The effects of internal energy transfers on power cycle efficiency

This paper discusses the effects that the internal energy transfers have on the efficiency of a closed condensing nonflow through transcritical power cycle with staged heat input. The cycle uses a combined solvent and solid solute as its working fluid. The differential in excess enthalpies of solution between the cycle’s subcritical liquid range at its i0836-1398-28-1-115-T2 and supercritical fluid range near its i0836-1398-28-1-115-T1 causes an internal temperature elevation of input heat. The effect on cycle efficiency produced by kinetic energy transferred from molecular translation to potential during gas to liquid phase change at the cycle’s i0836-1398-28-1-115-T2 is discussed. Variations in the solvent’s enthalpy change though the supercritical region is shown to be an accurate predictor of the density at which retrograde solubility initiates. Methanol and ferrocene are used in the cycle to demonstrate the impossible demand of the second law that positive excess enthalpies for solid solutes must be higher in low-density supercritical fluids beyond the retrograde region than in the subcritical liquid range.