Convection of Heat and Similitude, 699 



(1) Thin ( 'ylinder$. 



Kennelly* and Morris t have investigated the cooling o£ 

 thin wires in streams of air. King j has given, pefttgps, the 

 most comprehensive investigation, working over a wide 

 range. He used wires ranging in diameter (d) from 

 0*003 cm. to 0*015 cm. He worked at velocities (v) of 

 17 to 900 cm. per sec, and at temperature excesses (0) 

 (wire over air) of 200° C to 1200° C. As a result he gives 

 a formula, which may be written 



H/tf = B x /(«0 + (10) 



H is the heat-loss per cm. of: wire, B and C are practically 

 constant. B has a slight coefficient depending on the 

 temperature excess of the wire ; C has a larger coefficient, 

 and also depends somewhat on the diameter of the wire. 

 We may note that, in (9), "A" refers to unit area of 

 the body. If the body is a long cylinder, the length 

 obviously does not affect " h." It readily follows for long 

 cylinders (diameter " d ") that the rate of loss of heat "H" 

 per unit length is given by 



H = (kff)F(vde/k). . . . . . (11) 



Thus King's results show that the formula (11), which for 

 these experiments reduces to 



H/0 = F(yd), (12) 



is very satisfactory, but slight corrections seem necessary. 

 The results are in a form which readily shows this, being 

 essentially the evaluation of the constants B and C in his 

 theoretical formula. 



(2) Spheres and Thick Cylinders. 



Compan §, using a sphere, verified Bo-ussinesq's approximate 

 equation within narrow limits of temperature and air- velocity, 

 but he did not use bodies of different size. However, Hughes || 

 has investigated the cooling of cylinders (05 to 15 cm. diam.) 

 over a range of air-velocity from 2 to 15 metres per sec. 



The experimental data are given in a full table in his 

 paper, and curves are given between the heat-loss "H" 



* Kennelly, Trans. A. I. E. E. xxviii. p. 363 (1909). 



t Morris, ' Electrician,' Oct. 4, 1912, p. 10o6. 



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



§ Compan, he. cit. 



|| Hughes, Phil. Mag. xxxi. p. 118 (1916). 



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