2 Loss of Heat from Covered Steam Pipes 



through the cylindrical covering by virtue of the conductivity of 

 that covering, and when it has reached the surface it is dissipated 

 to the surrounding objects and the surrounding air by radiation 

 and contact of air. 



We have then two phenomena to deal with, the conduction 

 of the heat through the covering and its escape from the surface 

 of the same. 



For the latter Pclet gives the following laws : ' ' The quan- 

 tity of heat emitted by a surface at constant temperature depends 

 on the radiation and the contact of air. " 



"The quantity of heat emitted by radiation, per square foot 

 of surface, per hour, is independent of the form and size of the 

 body, provided that it has no reentrant portions. It depends 

 solely on the nature of the surface of the body, on the excess of 

 its temperature over that of the objects to which radiation takes 

 place, and on the absolute value of the temperature of these 

 objects." 



For paper and cloth, P6clet found that color had no influence 

 on the radiation. 



The following table gives the values found by him for radi- 

 ation from different surfaces : 



VALUES OF K. 



B. T. U. PER HOUR PER SQUARE FOOT PER ONE DEGREE. 



Tin plate 086 Cast iron, new . . . .650 



Polished sheet iron . . .092 " " rusty . . . .688 



Ordinary " " . . .567 Sheet iron, rusty . . .688 



Oil paint " " . . .759 Paper 772 



Plaster or wood . . . .737 Calico or canvas . . .747 



The coefficients by which these numbers must be multiplied 

 for any excess of temperature are given in figure 2 . The tem- 

 perature of the objects radiated to would generally be the same 

 as that of the surrounding air. It is taken so in all calculations 

 throughout this article. 



The coefficients by which the numbers in the table must be 

 multiplied for any given temperature of the objects radiated to 

 are given by figure 3. 



For an example take a covering on a hot steam pipe. The 

 surface of these coverings is invariably formed by canvas. 



