THERMAL EFFICIENCY 33 



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

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

 part W into work, then 



T T 



WQ. (Carnot's Equation). 

 * i 



T -T 



Evidently the fraction - ^W~ 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 _ y 



than ^p ' of the amount given can be converted into work. 

 J- 1 



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 ,, 



IParson's turbine 15-18 ,, 



(Petrol (motor) - 22-24 

 Internal (aero) - 26-28 



Combustion - 1 Coal gas (stationary) 29-31 



I Diesel 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+38=311 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. 



T T 



Efficiency = * =E, 

 * i 



or transposing 



B.B. 



