. Power, heating and ventilation ... a treatise for designing and constructing engineers, architects and students . can Radiator Company, is shown in Fig. 153. This isconstructed especially for hot-blast work and is made up of sec-tions with projecting hollow pins for increasing the radiatingsurface and for breaking up the air currents as they pass betweenthe sections. Heaters of this type are made in three sizes, asfollows: the 40-inch section, containing lll^ square feet of sur-face; the 50-inch section, containing 14 square feet; and the 60-inch section, containing 17 square feet. FORCED BL
. Power, heating and ventilation ... a treatise for designing and constructing engineers, architects and students . can Radiator Company, is shown in Fig. 153. This isconstructed especially for hot-blast work and is made up of sec-tions with projecting hollow pins for increasing the radiatingsurface and for breaking up the air currents as they pass betweenthe sections. Heaters of this type are made in three sizes, asfollows: the 40-inch section, containing lll^ square feet of sur-face; the 50-inch section, containing 14 square feet; and the 60-inch section, containing 17 square feet. FORCED BLAST HEATING AND VENTILATION 221 Table LIV, gives working data relating to this type of heater. Efficiency of Pipe Heaters.—The efficiency of the heaters usedin connection with force blast varies greatly, depending upon thetemperature of the entering air, its velocity between the,pipes,the temperature to which it is raised and the steam pressure car-ried in the heater. The general method in which the sectionsare made up is also an important factor. The ordinary form of pipe heater is so constructed that about. Fig. 153. Vento Cast Iron Heater. • of the over-all or gross area is free for the passage of air;that is, a heater 6 feet wide by 7 feet high will have a grossarea of 6X7^ 42 square feet, and a free area between thepipes of 42 X 0-4 = square feet. The allowable velocity of air flow through a heater of thistype commonly runs from 800 to 1500 feet per minute; the lowervelocities applying to general ventilating work, as in schools and•churches and the higher, to factory heating. The final temper-ature to which the air will be raised, in any given case, dependsupon the depth of the heater, or number of rows of pipe whichit contains. For example, under certain conditions, air enter- 222 HEATING AND VENTILATING PLANTS ing a 4-row heater at zero will have a final temperature of 4,3°,while if the depth of heater is increased to 16 rows, the finaltemperature will bec
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