The effective thermal energy density of R134a subjected to an isobaric or isochoric process is determined and evaluated in the two-phase and supercritical regimes. The results are qualitatively extended to other fluids via the principle of corresponding states. It is shown that substantial increases in volumetric energy density can be realized in the critical region for isobaric processes. Also, for isobaric processes which utilize the full enthalpy of vaporization at a given pressure, there exists a pressure at which the volumetric energy density is a maximum. For isochoric processes (supercritical and two-phase), it is found that there is no appreciable increase in volumetric energy density over sensible liquid heat storage; the effective specific heat can be enhanced in the two-phase, isochoric regime, but only with a significant reduction in volumetric energy density.

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