The Characteristics of Vapor-Compression Evaporators at Steady State (Report 1)

Abstract

We reach the well known conclusion that the coefficient of performance of vapor-compression evaporators becomes higher as the temperature difference in the heat-exchanger becomes smaller, if we consider the system to be an application of the inverse-Carnot cycle. However, when we take into account the condition that the steady state should be maintained under thermal equilibrium, we find that the coefficient of performance is not merely a function of the temperature difference alone. The authors have studied the effectes of "relative heat transfer number", "supplied energy coefficient" or "coefficient of heat supply", "extraction ratio", effectiveness of the preheater, rise of the boiling point of the solution and so forth upon the thermal equilibrium and the coefficient of performance of evaporators, and clarified the steady state characteristics of vapor-compression evaporators under the condition of thermal equilibrium. The diagrams showing the effects of the above stated factors are given in this paper. The "relative heat transfer number" is a dimensionless one newly introduced by one of the authors and it represents the characteristic feature of vapor-compression evaporators regardless of their geometrical dimensions. The authors believe that the diagrams shown in the paper are of use for the design as well as for the choice of operating conditions of this kind of evaporators.