Numerical simulation of bubble flow homogenization in industrial scale wine fermentations

- Model for 3D gas and liquid flow in wine fermentation vessels.
- Model to assess mixing and homogeneity, e.g. of nutrient additions.
- Homogeneity achieved quickly if adequate bubble formation is present.
- Short mixing times imply long-term fermentation models can be reduced to 1D.
- Results can be used to optimize vessel geometry, cooling equipment and other process parameters.

A detailed understanding of mixing and homogenization during food processing is essential for process control and optimization, but often hard to achieve on industrial scales. We used 3D CFD simulations to analyze bubble flow induced mixing of yeast nutrients in industrial scale wine fermentations for different vessel geometries. Employing boundary conditions resembling the common set-up of bubble column simulations, an Eulerian multiphase model was experimentally validated and then used to describe the gas-liquid flow. Mixing behavior was evaluated based on passive tracer distributions implied by three different dosage locations. Average homogenization times ranged between (71 ± 8) s and (100 ± 9) s for most active fermentations, with significant differences depending on tank geometry. Mixing times were approximately twice as long in early stages of fermentation. For the simulation scenarios investigated, CO2 bubble-induced flow during active fermentation is shown to effectively prevent unwanted nutrient inhomogeneities.

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