1. Refrigeration System Components
T. E. Mechanical Engineering
SEM - VI
Dept. of Mechanical Engineering
PVG, College of Engineering, Nashik

2. Basic components of Refrigeration system

3. Compressor Introduction Heart of VCC refrigeration system Function
30 – 40% of Total cost plant

4. Compressor Classification Based on working principle
A) Positive displacement type compressors
i) Reciprocating type compressor
a) Single acting
b) Double acting
ii) Rotary type with sliding vanes compressor
iii) Rotary screw type compressor
iv) Rotary scroll type compressor
iv) Orbital compressor
v) Acoustic compressor
B) Roto-Dynamic type compressors
i) Axial Flow type compressor
ii) Radial flow type compressor
a) Centrifugal compressor
Based on the arrangement of compressor motor/external drive
1) Open type
2) Hermetic/sealed type
3) Semi-hermetic type

5. Compressor
Reciprocating type compressor

6. Compressor Open type of compressor Advantage - high efficiency
Disadvantage - leakage of refrigerant, so required refrigerant reservoir & regular maintenance.
Applications-
Used for
Low specific volume & high condenser pressure
Low capacity plants
R-12, R-22, ammonia etc.

7. Compressor
Hermetic sealed compressor

8. Compressor Advantages No leakage Less noise as compared
Compact in size
Dust free
Disadvantages
Not used for wide range
Heat cannot rejected to surrounding
Maintenance of piston & valves is difficult or not possible
Applications
Used for
Small capacity refrigeration system
Domestic refrigerators, freezers & AC
Window AC & Water cooler etc.

9. Compressor Semi-hermetic sealed compressor
Developed to avoid the disadvantages of Hermetic compressor.
Advantages -
Maintenance is easy
Efficiency is high - cooling motor is provided
Disadvantage-
Cost is higher compared to hermetic compressor
Applications
Used for
Refrigerants R-134a, R-407C, R-404A, R-507A, & R-22.

10. Compressor
Rotary type with sliding vanes compressor

11. Compressor Advantages It is simple, compact design
Low rotation speeds resulting lower vibrations & noise
Lower cycle temperature reduce wear, oil consumption & leakage
Low need for maintenance
Applications
Domestic refrigerators, freezers and air conditioners.

12. Compressor
Rotary screw type compressor

13. Compressor Advantages- Better performance per hp Improved reliability
Low cost
Fewer moving parts
Less vibration
Less refrigerant loss
Applications: used in small scale refrigeration applications ( household & commercial units)

14. Compressor Rotary scroll type compressor Advantages: Higher efficiency
Better part load performance & operating characteristics
Applications:
Supercharger
Vacuum pump

15. Compressor
Centrifugal compressor

16. Factors affecting Performance of the Compressor
Compressor speed
Suction pressure
Suction temperature
Discharge pressure
Type of refrigerant

17. Compressor selection criteria
Refrigeration capacity
Volumetric flow rate
Compression ratio
Thermal & physical properties of the refrigerant

18. Condenser Introduction
Condensers and evaporators are heat exchangers in which the refrigerant undergoes a phase change
Heat rejected to an external fluid
Proper design and selection is essential for good system performance

19. Condenser Classification Selection criteria for condenser type
Water cooled condensers
a) double tube or tube-in-tube type
b) shell & tube type
c) shell & coil tube type
Air cooled condensers
a) natural convection type
b) forced convection type
Evaporative condensers
Selection criteria for condenser type
Condenser heat capacity
Condensing temperature and pressure
Flow rate of refrigerant
Design temperature for and/or air
Climate conditions

20. Double tube or tube-in-tube type condenser

21. Shell & tube type condenser
Shell & coil tube type
condenser

22. Air cooled condensers Advantages No water requirement
Standard outdoor installation
Elimination of freezing, scaling & corrosion problems
Elimination of water piping, circulation pumps & water treatment
Low installation cost
Low maintenance & service requirement
Disadvantages
High condensing temperatures
High power requirements per KW of cooling
High noise intensity because of fan

23. Natural convection type
Forced convection type

24. Evaporative condensers
Characteristics
Water treatment is necessary to maintain properties
Minimum space requirement
Small piping sizes & short overall lengths
Small system pumps

25. Expansion Devices Function- Classification
- Reduce pressure from condenser pressure to evaporator pressure
- Regulate the refrigerant flow
Classification
fixed opening type
1) Capillary Tubes
2) Orifice
Variable opening type
1) Hand (manual) expansion valves
2) Constant pressure or Automatic Expansion Valve (AEV)
3) Thermostatic Expansion Valve (TEV)
4) Float type Expansion Valve
a) High Side Float Valve
b) Low Side Float Valve
5) Electronic Expansion Valve

26. Capillary Tubes Capillary Tubes
Diameter of capillary tube- range from 0.5 mm to 3 mm & length 1 m to 6 m.
Pressure reduction factors-
Frictional resistance between refrigerant and tube wall
Liquid refrigerant evaporates into mixture of liquid & vapour

27. Capillary Tubes Advantages Disadvantages It is inexpensive
It does not have any moving parts hence it does not require maintenance
Starting torque requirement of the motor is low
Ideal for hermetic compressor based systems.
Disadvantages
It cannot adjust itself to changing flow rate conditions
It is susceptive to clogging, hence required filter driver
Slugging of compressor is occur because of liquid refrigerant may get enter into compressor during off-cycle, hence provide accumulator after evaporator

28. Automatic Expansion Valve (AEV)
Maintain a constant pressure & thereby a constant temperature in Evaporator.
𝐹 𝑠 = force due to the adjustable spring
𝐹 𝑜 = 𝑃 𝑜 . 𝐴 𝑜 = Atmospheric force
𝐹 𝑒 = force due to evaporator pressure
𝐹 𝑓𝑠 = force due to follow-up spring
If 𝐹 𝑒 + 𝐹 𝑓𝑠 > 𝐹 𝑜 + 𝐹 𝑠 Valve will be
closed
If 𝐹 𝑒 + 𝐹 𝑓𝑠 < 𝐹 𝑜 + 𝐹 𝑠 Valve will be
open
During off-cycle:
𝐹 𝑒𝑜 + 𝐹 𝑓𝑠𝑜 > 𝐹 𝑜 + 𝐹 𝑠𝑜

29. Thermostatic Expansion Valve (TEV)
Most versatile expansion valve
Maintain constant degree of superheat at the exit of evaporator, hence preventing slugging of compressor
Capillary tube with power fluid, may be same or crossed

30. Float type Expansion Valve
normally used with flooded evaporators in large capacity refrigeration systems
Depending upon the location of the float chamber
low-side float valve
high-side float valve
Low-side float valves: maintains a constant liquid level in a flooded evaporator or a float chamber attached to the evaporator.
high-side float valve: maintains the liquid level constant in a float chamber that is connected to the condenser on the high pressure side

31. Electronic Expansion Valve

32. Evaporators Introduction
Evaporator like condenser is also a heat exchanger
In an evaporator the refrigerant boils or evaporate and in doing. So absorbs heat from the substance
The name evaporator refers to the evaporation process occurring in the heat exchanger
Classification
Based on the heat transfer process
1) natural convection type- fluid being cooled, flows due to natural convection currents arising due to buoyancy force due to density difference. Refrigerant flows inside tube.
2) forced convection type- A fan or a pump is used to circulate the fluid being refrigerated & make it flow over the H.T surface. Refrigerant flows outside tube.
Refrigerant flow Inside or Outside of tubes
Flooded and Dry Type

33. Natural convection type of evaporators
used in domestic refrigerators and cold storages
Advantages
Evaporator occupies less floor space
Operate for longer periods without defrosting
Simple to make and easy to maintain
Very useful when low air velocities and minimum dehumidification of the product is required
Disadvantages
Long lengths are required as overall heat transfer coefficient is small

34. Flooded type evaporators
Mass balance at steady state
𝑋 4 . 𝑚 + X. f. 𝑚 = 𝑚
f = 1− 𝑋 4 𝑋
Where, f = Recirculation
factor

35. Flooded type evaporators
Typically used in large ammonia systems
The refrigerant enters a surge tank through a float type expansion valve
the compressor directly draws the flash vapour which improves the performance
liquid refrigerant enters the evaporator from the bottom of the surge tank
the mixture of liquid and vapour flows along the evaporator tubes
the vapour is separated as it enters the surge drum or surge tank & unevaporated liquid is re circulated

36. Flooded Type Shell-and-Tube Evaporator
liquid to be chilled flows through the tubes
The refrigerant is fed through a float valve which maintains a constant level of liquid refrigerant in the shell
Both single and multi pass arrangements are possible
These are also available in vertical configuration
Since the shell is not completely filled with liquid refrigerant superheating is also possible
Available in larger capacities ranging from 10 TR to thousands TR

37. Dry type evaporators
A part of the heat transfer is used for superheating the vapour
A thermostatic expansion vale or a capillary tube is used in conjunction with a dry evaporator
Flow of refrigerant inside tube
uses fins inside the tube
requires less refrigerant and has positive lubricating oil return
normally used for small and medium capacity refrigeration plants with capacity ranging from 2 TR to 350 TR

38. Direct expansion type, Shell-and-Tube Evaporator