Document Lp9rG4vjZgKmGmqmVzR6VG7Xb

1 838 CHAPTER 37 1953 Guide condenser. These losses result in a greater compression ratio, and therefore greater power requirements, as well as a lower volumetric efficiency and higher displacement requirements. Pressure losses in the liquid line between condenser or receiver and the expansion valve may result,in some flashing of the liquid refrigerant, unless the liquid is subcooled. In all cases, frictional losses should be kept to a minimum, and piping should be selected which will give the smallest loss consistent with overall economy in the system. 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 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 Table 5. Fbeon-12 Liquid Lines, Tons Capacity peb 100 Ft Equivalent Length Pbessube Dbop peb 100 Ft Equivalent Length, Psi * 3 5 10 20 fOD I OD 4 IPS f OD 1 IPS f OD 1 IPS H OD li IPS If OD 1 IPS If OD 2 IPS 24 IPS 3 IPS 34 IPS 4 IPS 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. L14 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. 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. 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 psi 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 tbe operating pressure range. Since return of the oil to the compressor must be considered in the case of Freon and methyl chloride, for these refrigerants the minimum velocity should be 500 fpm 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 839 '"Table 6. Maximum Tons of Compbessob. Capacity fob Fbeon-12'Lines:-: ... (Only for temperatures indicated) i;:. . . Line Size, Inches 4 OD i IPS 5 I OD 4 IPS OD 13 IPS 14 OD 1 IPS Suction.Lines Based on 105 F Condensing Temperatube Pei Pressure Drop per 100 Ft Equivalent Length at 40 F Saturation i 1 2 .3 - 4 , 0.14 0.17 0.25 0.35 0.20 0.24 0.35 0.45 0.28 0.34 0.51 0.65 0.35 0.42 0.62 0.79 0.41 0.49 0.73 0.93 0.55 0.68 1.26 1.43 0.76 1.10 0.94 1.35 1.80 . 2.57 2.01 V 2.89 1.34 1.65 3.17 3.54 1.58 1.92 3.76 4.17 Discharge Lines Condensing Temperature 5 . 116 F' 1 90F 0.45 0.54 0.81 1.03 1.43 1.87 1.15 1.60 1.75 2.12 4.15 4.60 2.97 3.26 5.05 '5.29 2.38 2.62 4.05 4.25 If OD li IPS if OD 14 IPS 24 OD 2 IPS 2f OD 24 IPS 3f OD 3 IPS 3f OD 34 IPS 44 OD 4 IPS 5 IPS 6 IPS 8 IPS 10 IPS 12 IPS 2.21 2.70 3.40 4.05 3.12 3.82 4.78 5.75 4.45 5.37 6.79 8.10 5.50 6.72 8.42 10.12 6.38 7.68 9.77 11.6 7.05 8.48 10.8 12.8 . 7.72 9.16 10.92 12.5 6.19 7.35 8.75 10.0 6.12 7.66 12.0 12.0 8.60 10.9 17.1 17.1 12.1 15.3 24.0 24.0 15.1 19.2 30.1 30.1 17.4 32.2 34.6 34.6 19.2 24.5 38.2 38.2 19.2 20.6 32.2 32.2 15.3 16.5 25.9 25.9 19.1 20.9 27.8 30.2 27.2 29.4 39.7 43.2 38.2 42.3 55.7 61.0 47.8 51.8 69.8 76.1 55.0 60.0 80.3 87.0 60.7 .66.2 88.7 96.0 51.5 54.5 72.0 78.8 39.8 43.8 57.6 63.3 38.6 55.-2 78.0 97.3 111 123 95.8 77.1 40.7 58.6 83.0 103 118 130 101.6 81.6 71.3 100 141 176 203 224 171.5 137.8 126 183 257 . 322 366 403 266 214 211 297 422 523 602 664 461 370 352 503 712 887 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 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 5, 6 and 7 are published in ACRMA Equipment Standards-1946, of the Air Con ditioning and Refrigerating Machinery Association, and are used by permis- Table 7. Appboximate Suction-line Capacity Factobs fob Equal Pbessube Dbop of Fbeon-12 Satubated Suction Temperatube, F. 60 40 30 20 10 0 -10 -20 Factor......................................... 1.09 1.00 0.92 0.86 0.80 0.74 0.66 0.56