. The steam-engine and other heat-motors. the heater per hour;Ts = temperature of steam to be condensed (at constant pres-sure) ;h = temperature of the hot liquid (if other than steam) at any point;hx and tht are initial and final temperatures of the hot fluid;te = temperature of the cold fluid at any point;tei and tc2 are initial and final temperatures of the cold fluid;th — tc = the difference in degrees F. between the hot and cold fluid at any Mean Temperature, Tm.—In an endeavor to find the mean(temperature between the heating and cooling sides we see that,four cases may occur: F
. The steam-engine and other heat-motors. the heater per hour;Ts = temperature of steam to be condensed (at constant pres-sure) ;h = temperature of the hot liquid (if other than steam) at any point;hx and tht are initial and final temperatures of the hot fluid;te = temperature of the cold fluid at any point;tei and tc2 are initial and final temperatures of the cold fluid;th — tc = the difference in degrees F. between the hot and cold fluid at any Mean Temperature, Tm.—In an endeavor to find the mean(temperature between the heating and cooling sides we see that,four cases may occur: Fig. 130. The hot fluid maintains a constant temperature Kand there is a continuous rise in temperature in the cold fluid;Fig. 131. The cold fluid has a constant temperature butthe hot fluid varies in temperature; Fig. 132. Both fluids change in temperature and both flow,in the same direction, in currents parallel to the heating surface. 246 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. i \< Fig. 130. rTNv T s4 HO J I . l -:- * Fig. —J SL, Fig. 132. T --):? Fig. 133. CONDENSERS AND AIR-PUMPS. 247 This would occur in concentric tubes, one carrying the coldand the other the hot fluid; Fig. 133. Both fluids change in temperature but both flow-in opposite directions parallel to the heating following discussion is limited to the case of feed-waterheaters, as is illustrated by Fig. 130. Steam at constant tem-perature. Ts, gives up heat to water, raising its temperature from tcx tO tc2. Formula for Tm.—Case I.—In a time dt the temperature ofthe water will rise an amount dd where d = Ts — tc. FAddt = Wdd = heat transferred in time dt, r rdo ~iT8-*ci FA / dt = W / V- = TT log- 0 = FAt. *A) «/ o }Ts-tCi Let £ = 1 hour, As FA = the number of transmitted by the heatingsurface per hour for one degree difference in temperature, FATm = TT-log, 7^r-Tm = total heat transmitted =W(Tcx- Tc2). s TCl-Tc: (Ts~tC2)-(Ts-tCl) d2-dl Ts — TCl . Ts — tCl di1 I where
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