The design features of rising falling evaporator or concentrator produce high tube velocities and assure uniform product distribution and high coefficients of heat transfer.The rising  film evaporator works on uniform metered flow entering the bottom of the steam chest and rises through the first pass with rapidly increasing velocity.After leaving the first pass the flow of the vapor liquid mixture is reversed and directed downward through the second pass at extremely high velocity.The mixture then enters the separator where the vapor and liquid are separated.
    When not designed as a circulation unit, the rising film evaporator provides once through evaporation of heat-sensitive materials, requiring minimum retention time.It is particularly adaptable to multiple effect systems but provides a lesser turn-down capability than the RRFC configuration.

The Advantage of Rising Film Evaporator
1.High tube velocity minimizes fouling.
2.Able to achieve high concentrations at low temperatures.
3.Risk of entrainment is greatly reduced since the major portion of the liquid passes directly out of steam chest rather than being re-entrained with vapor from the separator.
4.System may be turned down without loss of efficiency or effectiveness.
5.Holding time is a matter of seconds.
6.Suitable for evaporation of a wide range of liquid concentrations.
7.Low headroom requirement.