CFD + Drying sugar beets

Drying out sugar beets isn’t usually a practice undertaken in their production – at least, not intentionally – and we’re not looking to change this – intentionally. The topic has come up after it became clear in one of my other projects that ventilation isn’t just good for cooling beets, it has the ability to also dry them out a lot. The data isn’t out yet, but after a week of 5m/s air flow, the beets had lost 10% in weight. Given the beets were washed, I’m assuming this was just water (and hoping it was not sucrose). This was only possible under experimental conditions – no rain, a much smaller domain than a full clamp, etc.

With the foresight that comes with experience, or maybe just with luck, the lecturer of the CFD course I took at Lund assigned me the task of understanding the basics of the drying process and how one might model this with CFD. It wasn’t the topic I was hoping for – I wanted to do something on porous materials – but sometimes what you want isn’t what you need.

My approach was to write a (very basic) description of the physics of the drying process, give some specifics of how these processes relate to food stuffs, then present a plan for a CFD analysis of drying in sugar beets. The description is based on the geometry in the above picture, but actually only models the air around the central shape, with a focus on the air near the surface of the sugar beet. Before starting, I was convinced that diffusive mass transfer would be the focus of a CFD analysis. In the end, convective heat transfer was the star. This allows the modelling of the movement of heat from the solid sugar beet across its surface and into the moving air surrounding it. From this, mass transport can also be derived. The convective heat transfer coefficient;

\[ CHTC = \frac{q_{c,w}}{T_w – T_{ref}} \]

where;

• q_c,w is the convective heat flux normal to the wall
• T is temperature
• w is the wall
• ref is somewhere in the air away from the wall.

My conclusions are:

• A CFD model of the drying of sugar beets at the level of an individual beet is possible
• Sugar beets don’t seem to be have studied on this level
• KU Leuven seems to be “the place” work like this is done
• I’m going to have to re-work the assignment – it feels very amateurish – especially if I implement the plan. But you’re welcome to read it:

Thank you Hesam!