refrigerantcompressor - VCRS COPMONENTS.pptx

compressor

1. REFRIGERATION EQUIPMENTS

2. COMPRESSORS Compressors are work absorbing devices which are used for increasing pressure of fluid at the expense of work done on fluid. Compressors are invariably used for all applications requiring high pressure air. Some of popular applications of compressor are for driving pneumatic tools and air operated equipments, spray painting, compressed air engine, supercharging in internal combustion engines, material handling (for transfer of material), refrigeration and air conditioning chemical industry etc. Out of several equipments like compressor, condenser, evaporator, expansion devices etc. in refrigeration system compressor is considered the heart of the refrigeration systems, because it pumps the refrigerant through the system A refrigerant compressor 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

3. TYPES OF COMPRESSORS : Fundamentally there are two types of compressors Positive displacement compressors Non- positive displacement compressors

4. In the positive-displacement type, a given quantity of air or gas is trapped in a compression chamber and the volume it occupies is mechanically reduced, causing a corresponding rise in pressure prior to discharge. The reciprocating compressors are which the vapour refrigerant is compressed by the reciprocating (i.e. back and forth) motion of the piston, called reciprocating compressors. These compressors are used for refrigerants which have comparatively low volume per kg and a large differential pressure, such as ammonia, R-12, R-22, etc.

5. Suction line Discharge line Valve plate Head Discharge valve Suction valve Piston Rings Crankshaft Connecting Rod

6. COMPRESSION PROCESS - EXPANSION Piston is the highest point in the cylinder Referred to as top dead center Both the suction and discharge valves are closed Cylinder pressure is equal to discharge pressure As the crankshaft continues to turn, the piston moves down in the cylinder The volume in the cylinder increases The pressure of the refrigerant decreases

7. Suction valve closed Discharge valve closed Piston moving downward in the cylinder Refrigerant trapped in the cylinder Pressure of the refrigerant in the cylinder is equal to the discharge pressure

8. COMPRESSION PROCESS – SUCTION As the piston moves down, the pressure decreases When the cylinder pressure falls below suction pressure, the suction valve opens The discharge valve remains in the closed position As the piston continues downward, vapor from the suction line is pulled into the cylinder Suction continues until the piston reaches the lowest position in the cylinder (bottom dead center) At the bottom of the stroke, suction valves close

9. Suction valve open Discharge valve closed Piston moving downward in the cylinder Pressure of the refrigerant in the cylinder is equal to the suction pressure Suction gas pulled into the compression cylinder

10. COMPRESSION PROCESS - COMPRESSION Piston starts to move upwards in the cylinder The suction valve closes and the discharge valve remains closed As the piston moves upwards, the volume in the cylinder decreases The pressure of the refrigerant increases Compression continues until the pressure in the cylinder rises just above discharge pressure

11. Suction valve closed Discharge valve closed Piston moving up in the cylinder Pressure of the refrigerant in the cylinder is equal to the suction pressure Volume is decreasing, compressing the refrigerant

12. COMPRESSION PROCESS - DISCHARGE When the cylinder pressure rises above discharge pressure, the discharge valve opens and the suction valve remains closed As the piston continues to move upwards, the refrigerant is discharged from the compressor Discharge continues until the piston reaches top dead center

13. Suction valve closed Discharge valve open Piston moving up in the cylinder Pressure of the refrigerant in the cylinder is equal to the discharge pressure Discharge gas pushed from the compression cylinder

14. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

15. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

16. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

17. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

18. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

19. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) V p V 1 2 3 4

20. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

21. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

22. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

23. p V 1 2 3 4 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes)

24. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

25. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

26. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

27. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

28. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

29. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

30. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

31. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

32. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

33. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

34. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

35. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

36. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

37. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

38. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

39. 1 – 2 polytropic compression (2 delivery valve opens) 2 – 3 delivery at constant pressure and temperature (3 delivery valve closes) 3 – 4 polytropic expansion (4 suction valve opens) 4 – 1 suction at constant pressure and temperature (1 suction valve closes) p V 1 2 3 4

40. RECIPROCATING COMPRESSORS : The states of the refrigerant in a reciprocating compressor can be expressed by four lines on a PV diagram as shown in Fig 1 2 4 3 Clearance Discharge volume Suction intake volume Total cylinder volume Piston displacement volume pressure

41. WORK DONE BY A RECIPROCATING COMPRESSOR Without clearance volume theoretical compression may be considered as constant entropy and constant temperature. Actual compression close to Polytropic process Here 1-2 is isentropic process 1-2 ’ is polytropic process 1-2 ” is isothermal process Work done per cycle Considering compression as polytropic process 4 1 3 2 2 ’ 2 ” p v P 1 P 2 v 1 A ” A ’ A

42. Work done per cycle Considering compression as isothermal process 2 2 ’ 2 ” p v P 1 P 2 v 1 A ” A ’ A Work done per cycle Considering compression as isentropic process

43. WORK DONE BY A RECIPROCATING COMPRESSOR With clearance volume Work done by compressor W= W= W= 1 2 4 3 Clearance(V 1 ) Discharge volume Suction intake volume( V a ) Total cylinder volume(V 1 ) Piston displacementV s volume pressure

44. VOLUMETRIC EFFICIENCY Defined as ratio of actual volume taken in per stroke to the stroke volume η v = Applying pv n = C at states 3 and 4 Substituting the value of v 4 in η v We get Where is the clearance factor

45. ROTARY COMPRESSORS ROLLING PISTON TYPE ROTARY COMPRESSORS: Rolling piston or fixed vane type or single stationary blade type compressors are used in small refrigeration systems ( upto 2 kW capacity) This compressors belong to the class of positive displacement type as compression is achieved by reducing the volume of refrigerant. It consists of stationary cylinder, a roller and a shaft, The rotating shaft of the roller has its axis of rotation that matches with the centerline of the cylinder The shaft has an eccentric with respect to the roller. A single vane or blade is positioned in the slot of non-rotating cylindrical block by means of spring. The rotating motion of the roller causes a reciprocating motion of the single vane. The gas is compressed as the rotor revolves due to the eccentrical assembly of the rotor and the cylinder. Rotor shaft

46. They operate on rotors which rotate on an eccentric shaft. Gas enters through a space between the rotor and the cylinder through a suction port. Fig 1 shows the completion of intake stroke and the beginning of compression stroke Fig2 shows the compression of refrigerant vapour ahead of the roller and the new intake starts Fig3 shows mid position of roller in the cylinder more refrigerant vapour is drawn while the compressed refrigerant is discharged A discharge port on the opposite releases the compressed air. Fig1 Fig2 Fig3

47. Fig4 shows most of compressed vapour refrigerant is discharged through discharge port. A new charge of refrigerant is drawn into cylinder Rotary compressors are popular in domestic refrigeration and suited for applications where large volumes of vapor are circulated and where a low compression ratio is desired Fig 4 Rotary compressors have high volumetric efficiencies due to negligible clearance. They are normally used in a single stage up to a capacity of 5 TR with R-114

48. ROTATING VANE OR BLADE TYPE COMPRESSOR The rotary vane compressor employs a series of rotating vanes or blades, which are installed equidistant around the periphery of a slotted rotor. The vanes move back and forth radially in the rotor slots The rotor is mounted eccentrically in a steel cylinder so that the rotor nearly touches the cylinder wall on one side The vanes are held firmly against the cylinder wall by action of the centrifugal force developed by the rotating rotor.

49. The suction vapour drawn into the cylinder through suction ports in the cylinder wall is entrapped between adjacent rotating vanes. The vapour is compressed as the vanes rotate from the point of maximum rotor clearance to the point of minimum rotor clearance. The compressed vapour is discharged from the cylinder through ports located in the cylinder wall near the point of minimum rotor clearance. It is preferred for low temperature applications It is used a booster is the first stage of a two-stage compression process.

50. ROTARY SCREW COMPRESSOR: 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. As the left rotor turns clockwise, the right rotor rotates counterclockwise. This forces the gases to become trapped in the central cavity. The space in which the air is trapped becomes smaller as it moves down the axis of the screw. Finally compressed air discharge from the opposite end of intake. Screw compressors can handle fairly large amounts of refrigerant flow rates compared to other positive displacement type compressors . Screw compressors are available in the capacity range of 70 to 4600 kW. Compared to reciprocating compressors, screw compressors are balanced and hence do not suffer from vibration problems.

51. SCROLL COMPRESSOR A scroll compressor actually consists of two scrolls or spirals. One scroll is moving, whereas the second one is fixed (attached to the compressor body). The first scroll orbits (rotates) in a path defined by its mating fixed scroll. The orbiting scroll is connected to the compressor's crankshaft. As a result of the scroll's movement, gas pockets are formed between the two scrolls. At the outer part of the scrolls, the pockets suck in gas and then move towards the center of the scroll, where the compressed gas is discharged. As the gas moves into the continuously smaller internal pockets, both its temperature and pressure are increased. Thus a desirable discharge pressure is achieved by the motion of the compressor scrolls. The absence of pistons for gas compression enables scroll compressors to reach 100% volumetric efficiency, leading to reduced energy costs. due to the absence of several moving parts, they can operate with less vibration scroll compressors have been successfully used in applications involving food and fruit refrigeration, truck transportation, marine containers as well as residential and small to medium scale commercial air-conditioning applications.

52. CONDENSERS Refrigeration cycle on T-s diagram Condensers are basically heat exchangers in which the refrigerant undergoes a phase change. In condensers the refrigerant vapour condenses by rejecting heat to an external fluid, which acts as a heat sink. In a typical refrigerant condenser, the refrigerant enters the condenser in a superheated state. first de-superheating and then condensing of vapor takes by rejecting heat to an external medium. The refrigerant may leave the condenser as a saturated or a sub-cooled liquid

53. Classification : Air Cooled Condenser Water Cooled Condenser Evaporative Condensers

54. Air cooled condenser Air is used as fluid for cooling purpose i.e. refrigerant rejects heat to air flowing over a condenser . These are further classified as (a) natural convection and (b) forced-air type . Natural convection type The finned type condensers are mounted either below the refrigerator at an angle or on the backside of the refrigerator. Air comes in contact with warm condenser tubes, it absorbs heat from the refrigerant The rate of flow of heat from the refrigerant to air will be small. The natural convection type condensers are either plate surface type or finned tube type. Figure shows the schematic of a wire-and-tube type condenser commonly used in domestic refrigerators .

55. 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.

56. WATER COOLED CONDNSERS Depending upon the construction it is further Classified as: Double pipe or tube-in-tube type Shell-and-coil type Shell-and-tube type

57. Tube-in-Tube or Double Pipe Condenser DOUBLE PIPE OR TUBE-IN-TUBE TYPE In this type, a smaller diameter pipe inserted inside a bigger diameter pipe is bent to the desired form. The cold water flows through the inner tube The refrigerant through the annular space between the two tubes Headers are used at both the ends to make the length of the condenser small and reduce pressure drop . The flow of refrigerant may be in direction opposite or in the same direction of refrigerant Double pipe condensers are normally used up to 10 TR capacity.

58. 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 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 condenser

59. SHELL AND TUBE CONDENSER It consists of straight tubes with integral fins are stacked inside a cylindrical shell The tubes are expanded into grooves in tube sheet holes which are welded to the shell at the both ends 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. 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

60. 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.