Shellside evaporation in a TEMA E-shell: flow patterns and transitions

The paper describes some results from a research programme to study forced flow shellside boiling in a TEMA E-type shell and tube heat exchanger. It focuses on the particular issue of the effect of apparent transitions in the two-phase flow pattern. The results from the programme show a drop in the heat transfer performance at lower mass fluxes and higher vapour qualities. The sudden drop in performance may be caused by a change in the two-phase flow pattern on the shellside from a homogeneous type to a stratified type of flow with separation of the liquid and vapour phases. Support for this conclusion is that the transition in heat transfer performance appears to coincide with a change in the behaviour of the measured two-phase pressure drop multiplier. A model is described which allows for the effects of separated flow and also attempts to predict the apparent transition in the two-phase flow pattern.