A theoretical analysis of bubble-related fouling in ultra heat treatment plants for milk

A thermodynamically based theoretical analysis of bubble formation on hot heat-exchanger wall surfaces in systems for continuous indirect thermal treatment of milk was performed. Whereas previous research on bubble -related fouling has been experimental with just hypothesis about mechanisms behind the impact of bubble formation on fouling, this research contribute with a novel theoretical anadlysis. The analysis was based on the combined effect of bubble formation due to decreased gas solubility caused by heating, and water evaporation into the thus formed bubbles. The analysis arrived at equations for the relationship between the conditions (amount of dissolved gas, pressure, temperature) and the amount of evaporated water, which causes drying at the hot wall surfaces. The calculated amount of evaporated steam correlated well with the amount of foulant reported in previous research. The analysis demonstrates that bubble formation on hot wall surfaces is strongly related to the presence of dissolved air. Moreover, the analysis provides complementary explanations to reasons for the benefits with commonly applied solutions to reduce fouling, such as small delta-T and preholding. The derived equations and diagrams, e.g. the equation for the minimum pressure required to eliminate formation of bubbles, are applicable when designing plants in order to minimize fouling.

Automated summary

This study presents a thermodynamically based theoretical analysis of bubble formation on hot heat-exchanger wall surfaces in the context of continuous indirect thermal treatment of milk. The analysis contributes a novel perspective by combining the effects of decreased gas solubility and water evaporation on bubble formation. The derived equations and diagrams offer valuable insights for designing plants to minimize fouling.