Thermal diffusion in a packed column

Abstract

In the past a number of investigators (1 to 6) have shown interest in the use of the thermal-diffusion column to make specialized separations. The customary thermaldiffusion column presents construction difficulties because the distance between the hot and cold walls must be veiy small, on the order of 0.02 in., to obtain reasonable separations. Large plate spacing may be tolerated, however, if an obstruction to flow is placed in the space between the walls. A number of investigators have experimented with baffles; Washall and Melpolder (7) recently did work on a spiral-wrapped column. The first packed column was reported in 1948 by Debye and Bueche ( 8 ) , and the only work on the effects of operating variables on separations in packed columns done to date was reported by Sullivan et al. in 1957 (9).In a previous paper ( l o ) , the transport equation for the packed thermal-diffusion column was developed by modifying the differential equation basic to the convective velocity distribution. This equation contains one term representative of the driving force for convection, namely gravity and the horizontal density gradient, one term for the transmission of drag force through the fluid by viscous shear, and one term for the drag of the packing on the fluid. The first two terms are the starting point for the column without packing.The same kind of transport equation resulted for the packed column as for the column without packing, but the coefficients H and K vary in a different manner with plate spacing, and a new variable, the packing permeability, is involved. In the work reported here these transport equations were tested in batch operation by varying these parameters. EXPERIMENTAL WORKThe thermal-diffusion column used consisted of parallelvertical plates, the working space of which was about 2 ft. high by 4 in. wide ( 1 1 ). Heat was supplied by a steam jacket ALDEN H. EMERY, JR., and MAURICE LORENZPurdue University, Lafayette, Indiana on the hot plate and removed by cold water flowing in a jacket on the cold plate. The plates included three large ports to fill and drain, two pressure taps in the center portion to measure permeabilities, five hypodermic needles for withdrawing samples, and nine thermocouples. The plates were spaced by a solid steel plate, the center of which was removed to form the working space. Plastic tape formed the gasket between the spacer and the plates.Three packing materials were used: steel wool, coarse glass wool of about 20-p diam., and fine glass wool of about 2-fi diam., the variety usually found in laboratories. The permeability of each packing could be varied by changing the density of packing. This was limited at the low-permeability end by the maximum amount that could be compressed into the working space without warping the plates and at the high-permeability end by the amount that would maintain its shape in the working space without forming channels. In addition, these three materials cover different ranges of permeability. The total permeability range covered was from 2 ...

Étude de la thermogravitation dans une couche fluide horizontale

“…We restrict our work to the two dimensional study. By using the Boussinesq approximation, the equations of conservation of mass, energy, momentum and species for the binary mixture are given by the system of equations (1)(2)(3)(4). The associated boundary conditions are given by (5-9).…”

“…Thermogravitational technique consists usually in vertical [2] or tilted cavity [6] bounded by two rigid differentially heated vertical walls and adiabatic horizontal walls, and filled by a binary fluid or by a homogeneous isotropic porous medium saturated by a two-component fluid [3].…”