1. Unit: 5 Compressors and their
typestypes
Prepared by:
Ankur Sachdeva (ME)
Assistant Professor
KIET Group of Institutions
Ankur Sachdeva, Assistant Professor (ME)
2. Recapitulation of VCRS
• Compressor: It is a machine used to
compress the refrigerant from the
evaporator and to raise its pressure
so that the corresponding
temperature is higher than that of
the cooling medium.
• Condenser: It is an important device
used in the high pressure side of a
refrigeration system. Its function is to
used in the high pressure side of a
refrigeration system. Its function is to
remove heat of the hot vapour
refrigerant discharged from the
compressor.
• Throttling Device: It divides the high
pressure side and the low pressure
side of a refrigeration system.
• Evaporator: Its function is to absorb
heat from the surrounding location
or medium which is to be cooled, by
means of a refrigerant.
Ankur Sachdeva, Assistant Professor (ME)
3. Devices and Controls used in
Refrigeration
Ankur Sachdeva, Assistant Professor (ME)
5. Compressors
• It is the most important part of any vapour
compression refrigeration system and usually most
costliest.
• It removes low temperature and low pressure
refrigerant vapours from the cooling coil through the
suction line.suction line.
• It compresses these refrigerant vapours by increasing
the pressure and temperature resulting in an increase
of boiling point of the refrigerant,
• It discharges the refrigerant vapours of high
temperature and pressure to condenser through
discharge line.
Ankur Sachdeva, Assistant Professor (ME)
7. Classification of Compressors
2. Based on arrangement of compressor
motor or external devices
- Open Type
- Hermetic (or Sealed Type)- Hermetic (or Sealed Type)
- Semi-Hermetic (Or Semi-Sealed Type)
Ankur Sachdeva, Assistant Professor (ME)
8. Reciprocating Compressor
• A reciprocating compressor is
also called a piston compressor
which adopts the back and forth
piston motion in a cylinder
synchronized with suction and
discharge valves to compress the
vaporized refrigerant from a low
pressure and temperature to a
high pressure and temperature.high pressure and temperature.
• The motion of the piston is
achieved via a crankshaft which
converts motor rotations to
piston reciprocations.
• Each operation cycle includes
three actions: suction,
compression and discharge. Each
crankshaft rotation can achieve
these three actions in sequence;
as a result, the gas displacement
is discontinuous which causes
vibration.Ankur Sachdeva, Assistant Professor (ME)
9. Rotary Vane Compressor
• A rotary-vane compressor is also
known as a rotary piston compressor
because the function of the vane is
similar to that of a piston .
• The fixed casing is known as a
cylinder. The vane splits the space
between the cylinder and the rolling
piston into two sections (suction and
discharge).discharge).
• As the rolling piston rotates, these
two volumes are increased and
decreased to achieve gas suction,
compression and discharge.
• This compressor type can also be
sub-classified by the drive speed
(constant and variable) and number
of vanes.
• Each operation cycle includes five
actions: start, suction, compression,
discharge and end.
Ankur Sachdeva, Assistant Professor (ME)
10. Working of a Rotary Vane
Compressor
Ankur Sachdeva, Assistant Professor (ME)
11. Screw Compressor
• Screw compressors use a pair
of helical rotors or screws
which mesh together to
compress the refrigerant
between them.
• They can produce high
pressure for a small quantity
of gas and consume lessof gas and consume less
power than reciprocating
compressors.
• They have low to medium
initial and maintenance costs
and few moving parts.
• However, they have difficulty
in dirty environments, high
rotational speeds, and shorter
life expectancies than other
designs.
Ankur Sachdeva, Assistant Professor (ME)
12. Working of Screw Compressors
Ankur Sachdeva, Assistant Professor (ME)
13. Scroll Compressor
• Scroll compressors use two offset
spiral disks nested together to
compress the refrigerant. The upper
disk is stationary while the lower disk
moves in orbital fashion.
• Scroll compressors are quiet,
smooth-operating units with few
moving parts and the highest
efficiency ratio of all compressor
moving parts and the highest
efficiency ratio of all compressor
types.
• A rotary-scroll compressor is used to
compress larger volumes of gaseous
refrigerant to a higher pressure and
temperature via a fixed and orbital
scroll.
• Scroll compressors are commonly
used in automobile air conditioning
systems and commercial chillers.
Ankur Sachdeva, Assistant Professor (ME)
14. Working of Scroll Compressors
Ankur Sachdeva, Assistant Professor (ME)
15. Centrifugal Compressor
• Centrifugal compressors use the
rotating action of an impeller wheel
to exert centrifugal force on
refrigerant inside a round chamber
(volute).
• Unlike other designs, centrifugal
compressors do not operate on the
positive displacement principle, but
have fixed volume chambers.
• They are well suited to compressing• They are well suited to compressing
large volumes of refrigerant to
relatively low pressures. The
compressive force generated by an
impeller wheel is small, so systems
that use centrifugal compressors
usually employ two or more
stages (impellers wheels) in series to
generate high compressive forces.
• Centrifugal compressors are desirable
for their simple design, few moving
parts, and energy efficiency when
operating multiple stages.
Ankur Sachdeva, Assistant Professor (ME)
17. Open Type Compressor
• In this type, compressor and
motor works as two
separate units and they
have a distinct casing for
both of them.
• The compressor is
connected to the motor byconnected to the motor by
a belt or crankshaft.
• Open type compressors are
not leak proof as they are
most susceptible to the
leaks.
• They rely on shaft seals in
order to prevent leakage of
working fluids and then to
retain the internal pressure.
Ankur Sachdeva, Assistant Professor (ME)
18. Hermetic (Sealed Type)
Compressor
• In hermetic compressors,
the motor and the
compressor are enclosed in
the same housing to
prevent refrigerant leakage.
• The housing has welded• The housing has welded
connections for refrigerant
inlet and outlet and for
power input socket.
• As a result of this, there is
virtually no possibility of
refrigerant leakage from the
compressor.
Ankur Sachdeva, Assistant Professor (ME)
19. Semi-Hermetic
( or Semi-Sealed Type) Compressor
• Semi-hermetic compressor
also encloses the motor
compressor by common
housing.
• It prevents the leakage of
the fluid.
• It prevents the leakage of
the fluid.
• In a semi-hermetic
compressor, the casing is
bolted together instead of
rigidly welding.
• The casing can be opened
to repair motor and other
components
Ankur Sachdeva, Assistant Professor (ME)
