An analytical expression in terms of temperature only for optimizing the flash cycle for geothermal power plants

Abstract

A method is described to express the efficiency η and the specific power output W of a vapour flash power plant by a function of the given cycle terminal temperatures and of the flash temperature regarded as a variable. The method depends on the facts that (a) enthalpy is conserved during the flashing process, (b) dryness fractions can be expressed in terms of saturation entropies or enthalpies and (c) the expansion end enthalpy can be expressed in terms of saturation entropies and latent enthalpy. Because saturation enthalpies and entropies and also latent enthalpy can each be expressed algebraically in terms of the flash temperature alone, expressions may be found for η and W which do not require reference to the Steam Tables and are therefore well suited for computer use. The method is explained for both the single- and double-flash cycle. An example is worked out for the single-flash cycle using crude approximations for purposes of illustration. The method can be invested with any degree of accuracy required.