1. Refrigeration Cycles

2. Learning Outcomes
Demonstrate understanding of basic vapor-compression refrigeration and heat pump systems.
Develop and analyze thermodynamic models of vapor-compression systems and their modifications, including
sketching schematic and accompanying T-s diagrams.
evaluating property data at principal states of the systems.
applying mass, energy, entropy, and exergy balances for the basic processes.
determining refrigeration and heat pump system performance, coefficient of performance, and capacity.

3. Learning Outcomes
Explain the effects on vapor-compression system performance of varying key parameters.
Demonstrate understanding of the operating principles of absorption and gas refrigeration systems, and perform thermodynamic analysis of gas systems.

4. History of Refrigeration
 First successful commercial refrigeration system was produced in 1857 by James Harrison and D.E. Siebe using ethyl ether as refrigerant.

5. …..how does refrigeration work?

6. Let’s try to define…
Refrigeration makes thing cold....

7. Refrigeration
is cooling of a system below the temperature of the surroundings

8. Refrigeration is REMOVAL OF HEATQL
TH >> TL QL TH TL
Refrigeration is
REMOVAL OF HEAT

9. 1000C -100C QL QL TH >> TL TH TL 1100C 00C Water
at pressure…?
at atmospheric condition QL QL
TH >> TL TH TL
1100C
00C

10. Saturated Temperature (0C)
Pressure (bar)
Saturated Temperature (0C) 1
100
0.75
91.78
0.5
81.33
0.25
64.97
0.1
45.81
0.075
40.29
0.05
32.88
0.025
21.08
0.01
6.98

11. Boiling point temperature of some Important Refrigerants at atmospheric condition
Freon – C
Freon – C
R-134a C
Ammonia C

12. R-X W 350C QH vapour, pH, 450C liquid, pH, 450C 450C
Condenser
vapour, pH, 450C
liquid, pH, 450C
450C
Compressor
R-X W
Capillary tube
vapour, patm, -300C
Vapour, plow, -300C
Liquid, patm, -300C
Liquid, plow, -300C
-300C QL
Evaporator QL
TH >> TL TL
-200C
350C TH

13. Refrigeration is Removal & Relocation
of Heat

14. Basic components & typical operating conditions:

15. Refrigeration -vs- Heat Pump

16. Searching for Ideal Cycle….

17. Searching for Ideal Cycle….

18. Compare the COP of CARNOT refrigerator in summer and winter.
Comparing the CARNOT Refrigeration Cycles….
Assignment: 01
Compare the COP of CARNOT refrigerator in summer and winter.
TH/high
TH/low TL TL

19. Comparing the CARNOT Refrigeration Cycles….
Assignment: 02
Compare the COP of CARNOT refrigerator & air conditioner in same weather condition. TH
TL/high
TL/low

21. Vapor-Compression Refrigeration Cycle
Most common refrigeration cycle in use today
Two-phase
liquid-vapor mixture
There are four principal control volumes involving these components:
Evaporator
Compressor
Condenser
Expansion valve
All energy transfers by work and heat are taken as positive in the directions of the arrows on the schematic and energy balances are written accordingly.

22. Vapor-Compression Refrigeration Cycle
The processes of this cycle are:
Process 4-1: Two-phase liquid-vapor mixture of refrigerant is evaporated through heat transfer from the refrigerated space.
Process 1-2: vapor refrigerant is compressed to a relatively high temperature and pressure requiring work input.
Process 2-3: vapor refrigerant condenses to liquid through heat transfer to the cooler surroundings.
Process 3-4: liquid refrigerant expands to the evaporator pressure.
Two-phase
liquid-vapor mixture

23. Vapor-Compression Refrigeration Cycle
Engineering model:
Each component is analyzed as a control volume at steady state.
Dry compression is presumed: the refrigerant is a vapor.
The compressor operates adiabatically.
The refrigerant expanding through the valve undergoes a throttling process.
Kinetic and potential energy changes are ignored.

24. Vapor-Compression Refrigeration Cycle
 Operations in Idealized VCRC:
Evaporator:
Isobaric Heat Absorption
Compressor:
Isentropic compression
Condenser:
Isobaric Heat Rejection
Expansion valve:
Iso-enthalpic throttling

25. Vapor-Compression Refrigeration Cycle
VCRC in Domestic Refrigerator and Air Conditioner:

26. Vapor-Compression Refrigeration Cycle
 Operations in Idealized VCRC: TH
All processes of the cycle shown in figure are internally reversible except for the throttling process. Despite the inclusion of this irreversible process, the cycle is commonly referred to as the ideal vapor-compression cycle. TH TC TC

27. Vapor-Compression Refrigeration Cycle
 Operations in Idealized VCRC: TH TC

28. Vapor-Compression Refrigeration Cycle
 p-h diagram for Water :

29. Vapor-Compression Refrigeration Cycle
Applying SFEE
Evaporator
Compressor
Assuming adiabatic compression
Condenser
Expansion valve
Assuming a throttling process

30. Vapor-Compression Refrigeration Cycle
Performance parameters
Coefficient Of Performance (COP):
Maximum theoretical COP:
Refrigerating Effect / Refrigeration Capacity:

31. Vapor-Compression Refrigeration Cycle
Performance parameters
Refrigerating Effect:
Ton of Refrigeration
= 3.5 kJ/sec
1 ton of refrigeration relates that rate of heat removal from the refrigerated space by the cycle which is able to freeze a ton (2000 lb) of water at 0°C to ice at 0°C in 24 hours.
Tonne of Refrigeration
= kJ/hr = 3.86 kJ/sec

32. Vapor-Compression Refrigeration Cycle
Example:
Refrigerant 134a is the working fluid in an ideal vapor-compression refrigeration cycle where saturated vapor enters the compressor at -100C and saturated liquid leaves the condenser at 260C. The mass flow rate of the refrigerant is 0.08 kg/s. Determine
the compressor power, in kW,
the refrigeration capacity, in tons,
the coefficient of performance, and
the coefficient of performance of a Carnot refrigeration cycle operating between warm and cold regions at 16 and 00C, respectively.

33. Actual Vapor-Compression Cycle

34. Actual Vapor-Compression Cycle

35. Actual Vapor-Compression Cycle
Introducing
Suction Line Heat Exchanger

36. Example: 02
A vapour compression cycle works on Freon-12 refrigerant with condensation temperature of 40ºC and evaporator temperature of – 20ºC. Refrigeration effect of 2.86 ton is desired from the cycle. The compressor runs with 1200 rpm and has clearance volume of 2%. Considering compression index of 1.13 and following data determine.
(a) the COP
(b) the piston displacement in the reciprocating compressor used for compression.
Properties of Freon - 12

37. Specific heat of liquid refrigerant = 1.055 kJ/kg K
Example: 03
A commercial refrigerator operates with R-12 between bar and bar. The vapour is dry and saturated at the compressor inlet. Assuming isentropic compression, determine the theoretical COP of the plant. The isentropic discharge temperature is C. If the actual COP of the plant is 80% of the theoretical, calculate the power required to run the compressor to obtain a refrigeration capacity of 1.5 TR. If the required sub cooled through 100 C after condensation, calculate the power required. The properties of R-12 are given below:
Specific heat of liquid refrigerant = kJ/kg K
Sat Temp (0C)
Saturation pressure(bar)
Enthalpy(kJ/kg)
Entropy(kJ/kgK)
Liquid
Vapour
-25
1.237
13.33
176.48
0.0552
0.7126 55
13.672
90.28
207.95
0.3197
0.6774

39. Halocarbon compounds: Halocarbon group includes refrigerants containing one or more of three halogens such as chlorine, fluorine and bromine. These refrigerants are traded in market under the brand names of Freon, Genetron, Isotron and Arctron. Halocarbons, specially chlorine containing halocarbons (chloro fluoro carbons, CFCs) were commonly used from about 1940 to 1990s in most of vapour compression systems. But due to disastrous effect of chlorine in refrigerant upon the earth’s protective ozone layer the efforts are being made to replace the use of CFCs by the class of refrigerants having hydrogen in place of chlorine. Such new ecofriendly refrigerants are called hydrofluoro carbons (HFCs) for example
R–134a (CF3 CH2F) can replace R-12 (CCl2F2).

40. Halocarbon compounds:
REFRIGERANT
Halocarbon compounds:
Inorganic compounds:
Name
Chemical name
Chemical formula
R11
Trichloro mono fluoro-methane
CCl3F
R12
Dichloro difluoro-methane
CCl2F2
R22
Monochloro difluoro-methane
CHClF2
R134a
Tetra Fluoro ethane
CF3 CH2F

41. REFRIGERANT DESIRED PROPERTIES OF REFRIGERANTS
(i) Low Boiling temperature at atmospheric conditions.
(ii) Low freezing temperature at evaporator pressure.
(iii) Higher Critical temperature than the condenser temperature.
(iv) Large latent heat at evaporator temperature
(v) Small specific volume at compressor inlet.
(vi) Large Specific heat of refrigerant in vapour form.
(vii) Thermal conductivity of refrigerant should be high.
(viii) Viscosity of refrigerants should be small
(ix) Refrigerant should be chemically inert and non toxic.
(x) Refrigerant should be non-flammable.
(xi) Refrigerant may have pleasant distinct odour so as to know about its leakage.
(xii) Refrigerant should be readily available at lesser price.

42. DESIRED PROPERTIES OF REFRIGERANTS
(i) Boiling temperature of refrigerant should be quite low at atmospheric conditions for effective
refrigeration. For refrigerants having higher boiling temperatures at atmospheric conditions the
compressor is run at higher vacuum.
(ii) For an ideal refrigerant the freezing temperature of refrigerant should be quite low so as to
prevent its freezing at evaporator temperature. Freezing point temperature should be less than
evaporator temperature. For example, refrigerant R–22 has freezing point of – 160ºC and normally
most of refrigerants have freezing point below – 30ºC.
(iii) Critical temperature of the ideal refrigerant should be higher than the condenser temperature for
the ease of condensation.
(iv) Refrigerant should have large latent heat at evaporator temperature as this shall increase the
refrigerating capacity per kg of refrigerant.
(v) Refrigerant should have small specific volume at inlet to compressor as this reduces compressor
size for same refrigeration capacity.
(vi) Specific heat of refrigerant in liquid form should be small and it should be large for refrigerant in
vapour form, since these increase the refrigerating capacity per kg of refrigerant.
(vii) Thermal conductivity of refrigerant should be high.
(viii) Viscosity of refrigerants should be small for the ease of better heat transfer and small pumping
work requirement.
(ix) Refrigerant should be chemically inert and non toxic.
(x) Refrigerant should be non-flammable, non explosive and do not have any harmful effect upon
coming in contact with material stored in refrigeration space.
(xi) Refrigerant may have pleasant distinct odour so as to know about its leakage.
(xii) Refrigerant should be readily available at lesser price.

43. Selecting Refrigerants
Refrigerant selection is based on several factors:
Performance: provides adequate cooling capacity cost-effectively.
Safety: avoids hazards (i.e., toxicity).
Environmental impact: minimizes harm to stratospheric ozone layer and reduces negative impact to global climate change.

44. Example: 04 Find the compressor power required per TR.
If actual COP is 85% of the ideal, find compressor input for 3 ton capacity.
If actual COP is 75% of the ideal, find capacity of cycle for 4kW compressor rating.
Find the effect of superheating on refrigeration effect & COP.

45. A vapour compression cycle works on Freon-12 refrigerant with condensation temperature of 40ºC
and evaporator temperature of – 20ºC. Refrigeration effect of 2.86 ton is desired from the cycle. The
compressor runs with 1200 rpm and has clearance volume of 2%. Considering compression index of
1.13 and following data determine.
(a) the COP
(b) the piston displacement in the reciprocating compressor used for compression.
Properties of Freon - 12

46. Refrigerant Types and Characteristics
Global Warming Potential (GWP) is a simplified index that estimates the potential future influence on global warming associated with different gases when released to the atmosphere.

47. Refrigerant Types and Characteristics
Chlorofluorocarbons (CFCs) and Hydrochlorofluorocarbons (HCFCs) are early synthetic refrigerants each containing chlorine. Because of the adverse effect of chlorine on Earth’s stratospheric ozone layer, use of these refrigerants is regulated by international agreement.
Hydrofluorocarbons (HFCs) and HFC blends are chlorine-free refrigerants. Blends combine two or more HFCs. While these chlorine-free refrigerants do not contribute to ozone depletion, with the exception of R-1234yf, they have high GWP levels.
Natural refrigerants are nonsynthetic, naturally occurring substances which serve as refrigerants. These include carbon dioxide, ammonia, and hydrocarbons. These refrigerants feature low GWP values; still, concerns have been raised over the toxicity of NH3 and the safety of the hydrocarbons.