A. Introduction

The author would like to acknowledge the use he has made of the previous article in HEDH, written by R. Sardesai in 1983. However a significant change in approach has been adopted and the present article has been written as a consistent extension to Section 186. Section 186, Webb and McNaught (1980) and Webb (1990) should be read as pre-cursors to the present article.

The formation of a second immiscible condensate phase during condensation can affect the behaviour in a number of ways and reliable design should account for the possibility. Firstly various modes of condensation may occur. Thus it is possible for a single phase condensate to be formed. Vapours, which will form the other phase, act as non-condensing species imposing a greater gas-side resistance. Secondly when both liquid condensates are present the nature of the flow pattern will influence the condensate film heat transfer coefficient.

The various modes of heat transfer which are possible may be identified by consideration of the phase diagram, Figure 1, which applies for the case of mixtures which may be considered fully immiscible as liquids. The state of the mixture may lie in any of the four regions of the diagram, vapour, two-phase with liquid 1 present, two-phase with liquid 2 present or all liquid. Vapour-liquid equilibrium states with liquid 1 and 2 occur along FE and EG respectively, with the azeotrope at E, where vapour and both liquid phases co-exist at equilibrium.