Document ORY5NbnjnjadZwm6bdObk2mL

496 CHAPTER 39 1946 Guide Table 8. Pressure Losses in Dichlorodifluoromethane Discharge or Hot Gas Lines3 bLcngth of tubing includes the average number of fittings. requiring double suction risers, one large and one small. The large riser should be trapped to insure oil return while the small riser should be sized for a velocity of 3,000 fpm at minimum load; and the large riser then sized to handle the balance of the load at a velocity not less than 2,000 fpm. The total pressure loss in the suction piping, including valve losses, is usually between 2 and 3 psi while hot gas line losses are held to approximately 4 psi and liquid line losses are not greater than 5 psi. As protection against re-condensation on the cylinder head of the compressor, a surge drum is sometimes installed' in the discharge line close to the compressor; this protection is especially desirable on systems using evaporative condensers where sun effect during shut-down may be serious. The Steam Jet Srstem The steam jet system under certain circumstances is desirable for use in air conditioning *. Steam supplies directly the power used for com pressing the refrigerant, thus eliminating the losses connected with other methods of supplying energy.. As the compression ratio between the evaporator and condenser under normal circumstances is large, the mechanical efficiency of the equipment is somewhat lower than that of the positive mechanical type compressor. The condensing water require ments are considerably greater, as both the refrigerant and the impelling steam must be condensed. Refrigeration 697 Table 9. Pressure Losses in Dichlorodifluoromethane Liquid Refrigerant Likes 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 Fra Pipe Sizes. Inches H m 1H lH 0.6 0.9 1.3 1.8 2.3 0.6 2.9 0.8 3.6 1.0 4.3 1.2 5.1 1.4 5.9 1.6 6.9 1.8 7.9 2.1 9.0 2.3 0.8 2.9 1.0 3.5 1.3 4.3 1.5 5.0 1.8 6.7 2.4 8.7 3.1 3.9 0.7 0.8 1.1 1.4 1.7 4.7 2.1 6.7 3.0 9.0 4.0 5.1 6.3 7.9 9.2 "Length of tubing indudes the average number of fittings. The steam jet system functions on the principle that water under high vacuum will vaporize at low temperatures. Steam jet boosters or com pressors of the type commonly used in power plants for various processes will produce the necessary low absolute pressure to cause evaporation of the water. A diagrammatic representation of a typical steam ejector water cooling system is shown in Fig. 2. The figures correspond to an average repre sentative system. The water to be cooled enters the evaporator and is cooled to a temperature corresponding to the vacuum maintained. Because of the high vacuum, a small amount of the water introduced in the evaporator is flashed into steam. As this requires heat, and the only source of heat is the rest of the water in the evaporator tank, this other water is almost instantly cooled to a temperature corresponding to the boiling point determined by the vacuum maintained. The amount of water flashed into steam is a small percentage of the total water circu lated through the evaporator, amounting to approximately li lb per hour per ton of refrigeration developed. The remainder of the water at the desired low temperature is pumped out of the evaporator and used at the point where it is required. The ejector compresses the vapor which has been flashed in the evapor ator, plus any.entrained air taken from the circulated water, to a some what higher absolute pressure and the vapor and air mix with the impel-