The liquid feed is introduced at the top of the calandria, where a distribution system ensures the formation of a uniform liquid film along the inner walls of the heating tubes. As the film flows downward under gravity, it is heated externally and begins to boil, partially evaporating along its path. The downward flow is further promoted by the co-current flow of vapor generated during boiling.

Separation of the remaining liquid film and vapor takes place in the lower section of the calandria and is completed in a downstream centrifugal droplet separator. To prevent dry spots—which can cause fouling and deposit accumulation—it is critical to maintain complete and even wetting of the entire heating surface. This can be achieved by using longer heating tubes, dividing the evaporator into multiple compartments, or implementing product recirculation.

• Best product quality, gentle evaporation, mostly under vacuum, and extremely short residence times in the evaporator.
• Simple process control and automation.
• Flexible operation, quick start-up and easy switchover from operation to cleaning, uncomplicated changes of product.
• High efficiency heat transfer — it is possible to design multiple-effect, thermal vapour recompression, and mechanical vapour recompression systems.

• Particularly suited for temperature-sensitive products, such as dairy products, fruit juices, plant extracts, sugar, and blood plasma.
• For liquids which contain small quantities of solids and have a low to moderate tendency to form incrustations.