THE LOSS OF HEAT FROM COVERED STEAM 



PIPES 



In the last few years a number of elaborate and careful tests 

 have been made on various coverings for steam pipes. These 

 tests have been made for the intending purchaser with the point 

 of view of ascertaining the most efficient of the pipe coverings 

 regularly on the market. They have no doubt served this pur- 

 pose admirably, but it has occurred to the writer that they might 

 also be made to serve the purpose of guiding the manufacturer as 

 to the true values of the materials used in the coverings, and to 

 aid the engineer in computing the losses from pipes already cov- 

 ered, or the saving to be effected by increasing the covering or 

 using a more efficient material. 



The true value of the different materials used in the tests 

 has been notably obscured by the different thicknesses, and no 

 law governing the general subject has been even hinted at in the 

 published reports of the tests. 



As long ago as 1850 the great French physicist Peclet (Pec- 

 let-Traite de la Chaleur Paris, 1860) investigated with wonder- 

 ful skill and patience the laws of the emission of heat from a 

 surface maintained at constant temperature, and the laws of con- 

 duction of heat through materials of low conductivity. His 

 experiments, though on a small scale and strictly laboratory 

 ones, were so cleverly planned and skillfully executed that the laws 

 empirically deduced from them could hardly fail to be correct. 



The loss of heat from covered pipes is only one of their many 

 practical applications. 



When an iron steam pipe, of customary thickness, covered 

 with material of low conductivity, is filled with steam at rest or 

 moving with ordinary velocity, the amount of heat escaping 

 through the covering is so small compared with what the metal 

 of the pipe could transmit, that the outer surface of the pipe 

 attains the same temperature as the steam within it. 



Leaving the surface of the pipe, the heat is transmitted 



