Fouling Dependency of Air in Dairy Processing
Abstract: In this master thesis project, the formation of fouling on heat exchanger surfaces in dairy processing and mainly the influence of air was examined. Based on prior experimental findings regarding the influence of air bubbles in combination with calculations based on solubility properties of air in milk, a hypothesis was stated. Milk can enter the processing system without any undissolved air, with altered equilibrium due to change in temperature and pressure the solubility can decrease. From this phenomenon, air bubbles can be created which are simultaneously filled with steam at the corresponding steam pressure. Assuming the steam is evaporated from the boundary layer of the bubble a local increase in TS would be present, creating a fouling footprint. The influence of dissolved air and processing pressure on the fouling rate was examined in the thesis and the reason behind the creation of fouling is assumed to be drying. A lab scale tubular heat exchanger UHT was used in the experiments and a part of the thesis is focused on the instrumentation of the machine. The results points in two directions. While processing milk entering with a high level of dissolved air, an increased process pressure led to a decreased initial fouling rate and prolonged induction period. The results from processing milk with low level of dissolved oxygen were inconclusive. Either a point of low enough oxygen level and high enough pressure was reached for nil creation of bubbles, or the milk properties were changed from the pre-processing which intended to lower the oxygen level.
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