**1. Introduction**

728 Mass Transfer - Advanced Aspects

Loria, H., Trujillo-Ferrer, G., Sosa-Stull, C. & Pereira-Almao, P. R. (2011). Kinetic Modeling

Massabò, M., Catania, F. & Paladino, O. (2007). A New Method for Laboratory Estimation of the Transverse Dispersion Coefficient. Ground Water, Vol. 45 No. 3 pp. 339-347 Michaelides, E. E. (2006). Particles, Bubbles & Drops: Their Motion, Heat and Mass Transfer,

Pereira-Almao, P. (2007). Fine Tuning Conventional Hydrocarbon Characterization to

Pereira-Almao, P., Hill, J., Wang, J. & Vasquez, A. (2005). Ultra Dispersed Catalyst for

Pereira-Almao, P. R., Ali-Marcano, V., Lopez-Linares, F. & Vasquez, A.

Ramalho, R. S. (1983). Introduction to Wastewater Treatment Processes, Academic Press,

Robbins, G. A. (1989). Methods for Determining Transverse Dispersion Coefficients of

Schulz, H., Brand, P. & Heyder, J. (2000). Particle Deposition in the Respiratory Tract, In:

Zhang, Z., Kleinstreuer, C., Donohue, J. F. & Kim, C. S. (2005). Comparison of Micro- and

Perry, R. H. (1997). Perry's Chemical Engineers' Handbook, McGraw-Hill, New York

Sands Resource Workshop, Lake Louise, AB, May 1-4, 2007

Catalysts. Energy & Fuels, *In Press*

National Meeting, Atlanta, GA, USA

Aerosol Science, Vol. 36 No. 2 pp. 211-233

World Scientific, New Jersey

2007/059621 A1, 2007.

25 No. 6 pp. 1249-1258

New York

New York

of Bitumen Hydroprocessing at In-Reservoir Conditions employing Ultradispersed

Highlight Catalytic Upgrading Pathways, Proceedings of Variability of the Oil

Processing Heavy Hydrocarbon Fractions, Proceedings of AICHE, 2005 Spring

(2007).Ultradispersed Catalysts Compositions and Methods of Preparation. WO

Porous Media in Laboratory Column Experiments. Water Resources Research, Vol.

Particle-Lung Interactions, P. Gehr and J. Heyder, (Ed.), 229-290, Marcel Dekker,

Nano-size Particle Depositions in a Human Upper Airway Model. Journal of

Packed beds are widely used in industrial mass transfer operations, including absorption, stripping, adsorption and distillation. The packing material offers a large surface area available for heat and mass transfer between gas-liquid or fluid-solid phases for a given volume. Distillation, absorption, adsorption and extraction are typical applications of packed columns. In the design of a packed column, the averaged mass transfer coefficient is usually used and assumed to be constant at all locations in the column. This is due to the fact that studies of mass transfer in a packed bed are generally based on a macroscopic approach. In this approach, the averaged mass transfer coefficient is determined based on the conditions of the inlet and outlet streams without consideration of local fluid dynamic and local mass transfer at different locations within the bed. Local mass transfer in a packed bed is in fact dependent on local liquid velocity. The local mass transfer coefficient thus varies with locations in the packed bed due to the variation of velocity and the random nature of liquid spreading in the bed. Therefore, the use of the averaged mass transfer coefficient often renders uncertainty in design and scaling-up of a packed column.

Among different methods, dissolution (Kumar et al., 1977; Sedahmed et al., 1996; Guo and Thompson, 2001) and gas absorption (Aroonwilas et al., 2003; Linek et al., 2001) are the two popular methods that have been used to obtained the average mass transfer coefficient. More recently, direct measurements of the local mass transfer coefficient in a packed bed was developed using an electrochemical technique (Gostick et al., 2002), and a mathematical model for local mass transfer coefficient in a packed bed was proposed (Dang-Vu et al., 2006a). The mass transfer coefficient is strongly dependent on liquid distribution in a packed bed. Liquid distribution is in turn dependent on the packing size and type, and the design of the liquid distributor.

Several studies on liquid velocity and distribution in a packed column have been carried out using different techniques, such as: liquid collecting method (Hoek et al., 1986; Kouri and Sohlo, 1996; Dang-Vu et al., 2006b), tracing method (Macias-Salinas and Fair, 1999; Inglezakis et al., 2001), conductance probe (Tsochatzidis et al., 2002), and tomographic measurements (Loser et al., 1999; Reinecke and Mewes, 1997; Yin et al., 2002; Bolton et al., 2004; Ruzinsky and Bennington, 2007). The liquid collecting method has been used widely to investigate liquid distribution in a packed column due to its simplicity in measurements

Measurement of Liquid Velocity and Liquid Distribution

by - pass

tracer injection line

flowmeter

feed pump

16

1 2

8 9 10

column. A reference in the ERT system was taken before the injection of the tracer. This reference acted as a base line from which the increase in the conductivity was observed when the tracer reached the electrodes. This reference conductivity was about 1.00 mS.cm-1. The ERT system recorded the conductivity profiles at 6 planes along the column

For the downward flow mode, water was pumped to the top of the column. A 1.5% wt salt solution (conductivity = 29.9 mS.cm-1) was used as the tracer for better conductivity measurements due to the liquid hold up and channelling that tended to dilute the tracer

return pump

Fig. 1. Schematic diagram of the experimental set-up for ERT

15

11

12

Fig. 2. Arrangement of the electrodes on the column wall

simultaneously.

13

14

liquid tank

in a Packed Bed Using Electrical Resistance Tomography 731

P1

3

electrodes

4

5

6

7

packed column

P2

P3 P4

P5

P6

electrode planes

ERT system

(Hoek et al., 1986; Kouri and Sohlo, 1996; Farid and Gunn, 1978; Kunjummen et al., 2000). In this method, liquid is collected in an array of cells or concentric cylinders at the bed outlet. The liquid collecting duration is also recorded. Liquid velocity obtained from the measured liquid volume is then used to quantify the liquid distribution in the bed. However, the liquid velocity obtained from the liquid collecting method is an axially aggregated flow through the packed bed at a certain radial location, which doesn't reveal the local liquid distribution at various axial distances along the bed. Therefore, in the present study measurements of liquid distribution and velocity at various axial distances in a packed bed were carried out, using electrical resistance tomography (ERT). The ERT system can quantify the liquid distribution and liquid velocity in the packed bed without disturbing the flow field since it is a non-intrusive technique. In addition, measurements at different locations in the packed bed can be measured simultaneously without the need for changing the bed height, which is of advantage over the liquid collecting method.
