Document LR2emBRgpq6ExdqERJ1Le0j3

854 CHAPTER 37 1956 Guide Table 3. Properties of Monofluobotrichlobomethane (CCIjF) Sat.. Temp. F Abb. Pbebs. Lb per Sq In. Volume . Liquid Vapor t Enthalpy and Entropy Taken From --40 F Enthalpy Entropy 25 F Superheat 50 F Superheat Liquid Vapor Liquid Vapor En thalpy En tropy En thalpy En tropy 0. ,6 10 15 20 25 30 35 40 -4550 55 60 65 70 75 80 85 90 95 100 105 2.59 0.01020 2.96 0.01024 3.38 0.01028 3.85 0.01032 4.36 0.01036 4.94 0.01040 5.57 0.01045 6.27 0.01049 7.03 0.01053 7.88 0.01057 8.79 0.01062 9.80 ' 0.01066 10.90 0.01071 12.10 0.01076 13.40 0.01081 14.80 0.01086 16.30 17.90 19.70 21.60 23.60 25.90 0.01091 0.01096 0.01101 0.01106 0.01111 0.01116 13.700 . 7.81 12.100 8.8110.700 9.82 9.530 10.80 .8.490 11.90. 7.580 12.90 90.4 91.2 92.0 92.8 93.7 94.5 6.770 13.90 6.080 14.90 5.460 16.00 4.920 17.00 . 4.440 18.10 95.3 96.1 96.8 97.6 98.4 4.020 19.10 99.2 3.640 20.20 100.0 3.300 21.30 . 100.8 3.000 22.40 101.5 2.740 23.50 102.2 2.500 2.280 2.090 1.918 1.761 1.620 24.50 102.9 25.60 103.6 26.70 104.4 27.80 105.1 28.90 : 105.7 30.10 106.4 0.0178 0.0200 0.0222 0.0243 0.0264 0.0286 0.0307 0.0328 0.0349 0.0370 0.0391 0.0412 0.0432 0.0453 0.0473 0.0493 0.0513 0.0533 0.0553 0.0573 0.0593 0.0613 0.1975 0.1974 0.1973 0.1971 0.1970 0.1969 0.1969 0.1968 0.1968 0.1967 0.1967 0.1967 0.1967 0.1967 0.1967 0.1967 0.1966 0.1966 0.1966 0.1966 0.1965 0.1965 93.9 94.7 95.5 96.3 97.2 98.0 98.8 99.6 . 100.3 . 101.1 101.9 102.7 103.5 104.3 105.0 105.7 106.4 107.1 107.9 108.6 109.2 109.9 0.2049 0.2047 0.2045 0.2043 0.2041 0.2039 0.2038 0.2037 0.2036 0.2035 0.2034 0.2033 0.2033 0.2032 0.2032 0.2031 0.2030 0.2029 0.2028 0.2028 0.2027 0.2026 97.4 97.2 99.0 99.8 100.7 101.5 102.3 103.1 103.8 104.6 105.4' 106.2 107.0 107.8 108.5 109.2 109.9 110.6 111.4 112.1 112.7 113.4 0.2120 0.2117 0.2114 0.2111 0.2109 0.2107 0.2105 0.2103 0.2101 0.2099 0.2098 0.2097 0.2096 0.2094 0.2093 0.2092 0.2090 0.2089 0.2088 0.2087 0.2085 0.2084 Values- of v, and Vd for use in Equation 4 can be obtained directly or by calculation from the tables of properties of refrigerants. By a reversal of this same procedure the tabular data can be used to determine the state of a mixture leaving an expansion valve. Consider a valve to which saturated liquid at pressure p, is admitted, and a mixture of saturated liquid and vapor at pressure Pd is discharged. The quality of the material at discharge is then determined by making use of the fact that the expansion process is completely irreversible, is a throttling process, and hence, occurs without change in enthalpy. Thus, the enthalpy of the mix ture, hm, is e'qual to the enthalpy of the saturated liquid at the entrance state, hi,, and can therefore be read from the table. Thus, ':. or, : Af. ha, ~ Avd (1 i) (Ayd Afj) (5) where " x -- (ha -- ha) 4- (Ayd -- ha) (6) Af. = enthalpy of saturated liquid at entrance to expansion valve. Am = enthalpy of mixture. Art = enthalpy of saturated vapor at discharge. Afd = enthalpy of liquid at discharge. x = proportion of liquid in the mixture, decimal. Vapor Compression Refrigeration Cycle Simple Cycle. The refrigerant cycle is the series of state changes (which occur in the conditioning processes) needed to restore the refrigerant to a condition in which it will possess the ability to extract heat from the space to be cooled. For all compression-type systems the cycle consists of four processes: heat gain in the evaporator; pressure rise in the compressor; Refrigeration 855 heat loss in the condenser; pressure loss in the expansion valve. The com pression process is accomplished at the expense of energy added to the compressor in the form of shaft work, and the expansion process could be carried out, if the economics of the system would permit, in an expanding engine with consequent release of energy as shaft work. In ordinary sys tems, however, the additional first cost and maintenance costs of an expand ing engine so greatly exceed the advantage resulting from the work realized, that such engines are not used, and the pressure reduction is allowed to occur irreversibly in an expansion valve. Basically, then, a refrigeration cycle consists of two heat transfer processes and two pressure change proc esses, no work entering into the heat transfer processes and--in the simple cycle--no heat transfer occurring during the pressure-change processes. The most common and least complicated type of refrigeration cycle is called the simple saturation cycle, and is shown diagrammatically in Fig. 3 and plotted upon pressure-enthalpy coordinates in Fig. 4. For this system, Heat of Compression Added to Gas saturated vapor flows without gain or loss of heat from the evaporator to the suction of the compressor. During passage through the compressor the energy added as shaft work goes entirely to increase the enthalpy of the refrigerant, and the compression process, which is assumed to occur irreversibly and without external heat transfer, is characterized by constant entropy. Thus, the state of the superheated vapor leaving the compressor can be determined from the tables of thermodynamic properties by noting the discharge pressure and fixing, also, the entropy of the saturated vapor at entrance to the compressor. Superheated vapor from the compressor flows to the condenser where de-superheating and condensation take place. From the condenser the re frigerant flows to the expansion valve, undergoes a constant-enthalpy pres sure reduction, and returns to the evaporator where it again removes a quantity of undesired heat. When the evaporator is arranged to permit direct cooling of room air by the refrigerant, the system is said to be of the direct expansion type, while a system in which the evaporating refrigerant cools water or brine, which in turn cools the air, is said to be indirect. Although many differences exist between most actual systems and that of the simple saturation cycle, this latter is, nonetheless, of great value in that it provides an extremely simple method of rapidly achieving an approximate