Examination of the mass-heat transfer analogy for two-phase flows in narrow channels: Comparison of gas bubble enhancement of membrane separation and heat transfer to vapour bubbles in boiling

The analogy between heat and mass transfer is frequently employed in single-phase flows. Here the analogy is examined for two processes involving two-phase flow in meso-channels with bores ≤1 mm: the injection of gas bubbles to enhance the ultrafiltration of large molecules in aqueous solutions using hollow fibre membranes and flow boiling in the confined-bubble regime. This paper considers the local mechanisms in these superficially similar processes, based on information from experiments and numerical simulations and discusses the extent to which they are indeed similar. It is concluded that there is no useful analogy between mass and heat transfer in these processes but they share a requirement for accurate estimation of the thickness of the liquid film between confined bubbles and the channel wall at high Reynolds numbers.