Document jBME0aMLDxOaq6KvLvRNG0OQ2

454 CHAPTER 20 . 1950 Guide Tabu) 1. Obifice Catacihes fob Low Pbessubb Steam. Systems .This table is based on data from actual tots* Orifice Diameter 64ths of AN INCH 7 8 9 .10 11 12 13 14 15 16 1? 18 19 20 21 6 IN. Hg Differential 5 in. Hg Differential 4 in. Hg. Differential 2 in. Hg 1 in. Hg Differential Differential Capacity Expressed in Square Feet E D R 18-23 23-29 29-36 36-44 . 44-52 52-62 62-72 72-83 83-94 94-106 106-119 119-133 133-148 148-163 163-179 16-21 21-27 27-33 33-40 40-48 48-57 57-66 66-76 76-86 86-97 97-109 109-122 122-135 135-149 , 149-164 15-19 19-25 25-30 30^37 37-44 44-51: 51-59 59-67 67-76 76-86 86-97 97-108 108-120 120-133 133-145 10-13 13-17 17-21 21-26 26-31 31-37 37-43 43-49 49-56 56-64 64-72 72-80 80-88 88-98 98-107 8-11 11-14 14-17 17-20 20-24 24-28 28-32 32-37 37-42 42-47 47-52 52-58 58-64 64-71 Capacity Expressed in Ponnds per Hour 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 4.5-5.8 5.8-7.3 7.3-9.0 9.0-11.0 11.0-13.0 13.0-15.5 15.5-18.0 18.0-20.8 20.8-23.5 23.5-26.5 26.5-29.8 29.8-33.3 33.3-37.0 37.0-40.8 40.8-44.8 4.0-5.3 5.3-6.8 6.8-8.3 8.3-10.0 10.0-12.0 12.0-14.3 14.3-16.5. 16.5-19.0 19.0-21.5 21.5-24.3 24.3427.3 27.3450.5 30.5-33.8 33.8-37.3 37.3-41.0' 3.5-4.8 4.8-0.3 6.3-7.5 7.5-0.3 9.3-11.0 11.0-12.8 12.8-14.8 14.8-16.8 16.8-19.0 19.0-21.5 21.5-24.3 24.3-27.0 27.0-30.0 30.0-33.3 33.3 36.3 2.5-3.3 3.3-4.3 4.3-5.3 5.3-65 6.5-7.8 7.8-9.3 9.3-10.8 10.8-12.3 12.3-14.0 14.0-16.0 16.0-18.0 18.0-20.0 20.0-22.0 22.0-24.5 24.5-26.8 2.0-2.8 : 2.8-3.5 3.5-4.3 4.3-5.0 5.0-6.0 6.0-7.0 7.0-8.0 8.0-93 9.3-10.5 10.5-11.8 11.8-13.0 13.0-14.5 14.5-16.0 16.0-17.8 I ~ I ______ Note.--Hw radiator orifice {dates reooaameodod in this table are made of brass stampings 0.023 in. thick, cup-eFhlaopweodftoStbeeaminsTehrrteoduginh rOardifiiacetosrinvatolvReaudniiaotnosm. , by 8J3. Sanford and C. B`. Sprenger (AB.H.VJ3. Teans- AcnOOT, Vd. 87,1831, p. 871). ; rapid, uniform and without noise, and the release of air should be facili tated as much as possible, as an air bound system will not heat readily nor properly. In designing the piping arrangement it is desirable to maintain equivalent resistances in the supply'and return piping to and from a radiator. Arranging the piping so the total distance from the boiler to the radiator is the same as the return piping distance from the heating unit back to the boiler, tends to obtain such a result. The condensate which occurs in steam piping as well as in radiators must be drained to prevent impeding the ready flow of the steam and air. The effect of back pressure in the returns and excessive re-vaporization, such as occurs where condensate is released from pressures considerably higher than the vacuum or pressure in the return, must be avoided. It is important that steam piping systems distribute steam not only at full destpnload, but during excess and partial loads. Usually the average winter steam'demand is less than half of the demand at the design outside Steam Heating Systems and Piping 455 temperature. Moreover, in rapidly warming up a system even in moder ate weather, the load on the steam main and returns may exceed the maximum operating load for severe weather, due to the necessity of raising the temperature of the metal in the system to the steam temperature, ana the building to the design indoor temperature. Investigations of the return of condensate have revealed that as high as 143 per cent of the design condensation rate may exist under conditions of actual operation. The piping design of a heating system is greatly influenced by its operat ing characteristics. Heating systems do not operate under constant condi tions as conditions change continually, due to variation in load. As the system is being filled with steam, the pressures existing in various locations may be different from those which exist for appreciable periods at other locations, although , at equilibrium conditions the pressures are approximately the same. In designing piping it is of especial'importance to arrange the system to preclude trouble caused by such pressure dif ferences. The systems which readily release -the air, permit uniform pressures to be attained in much shorter time intervals than those which are sluggish. Results are given in Mg. 18 from investigations1 to deter; mine the rate of condensate and air return from a two-pipe gravity heating system. Variations in the steam pressure during the warming-up period; when the rate of air elimination and condensation is high, are clearly indicated in these curves. It is evident that the condensate flow during the initial warming-up period reaches a-peak, which is greater than the constant condensingrate eventually reached when the pressure becomes uniform. Moreover, the peak condensing rate is obtained when the system steam pressure is lower than that existing during a period of constant condensing rate. It will also be noted that the peak rate of air elimination does not coincide with the higher condensing rate. Steam Flow The rate- of flow of dry steam of steam with, a small amount of water flowing in- the same direction, is in accordance with the general laws of gas flow, and isafuhetion of the length,and diameter of the pipe, .the'density of the steam, and the pressure drop-through the pipe: -This relationship