22 Loss of Heat from Bare Steam Pipes 



The loss of heat by air contact depends on the diameter of 

 the pipe, on its position, whether vertical or horizontal, and on 

 the difference of temperature between its outer surface and the 

 surrounding air. We may express it by the following equation : 



Loss by air contact in B. T. U. per square foot per hour = 

 A" X C X diff. of temp., in which A" is the term affected by the 

 diameter and position of the pipe and is given by Figs. 4 and 5. 

 C is a coefficient determined by the amount of the difference of 

 temperatures and its value is given by Fig. i . The difference of 

 temperatures is that of the steam and the surrounding air. 



The loss of heat due to radiation depends on the nature of 

 the surface of the pipe, on the difference of temperatures and on 

 the temperature of the surrounding objects thus : 



Loss due radiation in B. T. U. per sq. ft. per hour = A~X C X 

 C" X diff. of temp., where A' is a number depending on the 

 nature and condition of the surface of the pipe, C a coefficient 

 depending on the amount of the difference of temperatures, its 

 values being given by Fig. 2, and C" a coefficient, given in Fig. 

 3, depending on the temperature of the surrounding objects. 

 The temperature of the surrounding objects we must usually 

 consider to be the same as the temperature of the surrounding 

 air. 



Summarizing we have : 



Loss of heat in B. T. U. per sq. ft. per hour 

 = (A + R) X diff. of temp. 

 = [(A" X O + (A~ X C X C"] X [diff. of temp.] 



A study of this formula will show that all its parts except 

 A' are rigorously fixed by Peclet's deductions from his experi- 

 ments. For that matter K is given by his experiments within 

 narrow limits and might be expected to have the value .64. 



There are, however, enough reliable experiments on a large 

 scale to make it preferable to deduce K directly from them. 



The table on the following page gives the results of a num- 

 ber of careful and 'reliable tests, most of which were on a large 

 enough scale to give results of assured practical value. 



In the previous paper references will be found to the pub- 

 lished data of these tests. 



Prof. Jacobus has kindly furnished additional data in regard 



