in this ppt presentation slide about a condensation of vapor and drop wise condensation

1. VADODARA INSTITUTE OF ENGINEERING
PRESENTATION ON “CONDENSATION
OF VAPOUR FILM WISE AND DROP FILM
WISE CONDENSATION ”
PREPAID BY
I. DHRUMIL VALAND (16 ME 358)
II. SAGAR WAGHELA (16ME 359)
III. AVDHESH YADAV (16ME 360)
IV. RAJAT YADAV (16 ME 361)
GUIDE BY
MR.PRAGNESH KANDOLIA
ASS.PROF
VIER KOTAMBI

2.  Condensation
When a vapour is exposed to a surface at a temperature below
Tsat, condensation in the form of a liquid film or individual the
droplets occurs on the surface.
Condensation can also occur on the free surface of a liquid or
even in a gas other

3.  Drop wise
Condensation
heat transfer coefficients canbe mo
re than 10 times larger than film co
ndensation dropwise condensation,
characterized by countless droplets
of varying diameters on the conden
sing surface instead of a continuous
liquid film, is one of the most effect
ive mechanisms of heat transfer, an
d extremely large heat transfer coef
ficients can be achieved with this
mechanism

4.  Drop wise condensation occurs when a vapour condenses on a
surface not wetted by the condensate. For non-metal vapours, drop
wise condensation gives much higher heat transfer coefficients than
those found with film condensation. For instance, the heat transfer
coefficient for drop wise condensation of steam is around 10 times
that for film condensation at power station condenser pressures and
more than 20 times that for film condensation at atmospheric
pressure. In circumstances where the film wise coefficient is of
similar magnitude to that on the cooling side, a change of mode to
drop wise condensation offers a potential improvement in overall
coefficient by a factor of up to around .

5.  The high heat transfer coefficients obtainable with drop wise
condensation are very susceptible to reduction by the presence in the
vapour of noncondensing gas. In the absence of significant vapour
velocity, very small gas concentrations lead to appreciable lowering of
the heat transfer coefficient. This was largely responsible for wide
discrepancies between early published values.

6.  Theory and experiment also indicate that the heat transfer coefficient decreases
with decreasing pressure. Although in closed form and in principle applicable to
any fluid, the expression giving the heat transfer coefficient is lengthy. An empirical
equation in good agreement with both theory and experiment for dropwise
condensation of pure, quiescent steam is:

7.  Vapour may condense onto a cooled
surface in two distinct modes known
as filmwise and dropwise. For the
same temperature difference
between the vapour and the
surface, dropwise condensation is
several more times effective than
filmwise. However it involves special
surface finishes or treatment in
order to maintain dropwise
condensation and for this reason,
though desirable, it seldom occurs in
real plant operation.
Vapour film wise condensation

8.  The process of drop wise condensation is enhanced by the special
water cooled condenser surface finish that prevents wetting of the
surface. Condensation then occurs in droplets which grow and fall
under gravity. These falling droplets wipe the surface clean ready for
more droplets to form. This continuous cleaning puts the water cooled
surface in direct contact with the vapour.
 The duplicate film wise condenser is not specially treated and allows
condensation to form as a film. This effectively grows and runs down
the condenser gaining thickness as it falls. The film effectively acts as a
resistance to heat transfer, as heat must be conducted through this
film to the internal cooling water.

9.  Thermocouples are fitted to the
surfaces of both condensers
allowing the direct comparison
of surface temperatures in both
film wise and drop wise
condensation.
 The H102 standard
instrumentation allows heat
transfer rates and surface heat
transfer coefficients from both
condensers to be compared.

10.  Film vs. Drop wise
•In film condensation, the surface is blanketed by a liquid film of increasing thick
ness, and this “liquid wall” between solid surface and the vapour serves as a resi
stance to heat transfer. In drop wise condensation, however, the droplets slide
the droplets slide down when they reach a certain size, clearing the surface and
exposing it to vapour. There is no liquid film in this case to resist heat transfer.
As a result, heat transfer rates are more than 10 times larger in drop
wise condensation.

11.  Applications of condensation
Condensation is a crucial component of distillation, an important laboratory and
industrial chemistry application.
Because condensation is a naturally occurring phenomenon, it can often be used to
generate water in large quantities for human use. Many structures are made solely for
the purpose of collecting water from condensation, such as air wells and fog fences.
Such systems can often be used to retain soil moisture in areas where active
desertification is occurring—so much so that some organizations educate people living
in affected areas about water condensers to help them deal effectively with the
situation.
It is also a crucial process in forming particle tracks in a cloud chamber. In this case,
ions produced by an incident particle act as nucleation centres for the condensation of
the vapour producing the visible "cloud" trails.
Furthermore, condensation is a critical step in many industrial processes, such as
power generation, water desalination, thermal management, refrigeration, and air
conditioning

12. THANK YOU