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Title: Effects of antifoams on gas-liquid dispersion
Author: Salih, M. A.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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The use of antifoam solution to control any foaming tendency is a very important aspect of fermentation processes. However, an antifoam solution will affect the mass transfer characteristics of a fermentation broth as well as suppressing foam so that both mass transfer and foam behaviour have been studied in the present work. The behaviour of a transient foam, which is produced by the antifoam itself, was investigated by means of a small two-dimensional bubble column. This bubble column consisted of two glass plates separated by a 10 mm thick frame of PTFE. Bubbles were produced from sintered-glass spargers of two pore sizes. Measurements of the average bubble diameters in the foam for different concentrations of solution were carried out from still photographs of the foam using an image analyzer. Two types of antifoams were investigated, polypropylene glycol (PPG) and a silicone oil emulsion. The two PPG concentrations used were 0.05 and 0.15 g/l both with and without adjustment of the pH and the addition of an electrolyte, NaCl. The silicon emulsion concentration was 0.015 g/l. Bovine serum albumen BSA as a foaming agent at a concentration of 0.20 g/l was investigated by itself, and with each of the antifoams. In each experiment, the height of foam layer was recorded as a function of the superficial gas velocity. A constant flow tank has been designed to allow the foam to overflow and to enable measurements of the mass transfer characteristics of the froth (or broth) layer only. These characteristics are: volumetric mass transfer coefficient KLA, Sauter mean bubble diameter b, gas hold-up g, interfacial area A, and mass transfer coefficient KL. The value of KLA was calculated from a mass balance of steady-state dissolved oxygen. The gas hold-up was estimated from the differences in heights of gassed and ungassed solution. A photographic technique was applied to measure the bubble diameter. Thus, the interfacial area A was simply calculated using the formula (A = 6 g / b). Finally, the value of KL value was determined.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available