Document Qx41MZvjOX7r5qmv22x2eZVL

.854 CHAPTER 37 1955 Guide #' Table 3. Properties of Monofluorotrichloromethane (F-ll) Sat. Temp. F- Abb. T'eess. Lb peb Sq In. Volume Enthaut and Entbopt Taken Fbom --40 K Enthalpy Entropy -- .25 F Superheat 50 F Superheat Liquid Vapor Liquid .Vapor Liquid Vapor En thalpy En En tropy : thalpy En tropy 6 ' 6- " 10 15 ' 20 25 2.59 0.01020 2.96 0.01024 3.38 0.01028 3.85 0.01032. 4.36 . 0.01036 4:94 0.01040 13.700 12.100 10.700 9.530 8.490 7.580 7.81 8.81 9.82 10.80 11.90 12.90 90.4 91.2 92.0 92.8 93.7 94.5 0.0178 -0.0200 0.0222 0.0243 0.0264 0.0286 0.1975 0.1974 0.1973 0.1971 0.1970 0.1969 93.9 94.7 95.5 96.3 97.2 98.0 ' 30 : 35` 40; L c.45 i . 50? 5.57 6.27 7.03 7.88 . 8.79 V 0.01045 0.01049 0.01053 0.01057 0.01062 6.770 6.080 5.460 4.920 4.440 13.90 14.90 16.00 17.00 18.10 95.3 ' 96.1 96.8 . 97.6 .98.4 0.0307 0.0328 0.0349 0.0370 0.0391 0.1969 0.1968 .0.1968 0.1967 0.1967 98.8 99.6 100.3 101.1 101.9 55 60 65 ' 70 '76 . 9.80 : 10.90 12.10 13.40 14:80 0.01066 0.01071 0.01076 0.01081 0.01086 4.020 3.640 3.300 : 3.000. 2.740 19.10 20.20 21.30 22.40 23.60t 99^2 100.0 . 100.8 101.5 102.2 0.0412 0.0432 0.0453 0.0473 0.0493 0.1987 0.1967 0.1967 0.1967 0.1967 102.7 103.5 104.3 105.0 105.7 80 85 90 - 95 ,100 , - 105 16.30 17.90 19.70 2L60 23.60. 25.90 0.01091 ' 0.01096 0:01101 0.01106 0.01111 0.01116 2.500 2.280 2.090! 1.918. 1.761 1.620 24.50 25.60,, 26.70., 27.80 28.90 30.10 102.9 103.6 104.4 105.1 105.7 106.4 0.0513 0.0533 0.0553 0.0573 0.0593 0.0613 0.1966 0.1966 0.1966 0.1966 0.1965 0.1965 106.4 107.1 107.9 108.6 109.2 109.9 0.2049 0.2047 0.2045 0.2043 0.2041 0.2039 97.4 : 97.2 99-0 99.8 100.7 101.5 0.2120 0.2117 0.2114 0.2111 0.2109 0.2107 0.2038 0.2037 0.2036 0.2035 0.2034 102.3 103.1 103.8 104.6 105.4 0.2105 0.2103 0.2101 0.2099 0.2098 0.2033 0.2033 0.2032 0.2032 0.2031 106.2 107.0 107.8 108.5 109.2 0.2097 0.2096 0.2094 0.2093 0.2092 0.2030 0.2029 0.2028 0.2028 0.2027 0.2028 109.9 110.6 111.4 112.1 112.7 113.4 0.2090 0.2089 0.2088 0.2087 0.2085 0.2084 . Values of v, and t>d 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, Am, is equal to the enthalpy of the saturated liquid at the entrance state, h!a, and can therefore be read from the table. Thus, T, ;. t[> -- Am -- Avd (1 3.) (A.J Afd) (5) X' -- (Am Afd) -1" (llvd Afd) -shere hi, = enthalpy of saturated liquid at entrance to expansion valve. hm = enthalpy of mixture. h,i =: enthalpy of saturated vapor at discharge. Aid = enthalpy of liquid at discharge. > * = 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 t^n j-6 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 ^-superheating and condensation take place. From the condenser the rengerant 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 rect cooling of room air by the refrigerant, the system is said to be of the sponsion type, while a system in which the evaporating refrigerant Alfk Wa^r or brine, which in turn cools the air, is said to be indirect. hough many differences exist between most actual systems and that of it n Slm.^e saturation cycle, this latter is, nonetheless, of great value in that Provides an extremely simple method of rapidly achieving an approximate