2. ▶ Condensation is the change of the physical
state of matter from gas phase into liquid
phase, and is the reverse of vaporization.
▶ The word most often refers to the water cycle.
It can also be defined as the change in the state
of water vapor to liquid water when in contact
with a liquid or solid surface or cloud
condensation nuclei within the atmosphere.
Condensation
3. Based on whether the condensate wets the surface or
does not wet the solid surface
1. Drop-wise condensation:
▶ Condensate accumulates on the surface in the form of
droplets
▶ Heat transfer coefficient is 4 to 8 times higher
1. Film condensation:
▶ Condensate wets the surface and forms a film on
surface
▶ Heat transfer coefficient is lower
Condensation Types
4. ▶ Heat Exchanger device
▶ Important component of Refrigeration
system.
▶ Refrigerant enters the condenser in
superheated form
▶ Refrigerant undergoes phase change from
vapour to liquid.
Condenser
5. ▶ Refrigerant vapor condenses by rejecting heat to
heat sink.
▶ Heat sink does not undergo phase change.
6. ▶ Process 2-3 is condenser process.
Refrigeration Cycle
7. ▶ Based on external fluid, Condensers are classified as :
a. Air cooled Condenser
b. Water cooled Condenser
c. Evaporative Condenser
Classification of Condensers
8. ▶ Based on direction of
flow of fluid:
1. Vertical Condenser
2. Horizontal Condenser
Classification of Condensers
10. ▪ Heat transfer from condenser is by natural convection
and radiation.
▪ Large surface area is required.
▪ Two types
i. Plate surface type
ii. Finned tube type.
Natural Convection Type
11. ▶ Used in small refrigerators and freezers
▶ Refrigerant carrying tubes are attached to outer walls
of refrigerator.
▶ The whole wall of refrigerant acts as a fin.
▶ Also called as flat back refrigerators.
Plate surface type
12. ▶ Mounted either below the refrigerator at an angle or
on the backside of the refrigerator.
▶ Warm air rises up and to assist it an air envelope is
formed by providing a jacket on backside of the
refrigerator.
▶ fin spacing is kept large to minimize the effect of
fouling by dust and to allow air to flow freely with
little resistance .
Finned tube type
13.
14. Forced Convection
▶ Circulation of air over the condenser surface is
maintained by using a fan or a blower.
▶ Use fins to increase heat transfer.
▶ Used in window air conditioners, water coolers and
packaged air conditioning plants.
15.
16. Water Cooled Condenser
▶ Water is used as an external fluid.
▶ They are of 3 types:
I. Double pipe or tube in tube type
II. Shell and coil type.
III. Shell and tube type.
17. ▶ Double pipe condensers are normally used up to 10 TR
capacity. Figure 22.4 shows the schematic of a double pipe
type condenser. As shown in the figure, in these condensers
the cold water flows through the inner tube, while the
refrigerant flows through the annulus in counter flow.
Headers are used at both the ends to make the length of
the condenser small and reduce pressure drop. The
refrigerant in the annulus rejects a part of its heat to the
surroundings by free convection and radiation. The heat
transfer coefficient is usually low because of poor liquid
refrigerant drainage if the tubes are long.
Double pipe or tube in tube type
18. ▶ These condensers are used in systems up to 50 TR
capacity. The water flows through multiple coils, which
may have fins to increase the heat transfer coefficient.
The refrigerant flows through the shell. In smaller
capacity condensers, refrigerant flows through coils
while water flows through the shell. Figure 22.5 shows
a shell-and-coil type condenser. When water flows
through the coils, cleaning is done by circulating
suitable chemicals through the coils.
Shell and coil type.
19. ▶ This is the most common type of condenser used in systems from 2 TR upto
thousands of TR capacity. In these condensers the refrigerant flows through
the shell while water flows through the tubes in single to four passes. The
condensed refrigerant collects at the bottom of the shell. The coldest water
contacts the liquid refrigerant so that some subcooling can also be obtained.
The liquid refrigerant is drained from the bottom to the receiver. There might
be a vent connecting the receiver to the condenser for smooth drainage of
liquid refrigerant. The shell also acts as a receiver. Further the refrigerant also
rejects heat to the surroundings from the shell. The most common type is
horizontal shell type. A schematic diagram of horizontal shell-and-tube type
condenser is shown in Fig. 22.6.
▶ Vertical shell-and-tube type condensers are usually used with ammonia in
large capacity systems so that cleaning of the tubes is possible from top while
the plant is running.
Shell and tube type
20.
21.
22.
23. ▶ Latent heat of fluid for conversion from vapour to
liquid
▶ Overall heat transfer coefficient of heat exchanger
▶ Log mean temperature difference
▶ Operating pressure
▶ Mass flow rate of cooling water
▶ Space availability
▶ Capacity and requirements
Condenser Design Considerations
24. ▶ Logarithmic mean temperature difference:
▶ Mass flow rate of cooling water:
Condenser Design Calculations
25. ▶ Heat transfer area:
▶ Number of tubes:
n= Required area of heat transfer/Heat transfer
area of one tube
Condenser Design Calculations
26. ▶ The air leaks through the joints and packing and into
condenser where the pressure is below the
atmospheric pressure.
▶ The boiler feed water contains dissolved air. From the
boiler it is carried off by steam and to the turbine and
finally to the condenser.
▶ Normally the quantity of air leakage in surface
condenser is 0.05% of steam condensed.
Sources of air leaks in condensers
27. ▶ It is increases the back pressure on the turbine with
the effect that there is less enthalpy drop and low
thermal efficiency of plant.
▶ It reduces the rate of condensation of steam, because
air having poor thermal conductivity reduces the
overall heat transfer from steam air mixture.
▶ The presence of air in the condenser increases the
corrosive action
Effect of air leakages
28. ▶ Copper(HTC= 399 W/mK)
▶ Aluminium(HTC= 235 W/mK)
▶ Steel(HTC= 43) Varies with grades of steel
Materials used
30. Water cooled
1. Efficient than air cooled
2. Used for swimming pools
3. Condensers piped for city
water flow
4. Requires regular
maintenance
Applications
32. ▶ Water used once and then “wasted” down the
drain
▶ Economical if water is free or if the system is
small
▶ The main drawback is that the water
temperature can vary a great deal
▶ Typical water temperature is about 75°F
▶ 75°F wastewater requires a flow of about 1.5
gpm per ton of refrigeration to absorb the heat
rejected by the condenser
▶ Water typically leaves the condenser at 95°F
Wastewater Systems
34. ▶ Device used to remove heat from the water
used in recirculated water systems
▶ Towers can cool the water to a temperature
within 7°F of the wet bulb temperature of the air
surrounding the tower
▶ If the wet bulb temperature is 90 degrees, water
can be cooled to a temperature as low as 83°F
▶ Natural draft, forced draft, or evaporative
Cooling Towers
36. ▶ Have larger surface areas than standard
condensers
▶ Allow systems to operate at lower
pressures
▶ Allow systems to operate more efficiently
▶ Can operate with head pressures as low
as 10°F higher than the outside ambient
temperature
High Efficiency Condensers
