The introduction of water into a gas turbine circuit is known to provide benefits of increased efficiency and specific work output. There are several methods of humidification but the use of a pressurised saturator in an evaporative cycle offers many attractive features. This two-part paper presents an in-depth study of the saturator, in Part 1 via a thermodynamic approach and in Part 2 via a heat and mass transfer analysis. In Part 1, the pinch condition is shown to be the key reference state and an analytical expression is obtained for the pinch variables. Saturators with a given pinch condition form a family whose members have the same pressure, flow and enthalpy invariants. Each member has different outlet conditions which can be found computationally or analytically. The analytical approach gives insight into the effects of parameter changes. Minimisation of the entropy production rate is considered and the paper includes discussion on constraints on the operation of saturators and problems of scaling.

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