Evaporation
Evaporation is one of the main methods used in chemical industry for concentration of aqueous solutions that means the removal of water from solution by boiling the liquor in a suitable type of evaporator and withdrawing the vapor (Coulson & Richardson,1983). The objective of evaporation is to concentrate a solution consisting of non-volatile solute and a volatile solvent. In the overwhelming majority of evaporations the solvent is water. Normally, in evaporation the thick liquor is the valuable product and the vapor is condensed and discarded.
Agitated thin film evaporators, wiped film evaporators, are designed to spread a thin layer or film of liquid on one side of a metallic surface, with heat supplied to the other side. The unique feature of this equipment is not the thin film itself, falling and rising-film evaporators use thin liquid layers, but rather the mechanical agitator device for producing and agitating the film (APV, 2000).
Conventional heat transfer equipment may not be well suited for certain evaporation applications, particularly those involving heat sensitive products, viscous material or chemical constituents that exhibit fouling or foaming tendencies. For products like these, mechanically agitated
thin-film evaporators are often selected over more conventional evaporators because of their batter process economics and performance (Mutzenburg, 1965).
For these applications, the heat transfer is not actually wiped or scraped but a highly agitated thin film is spread on to the metallic heat-transfer surface.
Agitation has the benefits in thin film equipment other than liquid turbulence. The blades assure even distribution of the liquid over the metal heat transfer surface; they eliminate any channeling of liquid as the liquid flows down the evaporator; the considerable shearing effect decreases the apparent viscosity of most liquids, thus improving internal heat and mass transfer (Parker, 1965). Also the heat transfer coefficient
Agitated thin film evaporators, wiped film evaporators, are designed to spread a thin layer or film of liquid on one side of a metallic surface, with heat supplied to the other side. The unique feature of this equipment is not the thin film itself, falling and rising-film evaporators use thin liquid layers, but rather the mechanical agitator device for producing and agitating the film (APV, 2000).
Conventional heat transfer equipment may not be well suited for certain evaporation applications, particularly those involving heat sensitive products, viscous material or chemical constituents that exhibit fouling or foaming tendencies. For products like these, mechanically agitated
thin-film evaporators are often selected over more conventional evaporators because of their batter process economics and performance (Mutzenburg, 1965).
For these applications, the heat transfer is not actually wiped or scraped but a highly agitated thin film is spread on to the metallic heat-transfer surface.
Agitation has the benefits in thin film equipment other than liquid turbulence. The blades assure even distribution of the liquid over the metal heat transfer surface; they eliminate any channeling of liquid as the liquid flows down the evaporator; the considerable shearing effect decreases the apparent viscosity of most liquids, thus improving internal heat and mass transfer (Parker, 1965). Also the heat transfer coefficient