Falling Film Evaporator Video Lecture | Heat Transfer - Mechanical Engineering

in falling film evaporators long tubes
of diameters from five centimeter to 25
centimeter are used the liquid feed
enters from the top and the liquid flow
inside the tubes is by gravity but the
design gets complicated to get a uniform
distribution of the liquid as it flows
down inside the tubes to obtain improved
distribution of the flow distributors
are used also sometimes spray nozzles
are used to minimize any non uniform
distribution of the liquid feed the
falling film evaporators can handle more
viscous products then the rising film
evaporators because here now the flow is
mainly by gravity
typically heat sensitive products such
as orange juice concentration is done in
these types of evaporators the typical
residence time is fairly short anywhere
from twenty to thirty seconds in
comparison to three to four minutes in
the rising film evaporators there is
another variation of an evaporator
design that involves a rising film
section in the beginning part of the
evaporator and then a falling film
section in the second part of the
evaporator as seen in this animation so
the liquid feed first goes through the
rising film section where the feed gets
pre concentrated and then it is allowed
to fall by gravity in ten films in the
falling film section of the evaporator
again these types of variations allow
use of these evaporators for specific
applications for heat sensitive foods