Fast Calculation Model Of Thermodynamic And Transport Properties Of CO₂

As people pay more and more attention to environment problem, the replacement of Freon has become more urgent. Among all the alternative refrigerant, natural refrigerant, especially CO2 has arouse great attention by the industry. As the critical temperature of CO2 is low, the refrigeration cycle is transcritical. So it needs to establish the fast calculation model of thermodynamic and transport properties both in subcritical and supercritical region for the convenience of system simulation.In system simulation, explicit calculation model can avoid iteration and improve the speed of simulaiton greatly. This paper gives two methods to establish explicit fast calculation model of thermal properties as follows: enthalpy, entropy, density, heat capacity, sonic speed, viscosity, thermal conducticity and surface tension. First, based on rational fraction approximation, a uniform fast calcultion model for all the properties is presented. It’s convenient in cases of simulation of refrigeration system for its uniform expression; second, establish different model for different thermal properties. Use equation of state to calculate the thermal properties which can be calculated explicitly, and seek new relational expressions to calculate the thermal properties which can’t be calculated explicitly.This paper establish fast calculation model of thermal properties of CO2 by curve-fitting based on great amount of data. The accuracy is good and the speed of fast calculation model is one to four orders faster than those of the precisive models.