Convection of Heat and Similitude. 697 



Table I. 



Heat-Loss from Models calculated from Peclet's Formulae. 



(Test of relation h cc6/l for a series of models in which 

 #/ 3 = constant.) 



Model . Eelati ve value of h -7- (9/1) *. 



temperature, 



e°c, 



Lin oar t 

 dimensions, 



/ (cm.). 



( 

 Sphere. 



Horizontal 

 cylinder. 



Vertical 

 cylinder J. 



N 



Mean. 



60 



1000 



1-00 



1-00 



100 



1-00 



60 



10-62 



099 



101 



0-99 



LOO 



40 



11-45 



099 



102 



0*99 



1-00 



30 



12*60 



0-98 



104 



0-98 



1-00 



20 



14-42 



0-97 



1-06 



097 



100 



10 



18-17 



0-97 



111 



0*96 



101 



7*5 



2000 



0-97 



1-13 



0-96 



1-02 



480 . 



5 00 



116 



094 



1-09 



106 



094 



4000 



— 



— 



097 



097 



* Value given, for each shape, relative to value for first model of that 

 9hape. 



t For spheres and horizontal cylinders " I " is the radius, for vertical 

 cylinders it is the height. 



+ Vertical cylinders have height = 5 X radius. 



X.B. — In any test of data obtained from empirical formulae it should be 

 borne in mind that the formula will tend to be most reliable in 

 the central region of the experiments on which they are based, 

 and less reliable at the limits. . 



This table indicates that instead of the arbitrary form 

 &GCA0 1 ' 233 , where A has complicated empirical values, 

 Peclet's results may possibly be presented in the form 

 suggested by (5), 



h c* (0/1) F(0F). 



This could only be decided by a complete study of the 

 whole of his experimental results. However, the above 

 shows that it is fairly true for F{j?) = # ' 233 . In any case, 

 it would be valuable to express results in a form applicable 

 to models, and if this were found impossible the fact is 

 worth stating. 



An alternative way of testing Poclet's data is to plot 

 a curve with h-r-d/l as ordinate and 0/ 3 as abscissa. Of 

 course, only values of I and are taken which fall within 

 the range of the actual experiments. 



Phil Man. S. 6. Vol. 40. No. 240. Dec. 1920. 2 Z 



