Condensation Heat Transfer

1. Group Members:
1) Ansar Magdum (roll no:04)
2) Nisarg Nimbalkar (roll no:22)
3) Aditya Oke (roll no:23)
4) Devesh Pardhi (roll no:25)
5) Ashish Patange (roll no:26)
GUIDED BY: Prof. DR. M. P. DEOSARKAR

2. OUTLINE
• Introduction
• Condensation Types
• Film Condensation
• Hydraulic Diameter
• Modified latent heat of Vaporisation
• Reynolds Number
• Heat Transfer Correlations for Film Condensation
• Film Condensation inside horizontal tubes
• Dropwise Condensation
• Case Study
• Conclusions
• References

3. INTRODUCTION
Condensation: phase transformations, vapor g liquid
 Condensation occurs when the temperature of a vapor is reduced below its
saturation temperature Tsat. This is usually done by bringing the vapor into
contact with a solid surface whose temperature Ts is below the saturation
temperature Tsat of the vapor.
 Condensation can also occur on the free surface of a liquid or even in a gas when
the temperature of the liquid or the gas to which the vapor is exposed is below
Tsat. In the latter case, the liquid droplets suspended in the gas form a fog.
 Examples of condensation are :
1) Condensation of water from a mixture of steam and air.
2) Recovery of hydrocarbon solvents from air streams extractions/drying process

4. CONDENSATION TYPES
Two distinct forms of condensation are observed:
1. Film Condensation
2. Dropwise Condensation
 In film condensation, the condensate wets the
surface and forms a liquid film on the surface that
slides down under the influence of gravity. The
thickness of the liquid film increases in the flow
direction as more vapor condenses on the film.
 In dropwise condensation, the condensed vapor
forms droplets on the surface instead of a continuous
film, and the surface is covered by countless droplets
of varying diameters.
Dropwise and Filmwise condensation

5.  The liquid film starts forming at the top of the plate and
flows downward under the influence of gravity.
 The thickness of the film increases in the flow direction
x because of continued condensation at the liquid–
vapor interface.
 Heat in the amount hfg (the latent heat of vaporization)
is released during condensation and is transferred
through the film to the plate surface at temperature Ts.
 The velocity of the condensate at the wall is zero
because of the “no-slip” condition and reaches a
maximum at the liquid–vapor interface.
 The temperature of the condensate is Tsat at the
interface and decreases gradually to Ts at the wall.
FILM CONDENSATION

6. Flow Regime
Flow regime is determined depending on the Reynolds number,
 Dh = 4Ac /p = 4d = hydraulic diameter of the condensate flow, m
 p = wetted perimeter of the condensate, m
 Ac = pd = wetted perimeter x film thickness, m2, cross-sectional area of the
condensate flow at the lowest part of the flow
 rl = density of the liquid, kg/m3
 ml = viscosity of the liquid, kg/ms
 Vl = average velocity of the condensate at the lowest part of the flow, m/s
 m˙ = rlVl Ac mass flow rate of the condensate at the lowest part, kg/s

7. Hydraulic Diameter
 Note that the hydraulic diameter is again defined such that it reduces to the ordinary
diameter for flow in a circular tube, and it is equivalent to 4 times the thickness of the
condensate film at the location where the hydraulic diameter is evaluated.
That is, Dh = 4d.

8. Modified Latent Heat of Vaporization
 The latent heat of vaporization hfg is the heat released as a unit mass of vapor
condenses.
 However, the condensate in an actual condensation process is cooled further to
some average temperature between Tsat and Ts, releasing more heat in the
process. Therefore, the actual heat transfer will be larger.
 Rohsenow showed in 1956 that the cooling of the liquid below the saturation
temperature can be accounted for by replacing hfg by the modified latent heat of
vaporization h*fg, defined as
Cp l is the specific heat of the liquid at the average film temperature.
.

9. Modified Latent Heat of Vaporization
 We can have a similar argument for vapor that enters the condenser as superheated
vapor at a temperature Tv instead of as saturated vapor.
 In this case the vapor must be cooled first to Tsat before it can condense, and this heat
must be transferred to the wall as well.
 The amount of heat released as a unit mass of superheated vapor at a temperature Tv
is cooled to Tsat is simply
Cpv(Tv - Tsat), where Cpv is the specific heat of the vapor at the average temperature
of (Tv + Tsat)/2.
 The modified latent heat of vaporization in this case becomes
Rate of Heat Transfer
As : the heat transfer area

10. Reynolds number
 This relation is convenient to use to determine
the Reynolds number when the condensation
heat transfer coefficient or the rate of heat
transfer is known.
 The temperature of the liquid film varies from
Tsat on the liquid–vapor interface
to Ts at the wall surface.
 Therefore, the properties of the liquid should
be evaluated at the film temperature
Tf = (Tsat + Ts)/2,
which is approximately the average
temperature of the liquid.
 The hfg, however, should be evaluated at Tsat
since it is not affected by the subcooling of the
liquid.

11. Flow Regimes
 The flow of liquid film exhibits different regimes,
depending on the value of the Reynolds number.
 It is observed that the outer surface of the liquid film
remains smooth and wave-free for about Re ≤ 30,
and thus the flow is clearly laminar.
 Ripples or waves appear on the free surface of the
condensate flow as the Reynolds number
increases, and the condensate flow becomes fully
turbulent at about Re ≈ 1800.
 The condensate flow is called wavy-laminar in the
range of 450 < Re < 1800 and turbulent for Re >
1800.
Re ≤ 30 wave-free laminar
450 < Re < 1800 wavy-laminar
Re > 1800 turbulent

12. Heat Transfer Correlations for Film Condensation
 Consider a vertical plate of height L and width b maintained at a constant
temperature Ts that is exposed to vapor at the saturation temperature Tsat.
1- Vertical Plate
 The analytical relation for the heat transfer coefficient in film condensation
on a vertical plate described above was first developed by Nusselt in 1916
under the following simplifying assumptions:
1. Both the plate and the vapor are maintained at constant temperatures of Ts and
Tsat, respectively, and the temperature across the liquid film varies linearly.
2. Heat transfer across the liquid film is by pure conduction.
3. The velocity of the vapor is low (or zero) so that it exerts no drag on the condensate
(no viscous shear on the liquid–vapor interface).
4. The flow of the condensate is laminar and the properties of the liquid are constant.
5. The acceleration of the condensate layer is negligible.

13. Heat Transfer Correlations for Film Condensation
 the average heat transfer coefficient for laminar film condensation over a vertical
flat plate of height L
1- Vertical Plate – Laminar Flow
 g gravitational acceleration, m/s2
 rl, rv densities of the liquid and vapor, respectively, kg/m3
 ml viscosity of the liquid, kg/m · s
 h*fg = hfg + 0.68Cpl (Tsat - Ts) modified latent heat of vaporization, J/kg
 kl thermal conductivity of the liquid, W/m · °C
 L height of the vertical plate, m
 Ts surface temperature of the plate, °C
 Tsat saturation temperature of the condensing fluid, °C

14. Heat Transfer Correlations for Film Condensation
1- Vertical Plate – Laminar Flow
 All properties of the liquid are to be evaluated at the film temperature
Tf = (Tsat + Ts)/2.
 The hfg and rv are to be evaluated at the saturation temperature Tsat.
 At a given T, rv << rl , thus rl – rv ≈ rl except near the critical point

15. Heat Transfer Correlations for Film Condensation
1- Vertical Plate – Wavy Laminar Flow
 All properties of the liquid are to be evaluated at the film temperature
Tf = (Tsat + Ts)/2.
 The hfg and rv are to be evaluated at the saturation temperature Tsat.
 Empirical correlation for wavy laminar flow over a vertical plate
for rv << rl , 30 < Re < 1800

16. Heat Transfer Correlations for Film Condensation
1- Vertical Plate – Turbulent Flow
 All properties of the liquid are to be evaluated at the film temperature
Tf = (Tsat + Ts)/2.
 The hfg and rv are to be evaluated at the saturation temperature Tsat.
 Pr g Prl
 Empirical correlation for turbulent flow over a vertical plate
for rv << rl , Re > 1800

17. Heat Transfer Correlations for Film Condensation
1- Vertical Plate
 Nondimensionalized heat transfer coefficients for the wave-free laminar,
wavy laminar, and turbulent flow of condensate on vertical plates.

18.  For laminar film condensation on the upper surfaces of
plates, as an pproximation,
replacing g by g cos Θ for Θ ≤ 60°.
2 Inclined Plates, Laminar & Wavy Laminar Flow
Heat Transfer Correlations for Film Condensation
 Can also be used for wavy laminar flows
3 Vertical Tubes, Laminar Flow
 Equation for vetical plates can also be used to calculate the average heat transfer
coefficient for laminar film condensation on the outer surfaces of vertical tubes
provided that the tube diameter is large relative to the thickness of the liquid film.

19. 4 Horizontal Tubes & Spheres, Laminar Flow
Heat Transfer Correlations for Film Condensation
 Average heat transfer coefficient for film condensation on the outer surface of a
horizontal tube
 Comparison of vertical and horizontal tubes
For a sphere : Replace 0.729 by 0.815
For L > 2.77D, the heat transfer coefficient will be higher in the horizontal position.

20. 5 Horizontal Tube Banks
Heat Transfer Correlations for Film Condensation
 The average thickness of the liquid film at the lower tubes is
much larger as a result of condensate falling on top of them
from the tubes directly above.
 Therefore, the average heat transfer coefficient at the lower
tubes in such arrangements is smaller.
 This relation does not account for the increase in heat
transfer due to the ripple formation and turbulence caused
during rainage, and thus generally yields conservative results.

21. FILM CONDENSATION
INSIDE HORIZONTAL TUBES
 So far we have discussed film condensation on
the outer surfaces of tubes and other geometries,
which is characterized by negligible vapor
velocity and the unrestricted flow of the
condensate.
 For low vapor velocities:
 Reynolds number of the vapor is to be evaluated at the tube inlet conditions using
the internal tube diameter as the characteristic length.

22.  If the condensate does not wet the wall, because either it is dirty
or it has been treated with a non-wetting agent, droplets of
condensate nucleate at small pits and other imperfections on the
surface, and they grow rapidly by direct vapor condensation upon
them and by coalescence.
 When the droplets become sufficiently large, they flow down the
surface under the action of gravity and expose bare metal in their
tracks, where further droplet nucleation is initiated.
This is called DROPWISE CONDENSATION
Droplets
80°C
DROPWISE CONDENSATION
 Dropwise condensation has been studied experimentally for a number of surface–fluid
combinations. Of these, the studies on the condensation of steam on copper surfaces
has attracted the most attention because of their widespread use in steam power plants.
 P. Griffith (1983) recommended these simple correlations for dropwise condensation of
steam on copper surfaces:

23.  Droplets slide down when they reach a certain size, clearing the surface and
exposing it to vapor. There is no liquid film in this case to resist heat transfer.
 Heat transfer rates that are more than 10 times larger than those associated with film
condensation can be achieved with dropwise condensation.
 Thermal resistance of such drops is small; hence, heat transfer coefficients for
dropwise condensation are large; values of upto 30000 W/m2.K have been
measured. Hence, dropwise condensation is preferred over filmwise condensation.
 If the surface is treated with non-wetting agent (stearic acid) to promote dropwise
condensation, the effect lasts only few days, until the promoter is washed off or
oxidized.
 Bonding a polymer such as teflon to the surface is expensive and adds additional
thermal resistance.
 Gold plating is also expensive because of lack of sustainability of dropwise
condensation, present day condensers are designed based on filmwise
condensation. Filmwise condensation – conservative estimate.

24. CASE STUDY:
Experimental Study of Heat Transfer Using Water – Cooled
Condensers to Increase Oil Production from Plastic Waste
 Plastic waste handling has been carried out such as recycling plastic waste into fuel oil
using a mechanical cycle, using a heat exchanger, or using the principle of pyrolysis.
 The recycling process uses a mechanical cycle where the resulting product comes from
burning plastic waste used up to a certain temperature. The method of adding a heat
exchanger is intended to speed up the condensation process in the cooling pipe so that
it can produce more oil.
 Another method of recycle plastic waste using pyrolysis, plastic waste is heated at high
temperatures so that there is a change in the phase of solid plastic into gas, then there
will be a thermal cracking process.
 According thermal cracking is a pyrolysis process that is by heating the polymer material
without oxygen. This process is usually carried out at temperatures between 350 °C to
900 °C.
 Therefore, this research aims to look at the effect of heat transfer rate that occurs to
produce oil derived from the thermal cracking process using refrigerated heat
exchangers water.
Introduction:

25. Methodology/Experimental
 Types of research:
This research is an experiment carried out in the machine performance laboratory.
The main testing parameters consist of the plastic mass, processing time, temperature
and oil produced. The desired output parameter of plastic waste oil is the effect of
combustion time on temperature cooling and heat transfer rate.
 Test Equipment and Measuring Instruments:
The test equipment consisted of the main components of the reactor, a three-level
condenser, watercooled heat exchanger, firewood and oil palm shells, pipes and aqua
plastic that had been splashed. The measuring instrument used consisted of a digital
thermometer and laser, a weight scale, a thermocouple wire, and a stopwatch.
 Testing Procedure:
 Plastic waste from aqua bottles was weighed according to a specific dose. The type
of plastic used in this study was nonorganic type of Low Density Polyethylene.
These plastics are sorted, especially plastic used water bottles of small bottles of
aqua bottles of light colours.
 Plastic specifications refer to the thermal properties of non-organic Low Density
Polyethylene namely melting point, transition temperature and working temperature
according to table 1.

26.  The second step after the plastic is sorted then cleaned and cut into small pieces using a
plastic cutting machine that has been made by yourself. This simple waste processing
machine is made from used cans that serve as a container for cooking plastic waste heated
with firewood, then the combustion of steam enters or flows through condenser pipes so that
oil droplets come out which is equivalent to kerosene.
 For once the process takes about four hours and the weight of the material is 20 kg. Then the
heating process is carried out until the stable temperature approaches 400 0C for 30 minutes,
60 minutes and 90 minutes in the test equipment.
MATERIAL
TYPE
MELTING
POINT
TRANSITION
TEMPERATURE
WORKING
TEMPERATURE
PP 168 5 80
HDPE 134 110 82
LDPE 330 115 260
PA 260 50 100
PET 250 70 100
Table 1.Plastic Temperature data(temp. in degree Celsius)

27.  Comparison of pipe surface temperature with cracking time
 Comparison of heat transfer rate in the condenser
 Result:
From the LDPE type plastic waste processing research using the three-stage heat exchanger
into fuel oil above, it can be seen that the oil produced from plastic waste processing depends on
parameters including the type of plastic, fuel, time and process temperature.

28. CONCLUSIONS
 In the conversion process of LDPE type plastic waste with thermal cracking will
produce an optimal amount of oil at pyrolysis temperature 387 °C.
 Condenser 3 rate is higher than both the condenser 2 and 1 heat rate, Comparison
of the condenser 2 heat rate to the condenser 2 there is a decrease in the heat rate
ranges 65.6%.
 But when compared to condenser 1 a 91.8% reduction in the rate of heat is very
significant, this is due to a decrease in temperature distribution along the surface of
the pipe so that the density and vapor pressure decrease causing the total heat
transfer coefficient to decrease.
 From the analysis carried out when testing the heat exchanger on a non-organic
waste refining tool into fuel.
 We can conclude that the heat transfer temperature greatly affects the evaporation
of plastic waste that is converted into fuel and also affects the results produced by
the tool, namely 800 mL.

29. REFERENCES
1) Experimental Study of Heat Transfer Using Water – Cooled Condensers to Increase Oil Production from
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doi:10.1088/1742-6596/1764/1/012168
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Heat and Mass Transfer: Fundamentals & ApplicationsFourth Edition Yunus A. Cengel, Afshin J.
GhajarMcGraw-Hill, 2011Chapter 10 BOILING AND CONDENSATIONMehmet KanogluUniversity of
GaziantepCopyright © 2011 The McGraw-Hill Companies, Inc
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Polytechnic Institute, Troy, NY 12180, United States
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