Let’s talk about FALLING FILM once again: In the previous article, we discussed the HVAC application of Falling Film, which we refer to in our software as “Spray Evaporator”: https://www.unilab.eu/articles/technical-articles/thermodynamic-engineering-articles/falling-film-evaporators/. Falling film evaporators have tubes sprayed with refrigerant, which falls in cascade, covering them with a refrigerant film: hence the term falling film, recently introduced by Unilab in its SHELL software for Shell & Tube heat exchangers.
There is, however, another type of FALLING FILM, which has nothing to do with its HVAC counterpart, and to which the industry added the term “CHILLER”, which, once again, has nothing to do with the Chiller we know in the HVAC&R world.
By “Falling Film Chiller”, we mean in fact an exchanger built with a series of Pillow plates, side by side and inserted in a frame, in which an evaporation takes place on the inside of the plates, with a fluid that can be ammonia or a refrigerant. On the outside we have water, evenly distributed in a film to cover the sides of each of the Pillow plates.
The plates are placed at a distance of about 50/150mm from each other. A distribution plate allows the water to flow down steadily along the outer walls of each of the plates, forming a thin film of water 0.5/0.4mm thick. Hence the name FALLING FILM CHILLER, clearly different from its HVAC application. This type of product is called CHILLER precisely because it allows the cooling of water and products up to the proximity of the freezing point, but without freezing it!
The exchange coefficients depend on the thickness of the film layer spraying the plates: the thinner it is, the higher the exchange coefficient will be. The thicker it is, the lower the exchange coefficient will be. It is clear that with the same water flow rate, the smaller the number of plates, the greater the thickness of the film, with a consequent reduction of the exchange coefficient.
Produced by companies now well known in the market, both in Italy and abroad, for the development of these technologies, the FALLING FILM CHILLER is used in many fields of application, mainly in the Food & Beverage sector, but also in the chemical and pharmaceutical sectors!