Some Consequences of the Rapid Admission of Gas to an Evacuated Vessel

Abstract

IN recent work on the explosive decomposition of gaseous diethyl peroxide, we detected transient temperature rises accompanying the admission of gases into an evacuated vessel. The experimental arrangement¹ consisted essentially of a thermostated spherical vessel (1,222 ml.) fitted with a pressure transducer and a very fine thermocouple (0.0005 inch diameter platinum/platinum−13 per cent rhodium) which could be moved along the vertical diameter of the vessel. Gases were admitted to the evacuated vessel through an electromagnetic valve which was opened for a pre-set time interval (0.1 to 1.0 s). The pressure and temperature histories were displayed on an oscilloscope and photographed. Experiments revealed that when a complex species like diethyl ether was admitted to the hot evacuated vessel, the thermocouple registered small but significant temperature rises (up to 8° C above that of the vessel) even though the gas was initially 165° C cooler than the vessel. A systematic study with eighteen other gases of different mole-cularity showed that simple gases (high γ, low C_v) heated up dramatically on admission to the evacuated vessel (see Fig. 1). For example, when argon was admitted to the hot vessel (at 190° C) to give a final pressure of 10 mm mercury, the gas temperature rose to 275° C and, with 80 mm mercury pressure of argon in the same conditions, the gas temperature rose to 415° C.