الفهرس 
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Abstract
The objective of the present work is to investigate the effect of the presence of chemically active semicylindrical turbulence promoters on the rates of mass and heat transfer at the wall of a square stirred tank reactor where a diffusion-limited liquid-solid or gas-liquid-solid reaction is taking place. The rate of the reaction was expressed in terms of the mass transfer coefficient which was determined using the electrochemical technique. The influence of the following variables on the rate of mass transfer was studied: i. Promoter diameter. ii. Promoter orientation (horizontal/vertical). iii. Spacing between successive promoters. iv. Impeller rotation speeds. v. Impeller geometry (axial/radial flow turbines). vi. Physical properties of the solution. vii. Gas sparging (N2 superficial velocity). • The above-mentioned parameters were correlated to the mass transfer coefficient using dimensionless mass transfer equations. The results show that closely spaced turbulence promoters enhance the rate of mass transfer at the reactor wall by a degree higher than that of separated promoters. Depending on the operating conditions, the enhancement ratio in the mass transfer coefficients produced by the closely spaced promoters ranged from 1.04 to 1.8 for the single-phase (mechanically) stirred reactor, 1.24 to 2.62 for the gas sparged reactor (with no mechanical stirring), and 1.06 to 2.27 for the combined use of mechanical stirring and gas sparging. • These results recommend using the semicylindrical turbulence promoters as catalyst support for conducting diffusion-limited reactions in practice. Besides acting as catalyst support and increasing the rate of production, the semicylindrical turbulence promoters could offer the following added functions: i. The internal surface of these semicylinders can act as a cooler by which excess heat evolved from highly exothermic reactions can be rapidly removed by passing cold water through the inner surface of the promoters. This prevents thermal degradation of heat-sensitive substances and obviates the need for an external cooling jacket or internal cooling coil with a subsequent decrease in the capital costs of the reactor. ii ii. In case of high thermal loads, an external cooling jacket may be needed along with the use of internal cooling promoters. Here, the turbulence promoters lining the inner reactor wall would enhance the rate of heat transfer across the vessel wall to the peripheral cooling jacket. • Mechanical power consumption measurements under different conditions have shown that using the turbulence promoters did not cause a power penalty, i.e., the increase in mass and heat transfer rates by these promoters is higher than the increase in energy dissipation due to friction at the wall. • Gas sparging was found to be more effective than mechanical stirring in promoting the rate of heat and mass transfer at the flat wall and wall fitted with turbulence promoters. • The combined effect of gas sparging and mechanical stirring on the rate of heat and mass transfer was optimized in case of the reactions involving gas-liquid-solid phases at the flat wall and the wall with turbulence promoters.