Forced convective boiling of binary mixtures in annular flow. Part I: liquid phase mass transport

This is the first part of a paper devoted to the description of forced convective boiling of binary mixtures at high qualities. Here, a model for droplet interchange (entrainment and deposition) in the annular flow regime in vertical pipes is presented. This is based on the set of correlations proposed by Govan et al. (A.H. Govan, G.F. Hewitt, D.G. Owen, T.R. Bott, in: Proceedings of the Second UK National Heat Transfer Conference, Institution of Mechanical Engineers, London, UK, 1988, p. 33) for pure fluids. It is shown that interaction of droplet entrainment, deposition and transport give rise to a local discrepancy between mean concentrations of the liquid film and entrained droplets. Also, the results reveal the importance of the initial entrained fraction (amount of liquid entrained as droplets at the onset of annular flow); variation of this parameter influences the downstream distributions of concentration in both liquid streams. The detailed analysis for heat and mass transfer is discussed in the second part of the paper.