OP-II-3

OP-I-24and diffuse transmission through the solid packed bed adsorber. The polarised beamwas collimated by a series of mirrors and cylindrical lenses and was collected by animage intensifying low light detector based focal planar array technology. The imagereconstruction algorithm was based on the filtered back projection technique ofadaptative algebraic reconstruction.Circumference- averaged concentrations of water vapour in the packing andabove the packing have shown different trends of the adsorbed and the gaseousphase of water vapour as the adsorption occurred. Unlike the cross-sectionalexpansion of adsorbed phase, the gaseous phase expansion above the packingoccurred from the wall to the core centre of the packing bed. For any slice of theadsorbed phase however, the adsorbed phase extended through a periodic increasefrom the core packing to the wall and covered the whole of the cross-section of thebed. This behaviour is explained by the consequence of high velocities at the walland periodic local porosity in the core centre of the adsorber which led to lowresidence times, and conversely high mass transfer, than that in the vicinity of thewall. The radially periodic increase was concentrated in the range of non-dimensionalradial positions between 0.3-0.5 and 0.5-0.7 and these positions correspond in fact tolow local porosity values foreseen by the literature models.The experimental data of adsorbed water vapour, which counted for a voxelnumber of 64 x 64 x 460, radial resolution of 180 microns and axial resolution of 26microns, were utilized to calculate the local dispersion coefficients directly by usingthe 3D partial differential equation (PDE) of the dispersion model. The inlet and outletdata of the packed bed were used as the boundary conditions for the PDE equation.The effective dispersion coefficient was adjusted by an optimisation algorithm inorder to obtain the best fit between the measured and the calculated values at theoutlet. The results of local values at the exit were compared to those obtained byclassical methods of overall residence time distributions.References[1]. Coppens, M-O., Ind Eng Chem Res. 2005, 14, 5011-5019.[2]. S.P. Rigby and L. F. Gladden, Chemical Engineering Science, 1996; 51, 10 : 2263-2272.[3]. Roels, S. and Carmeliet J., International Journal of Heat and Mass Transfer. 2006, 49, 4762-4772.[4]. Asano, H., Nakajima, T., Takenaka, N., Fujii, T., uclear Instruments and Methods in PhysicsResearch A, 2005, 542, 241-247.[5]. Salem, K., Tsotsas, E., Mewes, D., Chemical Engineering Science, 2005, 60, 517-522.83