478 proceedings: philosophical society 



Determinations have been made of the velocity of flame propagation 

 under many conditions of fuel-to-air mixture ratio, compression, speed, 

 etc. The velocity appears to vary greatly under different conditions 

 and to increase as the flame spreads through the combustion space. 



The paper was illustrated by lantern slides. 



Discussion: The paper was discussed by Messrs. Hawkesworth, 

 White, Humphreys, Sosman and James. 



The second paper was presented by Mr. S. R. Parsons on Cooling 

 radiators for aircraft engines, and was illustrated by lantern slides. 



Airplane radiators absorb engine power because of air resistance and 

 weight, and the most efficient radiator will dissipate heat at the re- 

 quired rate with a minimum absorption of power. 



For the high rates of flow of water used in aeronautic practice, heat 

 transfer under given conditions of temperature and air flow is practically 

 independent of the rate of water flow; but the heat transfer is largely 

 influenced by conditions of the flow of air through the radiator, and 

 is found under given temperature conditions to be practically definite 

 for a given mass flow of air, whatever combination of density and linear 

 velocity produces that mass flow. The individual air streams passing 

 through the air tubes of cellular radiators appear to show turbulent 

 flow, and spiral vanes or other devices for increasing turbulence, while 

 they may increase the heat transfer, result in every case tested at the 

 Bureau of Standards in decreased efficiency, because of a dispropor- 

 tionate increase in air resistance. High thermal conductivity is of 

 negligible importance in the thin metal walls separating water passages 

 from air passages, but is of some importance in projecting "fins." 

 Highly polished surfaces dissipate heat more rapidly than surfaces only 

 ordinarily smooth. 



Air resistance is caused by impact on the front face of the radiator, 

 skin friction in the air passages, and suction on the rear face, the relative 

 importance of the three parts varying widely with different types of 

 construction. Skin friction appears to follow roughly the laws for 

 long tubes. For minimum air resistance, straight and smooth-walled 

 air passages are essential, for anything that deflects the course of the 

 air adds considerably to the resistance. The effects of forms of en- 

 trance to and exit from the air passages are of importance, but are not 

 well worked out. 



Conditions giving maximum mass flow of air through the radiator, 

 and to that extent tending to increase heat transfer for a given flying 

 speed, are identical with those giving minimum air resistance. 



Radiators for use on planes flying at the higher speeds should be 

 characterized by straight and smooth-walled air passages, and mini- 

 mum obstruction of frontal area for a given amount of cooling surface. 



The discussion is directly applicable only to radiators in "unob- 

 structed" positions on the airplane, where other parts of the structure 

 do not affect the flow of air through the radiator. 



