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Improving food spray-drying with Tetra-Pak

Dark blue background with a conical cyan foreground. On the right is the Tetra-Pak logo. Picture.
Hollow-cone spray illuminated using a laser with a stripy structure (lines seen on the left edge).

Most milk powders you buy have been produced through spray drying. This means that the milk after some preprocessing is injected under high-pressure through a small hole into a warm room. Then almost instantly, the liquid evaporates leaving the powder. The final product now has a longer shelf life, lower transport weight and can be stored in room temperature. However it is a very energy consuming industrial process. To further improve the drying process, we at the spray-imaging group have teamed up with Tetra-Pak where we are investigating among other different injection nozzle's to understand how one can produce droplets of specific sizes with minimum energy requirement.

Our investigation involves advanced imaging techniques using planar laser beams to estimate the produced drop-sizes. The main problem when imaging a spray is the same as when you are trying to see through a fog. You mostly just see a gray background blur. A solution here is to use structured illumination. By imposing a stripy illumination pattern (partly seen in the image above) we can extract the foreground light from the background blur. With structured illumination we can see better through the spray fog. But we can not see the small droplets for sizing. The sizing of the droplets can be done by using a technique called polarization ratio. It is known that when you shine a laser into a cloud of droplets, the light is reflected by the drops so that it seems that they are shining. The ratio of the parallel and perpendicular polarizations of this shining light is connected to the droplet size. To be more exact, the extracted polarization ratio is used to calculate the  surface mean diameter D21 that we use for our investigation.

By comparing the produced droplet sizes between different injectors, injection pressures and other parameters, we hope to assist in creating more efficient spray-drying equipment together with Tetra-Pak.

Edouard Berrocal -

Mehdi Stiti -