A. Introduction

The author would like to acknowledge the frequent use he has made of the previous article by D. Butterworth in HEDH in 1983. His material has been expanded to include many important developments in the understanding of mixed vapour condensation.

Over this period ever increasing reliance has been placed on proprietary, computerised design and rating programs. This being so, it is more necessary than ever for the design engineer to have a good understanding of the condensation process and the limitations of the design methods available to him.

Mixture condensation differs from pure vapour condensation in two ways. Firstly the temperature of the condensing process changes through the condenser, and secondly, mass transfer effects are introduced in addition to those of heat transfer.

Figure 1 shows a typical condensation, or cooling curve, for a mixture of vapours. It is a plot of saturation, or dew temperature, T_g^*, against specific enthalpy, h, and gives an approximation to the path followed by a condensation process through a condenser, (Section B).

, coolant temperature and pressure, , described in Section C(d). The formulation of the latter equation is outside the scope of this section but pressure drop is considered in for tubes and for shellside flow in tubular exchangers.

at = .