Comparative study of the performance of three- and four-parameter correlation equations for the temperature dependence of the enthalpy of vaporization for pure substance refrigerants

A few commonly used correlation equations of the enthalpy of vaporization which is essential to the analysis of refrigeration cycles are reviewed. A new four-parameter correlation equation is proposed assuming that the enthalpy of vaporization could be represented by a function having a linear term to the temperature and an additional term which slowly decreases as the temperature increases. It is not a common practice to measure the enthalpy of vaporization by experiment; therefore, performance of the new correlation equation for the temperature dependence of the enthalpy of vaporization is examined using numeric data from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) tables for 22 pure substance refrigerants. The new correlation equation and other existing ones are fitted to the data optimizing the root mean squared deviation. All data points are weighted equally and NBP (normal boiling point) is used as a fixed point since the NBP is important for refrigeration applications. The new four-parameter equation yields an average absolute deviation of 0.05% for 22 refrigerants which is smaller than those of other four-parameter equations, such as Guermouche–Vergaund (0.08%), Aerebrot (0.13%), Radoz–Lyderson (0.08%), and Somayajulu four-parameter equation (0.08%).After the optimization, it is found that a specific exponent in the new equation has approximately the same value for almost every substance tested so that the original four-parameter correlation could be reduced to a three-parameter one. The new three parameter correlation yields an average absolute deviation of 0.14% for the same 22 refrigerants, which also is smaller than those of other three-parameter correlations, such as Xiang (0.18%), Majer–Svoboda–Pick (0.18%), and Somayajulu three-parameter equation (0.27%).