Thermodynamic Correlations, k – Exponents, Speed of Sound, and COP Data for Binary Refrigerant Mixtures

Abstract

Our study covers thermodynamic performance quantities for binary refrigerant mixtures of R-32/R-134a with compositions of 20/80%, 30/70%, 40/60% by mass for a wide range of thermodynamic conditions (pressure: 0.2 - 3.0 MPa, temperature: 240 - 480 oK and saturated conditions). The primary thrust of the study is the calculation of coefficient of performance (COP) values for refrigeration systems. Additional attention is also given to speed of sound data and to isentropic process changes.

The relevant COPs are derived based on a simplified reference refrigeration cycle with one stage compression and throttling, saturated vapor and no liquid sub-cooling prior to the throttling valve. The COP values are given for various condensing and evaporating temperatures. For all calculations, a Peng – Robinson type equation of state is used to determine the necessary fluid properties. The enthalpy, entropy, and constant-pressure and constant-volume specific heats as well as the k-type isentropic change exponents are presented for all mixtures for the range of thermodynamics conditions listed above. Comparisons are made illustrating the influence of pressure and temperature on the k-type exponents kp,v, kT,v, and kp,T, and on the ratio of specific heats k (k = cp/cv). Furthermore, graphs with speed of sound data for this extended range of conditions are also given.

Keywords

• R-32/R-134a mixtures
• enthalpy
• entropy
• constant-pressure and constant-volume specific heats
• isentropic exponents
• coefficient of performance
• speed of sound