Document ykkQ8VGBDoG0wp7rGBZg497K4

948 CHAPTER 36 1958 Guide / he preferably designed with a pressure drop of less than 5 psi, and with 10 psi as the maximum. A velocity of 100 to 250 fpm is recommended to prevent a pressure drop great enough to cause vaporization of the refriger ant ahead of the expansion valve. If the evaporator is to be located at a higher elevation than the condenser or receiver, account should be taken of the pressure drop for each foot of static liquid lift. Approximate values are 0.26 psi per foot for ammonia, 0.57 psi per foot for dichlorodifluoromethane, 0.51 psi per foot for monochlorodifluoromethane, and 0.64 psi per foot for monofluorotrichloromethane. Where there is a possibility of va porization of some of the liquid before reaching the expansion valves, means for subcooling should be provided. Since a reduction of suction pressure at the compressor results in an appreciable reduction in capacity and more power input per ton of refrigera- Table 6. Dichlorodifluoromethane* (CCIjFj) Liquid Lines, Tons Capacity per 100 Ft Equivalent Length Line Size. Inches Pressure Drop per 100 Ft Equivalent Length, Psi 3 5 10 20 HOD HOD HIPS HOD H IPS H IPS Hod 1 IPS 1HOD IH IPS 1H OD 1H1PS IHOD 2 IPS 2H IPS 3 IPS m ips 4 IPS 0.88 2.89 4.86 4.86 9.73 9.73 10.5 21.4 21.4 36.9 36.9 62.0 62.0 124. 230. 364. 539. 753. 1.14 3.64 6.81 6.81 12.6 12.6 14.1 28.2 28.2 48.1 48.1 80.2 80.2 161. 297. 469. 704. 972. 1.80 5.56 10.2 10.2 18.5 18.5 21.8 41.3 41.3 70.5 70.5 114. 114. 231. 426. _ 676. 1005. 1385. - 2.58 8.50 15.8 15.8 27.0 27.0 33.0 60.8 60.8 101. 101. 160. 160. 328. 607. 972. 1430. 1945. Note: Tonnage values above those underlined give velocities of 300 fpm or less. a Refrigerant 12. tion, great care should be given to the proper sizing of suction lines between the evaporator and the compressor. Although comparatively high veloci ties, 500 to 5000 fpm, may be used, the optimum value will depend upon the refrigerant and the operating pressure range. Since return of the oil to the compressor must be considered in the case of the fluorinated hydro carbons and methyl chloride, for these refrigerants the minimum velocity should be 500 fpm for horizontal runs and 1000 fpm for vertical runs. For the former, the usual design velocities range between 1000 and 2000 fpm. Too high velocities create noise problems and excessive pressure drops The total pressure drop in the suction line should be between one and two psi, if the velocity can be kept to within the specified limits. Compressor discharge or hot gas lines may be designed with velocities from 1000 to 5000 fpm, except for dense gases such as carbon dioxide, where noise considerations will reduce the upper limit. A pressure drop of 2 to 4 psi is recommended for the discharge lines. Extensive tables are available in the literature for the determination of pressure drops through refrigerant lines with various refrigerants. The capacities listed in Tables 6, < and 8 are published in ARI Equipment Standards-1946, of the AirConditioning and Refrigeration Institute, and are used by permission. Refrigeration 949 Table 7. Maximum Tons of Compressor Capacity for CCIjP'j Lines* (Only for temperatures indicated) Line Size Inches Suction Lines Based on 105 F Condensing Temperature Psi Pressure Drop per 100 Ft Equivalent Length at 40 F Saturation i i 2345 Discharge Lines Condensing Temperature 115 F 90 F' . H OD H IPS H OD H IPS HOD y* ips 1WOD 1 IPS moD m ips moD 1H IPS 2H OD 2 IPS 2H OD 2H IPS ZH OD 3 IPS ZH OD ZH IPS 4HOD 4 IPS 5 IPS 6 IPS 8 IPS 10 IPS 12 IPS 0.14 0.17 0.25 0.35 0.55 0.68 1.26 1.43 2.21 2.70 3.40 4.05 6.12 7.66 12.0 12.0 19.1 20.9 27.8 30.2 38.6 40.7 71.3 126 211 352 550 8 Refrigerant 12. 0.20 0.24 0.35 0.45 0.76 0.94 1.80 2.01 3.12 3.82 4.78 5.75 8.60 10.9 17.1 17.1 27.2 29.4 39.7 43.2 55.2 58.6 100 183 297 503 780 0.28 0.34 0.51 0.65 1.10 1.35 2.57 2.89 4.45 5>37 6.79 8.10 12.1 15.3 24.0 24.0 38.2 42.3 55.7 61.0 78.0 83.0 141 257 422 712 1106 0.35 0.42 0.62 0.79 1.34 1.65 3.17 3.54 5.50 6.72 8.42 10.12 15.1 19.2 30.1 30.1 47.8 51.8 69.8 76.1 97.3 103 176 322 523 887 1373 0.41 0.49 0.73 0.93 1.58 1.92 3.76 4.17 6.38 7.68 9.77 11.6 17.4 32.2 34.6 34.6 55.0 60.0 80.3 87.0 111 118 203 366 602 1024 1582 0.45 0.54 0.81 1.03 1.75 2.12 4.15 4.60 7.05 8.48 10.8 12.8 19.2 24.5 38.2 38.2 . 60.7 66.2 88.7 96.0 123 130 224 403 664 1130 1748 1.43 1.87 2.97 3.26 5.05 5.29 7.72 9.16 10.92 12.5 19.2 20.6 32.2 32.2 51.5 54.5 72.0 78.8 95.8 101.6 171.5 266 461 725 1041 1.15 1.50 2.38 2.62 4.05 4.25 6.19 7.35 8.75 10.0 15.3 16.5 25.9 25.9 39.8 43.8 57.6 63.3 77.1 81.6 137.8 214 370 582 836 Table 6 shows the tonnage capacity normally allowed for CC12F2 liquid lines per foot equivalent length of pipe, and Table 7 the maximum tonnage for suction and discharge CC12F2 lines. Table 8 presents suc tion-line capacity factors for equal pressure drop. ACCESSORIES Dehydrators, oil separators, strainers, vibration eliminators, sight glasses, and various types of valves are accessories frequently needed for the proper installation and operation of refrigeration systems. Refrigerant-line de hydrators or dryers usually consist of copper containers fitted with tubing connections at either end, and contain a desiccant such as silica gel, acti vated alumina, or calcium chloride. The liquid refrigerant is circulated through the dryer during operation of the system, and the moisture content 01 m re'r*Serant charge is thus kept to a minimum. Oil separators are installed between the compressor and condenser to Prevent excessive oil removal from the compressor crankcase and its passage Table 8. Approximate Suction-line Capacity Factors for Equal Pressure Drop of CCLF, (Refrigerant 12) Saturated Suction Temperature, F. 50 40 30 20 10 0 . -10 Factor.......... 1.09 1.00 0.92 0.86 0.80 0.74 0.66