Theoretical estimation of the isobaric heat capacity cp of refrigerant

Based on theory of equation of state and residual function method, a theoretical development for estimating the isobaric heat capacity cp of refrigerant is carried out. Regarding cp as a derived thermodynamic property, then according to the general relation of the thermodynamics, two formulas for calculating cp of real fluid are derived from cubic Peng–Robinson equation of state (P-REoS) and modificatory Martin–Hou equation of state (M-H81EoS). Ten pure refrigerants and four mixed refrigerants are chosen to make detailed numerical calculation and theoretical analysis. A wide comparison with experimental data is made, a conclusion can be drawn that in vapor-phase region, the estimation precision is about 3% for both equation modelings; while in liquid-phase region, M-H81EoS modeling has predominance with an estimation precision of less than 10%. Moreover, comparison of cp values between estimated ones and that derived from popular REFPROP software is also conducted, the distribution of cp along with temperature are investigated for vapor and liquid phase respectively. The results show that all cp values present a monotonically increasing trend with temperature.