QUALITY OF STEAM. 121 



With both the condensing and throttling calorimeters the 

 water and steam are withdrawn from the boiler at the temper- 

 ature of the steam, and with a separator the water can only be 

 accurately measured when under pressure, so that the difference 

 between the steam and the moisture in the steam, as they leave 

 the boiler, is simply that the former has received the latent 

 heat due to the pressure, and the latter has not. There is, 

 however, imparted to the water in the boiler not only the 

 latent heat in the portion evaporated, but the sensible heat 

 due to raising the temperature of all the water from that of 

 the feed -water to that of the steam due to the pressure. 



In equation (3) the proportional part Q receives from the 

 boiler both the sensible and the latent heat, or the total heat 

 above the temperature of the feed = Q(H /,) thermal units, 

 and the part Pthe difference in sensible heat between the tem- 

 peratures of the steam and of the feed-water ~ P(T l y,) 

 thermal units. If all the water were evaporated, each pound 

 would receive the total heat in the steam above the tempera- 

 ture of the feed, or H y,. " The factor of correction for 

 the quality of the steam," when there is no superheating, is 

 therefore 





= Q + p (jr=j}-^ 



The superheating of the steam requires 0.48 of a thermal 

 unit for each degree the temperature of the steam is raised, 

 so for k degrees of superheating there will be 0.48^ thermal 

 units per pound weight of steam, and the " factor of correc- 

 tion for the quality of the steam " with superheating. 



,, * ._ . , 



1= ~^T^JT h ^-7' 



See also equation (7). 



