Document jgJ7wEZMV32pK7k0GrpXbqqn2

878 CHAPTER 37 1955 Gwa. - ' -A condenser. These losses result in a greater compression ratio, and therefore^ greater power requirements, as well as a lower volumetric efficiency higher displacement requirements. Pressure losses in the liquid list between condenser or receiver and the expansion-valve may result in soft!' flashing of the liquid refrigerant, unless the liquid is subcooled. . Int-aff cases, frictional losses should be kept to a minimum, and piping should be selected which will give the smallest loss consistent with overall economy - iri the system. ,T.,, Refrigerant liquid lines from the receiver to the expansion valve should be preferably designed with a pressure drop of less than 5 psi, and with io 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 Table 5. Freon-12 Liquid Lines, Tons Capacity per 100 Ft Equivalent Length Line Size, Inches iOD i OD i IPS f OD i IPS i OD 1 IPS li OD U IPS l|OD 11 IPS 1! OD 2 IPS 21 IPS 3 IPS 31 IPS 4 IPS Pressure Drop peb 100 Ft Equivalent Length, Psi 3 0.88 2.89 4.86 4.86 9.73 10.5 21.4 21.4 36.9 36.9 62.0 62.0 124. 230. 364. 539. 753. 5 1.14 3.64 6.81 6.81 12.6 14.1 28.2 28.2 48.1 48.1 80.2 80.2 161. 297. 469. 704. 972. 10 1.80 5.56 10.2 10.2 18.5 21.8 41.3 41.3 70.5 70.5 114. 114. 231. 426. 676. 1005. 1385. 20 2.58 8.50 15.8 15.8 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- 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 Freon-12, 0.51 p per foot for Freon-22, and 0.64 psi per foot for Freon-11. Where there is a possibility of vaporization of some of the liquid before reaching the ex pansion 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 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 oi to the compressor must be considered in the case of Freon and methyl chloride, for these refrigerants the minimum velocity should be 500 fp for horizontal runs and 1000 fpm for vertical runs. For the Freons, the usual design velocities range between 1000 and 2000 fpm. Too high velocities create noise problems and excessive pressure drops. The total Refrigeration 879 Table 6. Maximum Tons of Compressor Capacity for Freon-12 Lines (Only for temperatures indicated) Line Size Inches i OD IPS 5 OD A 3 IPS 1 OD 3 IPS 4 OD 1 IPS it OD H IPS H OD i IPS 21 OD 2 IPS 2f OD 21 IPS 31 OD 3 IPS 31 OD 31 IPS 41 OD 4 IPS 5 IPS 6 IPS s IPS !0 IPS 12 IPS Suction Lines Based on 105 F Condensing Temperature Discharge Lines Psi Pressure Drop per 100 Ft Equivalent Length at 40 F Saturation Condensing Temperature i 2 3 4 5 115 F 80 F 0.14 0.20 0.28 0.35 0.41 0.45 0.17 0.24 0.34 0.42 0.49 0.54 0.25 0.35 0.51 0.62 0.73 0.81 1.42 1.15 0.35 0.45 0.65 0.79 0.93 1.03 1.87 1.50 0.55 0.76 1.10 1.34 1.58 1.75 2.97 2.38 0.68 0.94 1.35 1.65 1.92 2.12 3.26 2.62 1.26 1.80 2.57i 3.17 3.76 4.15 5.05 4.05 1.43 2.01 2.89 3.54 4.17 4.60 5.29 4.25 2.21 3.12 4.45 5.50 6.38 7.05 7.72 6.19 2.70 3.82 5.37 6.72 7.68 8.48 9.16 7.35 3:40 4.78 6.79 8.42 9.77 10.8 10.92 8.75 4.05 5.75 8.10 10.12 11.6 12.8 12.5 10.0 6.12 8.60 12.1 15.1 17.4 19.2 19.2 15.3 7.66 10.9 15.3 19.2 32.2 24.5 20.6 16.5 12.0 .17.1 24.0 30.1 34.6 38.2 32.2 25.9 12.0 17.1 24.0 30.1 34.6 38.2 32.2 25.9 19.1 27.2 38.2 47.8 55.0 60.7 51.5 39.8 20.9 29.4 42.3 51.8 60.0 66.2 54.5 43.8 27.8 39.7 55.7 69.8 80.3 88.7 72.0 57.6 30.2 43.2 61.0 76.1 87.0 96.0 78.8 63.3 38.6 40.7 71.3 126 55.2 58.6 ICO 183 78.0 83.0 141 257 97.3 103 176 322 111 118 2C3 366 123 95.8 77.1 130 : 101.6 SI.6 224 171.5 137.8 403 266 214 211 297 422 523 602 664 461 370 352 503 712 887 1024 1130 725 582 550 780 1106 1373 1582 1748 1041 836 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 rom 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 PS1 's recommended for the discharge lines. Extensive tables are available in the literature for the determination of pressure drops through refrigerant mes with various refrigerants. The capacities listed in Tables 5, 6 5. ' ,are published in ARI Equipment Standards-1946, of the Air- ondihoning and Refrigeration Institute, and are used by permission. T* able 7. Approximate Suction-line Capacity Factors for Equal Pressure ---____ Drop of Freon-12 Saturated Suction Temperature, F. factor. | 50 1 40 I 30 I 1.00 j 0.92 20 0.86 10 0.80 0 0.74 -10 I -20 j 0.66 | 0.56