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 Total Downloads : 4006
 Authors : Jyoti Soni, R.C. Gupta
 Paper ID : IJERTV1IS7200
 Volume & Issue : Volume 01, Issue 07 (September 2012)
 Published (First Online): 25092012
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Exergy Analysis of Vapour Compression Refrigeration System with Using R407c And R410a
Exergy Analysis of Vapour Compression Refrigeration System with Using R 407C and R410A
Jyoti Soni
ME IVth Semester Student, Jabalpur Engineering College, Jabalpur
A B S T R A C T:
R.C. Gupta
Associate Professor, Jabalpur Engineering College, Jabalpur
This paper presents a theoretical performance study of a vapour compression refrigeration system with refrigerants R407C and R410A. A computational model based on energy and exergy analysis is presented for the investigation of the effects of evaporating temperatures, degree of subcooling, dead state temperatures and effectiveness of the liquid vapour heat exchanger on the coefficient of performance, second law efficiency and exergy destruction ratio of the vapour compression refrigeration cycle. A theoretical investigation showed that better performances of R407C in comparisons with R410A.
Keywords:Refrigeration System, Computational Model, exergetic Analysis, R407C and R410A

Recently, ozone layer depletion (ODP) and global warming potential have become one of the most important global issues researchers are proposed to resolve this issue. The Montreal protocol (UNEP, 1997) states the phasing out of CFCs and HCFCs as refrigerants that deplete the ozone layer (ODP) [1]. The Kyoto protocol (UNFCC, 2011) encouraged promotion of plans for sustainable development and reduction of global warming potential (GWP) including the regulations of HCFCs [2].
The refrigerant hydro chlorofluorocarbon (HCFC) chlorodifluoromethane (CHClF2), known from its ASHRAE classification as R22, is a most widely used refrigerant in residential, commercial, industrial and transport systems. It was initially recognized in 1928 and commercialization in 1936. R 22 has been applied in systems ranging from the smallest window air conditioners to the largest chillers and heat pumps, including those for district cooling and heating. However, R22 is one of a class of chemicals, hydrochloflourocarbons, being phase out, because of its high ozone depleting potential (ODP) and global warming potential (GWP). The issue of the uses of substance R223 that deplete the ozone layer has led to a search for environmentally friendly alternatives. Some R22 refrigerant substitutes that meet this requirement are a key process in this research.
Many investigations have been conducted in the research into substitutes for R22. Douglas et al. [3] presents a computer model based on costbased method for evaluates the performance of several leading R22 replacement candidates for window air conditioners. The result showed that the two leading R22 replacement candidate4s R407C and R410A had optimal costs that were nearly identical to R22. Aprea et al. [5] presented an experimental study for the substitutions of R22 in vapour compression plant with most widely used drop in substitute i.e. R407C. This experimental analysis was carried out with exergetic approach. The result showed that overall exergetic performance of the vapour compression plant working with R22 is consistently better than R407C. Aprea et al. [6] presented an experimental study to R22 phase out in vapour compression plant with reciprocating compressor. The result showed that R22 better than R407C because of because of better compression process due to
Degree of subcooling of liquid refrigerant in lvhe (K)
Degree of superheating of vapour refrigerant in lvhe (K)
Subscripts
c Condenser
r Space temperature
e Evaporator temperature comp Compressor
t Refrigerant throttle valve
o Dead state
Exergetic Efficiency
Effectiveness of the liquid vapour heat exchanger
Greek Notations
Coefficient of performance (nondimensional)
Exergy destruction rate (kW)
Exergy rate of fuel (kW)
Exergy rate of product (kW)
Thermal exergy loss rate (kW)
Exergy rate of refrigerant (kW)
Work rate (kW)
Enthalpy (kJ kg)
Exergy destruction ratio (nondimensional)
Temperature (K)
Entropy (kJ kg K)
Heat transfer rate (kW)
Pressure drop (bar)
Mass flow rate(kgs)
numbers of factors. But the isentropic and volumetric efficiencies of the semi hermetic compressor are better than that of R407C. Aprea et al. [7] investigated the performance of a vapour compression plant working both as a water chiller and as a heat pump. The refrigerants R22 and its substitutes R417A are used as a working fluid. The investigation has revealed that the coefficient of performance and exergetic efficiency of the plant working both as water chiller and as a heat pump, when the R22 is used as working fluid, are higher than R407A is used as working fluid. K. Comakli et al. [8] experimentally investigated the effects of gas mixture rat, evaporator air inlet temperature, evaporator air mass flow rate, condenser air inlet temperature, and condenser air mass flow rate on the coefficient of performance and exergetic efficiency of vapour compression heat pump systems. The investigation has shown that R22/404A mixtures can be used in replacement for R22 or R407A in vapour compression heat pump systems. V.P. Venkataramanamurthy et al. [9] performed the experimental comparison of energy, exergy flow and second law efficiency of R22 and its substitutes R436b in vapour compression refrigeration cycles. The analysis was presents investigation of the effects of the evaporating temperatures on the exergy flow losses and second law efficiency and coefficient of performance of a vapour compression refrigeration cycle. Dalkilic et al. [10] performed the theoretical analysis of a traditional vapour compression refrigeration system with mixture based on R134a, R 152a, R32, R290, R1270, R600 and R600a for various ratios and their results compared with R12, R22 and R134a as possible alternative replacements ranging from 30 to 10 . Vincenzo et al. [11] conducted an experimental analysis for comparing the performance of a vapour compression refrigerating unit with R22 and its substitutes R417A, R422A and R422D. The results revealed that R22 was energetically more efficient than the other fluids. The refrigerants R417A, R422A and R 422D has zero ozone depletion potential and they can easily replace the R22 in exiting system without having to change the lubricant or renewing the refrigerating unit and its accessories. This replacement accepted for particular easy operation and at a very low cost. Aprea et al. [12] presented an experimental investigation to study the environmental impact of R22 retrofit with R422D and to draw possible ecofriendly scenarios. The experimental analysis presents in terms of TEWI aimed to identify the global environment impact of R22 systems retrofitted with R422D. the results confirmed that the system lead to an increase of TEWI when retrofitted with R422D.
The literature survey is based on the study of R22 replacement and exergetic analysis. Most of the performance analysis of refrigeration system is investigated using an energy approach based on the first law of thermodynamics (i.e. by means of coefficient of performance). The energy analysis deals with only quantity of energy and it does not give the information that how, where and how much the
performance of the system degrade. Thus, modern approach to process analysis required to use the exergy analysis which provides the more realistic view of the process.
In this paper a computatinal model has been developed to calculate the coefficient of performance, exergetic efficiency and exergy destruction ratio for R407C and R410A based on energy and exergy concept. It is also studies the effects of evaporating temperatures, degree of subcooling, dead state temperature and effectiveness of liquid vapour heat exchanger on coefficient of performance (COP), exergetic efficiency and exergy destruction ratio. The main characteristics of the tested refrigerants as shown in table 1.
Table 1
The main characteristics of the tested refrigerants [13]
Refrigerant
R407C
R410A
Molar mass
86.20
72.58
Boiling point ()
43.56
51.6
Critical temperature ()
86.74
72.5
Critical pressure (bar)
4.6191
4.95
Critical density ( )
527.30
500
Critical volume ( )
0.00190
0.00205
Ozone depletion potential
0
0
Global warming potential
1526
1725
Certainty Class
A1
A1

A vapour compression refrigeration system consists of five components such as evaporator, liquid vapour heat exchanger, compressor, condenser and expansion valve. These components connected in a closed loop through piping that has heat transfer with the surrounding as shown in fig.1. At state 11, refrigerant leaves the evaporator at a low pressure, low temperature, saturated vapour and enter the liquid vapour heat exchanger where it absorbs the heat from high pressure temperature refrigerant flows from condenser. The refrigerant from the liquidvapour heat exchanger enter into compressor through the suction line in which both temperature and pressure increased at state 1. This process can be shown in fig.2. At state 2, it leaves the compressor as a high pressure, high temperature, superheated vapour and enter the condenser where it reject heat to surrounding medium at constant pressure after undergoing heat transfer in the discharge line. Refrigerant leaves the condenser at state 3, as high pressure, medium temperature, saturated liquid and enters the liquidvapour heat exchanger at state 33. The expansion valve allows to flowing the high pressure liquid at constant enthalpy from high pressure to low pressure. At state 4, it leaves the expansion valve as a low temperature, low pressure, and liquid vapour mixture and enters the evaporator where it absorbs the heat at constant pressure, changed into saturated vapour and cycle is completed.
Fig. (1) Schematic of typical vapour compression refrigeration system with a liquid vapour heat exchanger
Fig. (2) PressureEnthalpy Diagram showing effect of an idealized liquidvapour heat exchanger For the analysis following assumption are made:

Degree of subcooling of liquid refrigerant in lvhe = 5.

Isentropic efficiency of compressor = 75%.

Mechanical efficiency of compressor = 75%.

Electrical efficiency of compressor =75%.

Difference between evaporator and space temperature = 20.

Effectiveness of liquid vapour heat exchanger =0.8.

Evaporator temperature ranging from= 50 0.
8. Condenser temperature =40.

Mass flow rate of refrigerant = 1

Surrounding temperature (0)=30.

Pressure losses in pipelines are neglected.

Steady state operations are considered in all components.
The energy analysis based on first law of thermodynamic, the performance of vapour compression refrigeration system can be predicted in terms of coefficient of performance (COP), which is defined as
the ratio of net refrigerating effect produced by the refrigerator to the work done by the compressor. It is expressed as
=
= 1 4
2 2
(1)
The modern approach based on second law of thermodynamic i.e. exergy analysis can be used to measures the performance of the vapour compression refrigeration system. This analysis derives the concept of exergy, which is always decreasing due to thermodynamic irreversibilities. Exergy is the maximum useful work that could be obtained from the system at a given state in a specified environment. Exergy balance for a control volume undergoing steady state process is expressed as
= ( ) ( ) + [((1 0 ) ((1 0 ) ]
Â± (2)
Exergy destruction in each component of the cycle is calculated as

Exergy destruction in Evaporator
0
= 4 + 1 11
= 4 4 + 1 0 11 11 (3)

Exergy destruction in Compressor
= 1 + 2
= 1 1 +

Exergy destruction in Condenser
= 2 3
2 2 (4)
= 2 2 3 3 (5)

Exergy destruction in Throttle valve
= 33 4
= 33 33 4 4 (6)

Exergy destruction in liquid vapour heat exchanger
= 3 33 + 11 1
= (3 33 + 11 1) 0(3 33 + 11 1) (7)
Total exergy destruction in the system is the sum of the exergy destruction in different components of the system and is given by
= + + + + (8)
Thermal exergy loss rate in a component is given by
0
= 1 (9)
The term thermal exergy loss rate is related to external irreversibility which takes place because of temperature difference between the control volume and the immediate surroundings. It depends upon how the boundary of the system is selected. If the system includes the immediate surroundings then the boundary of the system is at the same temperature as the temperature of the immediate surroundings, hence the value of the thermal exergy loss become zero. If the system boundary does not include the immediate surroundings, the temperature difference between the system boundary and immediate surroundings exits. In vapour compression refrigeration system condenser is the component where heat is rejected. Then the equation (9) becomes:
0
= 1 (10)
When consider the thermal exergy loss total exergy destruction in the system is given as:
+ = + + + + (11)
Now, total exergy supplied is given by:
= + + (12)
For refrigeration system, product is the exergy of the heat abstracted into the evaporator from the space
to be cooled at temperature .
0
= 1
= 1
= 1 +
(13)
Exergy destruction ratio is the ratio of the total exergy destruction in the system to the exergy in the product and it is given by
=
Also, in terms of second law efficiency
= 1
1 (14)



Fig. 3 shows the effects of evaporator temperatures on coefficient of performance. The pressure ratio across the compressor decreases, with increase in evaporator temperature causing work required by the compressor derease and cooling capacity increases due to increase in refrigerating effect. Hence, the combined effects of these two factors increase the coefficient of performance (COP). R407C shows better COP than R410A at condenser temperature 40 and evaporator temperature ranging
from50 0. The maximum difference measured between R407C and R410A is 10.29% higher end of evaporator temperatures. Fig 45 shows the effect of evaporator temperatures on exergetic efficiency ( ) and exergy destruction ratio (EDR). With increase in evaporator temperatures exergetic efficiency increases till the optimum evaporator temperature and beyond the optimum temperature it decrease. The optimum evaporator is the temperature at which maximum exergetic efficiency is achieved. The curves trend for EDR almost reverses to curves of exergetic efficiency. The increasing and decreasing of exergetic efficiency depends upon the two factors, first factor is the exergy of cooling effects i.e.
1 0 . With increase in evaporator temperatures, increases while the term 1 0 reduces
407C
410A
COP
Tcond=40Â°C
5
4
3
50 45 40 E3v5apo3r0ator2T5em2p0erat1u5re(Â°10)
5
0
2
1
0
Fig. 3.Effect of evaporating temperatures on coefficient of performance
Second factor is compressor work required by compressor which decreases with increase in evaporator temperature. The term and have positive effect on increase of exergetic efficiency
while the term 1 0 have negative effect on increase of exergetic efficiency. The combined effect of
these two factors, increases exergetic efficiency increases till the optimum evaporator temperature and
beyond the optimum temperature decrease. The curves trend for EDR almost reverses to curves of exergetic efficiency because of exergetic efficiency is inversely proportional to exergy destruction ratio (EDR). The EDR decreases with increases in evaporator temperatures till the optimum evaporator temperature and beyond the optimum temperature it increase. The optimum evaporator is the temperature at which minimum EDR is achieved. The exergetic efficiency of R407C is 1419% is higher than R410A. Thus, of R407C is better than R410A.
5 0
E3v5apor3a0tor T2e5mp2er0atur1e5(Â°)10
50 45 40
407C
410A
Tcond=40Â°C
0.25
0.2
0.15
0.1
0.05
0
.
Fig. 4.Effect of evaporating temperatures on exergetic efficiency
Tcond=40Â°C
10
8
EDR 6
4
2
0
50 45 40Evap3o5rato3r0Tem25pera2tu0re(Â°15)
10 5 0
407C
410A
.
Fig. 5.Effect of evaporating temperatures on exergy destruction ratio (EDR)
Fig. 68 presents the effect of degree of subcooling on coefficient of performance (COP), exergetic efficiency and exergy destruction ratio (EDR). With increase in degree of subcooling cooling capacity increase because of increase in refrigerating effect and there is no change in compressor work, hence COP increases. From the study of equation (13)(14) it is evident that increase in COP increases the exergetic efficiency and decreases exergy destruction ratio (EDR). The rate of increase in COP is
9 10
(Â°
6 ng 7 ) 8
gre of ubcooli
2 De 3 e 4 S 5
0 1
407C
410A
2.9
2.8
2.7
2.6
2.5
COP
Tcond=40Â°C
3.2
3.1
3
.
Fig. 6.Effect of degree of subcooling on coefficient of performance
approximately 0.75%/of subcooling in case of R407C. The rate increase in COP is approximately 0.81%/of subcooling in case of R410A. The total increase in exergetic efficiency for R407C is 7.02% for 10 subcooling and for R410A is 8.01% for 10 subcooling.
Fig. 910 presents the effects of dead state temperature on exergetic efficiency and EDR. With increase in dead state temperature refrigerating effect and compressor work remains constant; hence
COP remains constant while the term 1 0 increases, hence exergetic efficiency increase and EDR
decrease. The curves trends of both R407C and R410A are identical and their curves for both
exergetic efficiency and EDR are nearly overlapping. The exergetic efficiency of R407C is 2.55.1% higher than R410A for considered range of dead state temperatures.
Tcond=40Â°C
0.12
0.115
0.11
0.105
407C
410A
0.1
0.095
0 1 2
3 Deg4ree o5f Sub6coolin7g (Â°8)
9 10
Fig. 7.Effect of degree of subcooling on exergetic efficiency
Tcond=40Â°C
9
8.5
EDR
8
7.5
7
6.5
0 1 2 3 4 5 6 7 8 9 10
Degree of Subcooling (Â°)
407C
410A
.
Fig. 8.Effect of degree of subcooling on exergy destruction ratio (EDR)
Tcond=40Â°C0.35
Te=0Â°C
0.3
0.25
0.2
0.15
0.1
0.05
0
25 30 35 40 45 50 55
Dead state temperature(Â°)
407C
410A
.
Fig. 9.Effect of dead state temperatures on exergetic efficiency
Te=0Â°C
16
14
12
EDR10
8
6
4
2
0
407C
410A
25
30
35 40 45 50 55
Dead state Temperature(Â°)
Tcond=40Â°C 18
.
Fig. 10.Effect of dead state temperatures on exergy destruction ratio (EDR)
Fig. 1113 shows the effect of effectiveness of liquidvapour heat exchanger on coefficient of performance (COP), exergetic efficiency and exergy destruction ratio (EDR). With increase in effectiveness of liquidvapour heat exchanger COP and exergetic efficiency decreases while EDR increases. The total COP decrease by15.50%, exergetic efficiency decrease by 9.8% and EDR increases by 18.56% for R407C. The total COP decrease by22.82%, exergetic efficiency decrease by 14.5% and EDR increases by 24.61% for R410A.
9 10
8
7
5 6
Effectiveness()
4
3
2
1
1
0
407C
410A
2
COP
Tcond=40Â°C
5
4
3
.
Fig. 11.Effect of effectiveness of liquidvapour heat exchanger on coefficient of performance
Tcond=40Â°C
15
14.5
14
13.5
13
12.5
12
11.5
407C
410A
1 2 3
8
9
10
4 5 6 7
Effectiveness ()
.
Fig. 12.Effect of effectiveness of liquidvapour heat exchanger on exergetic efficiency
Tcond=40Â°C
12
10
8
EDR 6
4
2
0
1 2 3 4 5 6 7 8 9 10
Effectiveness ()
407C
410A
Fig. 13.Effect of effectiveness of liquidvapour heat exchanger on exergy destruction ratio (EDR)
A computational model based on energy and exergy analysis is presented for the investigation of the effects of evaporating temperatures, degree of subcooling, dead state temperatures and effectiveness of the liquid vapour heat exchanger on the COP, second law efficiency and EDR of the vapour compression refrigeration cycle for R407C and R410A. The conclusions present in this analysis are given as follows.

The COP and exergetic efficiency of R407C are better than that of R410A. The EDR of R 410A are higher than that of R407C. This analysis performed at condenser temperature 40Â°C and evaporator temperature ranging from50 0.

For both refrigerants i.e. R407C and R410A, COP and exergy efficiency improve by subcooling of high pressure condensed liquid refrigerant. The total increase in exergetic efficiency for R407C is 7.02% for 10 subcooling and for R410A is 8.01% for 10 subcooling.

With increase in dead state temperatures exergetic efficiency increases and EDR reduces while oefficient of performance remains constant. The curves trends of both R407C and R410A are identical and their curves for both exergetic efficiency and EDR are nearly overlapping. The
exergetic efficiency of R407C is 2.55.1% higher than R410A for considered range of dead state temperatures.

With increase in effectiveness of liquidvapour heat exchanger COP and exergetic efficiency decreases while EDR increases. The total COP decrease by15.50%, exergetic efficiency decrease by 9.8% and EDR increases by 18.56% for R407C. The total COP decrease by22.82%, exergetic efficiency decrease by 14.5% and EDR increases by 24.61% for R410A.


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