766 



SCIENCE. 



[N. S. Vol. VIII. No. 205. 



sending the total, 21,200, toward the boiler ; 

 for use there ; losing, however, 250, en 

 route, and giving up the remainder, 20,950, 

 together with the heat of jacket-water, 

 joining the stream at the boiler, to reduce 

 the demand for and cost of fuel, by raising 

 the temperature of the water to be con- 

 verted into steam. 



The flow to the engine from the boiler 



27,260/142,150=0.15, fifteen per cent. 

 This is called the ' Thermal Efliciency of 

 the Engine,' perhaps more correctly Ther- 

 modynainic Efficiency of the Engine. The in- 

 dicated power is reported as 643 H. P. and 

 the demand for heat at the piston is thus 

 221 B. T. U. per I. H. P. per minute. 



Engine-friction absorbs work to the 

 equivalent of 1,870 B. T. TJ. per minute, 



-F 



V ~::zzM 









■J «.<!.. 



Losses and Transfers of Heat in Steam-power Plants. 



begins with a stock of 169,350 B. T. U. per 

 minute, but 3,100 are lost on the way by 

 conduction and radiation and by leakage 

 from the steam pipes, and the engine actu- 

 ally receives a balance of 156,150 B. T. U. 

 per minute. Of this, 7,400 go back in the 

 feed-water and 6,600 from the jackets, mak- 

 ing the net supply 142,150 B. T. U. per 

 minute. 



Of this net supply, only 27,260 are re- 

 ported to have been transformed into me- 

 chanical energy, to flow through the engine 

 and perform work, useful or other. The 

 efficiency of this operation is, therefore, but 



and this gives 25,390 B. T. TJ. as the 

 equivalent of the net, usefully applied, 

 work of bhe engine, and this gives us 237 

 B. T. U. per minute as the consumption of 

 energy per D. H. P., a measure of the 

 ' brake efficiencj',' as it is sometimes called. 

 The second of the two figures here rep- 

 resented, on the lower portion of the plate, 

 illustrates the ideal case, the ideal steam- 

 engine delivering the same quantity of 

 ' indicated ' power, and differing from the 

 real engine by operating in the ' Rankine 

 Cycle,' and in exhibiting no wastes by clear- 

 ance or friction, conduction or radiation — 



