Loss of Heat from Covered Steam Pipes 9 



Of course for any given pipe covering, we have to know the 

 value of C, the coefficient of conductivity. This we can obtain 

 by analyzing a test of the particular covering, then we can test 

 the theory by calculating the loss of heat for the conditions ob- 

 taining in some other test of the same covering under different 

 steam pressure, on a different sized pipe and with a different 

 thickness of covering. 



Or we may analyze this second test and determine C. If 

 this is the same as the C of the previous experiment, we know 

 that our calculation would have given the same loss of heat as 

 the experiment. 



It is this latter method that has been used here, and in this 

 way a table of values of C for nearly all the well known cover- 

 ings now on the market has been obtained. 



By the aid of the formulas just given and this table, one 

 may calculate the loss of heat from a covered pipe or boiler 

 under any conditions. 



METHOD OP DETERMINING THE VAL,UE OP THE COEFFICIENT OP 

 CONDUCTIVITY C FROM AN EXPERIMENT. 



As an example we will take Mr. Barrus' test on Keasbey's 

 Magnesia on a 2-inch pipe with i inch thickness of covering, and 

 155 B. T. U. lost per sq. ft. of pipe surface per hour. 



Temperature of steam, 365.2 F. 



Temperature of air, 64.6 F. 



The B. T. U. per foot run of pipe = ^~- = 96.2. 



1.61 



The surface of covering in sq. ft. per foot of pipe = 1.15. 



For a first approximation, take Q = 1.7. 



Then 96.2 = 1.15 X 1.7 (/ 64.6), (Eq. 2) and /, the tem- 

 perature of the surface of the covering, equals 114. The differ- 

 ence between this and the temperature of the air, 64.6, is 49.4 

 degrees. We can now make a closer approximation to Q as fol- 

 lows : For a canvas covering, K = .75, and for a cylinder 4^ 

 inches in diameter, 1C = .56 from Figure 4. 



Then for a difference of 50 degrees Fahrenheit. 

 K = -75 X 1.2 X 1.02 = .92 



A = .56 x 1.2 = AT 



