Local shifts of the fluid composition in a simulated heat pump using R-407C

Because of the potential variation of the fluid composition, lots of designers are concerned by the use of zeotropic refrigerant mixtures in refrigeration and air-conditioning systems. In this paper, a local simulation model of a water-to-water heat pump is proposed by adopting a modular approach. Thus, the overall model consists of the association of an elementary model for each basic component, namely the compressor, condenser, evaporator and receiver. Implemented with a ternary zeotropic blend R-134a/R-125/R-32, the computer simulation, based on the mass and energy conservation laws, allowed to evaluate not only the overall performances of the simulated machine, but also the circulating composition of refrigerant, the local temperature and heat transfer coefficient along heat exchangers and the local composition of refrigerant in each point of refrigerating circuit. The numerical results show that, compared to the nominal composition of R-407C (R-134a/R-125/R-32; 52/25/23%), the circulating composition in the machine is low in the less volatile component R-134a (−3% absolute variation) and rich in the most volatile component R-32 (+3% absolute). In the regions of condensation beginning and evaporation end, the local composition is noticeably different from both the circulating and nominal compositions. In these regions, the local mass composition of R-134a increases (+4/+10% absolute) whereas the local mass composition of R-125 and R-32 are in deficit (−3/−6% absolute).