Air oxidation studies in a long graphite channel

Abstract

Experiments on the oxidation of short tubes of graphite in air (1–4) have been extended to long channels of graphite where the oxygen is depleted as it flows through the channel. The theory of reaction in porous solids which was developed for the earlier work has been extended to cover this more general case. It is shown that a useful approximation to the general theory can be obtained by considering the channel as a series of short sections and introducing the axial concentration effects via the problem boundary conditions. The theory was tested by experiments carried out in a vertical channel of graphite 14 ft long, 2 in. i.d. and 8 in. o.d. constructed from six blocks of British nuclear grade graphite. The inner graphite surface was exposed to oxygen nitrogen mixtures which flowed through the bore of the tube. Evidence of the radial diffusional effect was obtained from gas concentration measurements at the outer surface. The oxygen was depleted by chemical reaction as it flowed through the channel bore giving rise to an oxygen concentration profile which was experimentally measured. No corresponding axial concentration gradient at the exterior surface was observed. The derived theory allowed the diffusional effects to be quantitatively estimated. Good agreement between the present results and previously reported values for similar graphites was obtained.