THERMAL INTERCHANGE WITH ENVIRONMENT 



285 



engineers, but it can be seen that, neglecting 

 free convection (and the small last term, 



h { I ), one can write 



is called Rejoiolds' Number {Re)-, 



hence we can say that, for forced convection, 



(11) NU==aRe'i\ 



The usual method is now to plot Nusselt's 

 Number against Reynolds' Number and 



Doing the same thing for men lying on 

 their backs on the floor, he found that 



He = 0.021 (F)i/2cal./cm.Vmin./°C. 



for the human body in general regardless of 

 size. 



Winslow, Herrington, and Gagge (41) 

 have determined the convection constants 

 in much the same way and have arrived at 

 the following formula for convection loss: 



He = (6.51 + 0.17) AT kg. cal./hr., for V 

 measured in ft./min., or 



He = 2.3 VV AT. 



a: 



X 16- 



-I 

 < 



10 



a 



< 



UJ 



I 



Ul 



> 



^ 2 



z 

 o 



U 



8 



9 



I 2 3 4 5 6 7 



WIND VELOCITY IN M/HR. 



Fig. 3. The convection loss of a cylinder at various wind velocities 



10 



thus obtain the value of a. Biittner (10) has 

 done this for spheres of several diameteis, 

 and finds 



a = 0.70, or 



A^L' = 0.70 Re''\ if V is greater 

 .2 m./sec, or 



070 /y.z)p^ 



D 



than 



H 



("') 



•52eal./cm.Vmin./°C. 



Either of these formulae appeared to fit their 

 data. Although the air velocities used by 

 Biittner (10) were higher than those used by 

 Winslow et al. (41), the values of convection 

 are in good agreement. 



The formulae given above are valid only 

 for a limited range of air velocities. Biitt- 

 ner (10) extended his measurements to 10 

 m. per sec, and it is at about this velocity 



