will not be transmitted so rapidly to the walls of the pipe as would the heat from 

 saturated steam. When a pipe is carrying saturated steam, assuming no loss in 

 pressure, the amount of heat radiated usually represents an equivalent conden- 

 sation. Where such a pipe carries superheated steam, again assuming no loss in 

 pressure, the amount of radiation represents only a decrease in the amount of 

 superheat, for condensation cannot take place until the temperature of the steam 

 is lowered to that of the saturated steam at the existing pressure and the temper- 

 ature of the walls is higher than the temperature of saturated steam where the 

 pipes are well covered and the steam is superheated an ordinary amount. 

 Obviously, therefore, where the degree of superheat is sufficiently high at the 

 boiler, an amount of heat could be radiated far in excess of what is found in well 

 covered steam lines, and the steam as delivered to the prime movers and 

 auxiliaries would still be dry or superheated. 



The loss through drips resulting from such line condensation in the average 

 plant using saturated steam is one which is ordinarily largely under-estimated. 

 Such a loss, which is frequently in excess of 5 per cent, can be greatly reduced, 

 if not entirely eliminated, where superheated steam is used. 



It is in the prime movers that the advantages of the use of superheated 

 steam are most clearly seen. 



In an engine, steam is admitted into a space that has been cooled by the steam 

 exhausted during the previous stroke. The heat necessary to warm the cylinder 

 walls from the temperature to which they have been reduced by the exhaust 

 can be supplied, in the absence of jackets, only by the entering steam, and 

 even where jackets are used a large amount of heat must be supplied in this 

 way. If this steam be saturated, such an adding of heat to the walls at the 

 expense of the heat of the entering steam results in the condensation of a portion. 

 This initial condensation is seldom less than from 20 to 30 per cent of the total 

 weight of steam entering the cylinder. It is obvious that if the steam entering 

 be superheated, it must be reduced to the temperature of saturated steam at a 

 corresponding pressure before any condensation can take place. If the steam be 

 superheated sufficiently to allow a reduction in temperature equivalent to the 

 quantity of heat that must be imparted to the cylinder walls and still remain 

 superheated, it is clear that initial condensation is avoided. In the case of a 

 simple engine, where the range of temperature change is a maximum, the degree 

 of superheat necessary to offset a cylinder condensation of, say, 20 per cent in 

 the case of saturated steam, would be excessive, notwithstanding the lower 

 conductivity of superheated steam. As cylinders are added, however, the range 

 of temperature change between the entering steam and the cylinder walls is 

 decreased and proportionately the degree of superheat necessary to prevent 

 initial condensation. 



With saturated steam the heat utilized in warming the cylinder walls to the 

 temperature of the entering steam is mainly lost, insofar as its ability to perform 

 work in the cylinder is concerned. It is true that as expansion progresses a 



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