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700 . CHAPTER 39 1948 Guide > Table 8. Pressure Losses in Dichlorodifluoromethane Discharge or Hot Gas Lines Capacity ... Btu per Hour' -- 10.000 . 15.000 20.000 25.000 30,000 40.000 . 50.000 60.000 70.000 80,000 . 90.000 100.000 125.000 150,000 175,000 200.000 250.000 300.000 400.000 500,000 600.000 ,800.000 1 000.000 1.250.000 1.500.000 .2,000,000 Pressure Drop in Pounds pes Square Inch per 100 Frb '' '' Line Sizes,. Inches ' K -K 2.3 1.0 4.9 2.0 8.5 3.4 5.3 7.5 K IK IK IK 2K ,2K 0.6 1.0 1.7 0.6 2.6 0.9 3.6 1.2 0.5 6.4 . 2.1 0.7 9.8 3.1 1.0 0.5 4.4 1.3 0.7 6.0 1.9 0.9 8.0 2,5 1.1 10.2 3.1 3.8 . 6.0 8.5 11.6 1.4 1.7 ' 0.5 2.6 0.7 3.8 1.0 5.1 . 1.3 6.7 10.4 1.7 2.6 . 3.7 6.7 10.5 0.6 0.9 1.2 2.2' 3.5 5.0 9.0 3K; 3K 0.5 0:9 1.5 0.7 2.1 1.0 3.8 1.8 5.8 2.9 9.5 4.4 6.4 11.3 "Soft annealed copper tubing up to and Iwrinrftng outside diameter and larger. in. outside diameter. Hard copper pipe ^Length of tubing includes the average number of. fittings. in. Compound Compression Cycles In large systems the compression process can be carried out in steps as the refrigerant passes through a number of cylinder ends arranged for operation in' series. Thermodynamically the advantage of compound compression arises from the fact that intercoolers can be placed between the stages of compression to extract heat from the vapor and thereby cause the over-all compression process to more closely approach the ideal condition of isothermal compression. Essentially, such, intercoolers-- whether of. the water or the flash refrigerant type-^serve the same purpose as a cooling jacket, but--with-greater effectiveness because of the more satisfactory heat,transfer conditions. Multiple Expansion Valves In the simple saturation cycle the saturated liquid entering the ex pansion valve commences to vaporize as soon as its pressure starts to drop. The vapor produced during the expansion process has no further use, in terms of refrigerating effect, since it has already picked up its latent heat of vaporization as a result of heat which it has extracted from' the urivaporized residue. Thus the instant such vapor forms, its usefulness is at an end, and to allow such material to undergo a further drop in pressure is uneconomical. Unfortunately, however, there is ho effective means-of extracting vapor continuously during the expansion Refrigeration 701 Table 9. Pressure Losses in Dichlorodifluoromethane Liquid Refrigerant Lines Capacity Btu per Hour 100.000 125.000 150.000 175.000 200.000 225,000 250.000 275.000 300,000 325,000 350.000 375.000 400.000 450.000 500.000 550.000 600.000 700.000 800.000 900,000 1,000.000 1,200.000 ` 1,400,000 1.600.000 1.800.000 2.000.000 2,200,000 ' Pressure Drop in Pounds per Square Inch per 100 Ftr Pipe Sizes. Inches - - K 0.6 0.9 ... 1.3 1.8 2.3 2.9 . 3.6 4.3 5.1 5.9 . 0.9 7.9 9.0 TH 0.6 0.8 1.0 1.2 1.4 1.6. 1.8 2.1 2.3 2.9 3.5 4.3 5.0 6.7 8.7 IK IK *; 0.8 ; 1.0 1.3 1.5 1.8 2.4 3.1 3.9 4.7 6.7 9.0 0.7 0.8 1.1 1.4 1.7 2.1 3.0 4.0 5.1 6.3 7.9 9.2 - aLength of tubing includes the average number of fittings. and re-compressing it. Thus in the simple cycle the. flash vapor must ' necessarily be allowed to drop to evaporator pressure. When a compound compression cycle is used there is at least one inter mediate pressure at which flash vapor can be extracted. In such cases all refrigerant from the condenser can be dropped through a first expansion valve to the higher suction pressure and the flash vapor then extracted and returned to the compressor. Some of the resultant liquid refrigerant then passes through the high-pressure evaporator while, the remainder proceeds through a second expansion valve in which its pressure is drop ped to the valve corresponding to the low-pressure evaporator. ` Pipe Sizes and Friction Losses Tjie effect on performance'of pressure losses in the piping of a refrigerat ing system has already been discussed. In all cases frictional losses shouldbe kept to a minimum and piping should be selected which'will give the' smallest loss, consistent with over-all economy of the system. Actual losses vary, of course, with the physical characteristics of the particular refrigerants, but, by way of. example, data1 will be given for one of the refrigerants, dichlorodifluoromethane (Frl2) which finds wide use in.air conditioning applications. Tables 8, 9, and 10 give the pressure loss per 100 ft of piping (including an average number of- fittings) for oil-free dichlorodifluoromethane;