Ventilation and heating : principles and application a treatise / B.F. Sturtevant Co.

Date:
[1896]
Catalogue details

Licence: Public Domain Mark

Credit: Ventilation and heating : principles and application a treatise / B.F. Sturtevant Co. Source: Wellcome Collection.

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    steam will, upon the condensation of that steam, reappear as available for heat- ing. The standard unit of heat is equivalent to the amount of heat necessary to raise the temperature of one pound of water through one degree Fahrenheit at its point of greatest density. A heat unit is not to be confounded with a degree of temperature, notwithstanding the fact the visible temperature of water, as expressed in degrees, and the total heat, as stated in heat units, are indicated by very nearly the same figures (see Table No. 3), the variation being due to the altered density of the water. If, therefore, one heat unit will raise the temperature of one pound of water through one degree under stated conditions, 890.69 units — given out by the condensation of one pound of steam of 86 pounds pressure — will heat 890.69 pounds of water through one degree. Allowing for the difference in specific heat, this same heat expenditure would result in raising the temperature of 890.69 X 4.2034 = 3,743.926 pounds of air through one degree. Supposing the air to be originally at a temperature of 320, then, if dry, its weight per cubic foot would be .0807 pounds (column 3, Table No. 1), and 3,743-926 pounds would be equivalent to Mffo¥- = 46,393 cubic feet. Upon this basis Table No. 4 has been calculated, it being assumed that the water of condensation is not cooled below the temperature of the steam from which it is condensed. The amount of heat that would thus increase the temperature of the volume of air through one degree would raise the temperature of half the amount through twice as many degrees, and so on in like proportion, so far as the unitial difference between the temperature of the air and of the steam will permit. As an illustration of the application of Table No. 4, suppose it is desired to heat 500,000 cubic feet of dry air from 320 to 92°, or through an increment of 60°, with steam of 75 pounds absolute pressure. By Table No. 4 it is seen that one pound of steam at the given pressure will raise 46,736 cubic feet of air at 320 through one degree, and consequently -W~= 778.93 cubic feet through 60°. To heat 500,000 cubic feet through 60° there will, therefore, be required 7T¥°II = 641.9 pounds of steam. Of course, it must be evident from the preced- ing that calculation has only been made of the amount of heat directly applied for heating. If the water of condensation can be returned to the boiler without material reduction of temperature, there need be but little loss in this direction; but where it is thrown away, as is frequently the case with exhaust steam, the total heat expenditure for producing the steam from the feed water at its initial temperature must be made the basis of calculation. The horizontal column at the bottom of the table indicates that the presence of vapor in the air, even to saturation, has but slight effect upon the values at low or moderate temperatures. 29 *
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