  Bubble size distribution 1 Introduction Closed cell aluminium foams display attractive combina- tion of functional and structural properties owing to their unique structure. Several routes exist to manufacture these foams, viz., direct foaming route, where liquid metal is foamed e.g., Alporas, Cymat etc. and indirect foaming route, where powder compact precursor is melted and foamed e.g., FOAMINAL, Alulight etc. Foams prepared from these routes have varying cell morphologies and distributions as each process gets stabilised by a separate mechanism and controlling parameters. From foam product design point of view, good control over process parameters and thorough understanding about the stabilisation mech- anisms is necessary. Though few research attempts in this direction are reported in the literature, they are insufficient and limited to some specific processes. Hence, the subject still remains as an important area of research in order to improve cell structural characteristics. Among various foam making processes, the ‘Alporas’ process as described in Miyoshi et al. [1], is based on liquid metallurgy route and is suitable for commercial production. In the ‘Alporas’process, the TiH 2 particles are dispersed in the melt, which immediately liberates hydrogen gas lead- ing to the formation of bubbles and foam expansion. Though a number of experimental studies on the ‘Alporas’ process describing the effect of process parameters on cell structure are found in the literature, theoretical treatments of foaming are relatively scarce. The current study is an attempt to investigate the ‘Alporas’ process by suit- able theoretical formulations and validate the findings with experimental data. It is worth mentioning here that unlike metallic foaming, the aqueous and polymer foaming sys- tems are extensively investigated and the phenomena such as foam stabilization, drainage and bubble coarsening are & S.N. Sahu snsahu2002@gmail.com 1 Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India 2 Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India 3 Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India 123 Trans Indian Inst Met DOI 10.1007/s12666-016-1020-7