. The steam-engine and other heat-motors . Fig. 229.—Separately Fired superheated steam had to possess that number of thermalunits in excess of those it possesses as saturated steam, it is evident SUPERHEATED STEAM AND STEAM-TURBIXES. 437 that the necessary temperature of the superheated steam wouldbe obtained from the equation ASA(Ts-T2)=xAL, or (Ts-T2)=~£ where Ts is the temperature of the superheated steam,To is the temperature of the saturated steam. If the above were true there would be very little gained bythe use of superheated steam, as we would simply substitute one. Fi
. The steam-engine and other heat-motors . Fig. 229.—Separately Fired superheated steam had to possess that number of thermalunits in excess of those it possesses as saturated steam, it is evident SUPERHEATED STEAM AND STEAM-TURBIXES. 437 that the necessary temperature of the superheated steam wouldbe obtained from the equation ASA(Ts-T2)=xAL, or (Ts-T2)=~£ where Ts is the temperature of the superheated steam,To is the temperature of the saturated steam. If the above were true there would be very little gained bythe use of superheated steam, as we would simply substitute one. Fig. 230.—Foster Superheater and Water Tubular BDiler. waste for another. It is found in practice that a very much lowerand more feasible degree of superheat is necessary. It varies, ofcourse, with the size and type of engine, ratio of expansion, some cases it is only .4 or .5 of the amount indicated by the for-mula above. For example, assume the latent heat of steam to aver-age 875 For each per cent of initial condensation there is aloss of If only .4 of this amount is required when thesteam is superheated, the number of degrees of superheat required for each per cent of initial condensation would be :—~— =7 degrees approximately. Hence the (approximate) rule. 438 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. To have the steam dry at cut-off, the necessary number ofdegrees of superheat of the steam on entrance to the cylinder isequal to the percentage of initial condensation—that would existwithout superheating—multiplied by 7. The superheat on leavingth
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