D • CONDUCTION OF HEAT 



In Fig. D,15a the graphs of /i, f^, and /s vs. are shown in the entire 

 range — 1 ^ 9 ^ 0. These graphs are drawn for pt = i and pc = t- 

 These values correspond to 66|-per cent increase in c and 33|-per cent 

 decrease in k from their initial values up to the melting point, on the 

 basis that the melting temperature T^ is | of the flame temperature Tg. 

 These values represent a rather wide range of variation in thermal 

 properties. 



Fig. D,15a. 



It is neither necessary nor useful to calculate temperature transients 

 beyond the time at which the fire side wall reaches the melting temper- 

 ature. Beyond this time the phenomenon of heat conduction changes in 

 character, and the results which are based upon the boundary condition 

 in Eq. 15-2 are no longer valid. This point will be discussed in more detail 

 in the next article. Hence one needs to consider only the range 



where 



-1 ^ e ^ e. 



A — _ — 1 



Thus if, say Tm = ITg, then the range of interest is 



-1 ^e^ -^ 



( 282 > 



