Boiling in narrow channels

Abstract

An experimental and theoretical study of the phenomena involved during boiling in narrow channels is presented. The channels are of a small size typical of those in the new micro-compact heat exchangers. Correlations and design methods used in the design of conventionally sized evaporators are summarised and the literature covering boiling in confined spaces is reviewed. It is shown that the published data are insufficient to allow the design of novel compact evaporators incorporating narrow channels to be undertaken with confidence. A dimensionless criterion for determining the channel size at which the effects of confinement are likely to be significant for different fluids has been derived. It has been demonstrated that the flow in narrow channels can be divided into three flow regimes; Isolated Bubble, Confined Bubble and Annular-Slug Flow. A new model has been proposed which allows the prediction of evaporative heat transfer coefficients in each regime and this model has been tested against the Author's and other measured data. A fair degree of corroboration was achieved and it is argued that the model yields a thermal design methodology for narrow channel evaporators.