MASS TRANSFER IN A PACKED BED OF RASCHIG RINGS AT LOW PECLET NUMBERS

Abstract

The mass transfer coefficients in non-irrigated packed beds of porous ceramic Raschig ring have been determined with the help of drying experiments in the constant rate period. Raschig rings of 6.8, 8.7, 10.4 and 16.2 mm outside diameter in packed beds of 50, i00, 150 and 200 nan height and i00 mm diameter have b~en investigatea. For Peclet numbers greater than about I0" the Sherwood numbers were found to lie above those calculated for a single sphere as is to be expected. The factor, which was determined from the data of other workers and also from the present work, was found to be 1.9. In the low Peclet number range (Pe > 1000) the experimentally determined Sherwood numbers were found to decrease sharply with Peclet number and were found to lie much below the single sphere values. The bypass model, for the non-uniform distribution of gas, presented for a packed bed of spheres by E.U. Schlunder /i/ and H. Martin /2/ has been extended here to apply to a packed bed of Raschig rings also. The model explains the characteristic variation of Sherwood numbers in the low Peclet number range, for almost all the experimental data, to a good degree of accuracy.