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As Internal Heat eXchanger (IHX) applications become more numerous for R-134a, and because they will likely become standard with R-1234yf, a detailed look at how they influence system parameters becomes necessary. This paper uses a proprietary air-conditioning system model to evaluate the system impact of three different IHX co-axial geometries. The three IHX cross-sections result in different heat transfer and pressure drops per unit length. The model assumes a 1,000mm suction line, including an IHX whose length is varied from 200mm to 800mm, in 100mm increments.

A low-pressure CO2-based climate-control system has the environmental benefits of CO2 refrigerant but avoids the extremely high pressures of the transcritical CO2 cycle. In the new cycle, a liquid “cofluid” is circulated in tandem with the CO2, with absorption and desorption of CO2 from solution replacing condensation/gas cooling and evaporation of pure CO2. This work compares the theoretical performance of the cycle using two candidate cofluids: N-methyl-2-pyrrolidone and acetone. The optimal coefficient of performance (COP) and refrigeration capacity are discussed in terms of characteristics of the CO2-cofluid mixture. Thermodynamic functions are determined either from an activity coefficient model or using the Soave equation of state, with close agreement between the two approaches. Reductions in COP due to nonideal compressor and heat exchangers are also estimated.