FACTOR OF EVAPORATION WITH SUPERHEATED STEAM When superheat 

 is present in steam during a boiler trial and superheated steam tables are 

 available, the method of calculating the factor of evaporation is the same as in 

 the case of saturated steam, namely : 



H- a 



Factor = 



i^ 



Where H=total heat in superheated steam, 



^=sensible heat in the feed water above 32 degrees Fahrenheit, 

 L=97O.4, the latent heat of evaporation at atmospheric pressure. 

 If no superheated steam tables are available but values of the specific heat of 

 superheated steam are at hand, this formula may be expressed : 



H'-<7+C p (T SU| -T.J 



Factor = 



L 



Where H'=total heat in the saturated steam at the pressure found in the trial, 

 <7=sensible heat in the feed water above 32 degrees Fahrenheit. 

 C p the mean specific heat of superheated steam at temperature and 



pressure existing in the trial, 

 T sup and T sat = temperatures of superheated and saturated steam. 



For approximate work a chart may be used for determining factors of 

 evaporation with superheated steam. Fig. 2 shows a graphic method of making 

 such determination, the chart being used as follows : From the gauge pressure 

 existing in the boiler trial, as shown by the scale on the left, proceed on a 

 horizontal line to the intersection with the curve of ultimate steam temperature. 

 From this intersection proceed vertically to the line of feed water temperature, 

 and from this latter point horizontally to the scale of factors at the right. 



