Document 7R0w4VqgZex140NK9jKXor5ng

456 Chapter 24 1945 Guide'.' -more surface isrequiredthanfotanyothertypeofcooler. However^with. large storage tanks'this type of cooling-can be utilized to advantage. When direct cooling of air is employed, the refrigerant is inside the coil and the air passes over it. Cooling depends upon convection and con duction for removing the heat from the air. The type bf coil, used can be either smooth or. finned, the finned coil being more economical in space Table 7. 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 per Square Inch per 100 Fib Line Sizes, Inches X X X IX ix m 2X 2X . 3X 3X 2.3 1.0 0.6 4.9 2.0 1.0 8.5 3.4 1.7 0.6 5.3 2.6 0.9 7.5 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 1.4 3.8 1.7 0.5 6.0 2.6 0.7 8.5 3.8 1.0 11.6 5.1 1.3 6.7 1.7 0.6 10.4 2.6 0.9 3.7 . 1.2 0.5 6.7 2.2 0.9 10.5 3.5 1.5 0.7 5.0 2.1 1.0 9.0 3.8 1.8 .5.8 2.9 9.5 4.4 6.4 11.3' Soft annealed copper tubing up to and including % in. outside diameter. Hard copper pipe % la* . outside diameter and larger. bLength of tubing includes the average number of fittings. requirement than the smooth coil. The fins, however, must be far enough apart so as not to retain the moisture which condenses out of the air. The indirect cooler, where brine is cooled by the refrigerant and the resulting co)d brine is used to cool either air or water, introduces several other considerations. It is not the most economical from a power con-i sumption standpoint, as it is necessary to cool the brine to a temperature sufficiently low so that there is an appreciable difference -between the average brine temperature and that .of the substance being cooled. This requires that the temperature of the refrigerant must be still lower, and consequently the amount of power required to produce a given amount of refrigeration increases due to the higher compression ratio. There are other considerations which make, such a system desirable. In the first place, where a toxic refrigerant is undesirable or cannot be used because of fire or other risks, especially in densely populated areas,, the brine can be cooled in an isolated room or building and . can then be circulated through the air conditioning equipment. This arrangement eliminates any possibility of direct contact between the air and refrigerant. - Refrigeration 457 REFRIGERANT-PIPE-SIZES The selection of proper, pipe sizes and frictional pressure losses varies with the installation and .the capacity of the system. Generally the suction piping should be selected so that the pressure loss is between\2 and ILlb per square inch. The pressure drop in liquid lines should be maintalhed' so as to permit no vaporization in the pipes with limiting Table 8. Pressure Losses in Dichlorodifluoromethane Liquid Refrigerant Lines \ Capacity Btu per Hour Pressure Drop in Pounds per Square Inch per 100 Fta Pipe Sizes. Inches. 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 * $00,000 000.000 1,200,000 1,400,000 1.600.000 1.800.000 2,000,000 2,200.000 X 0.6 0.9 1.3 1.8 2.3 2.9 3.6 4.3 5.1* 5.9 6.9 7.9 9.0 IX 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 IX 0.8 . 1.0 1.3 1.5 1.8 .2.4 3,1 3.9 4.7 6.7 9.0 IX 0.7 0.8 .1.1 1.4 1.7 2.1 3.0 4.0 5.1 6.3 7.9 9.2 Length of tubing includes the average number of fittings. pressure drops not to. exceed 5 lb per square inch. Hot or discharge gas lines should be limited, to approximately 4 lb per square inch pressure drop. All pressure drops mentioned are total system, losses and include ' not only the piping losses, but also the pressure losses in the valves, fittings and coils. Pressure drops for discharge or hot gas lines may be determined from Table 7. Pressure losses in liquid refrigerant lines of various sizes and capacities are-given in Table 8. Pressure drops of suction refrigerant pipe lines at varying capacities and refrigerant temperatures are given in Table 9.. Oil circulating with the refrigerant appreciably increases the pressure losses in both suction and discharge lines from that given in these tables. All tables are for 100 ft of pipe, including an average number of fittings, and for other lengths the losses are proportionate. Losses through control and regulating valves must be added to the other pipe losses to determine the total drop. All copper pipe referred to in these tables is of type L wall thickness and is designated by outside diameter. The effect'of the sizes of refrigerant lines on the system may be'studied