A long tube evaporator is a type of vertical shell and tube heat exchanger where the liquid being evaporated flows through long tubes and is heated by steam condensing on the outside of the tubes. Tubes are typically 25-50mm in diameter and 4-8 meters in length. There are two main types - climbing film evaporators where the feed is introduced at the bottom and a thin film of liquid rises along the heated tubes, and falling film evaporators where the liquid forms a thin film that falls along the heated tubes.

1. Long tube
evaporator
• A rising film or vertical long tube
evaporator is a type of evaporator
that is essentially a vertical shell and
tube heat exchanger. The liquid being
evaporated is fed from the bottom
into long tubes and heated with
steam condensing on the outside of
the tube from the shell side.

2. Construction
• A long tube evaporator consists of a
long tubular heating element
incorporating tubes, 25 mm to 50 mm
in diameter and 4 to 8 metres in
length. The tubular heating element
projects into a vapour
space/separator for removing an
entrained liquid from the vapour.

3. • The upper tube sheet of tubular exchanger is free and a
vapour deflector is incorporated in the vapour space just
above it. A return pipe connecting the vapour space to the
bottom of the exchanger is provided for natural circulation of
a unvaporised liquid. It is provided with inlet connections for
feed, steam and outlet connections for vapour, thick liquor,
condensate, etc. In this evaporator, the solution/liquor to be
concentrated is in the tubes and condensing steam surrounds
the tubes. Fig. shows a long-tube vertical

4. Working
• In this evaporator, feed enters the
bottom of the tubes, gets heated by
the condensing steam, starts to boil
part way up the tubes and a mixture
of vapour and liquid issues from
the top of tubes and finally impinges
at a high velocity on a deflector.

5. Diagram of
Long tube
evaporator

6. Two Main types of long tube evaporator
1. climbing-film
2. falling-film

7. Climbing-
film
evaporator
• The climbing film plate evaporator
is specifically designed to produce a
thin film during both the climbing and
falling phases. For the climbing film
evaporators, the feed is introduced at
the bottom of the tubes. Evaporation
causes the vapor to expand thus
causing a thin film of liquid to rise
along the tubes.

8. Diagram of
Climbing-film
evaporator

9. falling film
evaporator
• A falling film evaporator (FFE) is a
specific type of vertically oriented
shell and tube (S&T) heat exchanger
that is used to separate two or more
substances with different boiling point
temperatures.

10. Diagram of
falling film
evaporator

11. Sr no. Student Name. Enrollment number.
1. Thakor Priyanshu M. 216200305146
2. Chanawala Trushal k. 216200305147
3. Parmar chandresh k. 216200305150