Mode of condensati

1. CONDENSATION
Subject of
ADVANCE HEAT-TRANSFER
(2171911)
B.E. LEVEL FOUR
7TH Semester
Submitted by : KHAMBHAYATA MAYUR(130010119042)
Submitted to : MADHURI BHADAURIA

2. Contents
Introduction
Types of condensation
Laminar film condensation on a vertical surface
Turbulent film condensation on a vertical surface
References

3.  Introduction
Condensation occurs whenever a vapor comes into
contact with a surface at a temperature lower(t) than the
saturation temperature(tsat) corresponding to its vapor
pressure. The nature of condensation depends upon whether
the liquid thus formed wets or does not wet the solid surface.
Condensation may occur in two possible ways:
1. Dropwise condensation
2. Film condensation
Heat transfer rates in dropwise condensation may be
as much as 10 times higher than in film condensation.

4.  Dropwise condensation
 If on the other hand, the liquid
does not wet the solid surface,
the condensate collects in the
form of droplets, which either
grow in size or coalesce with
neighboring droplets and
eventually roll of the surface
under the influence of gravity.
This process is called “Drop
condensation”.
Fig.1 Dropwise condensation

5.  Film condensation
 If the liquid wets the surface, the condensate flows on the
surface in the form of a liquid film and the process is called
“Film condensation”.
Fig.2 Film condensation

6.  An analysis for filmwise condensation on a vertical plate
can be made on lines prepared by Nusselt.
 The film thickness on a vertical surface will increase
gradually from top to bottom as shown in Fig.3.
Fig.3 Film condensation on a vertical plate

7.  Laminar film condensation on a
vertical surface
If the velocity of the vapor is very high or the liquid
film very thick, the motion of the condensate flow would be
laminar. For laminar film condensation, The total heat
transfer to the surface,
Q = 𝒉As ( tsat - ts )
Where, 𝒉 = heat transfer co-efficient
𝒉 = 𝟏. 𝟏𝟑
𝝆 𝒍 ×( 𝝆 𝒍 − 𝝆 𝒗) × 𝒌 𝟑 × 𝒈 × 𝒉 𝒇𝒈
𝝁×𝑳 × 𝒕 𝒔𝒂𝒕 − 𝒕 𝒔
𝟎.𝟐𝟓
Note : While using above equation, all liquid properties are to be evaluated at
temperature (
𝑡 𝑠𝑎𝑡 + 𝑡 𝑠
2
) and ℎ 𝑓𝑔 should be evaluated at 𝑡 𝑠𝑎𝑡 .
As = Surface area

8.  Turbulent film condensation on a
vertical surface
When the plate on which condensation occurs is quite
long or when the liquid film is vigorous enough, the
condensate flow may become turbulent. For turbulent film
condensation, The total heat transfer to the surface,
Q = 𝒉As ( tsat - ts )
Where, 𝒉 = heat transfer co-efficient
𝒉 = 𝟎. 𝟎𝟎𝟕𝟕
𝝆 𝒍 × 𝝆 𝒍 − 𝝆 𝒗 × 𝒌 𝟑 × 𝒈 ×𝑹 𝒍
𝝁×𝑳 × 𝒕 𝒔𝒂𝒕 − 𝒕 𝒔
𝟎.𝟐𝟓
𝑹𝒍 = Reynolds number =
𝟒 𝒉 𝒕 𝒔𝒂𝒕 − 𝒕 𝒔 𝑳
𝒉 𝒇𝒈 × 𝝁 𝒍
Note : While using above equation, all liquid properties are to be evaluated at
temperature (
𝑡 𝑠𝑎𝑡 + 𝑡 𝑠
2
) and ℎ 𝑓𝑔 should be evaluated at 𝑡 𝑠𝑎𝑡 .
As = Surface area

9.  Fig.4 shows the variation of film thickness and film co-
efficient with plate height. The film thickness increase with
the increase of plate height. Heat transfer rate decrease
with the increase of plate height since thermal resistance
increase with the film thickness.
Fig.4 film thickness& film co-efficient Vs. Plate height

10.  References
 https://en.wikipedia.org/wiki/Condensation
 R. K. Rajput (2008), “HEAT AND MASS TRANSFER”,
New Delhi, CT: S. Chand