Intermediate thermodynamics

Property Diagrams for Propane and R134A

Prof. Patrick Lynch, MIE, UIC

For most refrigerants, the standard way of showing thermodynamic properties is by way of the pressure-enthalpy (P-h) diagram, where the y-axis is pressure (plotted in log scale), and the x-axis is specific enthalpy.

Lines of constant temperature and entropy are plotted there as well. Some plots also include density and/or specific volume isocurves. Rankine and inverse Rankine cycles (refrigeration cycles) are easy to plot with isobars, isenthalps, and isentropes.

It is not standard to plot T-s diagrams for refrigerants. One can use specialized software (some available online) to generate the contour lines for quality, enthalpy, pressure, density on such T-s diagrams; see plots in Figures 1 and 2 below that include isocurves, but no number labels. Additional resources may be found by scouring the literature, but this is beyond the scope of the present course and is left for a future exercise.

(See next pages)

Fig. 1: T-s diagram of propane.

Fig. 2: T-s diagram of Refrigerant 134A.