PROCEEDINGS 



OF THE 



Note on constant volume explosion experiments. By S. Lees, 

 M.A., St John's College. 



[Read 24 January 1921.] 



§ 1. Much work has been done in recent years in determining 

 the values of the volumetric heats of gases at high temperatures. 

 In the main, the experiments have been made either at constant 

 pressure with the gas heated externally, or at constant volume with 

 the heating produced by explosion in a closed vessel. A compre- 

 hensive collection of available data on this subject, with estimates 

 of the probable degrees of accuracy involved, has been given by 

 Mr D. R. Pye of Trinity College*. 



Such differences as occur in the results from the two methods 

 seem to be in one direction, the internal energy for a gas obtained 

 by constant pressure methods being slightly less than the value 

 obtained by constant volume methods. It seemed possible to the 

 author that the variations of temperature experienced at any 

 instant in different parts of an explosion vessel, might account for 

 some part of the difference in the values of the internal energy 

 obtained by the two methods. 



In this connection, the following extract from the first British 

 Association Report on Gaseous Explosions (1908) may be quoted: 



If the volumetric heat of the gas were constant, the equaUsation of these 

 temperatui'e differences by convection and conduction, could it take place 

 without loss of heat, would cause no change of piessure. The volumetric heat 

 is, however, not constant, but may quite possibly be 50 per cent, greater in 

 the hottest than in the coldest part of the mass. The attainment of thermal 



equilibrium must, in fact, cause a change of pressure The amount of the 



change might be the subject of rough calculation, taking an assumed disti'ibu- 

 tion of temperature and assuming values for the volumetric heat. Such a 

 calculation in the present state of knowledge would only be of value as showing 

 the possible order of magnitude of the quantity sought, and the assumptions 

 made could therefore be of a character to make the calculation fairly simple. 

 More accurate knowledge both of temperature distribution and of thermal 

 capacity will enable greater accuracy to be attained in the estimation of this 

 correction, which will be of such a kind that a method of successive approxima- 

 tion can be pursued, the revised values of thermal capacity resulting from its 

 application being applied to a more accurate calculation of the correction, if 

 necessary. 



* See Automobile Engineer, Feb., 1920. 



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