Utente:Ub/Sandbox: differenze tra le versioni

Versione delle 20:59, 24 giu 2006

Versione delle 21:00, 24 giu 2006

Riga 63:

The simplest cooling crystallizers are tanks provided with a [[mixer]] for internal circulation, where temperature decrease is obtained by heat exchange with an intermediate fluis circulatin in a jacket. These simple machines are used in batch processes, as in processing of [[pharmaceuticals]] and are prone to scaling. batch processes normally provide a relatively variable quality of product along the batch.

The ''Swenson-Walker'' crystallizer is a model, specifically conceived by Swenson Co. around [[1920]], having a semicylindric horizontal hollow trough in which a hollow [[screw]] conveyor or some hollow discs, in which a refrigerating fluid is circulated, plunge during rotation on a longitudinal axis. The refrigerating fluid is sometimes also circulated in a jacket around the trough. Crystals precipitate either on the bottomcold of the trough, orsurfaces on the surface of the screw/discs, from which they are removed by scrapers and settle on the bottom of the trough. The screw, if provided, pushes the slurry towards a discharge port.

A common practice is to cool the solutions by flash evaporation: A liquid at a given T₀ temperature is transferred in a chamber at a pressure P₁ such that the liquid saturation temperature T₁ at P₁ is lower than T₀, the liquid will release [[heat]] according to the temperature difference and a quantity of solvent, whose total [[latent heat]] of vaporization equals the difference in [[enthalpy]]. In simple words, I cool the liquid by evaporating a part of it.