Characteristics of a comb wiper for the film evaporator

In wiped-film evaporators, wipers with comb-wiping elements are often used. These elements are made of PTFE or electrocarbon and they bear on the conc ave evaporating area by the action of centrifugal force. This paper present s results of a study of the characteristics of such a wiper depending on th e peripheral liquid load on the top of the evaporator, on the wiper periphe ral speed and on the sense of wiper rotation. The shape of the residence-ti me distribution curves (RTD curves) and the residence-time values indicate the existence of three different hydrodynamic regimes for the film passage over the evaporating cylinder depending on operating conditions. Optimum di stillation conditions are obtained in a regime with increased liquid retent ion resulting in a higher residence time. The augmented residence time is a positive factor which enables efficient evaporation to be carried out unde r gentle conditions at lower evaporator temperatures. It is possible to dec rease or increase the passage of a liquid through the evaporator by a facto r of two by changing the sense of the wiper's rotation. The obtained result s show that there are interesting hydrodynamic conditions with intensive mi xing on the evaporating cylinder at lower peripheral speeds. In addition, t he longitudinal wave formation before the wiping element is minimized under these conditions.