The document provides a detailed examination of vapor compression refrigeration systems, outlining various components such as compressors, condensers, and expansion devices. It categorizes compressors into positive displacement and roto-dynamic types and discusses their specific designs, advantages, and disadvantages. Additionally, the document covers the classifications of condensers and evaporators, detailing their operational principles and applications in refrigeration systems.

1. Various Components of Vapor
Compression Refrigeration
Systems
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

2. Detailed Study of various Components:
Compressors Condensers Evaporators Expansion Devices
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

3. Compressor’s Classifications
1. Based on Working Principle:
 Positive Displacement Type
 Reciprocating type
 Rotary type with sliding vanes (rolling piston type or multiple vane type)
 Rotary screw type (single screw or twin-screw type)
 Orbital/Scroll compressors
 Roto-Dynamics
 Radial flow type, or
 Axial flow type
2. Based on arrangement of compressor motor or external drive:
Open type
 Hermetic (or sealed) type
Semi-hermetic (or semi-sealed) type
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

4. Positive Displacement Type
The flow of refrigerant to the compressor is not steady, the positive displacement type compressor is a
pulsating flow device.
Disadvantages:
 Prone to high wear
 Vibrations
 High noise level.
Roto-Dynamics Type
In roto-dynamic compressors, the pressure rise of refrigerant is achieved by imparting kinetic energy
to a steadily flowing stream of refrigerant by a rotating mechanical element and then converting into
pressure as the refrigerant flows through a diverging passage.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

5. Positive Displacement Type
• Reciprocating type:
 Valves:
 Suction valve attached to Evaporator end
 Delivery Valve attached to Condenser Inlet
Pressure during inlet is low while delivering its high inside the cylinder.
 The valves used are of reed or plate type, which are either floating or clamped.
 The piston speed is decided by valve type. Too high a speed will give excessive vapor velocities that will
decrease the volumetric efficiency and the throttling loss will decrease the compression efficiency.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

6. • Rotary Compressors
 Used in small refrigeration systems (upto 2 kW
capacity)
 Compression is achieved by reducing the volume of
the refrigerant.
 In this type of compressors, the rotating shaft of the
roller has its axis of rotation that matches with the
centerline of the cylinder, however, it is eccentric
with respect to the roller
 The rotating motion of the roller causes a
reciprocating motion of the single vane.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

7. • Rotary Screw(twin) Compressors:
1. Scroll compressors are orbital motion.
2. Suction and compression is obtained by using two
mating, spiral shaped, scroll members, one fixed and the
other orbiting.
3. The compression process involves ORBiTING
SCROLL and then as pressure increases the discharge
takes place axially
• Rotary Screw(twin) Compressors:
Two mating helically grooved rotors, one male and the
other female.
The male rotor has lobes, while the female rotor has
flutes or gullies.
The flow is mainly in the axial direction.
Suction and compression take place as the rotors unmesh
and mesh.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

8. Roto-Dynamic COMPRESSORS
 Centrifugal compressors; also known as turbo-compressors.
 Pressure rise takes place due to the continuous conversion of angular
momentum imparted to the refrigerant vapour by a high-speed impeller
into static pressure.
 Centrifugal compressors are steady-flow devices subjected to less
vibration and noise.
 As the refrigerant flows through the blade passages towards the tip of the
impeller, it gains momentum and its static pressure also increases.
 From the tip of the impeller, the refrigerant flows into a stationary
diffuser (4).
 In the diffuser, the refrigerant is decelerated and as a result the dynamic
pressure drop is converted into static pressure rise, thus increasing the
static pressure further.
 The vapours from the diffuser enters the volute casing (5) where further
conversion of velocity into static pressure takes place due to the
divergent shape of the volute.
 Finally, the pressurized refrigerant leaves the compressor from the
volute casing (6)
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

9. Condenser: Unit used to reject heat after sub-heating and also during sub-cooling
at constant pressure
Classifications:
Air Cooled Condenser
Water Cooled Condenser
Evaporative Condensers
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

10. Air Cooled Condensers….
Air is used as fluid for cooling purpose i.e. refrigerant
rejects heat to air flowing over a condenser.
Further Classifications:
1. Natural Convection Type:
 The finned type condensers are mounted either below the
refrigerator at an angle or on the backside of the
refrigerator.
 In case, it is mounted below, then the warm air rises up and
to assist it an air envelope is formed by providing a jacket
on backside of the refrigerator. The fin spacing is kept large
to minimize the effect of fouling by dust and to allow air to
flow freely with little resistance.
 A thin wires are welded to the serpentine tube coil. The
wires act like fins for increased heat transfer area. Figure 1.
shows the schematic of a wire-and-tube type condenser
commonly used in domestic refrigerators. Hence these
condensers are used for small capacity refrigeration systems
like household refrigerators and freezers.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

11. Air Cooled Condensers….
2. Forced Convection Type:
In forced convection type condensers, the
circulation of air over the condenser surface is
maintained by using a fan or a blower.
These condensers are normally uses fins on air-
side for good heat transfer. The fins can be
either plate type or annular type.
Forced convection type condensers are
commonly used in window, air conditioners,
water coolers and packaged air conditioning
plants.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

12. Water Cooled Condenser
Depending upon the construction it is further Classified as:
1. Double pipe or tube-in-tube type
2. Shell-and-coil type
3. Shell-and-tube type
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

13. Water Cooled Condenser…
1. Double Type Tube-In-Tube type:
Double pipe condensers are normally used up to 10 TR
capacity.
The cold water flows through the inner tube.
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.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

14. Water Cooled Condenser…
2. Shell-and-coil type::
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 4 shows a shell-and-coil type
condenser. When water flows through the
coils, cleaning is done by circulating suitable
chemicals through the coils.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

15. Water Cooled Condenser…
3. Shell-and-tube type::
• Used in systems from 2 TR upto thousands of TR capacity.
• 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 liquid refrigerant is drained from the bottom to the receiver.
• A vent connecting the receiver to the condenser for smooth
drainage of liquid refrigerant.
• The most common type is horizontal shell type.
• 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.
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

16. Evaporative Condenser
• Both air and water are used to extract heat from the
condensing refrigerant.
• Evaporative condensers combine the features of a
cooling tower and water-cooled condenser in a single
unit.
• In these condensers the water is sprayed from top part
on a bank of tubes carrying the refrigerant and air is
induced upwards. There is a thin water film around
the condenser tubes from which evaporative cooling
takes place.
• The heat transfer coefficient for evaporative cooling is
very large and can be operated at low condensing
temperatures (about 11 to 13 K above the wet bulb
temperature of air)..
• The role of air is primarily to increase the rate of
evaporation of water.
• The required air flow rates are in the range of 350 to
500 m /h per TR of refrigeration capacity
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

17. Expansion Devices
• Constant pressure or Automatic Expansion Valve (AEV)
• Thermostatic Expansion Valve (TEV)
• Capillary Tubes
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

18. Expansion Devices
Constant pressure or Automatic Expansion
Valve (AEV):
• The adjustment spring is usually set such that during off-cycle, the needle is pushed
against the orifice. Hence,
• During the off-cycle, the refrigerant will vaporize in the evaporator as a result the
evaporator pressure rises during the off-cycle .
• During on- refrigerant is not fed to evaporator while the compressor removes the
refrigerant from the evaporator and hence, the evaporator pressure Pe starts
decreasing at a very fast rate since valve is closed
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

19. Expansion Devices
Thermostat Expansion:
• A thermostatic expansion valve maintains
a constant degree of superheat at the exit
of evaporator
Minesh Vohra (15783) Asst. Professor (SME-M3-MD08)

20. Capillary tube
• It is a fixed restriction type device.
• 0.5m to 5m length and 0.5mm to 2.25mm diameter.
• Pressure drop due to friction and length of tube
• Advantages are simplicity, low cost, absence of moving parts.

21. EVAPORATOR:
Flooded Type Evaporator
• The amount of liquid refrigerant
circulated through the evaporator is
considerably in excess of that which
can be vaporised.
• Float valve is used for maintaining the
constant liquid level.
• Accumulator is used to prevent liquid
carry over to compressor.
• Give high rate of heat transfer
• Used in large installations, chemical
and food processing industries.

22. Dry or direct expansion type evaporator
• Amount of liquid refrigerant fed into the evaporator is limited to
that which can be completely vaporised by the time it reaches
the end of evaporator.
• Mostly used in producing refrigeration and having capacity
below 150 tonnes of refrigeration.Vapours
Liquid-
Vapours
Liquid

23. Bare tube evaporator
• Usually constructed of either steel pipe or copper tubing.
• Copper tubing is used in small evaporators using freon as refrigerant
whereas steel pipe is employed with large evaporators using
ammonia as refrigerant.
• Used in household refrigerators.
• Principle same as dry expansion type evaporator.

24. Plate surface Evaporator
• Made in different designs
• Tubing is attached to the plates whereas in other cases two sheets
may be pressed together to provide a path for refrigerant flow
between them.
• Used in domestic refrigerators or frozen food industry.

25. Finned Tube evaporator
• Finned coils are bare tube coils upon which metal plates or fins have
been installed.
• Fins increase the surface area and heat transfer rate
• Best suited for window type AC and other air-cooling application
where temperature is maintained above 1˚C.
• Adding a fan to the finned evaporator increases the performance.