Studies were made on the distribution of flow in packed beds with the aid of a diffusion-controlled electrode reaction, that is oxidation of ferrocyanide ion in a potassium nitrate solution on a platinum anode.11)
The experimental apparatus employed was as shown in Fig. 1. The test column was packed with the glass beads of the same size to a height of about 160 mm over the screen which was placed a little above the cathode of platinum plate. The average diameters of the packings used were of 4 sizes: 0.945, 3.17, 5.38 and 7.05mm, each for one experiment, and the inside diameters of the columns were of 2 sizes: 26 and 50.5mm, respectively. An electrode assembly used for the anode consisted of five rings of 0.1mm-diameter platinum wire. The radii of these rings were determined by the equation, 13)
r/R=[(2n-1)/10]^1/2, n=1, 2, 3, 4 and 5
(1)
Cemented on a large-mesh Saran screen, these five platinum rings were held concentrically. The leading wire was of PVC-coated 0.2mm platinum wire.
The electrode assembly was inserted into the bed and the measurements of limiting current, 3), 11) were made at various liquid flow rates. The mass-transfer coefficients were calculated by the equation:
k_F=i/FAC
(2)
The flow-distribution was measured at the positions shown in Fig. 2 and some of the experimental results in Fig. 3 and Table 1, are expressed in Sherwood number. A survey of these results show that the distribution of flow is mostly independent of the total flow rate. The distribution was smooth and the reppoducibility good when the sizes of packings used were 0.945 or 3.17mm, but not so when they were larger.
These experimental results were correlated in the form (Fig. 4)
Sh/(Sc)^0.3=kRew^m
(3)
Therefore, by means of the relation:
the values of(Rew)/(Rew)av at different radii could be calculated. The calculated results are shown in Table 2 and Fig. 5. It may be concluded that the distribution of flow in packed beds is practically uniform across the diameter of the pipe.