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Table A2 Pressure ratios for CO2, propane and some HFCs at various evaporation and condensation temperatures (RnLib, 2003). Appendix A – CO2 as a Working Fluid in Heat Pumps T0 TC -10°C 35oC -10°C 50oC 0°C 35oC CO2 3.4 (9 MPa) 4.2 (11 MPa) 2.6 (9MPa) R-290 R-407C 3.6 4.2 5.0 6.2 2.6 2.9 R-410A R-134a 3.7 4.4 5.3 6.6 2.7 3.0 3.8 4.5 0°C 50oC 3.2(11MPa) 3.6 4.3 Süss and Kruse (1998) concluded that the heat transfer and pressure losses in reciprocating CO2 compressors have a negligible influence on the volu- metric and isentropic efficiencies due to the low pressure ratio, and that internal leakages caused by the considerable pressure differentials could be reduced to a low level by means of appropriate design. Pettersen and Aarlien (1997) found that a reciprocating car air-conditio- ning CO2 compressor typically obtained 10 to 15 percentage points higher isentropic efficiency than an R-134a compressor at equal operating condi- tions. Tadano et al. (2000), Yanagisawa and Fukuta (2000), and Hubacher and Groll (2002) demonstrated by means of measurements the superior performance of several types of CO2 compressors for residential use. A1.6 Heat Exchanger Performance Pressure Drop CO2 has a considerably steeper saturation pressure curve than that of the commonly used working fluids. Figure A3 shows the slope of the satu- ration pressure curve (∂T/∂p) for CO2, propane and selected HFCs. As a result, the optimum mass flow rate in CO2 heat exchangers will be higher than that of equipment designed for propane or HFCs. Evaporation Table A3 shows thermophysical properties for CO2, propane and selected HFCs that are important for the convective evaporation and nucleate boiling processes (RnLib, 2003). The data are presented as average relative values for the temperature range from -10 to +10oC, and CO2 is the reference (=1.0). Since the data are provided for a 20 K temperature span they should only be regarded as approximate values. A5PDF Image | Residential CO2 Heat Pump System for Combined
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