3. Processes controlled by the advance of a water state change front

Unless otherwise stated, throughout this paragraph, heat and material exchanges with the surrounding environment are assumed to take place on the same side of the product.

Certain processes induce a change in the state of water within the product:

• evaporation for drying and baking;

• solidification for freezing ;

• sublimation for freeze-drying.

The appearance of a moving source term (at the point of transformation) introduces an additional difficulty in formulating and solving the transfer equations. This difficulty is often overcome by roughly dividing the domain into two zones with distinct properties, separated by a moving change-of-state front, and writing the equations for each zone separately. The problem can...