This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada
To ensure sterility of beverages through the food supply chain, beverages are often either filled with hot liquid and inverted to ensure sterility through the bottle or retorted or pasteurized with traditional methods. One of the big challenges is that there is a maximum temperature limitation to the fluid, because otherwise a risk of the plastic bottle failing or over-pressurization due to any gas in the headspace could occur. With many different types of lines, bottle shapes, cap shapes, and fluid properties, it can be challenging to determine if sterility has been achieved in every location of the beverage to guarantee that no microbes (i.e. mold, yeast) will grow which can be catastrophic in today’s business environment.
To try to better understand why different processing lines, bottle designs, and materials have performed significantly different (i.e. reported spoilage versus none), we have developed a multiphase phase, liquid and air, conjugated heat transfer model for how the fluids heat and sterilize the beverage bottle surfaces in STAR-CCM+. The model includes a semi-empirical formulation for evaporation/condensation within the bottle due to the high filling temperature and low ambient temperature. The CFD heat transfer is coupled with the conduction within the plastic and a microbial inactivation model to determine not only where the cold spot is within a bottle, but also the amount of log reduction of microbes. The model also includes the bottle motion, such as inversions, vibrations, and rotations, to accurately simulate flow within the bottle.
The model has been successfully validated multiple ways. We have used imaging of bubble locations to verify that the fluid flow is modelled correctly, used thermal couples and infrared images to measure temperature through the process to verify fluid and plastic temperatures, and we have used reported data on spoilage of different processing lines to validate the heat transfer and microbial inactivation at the plastic-fluid interface. Overall, the model shows promise in predicting and preventing beverage spoilage.