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Refrigeration System Components

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Presentation on theme: "Refrigeration System Components"— Presentation transcript:

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


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