﻿Convective Cooling in Fluids. 921 



where 



A = beat loss per unit time per unit area of the body, 



k= thermal conductivity of the fluid, 



c = capacity for heat of the fluid per unit volume, 



v = kinematical viscosity of the fluid, 



= temperature excess of the body, 



a = coefficient of density reduction of the fluid per degree 



rise of temperature, 

 g=z acceleration due to gravity, 

 L = linear dimensions of the body. 



For gases, cvjk is practically constant, and so experiments 

 with them cannot reveal the effects of this term. However, 

 the formula, restricted by its omission, has already been 

 shown for gases to be in good general agreement with 

 experimental results. In the investigation, early work on 

 miscellaneous small bodies has been considered *, and also 

 data for moderately heated large vertical surfaces from 2 

 inches to 9 feet in height |. Particular attention has been 

 given to the case of wires and long cylinders J, owing to the 

 wide range of size, temperature excess, gas nature and 

 pressure for which results were available. 



Liquids, however, cover a wide range of values of cvjk, 

 and so experiments on the cooling of wires in liquids were 

 undertaken to study the effects of this term. 



But, further, it was suspected that g and v might always 

 occur together in the equation in the form g/v, for any steady 

 velocity of the viscous streams will be determined by a 

 balance between the accelerating forces due to gravity and 

 the retardation due to viscosity. The formula would then 

 take the simple form 



IiL/k0 = F(L*dgac/kv) (2) 



The present paper investigates the possibility of such a 

 simplification, and therefore consists of two main parts — one 

 theoretical, in which more formal consideration is given to 

 convection in a viscous fluid ; and the other experimental, 

 where convective cooling of wires is studied for a series of 

 fluids of different viscosity with a view to experimental 

 verification of the formulas put forward. 



t Dept. of Scientific and Industrial Research. Food Investigation 

 Board Special Report, No. 9. 



\ Davis, Phil. Mag. xliii. p. 329 (1922). 



Phil. Mag. S. 6. Vol. 44. No. 263. Nov. 1922. 3 



