Scholarly article on topic 'Thermodynamic Performance Analysis of Eco friendly Refrigerant Mixtures to Replace R22 Used in Air Conditioning Applications'

Thermodynamic Performance Analysis of Eco friendly Refrigerant Mixtures to Replace R22 Used in Air Conditioning Applications Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Sharmas Vali Shaik, T.P. Ashok Babu

Abstract In the present study theoretical thermodynamic performance of a 0.8 TR window air conditioner with ten binary refrigerant mixtures consists of propylene (R1270) and propane (R290) was investigated based on actual vapour compression refrigeration cycle. All the investigated refrigerant mixtures consist of zero ozone depletion potential. Global warming potential of R22 is 1760 whereas GWP of all the studied refrigerant mixtures were below three and also these mixtures are closer to azeotropic containing the temperature glide below 0.4oC. Thermodynamic performance of all the refrigerant mixtures are computed at the evaporating and condensing temperatures of 7.2oC and 54.4oC (ARI conditions) respectively. The results revealed that the coefficient of performance for the mixture R1270/R290 (75/25 by mass %) was closer to R22. The percentage variation in cop for the mixture R1270/R290 (75/25 by mass %) was least by 0.97% among the ten investigated refrigerant mixtures when compared to R22. Refrigeration capacity of all the considered refrigerant mixtures was similar to that of capacity of refrigerant R22. The compressor discharge temperature for all the studied refrigerants were reduced in the range of 5.6-8.4oC when compared to the reference refrigerant R22. The power required per ton of refrigeration for the refrigerant mixture R1270/R290 (75/25 by mass %) was least among the ten investigated refrigerant mixtures. Since refrigerant mixtures consist of hydrocarbons, therefore they had better miscibility with the mineral lubricant oil. Overall the thermodynamic performance of a refrigerant mixture R1270/R290 (75/25 by mass %) was nearest to R22 and hence it is a suitable environmentally alternative refrigerant to substitute R22 used in residential air conditioning applications.

Academic research paper on topic "Thermodynamic Performance Analysis of Eco friendly Refrigerant Mixtures to Replace R22 Used in Air Conditioning Applications"

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Energy Procedía 109 (2017) 56 - 63

International Conference on Recent Advancement in Air Conditioning and Refrigeration, RAAR 2016, 10-12 November 2016, Bhubaneswar, India

Thermodynamic Performance Analysis of Eco friendly Refrigerant Mixtures to Replace R22 Used in Air conditioning Applications

Sharmas Vali Shaika, T. P. Ashok Babub*

aNational Institute of Technology Karnataka, Department of Mechanical Engineering ,Surathkal, Mangalore-575025, Karnataka, India. b*National Institute of Technology Karnataka, Department of Mechanical Engineering ,Surathkal, Mangalore-575025, Karnataka, India.

Abstract

In the present study theoretical thermodynamic performance of a 0.8 TR window air conditioner with ten binary refrigerant mixtures consists of propylene (R1270) and propane (R290) was investigated based on actual vapour compression refrigeration cycle. All the investigated refrigerant mixtures consist of zero ozone depletion potential. Global warming potential of R22 is 1760 whereas GWP of all the studied refrigerant mixtures were below three and also these mixtures are closer to azeotropic containing the temperature glide below 0.4oC. Thermodynamic performance of all the refrigerant mixtures are computed at the evaporating and condensing temperatures of 7.2oC and 54.4oC (ARI conditions) respectively. The results revealed that the coefficient of performance for the mixture R1270/R290 (75/25 by mass %) was closer to R22. The percentage variation in cop for the mixture R1270/R290 (75/25 by mass %) was least by 0.97% among the ten investigated refrigerant mixtures when compared to R22. Refrigeration capacity of all the considered refrigerant mixtures was similar to that of capacity of refrigerant R22. The compressor discharge temperature for all the studied refrigerants were reduced in the range of 5.6-8.4oC when compared to the reference refrigerant R22. The power required per ton of refrigeration for the refrigerant mixture R1270/R290 (75/25 by mass %) was least among the ten investigated refrigerant mixtures. Since refrigerant mixtures consist of hydrocarbons, therefore they had better miscibility with the mineral lubricant oil. Overall the thermodynamic performance of a refrigerant mixture R1270/R290 (75/25 by mass %) was nearest to R22 and hence it is a suitable environmentally alternative refrigerant to substitute R22 used in residential air conditioning applications.

© 2017 The Authors.PublishedbyElsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of RAAR 2016.

Keywords: Alternative refrigerants; Compressor discharge temperature; COP; ODP; GWP; Refrigeration capacity

* Corresponding author. Tel.:+ 91-9986548546 E-mail address: tpashok@rediffmail.com

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of RAAR 2016. doi:10.1016/j.egypro.2017.03.049

1. Introduction

A hydrochlorofluorocarbon refrigerant R22 is the most commonly used in heat pump, air conditioning and refrigeration applications because of its outstanding thermodynamic Properties. But R22 has unfavourable ecological effects like ozone depleting potential and high global warming potential. Therefore Montreal Protocol 1987, have been decided to phase out HCFCs in the developed countries by 2030 and for developing countries by 2040 [1, 2]. Therefore it is essential to develop the alternative refrigerants which are eco-friendly in nature in order to meet the requirements of Montreal and Kyoto protocols. In this context hydrocarbon refrigerants were eco-friendly in nature except its flammability. Therefore much attention was required for the hydrocarbons towards safety of the leakage from the system. Earlier various alternative refrigerants was proposed and tested to replace R22. An experimental investigation was carried out with R290 as an alternative to replace R22 used in window air conditioner. Results revealed that the performance of R290 was better when compared to R22 [3]. Experimental studies were conducted in a window air conditioner when it is retrofitted with mixture of R407C, propane (R290) and isobutane (R600a) without changing mineral lubricant oil. From this study it was observed that a blend of R407C/R290/R600a would be an appropriate alternative refrigerant to R22 [4]. Experimental tests were done with hydrocarbons and different blends consist of R1270, R290, R152a and RE170 as a substitute fluids to R22 used in both heat pump and air conditioning devices. Test results revealed that the performance of all the fluids was similar to R22 or superior to that of R22 [5]. Theoretical thermodynamic performance studies were carried out with various refrigerants like R290, R1270, R600a, R600, R32, R134a, R152a and their mixtures as a substitute fluids to R12, R22 and R134a. It was reported that the refrigerant mixture R290/R1270 (20/80 by wt. %) is an alternative to R22 among the other refrigerant mixtures investigated in the study [6]. Performance testing of R433A was conducted in heat pump test equipment under both heat pump and air conditioning working conditions. R433A is a binary mixture consists of 30% R1270 and 70% R290 on mass basis. Test results revealed that performance of R433A was better when compared to R22. Therefore R433A was a suitable alternative refrigerant to R22 [7]. Experimental testing of R432A was carried out as a substitute to R22 used in both heat pump and air conditioning devices. R432A is a binary blend consists of 80% R1270 and 20% RE170 on mass basis. Experimental results revealed that performance of R432A was higher than R22. Therefore R432A was an appropriate eco-friendly refrigerant to replace R22 used in both air conditioning and heat pump applications [8]. The present work focuses on performance investigation of ten binary refrigerant mixtures composed of propylene and propane as alternatives to replace R22. All the considered refrigerant mixtures are having zero ozone depletion potential and very small global warming potential less than three. In this study thermodynamic performance investigation of considered refrigerant mixtures is carried out based on actual vapour compression refrigeration cycle. In this work, effect of thermodynamic performance parameters like COP, compressor discharge temperature, refrigeration effect, refrigeration capacity, degree of subcooling, degree of superheating, type of refrigerant and power consumption per ton of refrigeration are considered for the performance investigation of selected refrigerants. In this study pressure drop at high pressure side of the system is taken as 0.4 bar whereas at low pressure side of the system is 0.2 bar._

Nomenclature

ARI Air conditioning and refrigeration institute ODP Ozone depletion potential

COP Coefficient of performance P Pressure (MPa)

GWP Global warming potential Qc Refrigeration capacity (W)

h Enthalpy (kJ/kg) RE Refrigeration effect (kJ/kg)

K Enthalpy at inlet of the compressor (kJ/kg) tc Condensing temperature (oC)

hu Enthalpy at outlet of the evaporator (kJ/kg) te Evaporating temperature (oC)

h2 Enthalpy at outlet of the compressor (kJ/kg) Td Compressor discharge temperature (oC)

Enthalpy at inlet of the evaporator (kJ/kg) w Power per ton of refrigeration (kW/TR)

HCFCs Hydrochlorofluorocarbons Wc Compressor work (kJ/kg)

m Mass flow rate of the refrigerant (kg/s)

2. Alternative refrigerants

In the present study ten binary refrigerant mixtures consists of propylene (R1270) and propane (R290) is considered to investigate the performance of the vapour compression refrigeration system. A matlab code is written to develop the thermodynamic properties of ten studied refrigerant mixtures by using martin-hou equation of state [9].The developed properties of refrigerant mixture are not available in literature and therefore they are compared with Refprop [10].The deviations of developed properties from Refprop were in the range of 1.5 to 4 % within the operating pressure and temperature. Hence the procedure followed to develop the properties is precise. The critical properties of the refrigerant mixtures are taken from the Refprop. Basic properties of refrigerants are given in tablel.

Table 1. Basic characteristics of investigated refrigerants

Refrigerant designation Composition Molecular Boiling Critical Critical ODP GWP Temperature

By mass % weight point Pressure temperature (100years) Glide (oC)

(kg/kmol) (oC) (Mpa) (K)

R22 Pure fluid 86.5 -40.81 4.99 369.3 0.055 1760 0

Ml (R1270/R290) 25/75 43.57 -43.73 4.3306 367.93 0 <3 0.35

M2 (R1270/R290) 35/65 43.36 -44.36 4.3601 367.21 0 <3 0.39

M3 (R1270/R290) 45/55 43.16 -44.97 4.3889 366.53 0 <3 0.37

M4 (R1270/R290) 55/45 42.96 -45.56 4.4172 365.92 0 <3 0.32

M5 (R1270/R290) 60/40 42.86 -45.84 4.4314 365.64 0 <3 0.29

M6 (R1270/R290) 65/35 42.76 -46.11 4.4458 365.37 0 <3 0.25

M7 (R1270/R290) 70/30 42.66 -46.37 4.4603 365.13 0 <3 0.21

M8 (R1270/R290) 75/25 42.56 -46.62 4.4751 364.92 0 <3 0.16

M9 (R1270/R290) 80/20 42.46 -46.85 4.4902 364.72 0 <3 0.13

M10 (R1270/R290) 85/15 42.37 -43.73 4.5057 364.55 0 <3 0.35

3. Thermodynamic performance analysis

Thermodynamic performance analysis of R22 and its various alternative refrigerant mixtures which is considered in this study is carried out based on actual vapour compression refrigeration cycle. In this thermodynamic analysis pressure drop in the condenser and evaporator, pressure drop through suction valve and discharge valve, superheating of the refrigerant vapour in the evaporator and subcooling of refrigerant liquid in the condenser is considered. The raise in temperature due to heat gain at compressor inlet and drop in temperature due to heat loss at compressor outlet is assumed as 10oC. The degree of subcooling and superheating is taken as 5oC and 10oC respectively. A matlab code is developed to compute the thermodynamic analysis of the vapour compression refrigeration system. Actual vapour compression refrigeration cycle on pressure-enthalpy diagram is shown in figure 1[11],

Fig. 1. Actual vapour compression refrigeration cycle on p-h diagram.

The descriptions of various state points of the cycle as shown in figure 1 are given in Table 2. The table 2 shows the description of different state points of the thermodynamic cycle [11].

Table 2. Descriptions of various state points of the thermodynamic cycle

State points Description of various states of the thermodynamic cycle

4-1m Evaporator pressure drop

1m-1l Superheat of refrigerant vapour in the evaporator

1l-1k Heat gain and superheating of the refrigerant vapour through the suction line

1k-1j Suction line pressure drop

1j-1 Suction valve pressure drop

1-2 Polytropic compression

2-2j Discharge valve pressure drop

2j-2k Discharge line pressure drop

2k-2l Heat loss and desuperheating of refrigerant vapour through the discharge line

2k-3 Condenser pressure drop

3-3j Subcooling of refrigerant liquid in the condenser

3j-3k Heat gain in the liquid line

Manufacturer catalogue data of 0.8 TR window air conditioner used for thermodynamic analysis of the cycle is given in Table 3 and 4 respectively. The table 3 lists the ARI operating conditions of the compressor whereas table 4 shows the pressure drop values at various points of the cycle [12].

Table 3. ARI conditions

Refrigerant Refrigeration capacity (TR) Evaporator temperature te (oC) Condensing temperature tc (oC)

R22 0.8 7.2 54.4

Table 4. Pressure drop values at various points of the cycle

Description Pressure drop in bar

Suction valve pressure drop 0.2

Discharge valve pressure drop 0.4

Suction line pressure drop 0.1

Discharge line pressure drop 0.1

Pressure drop in the evaporator 0.1

The calculations involved in the thermodynamic performance analysis of the vapour compression refrigeration cycle are given below.

1. Isentropic work of compression is determined by Wc = h2 — h1

2. Refrigerating effect is given by RE = hu — hA

3. Coefficient of performance is calculated as COP = RE/WC

4. Power consumption per ton of refrigeration W = 3.5167 x WC/RE = 3.5167/COP

5. Refrigeration capacity Qc = mx RE

Summary of results for the ten investigated refrigerant mixtures are given in Table 5.

Table 5. Summary of results for studied refrigerant mixtures

Refrigerant COP Variation in Td Power per ton of refrigeration Qc Refrigeration Wc

designation COP (%) (oC) (kW/TR) (W) Effect (kJ/kg) (kJ/kg)

R22 3.601 0 94.61 0.976 2813.36 136.941 38.019

M1 3.288 -8.69 86.14 1.069 2813.36 247.456 75.246

M2 3.273 -9.10 87.74 1.074 2813.36 252.508 77.135

M3 3.333 -7.44 87.80 1.054 2813.36 257.162 77.140

M4 3.394 -5.74 87.89 1.035 2813.36 261.464 77.023

M5 3.485 -3.22 86.72 1.008 2813.36 263.498 75.597

M6 3.456 -4.02 88.03 1.017 2813.36 265.469 76.799

M7 3.541 -1.66 86.98 0.993 2813.36 267.381 75.503

M8 3.566 -0.97 87.15 0.986 2813.36 269.216 75.482

M9 3.507 -2.61 88.70 1.002 2813.36 270.980 77.252

M10 3.534 -1.86 89 0.994 2813.36 272.641 77.131

4. Results and discussions

Thermodynamic performance of ten refrigerant mixtures are investigated to replace R22 used in air conditioning applications. The results and discussions for the investigated refrigerants are given below.

4.1 Refrigeration effect and compressor work

Figure 2 (a) shows the refrigeration effect of various refrigerant mixtures. Figure 2 (b) shows the compressor work of various refrigerant mixtures investigated in the present study. From the figure 2 (a) and 2 (b) it is observed that refrigeration effect and compressor work increase for ten mixtures R1270/R290 (M1, M2, M3, M4, M5, M6, M7, M8, M9 and M10 in table 5) due to their excellent liquid and vapour phase enthalpy properties when compared to R22. The results show that refrigeration effect of a refrigerant mixture M10 is higher among the ten studied refrigerant mixtures whereas compressor work for the refrigerant mixture M9 is higher among the ten investigated refrigerant mixtures when compared to base line refrigerant R22. ab

R22 Ml M2 M3 M4 M5 MS M7 M8 MO Ml(l Refrigerant Mixtures

R22 Ml M2 M3 M4 M5 MG M7 M8 M9 M10 Refrigeran! Mixtures

Fig. 2. (a) Refrigeration effect of various refrigerant mixtures; (b) Compressor work of various refrigerant mixtures.

4.2 Coefficient of performance and percentage variation in cop

Coefficient of performance (COP) is the ratio of refrigeration effect to the compressor work. COP is considered as an index of energy efficiency for a given apparatus when it is charged with a particular refrigerant. Therefore it is essential to investigate the COP of considered refrigerant mixtures against the R22 while selecting the alternative refrigerants. Figure 3 (a) shows the COP of various refrigerant mixtures. Figure 3 (b) shows the percentage variation in COP of various refrigerant mixtures. From the figure 2 (a) and 2 (b) it is observed that the both refrigeration effect and compressor work increase for all the investigated refrigerant mixtures. Therefore net effect on the COP of ten studied refrigerant mixtures either increases or decreases or remains same, depending upon the composition of refrigerant mixtures used and also on the operating conditions of the system. From the figure 3 (a) and 3 (b) it is observed that COP of a refrigerant mixture M8 is nearer to the refrigerant R22 whereas percentage variation in COP of a refrigerant mixture M8 is least among the ten investigated refrigerant mixtures. Result showed that refrigerant mixture M8 gives the COP which was closer to R22 and also least percentage variation in COP among the ten studied refrigerant mixtures when compared to R22.

Fig. 3. (a) COP of various refrigerant mixtures; (b) Percentage variation in COP of various refrigerant mixtures.

4.3 Compressor discharge temperature

Fig 4 shows the discharge temperature of the compressor for various refrigerant mixtures. While implementing alternative refrigerants the lifespan, consistency and durability of the compressor motor should be studied. These parameters can be investigated by computing the discharge temperature of the compressor. From the figure 4 it is observed that all the investigated refrigerant mixtures in this study revealed the 5.6-8.4oC decrease in discharge temperature of the compressor when compared to the reference refrigerant R22. Hence all the studied refrigerant mixtures would be applicable from the stand point of durability of the compressor life.

Fig. 4. Compressor discharge temperature of various refrigerant mixtures.

4.4 Power per ton of refrigeration

Figure 5 shows the power per ton of refrigeration for various refrigerant mixtures. If the power per ton of refrigeration is less, then the performance of the system can be increased. From the figure 5, it is observed that the power per ton of refrigeration for the refrigerant mixture M8 was closer to R22 and least among the ten investigated refrigerant mixtures. Therefore performance of the refrigerant mixture M8 was closer to R22, when compared to ten studied refrigerant blends.

Fig. 5. Power per ton of refrigeration for various refrigerant mixtures.

4.5 Refrigeration capacity

Refrigeration capacity is an essential performance parameter like coefficient of performance in the field of refrigeration and air conditioning. If the capacity of the system varies extremely for alternative refrigerant mixtures from that of reference refrigerant R22 then the compressor needs redesign completely, which will cause quite expensive. Hence it is necessary to look for alternative fluids which will provide a similar capacity to that of reference refrigerant R22. From the table 5 it is observed that similar capacity was chosen for all the investigated refrigerants to that of capacity of R22. Therefore no design modifications are required to the compressor. Hence the same size of compressor can be used for all the investigated refrigerant mixtures.

5. Conclusions

In the present study thermodynamic analysis of R22 and ten refrigerant mixtures consists of propylene and propane is investigated based on actual vapour compression refrigeration cycle. From this study the following conclusions are drawn.

• The COP of refrigerant mixture M8 (3.566) showed the nearest to that of COP of R22 (3.601) among ten investigated refrigerant mixtures. Percentage variation in COP of the mixture M8 was least by 0.97% among the ten studied refrigerant mixtures when compared to R22.

• Discharge temperature of compressor for all the investigated refrigerant mixtures were reduced in the range of 5.6oC-8.4oC when compared to reference refrigerant R22. The lower compressor discharge temperature increases the life of motor windings. Thus it is beneficial.

• The power per ton of refrigeration for the refrigerant mixture M8 (0.986 kW/TR) showed the nearest to that of power per ton of refrigeration of R22 (0.976 kW/TR) among the ten studied refrigerant mixtures. And also Refrigeration capacity of all the studied refrigerant mixtures had similar capacity to that of R22.

• Overall the refrigerant mixture M8 (R1270/R290 75/25 by mass %) is an appropriate eco-friendly alternative refrigerant to replace R22 among the ten investigated refrigerant mixtures from the stand point of COP, GWP and power per ton of refrigeration.

References

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