THERMAL DIFFUSION IN A PACKED COLUMN
Abstract
The purposes of this investigation were to develop equations describing the operation of a packed thermal diffusion column and to substantiate this description experimentally. An equation for the vertical transport of one component of a binary solution has been derived by using the permeability concept to characterize the packing.The experimental work consisted of a study of two variables, slit width and permeability, in a batch-operated parallel plate column. Temperatures and the composition of a cumene-cetane feed were held as nearly constant as was practical. The plate spacings studied were (nominally) 1/16, 1/8, 3/16, and 1/4 inch, and the permeabilities ranged from 2.79 to 55.4 x 10-7 in.2. These were achieved by packing steel wool and two types of glass wool to various densities, after selecting the packing materials because they brought about large enough (greater than about 2 mole per cent) separations with small enough (12 hours or less) relaxation times.The rate of approach to steady state was measured for fourteen combinations of slit width and permeability. In each case the steady state separation and the relaxation time were determined by a least squares fit of the concentration-time data to Powers' equation for the transient behavior of equicomposition binary mixtures. The separations and relaxation times so obtained were then correlated with plate spacing and permeability by means of the derived transport equation.Good agreement of theory and experiment was obtained in the steady state separation correlation in all respects. The theory also correctly describes the effect of permeability on the rate of approach, and gives the correct effect of slit width at all but the smallest plate spacing. The magnitudes of the relaxation times do not agree with the theory, however. It is suggested that this discrepancy is due to the inhomogeneity inherent in all packing materials. The theory correctly predicts that neither separation nor rate is a function of the type or size of fibrous packing if permeability is held constant.
Degree
Ph.D.
Subject Area
Chemical engineering
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