THERMAL EFFICIENCY 33 



between the absolute temperatures T l and T 2 , takes up Q cals. 

 from a heat reservoir at the temperature T 1 and transforms the 

 part W into work, then 



T T 



W=Q ^ 2 (Carnot's Equation). 

 * i 



T T 

 Evidently the fraction ^= 2 is that part of the Q units of heat 



^ i 



which represents the amount of energy made available for work. 

 That is, even under unattainably perfect conditions no more heat 



f rp 



than -^= - of the amount given can be converted into work. 



* i 

 This equation gives the efficiency of the heat engine. 



The most efficient steam engine yet constructed a Nordbeg 

 air compressor of 1000 h.p. converts 25 per cent, of the heat 

 energy it receives into work. Most steam engines are only 8 to 

 10 per cent, efficient, i.e. only 8 tons out of every 100 tons of 

 perfect fuel burned have their energy converted into work. 



TABLE IV. 



COMPARATIVE THERMAL EFFICIENCIES. 



(Compound (non-condensing) 8-12 per cent. 



Steam - ,, (condensing) 10-16 



I Parson's turbine - 15-18 



(Petrol (motor) - 22-24 



Internal I (aero) - 26-28 



Combustion -1 Coal gas (stationary) 29-31 



iDiesel - - 33-35 



Combined I.C. /Still engine 41 



and Steam -\Still-Diesel combination - 44 



Combined steam and electric generator - 55 



Animal body - 25-34 



If one were to consider the animal as a heat engine, then it 

 must operate between two temperatures. One of these tem- 

 peratures we know, viz. body temperature, which is 38 C. 

 or 273+38311 absolute. This is -the condenser or "sink" 

 temperature. The other temperature, that of combustion, 

 must be higher. How much higher may be calculated from the 

 equation above. 



r rp 



Efficiency-- 1 =E, 



* i 

 or transposing 



