A METHODOLOGY TO COMPARE REFRIGERANTS BASED ON THEIR THERMOPHYSICAL PROPERTIES

Resumen

To compare different refrigerants in a fair way has been always a matter of discusión. There are some properties like Isoentropic COP, volumetric capacities, pressure ratio that can be compared easily and supply some relevant information. However, how they are translated into real systems is not so direct. For instance, isentropic COP is obtained under the assumption that all the refrigerants are able to work in the same condensing and evaporating temperatures, but these variables depend on the temperature lift of the secondary fluid and in real systems, they will not be the same. The size of the heat exchangers and, hence, the cost depend on heat transfer coefficients and pressure drop, and extrapolating this data in a straightforward way is not easy; even the required refrigerant charge is not easy to determine.

In this work, the authors propose a methodology to compare different refrigerants based on the external operating conditions, the approach compares the system performance not only in terms of efficiency parameters but also in term of operation map, size and cost of the system and refrigerant charge. To do that, a basic modelling approach has been developed based on quite extended correlations for heat transfer coefficient, pressure drop and void fraction in the heat exchangers. The developed methodology does not pretend to be an exact design guide but a guide that researchers and students can use to estimate qualitatively the differences among refrigerants