Convection from Wires in a Stream of Air. 901 



Stanton * showed experimentally that for the same pipe 

 •and range of temperature the heat transmission varied as 

 o n_1 , where n is the index of v in the ordinary resistance 

 formula. 



2. The Convection Constants of Air. 



Below are given the formulae taken in this paper to 

 represent the variation with temperature of the convection 

 constants of air. Langmuir f, dealing with convection of 

 heat from the point of view of conduction through a 

 stationary film of gas in contact with the hot body, has 

 collected formulae for the convection constants for various 

 ^gases. From his paper we have, T being the absolute 

 temperature, 



., , , (150xlO- 7 )T* 

 viscosity (7;) = — i + T , (4j 



& = 4*6 x 10 _t> I 5 -z ,»,.,„ cais - P er cm - P er sec - 



1 -f- L L<±j 1 



per°C. . . (5) 

 .and since for air 



p = 0-001293 (273/T) gm. per c.c. 

 it follows that 



v(=v/P)=- — 1 124/T cm. 2 per sec (6) 



3. The Thermal Relation. 



For convection loss from thin wires in air, the most 

 •complete and satisfactory experimental results are those 

 given by King J, and he obtained to represent them a formula 

 which may be written 



H/t=B v /(«Z/ J /) + 0, (7) 



where v has been put for k/c. This agrees with the theory- 

 advanced by King and with (2), except that B and C vary 

 slightly with the temperature excess at which the wire 

 works, and that C increases with the diameter of the wire. 

 He gave empirical coefficients which allowed for this, and 



* Stanton, Phil. Trans, cxc. p. 07 (1897V 



f Langmuir, Phys. Rev. xxxiv. p. 401 (1912). 



% King, Phil. Trans. A, ccxiv. p. 373 (1914). 



