A. Introduction

It is useful to divide condensing duties into two main types

1. Pure or single component vapors with negligible non-condensing gas. This usually leads to isothermal condensation. For completeness, we can include here the case of an azeotropic mixture of vapors which effectively behave as a singlecomponent vapor.
2. Non-azeotropic mixtures of vapors or vapor in the presence of no-condensing gas. The vapor in the latter case may be single component or a mixture. These cases usually lead to a fall in condensing temperature from the condenser inlet to the outlet.

B. Pure vapor Condensers

The design of this type is relatively simple particularly if the feed vapor is saturated and if no condensate subcooling is required. With a single-phase coolant (say, cooling water) the mean temperature difference (MTD) is simply the logarithmic mean temperature difference (LMTD) given by