Short path distillation is a thermal separation technology operating at process pressures in the range of 1 to 0,001 mbar. It lowers the boiling temperature and is an excellent method for gentle thermal treatment of heat-sensitive, high-boiling products. The short path evaporator consists basically of a cylindrical body with a heating jacket, a rotor and an internal condenser.

For the thermal separation of a mixture the rotor creates a mechanically agitated, thin product film on the heating surface inside the body. By means of gravity the product flows down in a spiral path whereby the volatile portion of the product evaporates. The vapour passes by the shortest route and with practically no pressure drops onto the internal condenser. The non-volatile portion as well as the vapour condensate reach the lower part of the evaporator and are discharged to separate bottom product outlets. The residual vapours and inert gases flow through the vacuum nozzle to the vacuum system.

In the gap between the rotor blade and the heating surface, fluid is supplied to the heat transfer surface with intense heat and mass transport. This results in a good heat transfer performance even with viscous products. In addition, the formation of deposits is avoided and the intensive mixing also protects temperature-sensitive products from overheating. 

Another important task of the rotor is to stabilise the liquid film on the heating surface at high evaporation rates. This allows evaporation in the area of nucleate boiling without film rupture. At the same time the liquid film is pressed against the heating surface by the centrifugal force. This avoids the adverse evaporation mode in which a vapour layer with insulating effect is formed under the liquid film. Due to this operation principle extremely high specific evaporation rates are achievable.