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Title: Antifoam action in thin films and bubble dispersions
Author: Withey, A.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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The first procedure involved bubbling air at a superficial velocity of 7mm/s through a twice filtered concentrated dispersion of silicone antifoam, both in a foam column and in an agitated tank. The rate of removal from the solution of emulsion droplets, which were deposited as an oily layer at the surface, was determined by measuring the volume concentrations and size distributions of droplets in the liquid by means of a Malvern "MasterSizer" particle size analyser. The following general trends for the rates of removal of M30 antifoam drops were found. In a 30mm diameter foam column, rates of removal were in the following order of drop diameters: 100 μm > 50 μm > 35 μm > 20 μm > 10 μm > 5 μm In a 50mm diameter foam column and the agitated tank, the order was: 10 μm > 5 μm > 20 μm > 35 μm > 50 μm > 100 μm The second procedure involved bubbling air at various superficial velocities through solutions containing different concentrations of M30 antifoam and 0.2 g/L BSA. This procedure demonstrated that foam growth was linked to the extent of droplet removal from the solution. As the effectiveness of the antifoam decreased with time, foam height increased rapidly due to accumulation of bubbles at the base of the foam layer. The third procedure involved forming two captive hemispherical bubbles of 0.8 mm diameter which were almost touching. One bubble was very rapidly expanded by the injection of a further quantity of air, producing a thin film. Laser interference patterns formed by the film draining were studied by video image analysis techniques. Whenever, an antifoam droplet appeared to be present in or near the film rapid thinning and collapse of the film occurred.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available