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HVAC System Overview and Refrigerant Design 143 table 9.8 Performance comparison of co 2 and r-134a at various states state/variables r134a co 2 (r-744) state 1 Pressure (bar) 2.28 29.09 Temperature (°C) −6.7 −6.7 Enthalpy (kJ/kg) 246.76 738.79 Latent heat (kJ/kg) 204.8 249.95 Entropy (kJ/kg K) 0.934078 3.99821 Volume (m 3 /kg) 0.088029 0.0126485 state 2 Pressure (bar) 12.81 130 Temperature (°C) 54.4 104.4 Enthalpy (kJ/kg) 282.35 796.86 Entropy (kJ/kg K) 0.934078 3.99821 Volume (m 3 /kg) 0.01649 0.0041827 state 3 Pressure (bar) 12.81 130 Temperature (°C) 48.9 26.7 Enthalpy (kJ/kg) 121.581 559.2 Entropy (kJ/kg K) 0.24211 3.230048 Volume (m 3 /kg) 0.0009032 0.0012006 state 4 Pressure (bar) 2.28 29.09 Temperature (°C) −6.7 −6.7 Enthalpy (kJ/kg) 121.581 559.2 Entropy (kJ/kg K) 0.2593667 3.288624 Volume (m 3 /kg) 0.000034533 0.0042816 Refrigeration effect (h1 – h4) (kJ/kg) 125.18 179.59 Cooling capacity (kW) 5.275 5.275 Ref. flow rate (kg/h) 151.58 107.2 Compressor work (kW) 1.5 1.824 Compressor capacity/volume ref. flow (kW/m 3 ) 2318.33 19761.2 Compressor disp. of CO 2 with respect to R134a 1 8.52 Energy efficiency ratio (Btu/h W) 12 9.87 Condenser/cooler specific heat rejection (kJ/kg) 160.77 179.59 Condenser/cooler heat rejection (kW) 6.8 7.1 Coefficient of performance (COP) 3.52 3.09 Source: Goodbane, M. SAE Paper 1999-01-084, 1999. With permission.
144 The Role of the Chemist in Automotive Design TXV Heat Out: Vehicle Exterior Interior Condenser Underhood Compartment Evaporator Gas Cooler Heat In Work In Compressor FIgure 9.5 Diagram of traditional refrigerant and CO 2 system. Temperature 1 to 2 = Compression of vapor 2 to 3 = Vapor superheat removed in condenser 3 to 4 = Vapor converted to liquid in condenser 4 to 5 = Liquid flashes into liquid + vapor across expansion valve 5 to 1 = Liquid + vapor converted to all vapor in evaporator Saturated liquid 4 5 Liquid + Vapor FIgure 9.6 Vapor compression cycle. Entropy Heat Exchanger This cycle is typically expressed in a temperature–entropy diagram called a vapor compression cycle. Figure 9.6 illustrates this cycle. A CO 2 system operates slightly differently and requires an outside loop. The deviation is because CO 2 operates in the transcritical mode at typical ambient conditions (as mentioned earlier) and requires much higher pressures than a typical refrigerant system. Above the critical temperature (T c), distinct liquid and gas phases do not exist. Properties between the two phases are the same as one approaches this temperature. Above T c, a liquid cannot be formed; however, a solid can be formed with enough pressure. The T c for CO 2 is 31.1°C, whereas a typical system with R134a refrigerant is 101°C. In automotive applications, condensing in a refrigeration cycle takes place at around 38–60°C. Because of this, the condenser used in typical applications is replaced by a gas cooler that rejects heat. 3 2 1 Superheated vapor Saturated vapor
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THE ROLE OF THE CHEMIST IN AUTOMOTI
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CRC Press Taylor & Francis Group 60
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Contents Preface...................
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Contents ix 6.6 Thermal Properties
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Contents xi 11.4 Glass Microspheres
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The Author Herman Phlegm was born i
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3 3.1 IntroductIon Component Materi
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Component Materials in Automobiles
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6 6.1 IntroductIon Engineering Poly
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Engineering and Structural Polymers
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Page 110: Engineering and Structural Polymers
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