. Applied thermodynamics for engineers. ^ esti-mated in one case thatthe reduction in air con-sumption due to the in-crease of volume shouldhave been, theoretically,; actually, it was mechanical efficiency(Art. 214) of the engineis improved by the use ofpreheated air. Inone instance, Ken-nedy computed asaving of 225 cu. ft. of/rce air ( air at at-mospheric pressure and tem-perature) to have been ef-fected at an expenditureof lb. of coke. Unwinfound that all of the airused by a 72-hp. enginecould be heated to 300° 15 lb. of coke per 58 represents amodern fo
. Applied thermodynamics for engineers. ^ esti-mated in one case thatthe reduction in air con-sumption due to the in-crease of volume shouldhave been, theoretically,; actually, it was mechanical efficiency(Art. 214) of the engineis improved by the use ofpreheated air. Inone instance, Ken-nedy computed asaving of 225 cu. ft. of/rce air ( air at at-mospheric pressure and tem-perature) to have been ef-fected at an expenditureof lb. of coke. Unwinfound that all of the airused by a 72-hp. enginecould be heated to 300° 15 lb. of coke per 58 represents amodern form of preheater. Fig. 58. Art. 1«7.—Raud Air PreheaUT,. no APPLIED THERMODYNAMICS 188. Volume of Cylinder. If n be the number of single strokes peiminute of a double-acting engine, V the cylinder volume (maximum vol-ume of fluid), W the number of pounds of air used per minute, t; thespecific volume of the air at its lowest pressure p and its temperaturet, N the horse power of the engine, and U the work done in foot-poundsper pound of air, then, ignoring clearance (the space between the pistonand the cyhnder head at the end of the stroke), the volume swept tthrough by the piston per mmute = Wv =nV = WR—; whence P ^, WRt , . ™^, Txr 33000iV ^^ 3S000NRt V= ; and smce TFf/ = 33,000iV, T7 = —^r—; and V = -—^r np U - nUp 189. Compressive Cycle. For quiet running, as well as for otherreasons, to be discussed later, it is desirable to arrange the valvemovements so that some air is gradually compressed into the clear-ance space during the latter part of the return stroke, as along Ea^Fig. 57. This is accomplished by causing the
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