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Thermodynamic and Heat Transfer Implications of Working Fluid Mixtures in Rankine Cycles.

pdf icon Thermodynamic and Heat Transfer Implications of Working Fluid Mixtures in Rankine Cycles. (6895 K)
Radermacher, R.

International Journal of Heat and Fluid Flow, Vol. 10, No. 2, 90-102, June 1989.


fluids; heat pumps; mixtures; thermodynamic properties; thermodynamics; heat transfer; efficiency; tempeature; absorption; vapors; mass transfer


The theme of this article is to demonstrate the mutual influence of working fluid properties on the performance of Rankine cycles, heat transfer, and cycle variations. The limitations imposed on the traditional Rankine cycle inherent to the thermodynamics of pure fluids are described. Then, based on Gibbs' phase rule, the additional degree of freedom that is provided by a two-component working fluid mixture is introduced and its advantages and implications are discussed. The potential for efficiency improvement and capacity adjustment are detailed based on experimental results obtained with heat pumps. Further flexibility can be gained when the cycle is modified to allow for liquid sub-cooling and the introduction of a so-called solution circuit. With this component a large variety of vapor compression, absorption, and combined compression/absorption cycles becomes available, offering new solutions to old and new energy conversion applications such as heat pumping, heat transformation and power generation. New challenges arise from the fact that advanced cycles require very efficient heat and mass transfer surfaces and new heat transfer concepts. The situation is complicated by the nonlinear relationship between the amount of heat released per degree (during the phase change of the working fluid mixture) and the temperature change.