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Abstract
The objective of the present work is to develop a new heterogeneous liquid-solid batch and continuous stirred tank reactor suitable for conducting liquid-solid diffusion controlled catalytic and no catalytic reactions. The reactor consists of an array of vertical separated cylinders arranged parallel to the container wall around a rotating impeller in a square vessel. The cylinder array would serve two purposes, namely: the outer surface of the cylinder array will be used to conduct the diffusion controlled reaction, while the inner surface of the array tubes can be used as heat exchanger to control the reactor temperature. The performance of the reactor is evaluated by measuring the rate of liquid-solid mass transfer at the tube array. The present work was conducted using the technique of the diffusion controlled dissolution of copper in acidified dichromate.
Variables studied were:
1. Impeller rotation speed.
2. Geometry of the impeller (radial flow and axial flow impellers of the turbine type
were used).
3. Physical properties ofthe solution (p, p. and D).
4. Array cylinder diameter (d).
5. Cylinder spacing within the array (8).
6. Distance between the array and container wall (Lw).
7. Effect of superimposed axial flow in order to characterize the performance of the heterogeneous continuous stirred tank reactor.
The study revealed the following results:
For both the 90° turbine impeller (radial flow impeller) and the 45° pitched turbine (axial flow impeller):
1. The mass transfer coefficient increases with increasing the impeller rotational speed.
2. For a given Re, the dimensionless mass transfer coefficient Sh increases with increasing Sc number.
3. For a given rotation speed the mass transfer coefficient increases with decreasing the cylinder diameter.
4. Within a distance ranging from 1.75 to 3.5 cm between the array and the container wall, array location from the wall was found to have a little effect on Sh number.
5. For a given set of conditions, the mass transfer coefficient increases with increasing cylinder separation within the array.
6. Mass transfer data were correlated using the method of dimensional analysis, the following overall mass transfer correlation were obtained:
a. radial flow impeller: Sh = 0.852 ScO.33 Reo.s7 (sIT)o.s
For the conditions: 850 < Sc < 1322; 1925 < Re < 19197; 0.033< sIT < 0.1.
b. axial flow impeller: Sh = 1.027 SCO.33 Reo.4s (sIT)O.313
For the conditions: 850 < Sc < 1322; 1925 < Re < 19197; 0.033 < sIT < 0.1
7. The mass transfer data were also correlated in terms of specific energy dissipation, the following equations were obtained from dimensional consideration:
a. radial flow impeller: K = 5.9 Sc•O.66 (ue)O.2S
b. Axial flow impeller: K = 3.24 SC•O.6~ (ue)O.2S