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