Proceedings of Engineering and Technology Innovation, vol. 8, 2018, pp. 32 - 39 Comparative Analysis of Performance of R600a and R510a Refrigerants in a Retrofitted Refrigerating System Francis Olusesi Borokinni 1 , Babatunde Emmanuel Olatunbosun 2,* 1 Department of Mechanical Engineering, Yaba College of Technology, Yaba , Nigeria. 2 Department of Agricultural Engineering, Akwa Ibom State University, Ikot Akpaden, Nigeria. Received 26 July 2017; received in revised form 07 August 2017; accept ed 17 August 2017 Abstract Hydrocarbons, in the environmentally friendly group have drawn much attention of scientists and researchers for applicat ion as refrigerants. In this work, the performance of t wo eco -friendly hydrocarbon refrigerants (R510A and R600a ) in a retro fitted vapour comp ression refrigeration system was investigated e xperimentally and co mpared with the baseline hydro fluorocarbon refrigerant (R134a). Thermocouples and pressure gauges were fitted at the inlet and outlet of the compressor, condenser, and evaporato r to measure the temperature and pressure of the refrigerant at various stages of the re frigeration cycle . The results obtained showed that the coefficient of performance (COP) of the system using the two hydrocarbon refrigerants was higher than the coefficient of performance (COP) obtained using R134a as a working fluid. Genera lly, the two hydrocarbon refrigerants performed better than R134a, but R510A gave the best overall performance in that it exhibited the lowest discharge pressure of 0.656MN/m2and the highest refrigerating effect of 253.29kJ/kg. Keywor ds: hydrocarbon, refrigerant, retrofitted, thermocouple 1. Introduction Most of the refrige ration and air-conditioning system operate on vapour compression refrigeration cycle [1] in which the refrigerant change phases fro m liquid to gas and gas to liquid in a closed cycle to generate cooling in the evaporator. Refrigerants used in these systems are predominantly fro m a group of co mpounds called halocarbons (halogenated hydrocarbons) In 1974, Sherwood Rowland and Mario Molina predicted that chlorofluorocarbon (CFC) refrigerant gases would reach the high stratosphere and there damage the protective mantle of the oxygen allotrope, ozone. In 1985, with the discovery of the "ozone hole" over the Antarctic, the prediction of Rowland and Molina's was proved correct. CFCs are non-toxic, non-fla mmab le are used extensively as refrige rants in refrigerat ion units, aerosol propellants, electronic c leaning solvents, and blowing agents [2]. Over t ime, these CFCs get released into the a ir and often, strong winds carry the m into the stratosphere. When CFC molecules drift into the stratosphere, the UV-B and UV-C radiat ion fro m the sun releases their chlorine ato ms. Co mple x che mica l reactions in the at mosphere result in the format ion of chlorine mono xide, which reacts with the ozone molecu le to form o xygen and regenerates more ch lorine atoms that carry on converting the ozone mo lecules. Each ch lorine atom can destroy as many as 100,000 o zone molecules over 100 years. Thus, even a small a mount of CFCs can cause tremendous damage to the ozone layer [3 -4]. Therefore, they have been forbidden in developed countries since January, 1996. In 2010 production and usage of CFCs have been prohibited comp letely all over the world [5-6]. * Corresponding author. Email address: olat.tunde12@gmail.com Proceedings of Engineering and Technology Innovation, vol. 8, 2018, pp. 32 - 39 Copyright © TAETI 33 Many Studies have been carried out to find suitable rep lace ment for CFCs [7 -8] Transitional alternative co mpounds, such as hydro-chlorofluorocarbons (HCFCs), wh ich are less harmful to the o zone layer, inc luding R22, R123 and R124 will be phased out internationally by 2020 and 2030 in developed and developing countries respectively, because they still contain ozone depleting chlorine though their Ozone Dep letion Potentials (ODPs) are very sma ll and less than those of CFCs [9]. 2. Material and Method 2.1. Properties of selected refrigerants Two Hydrocarbon (HCs) and one HFC refrigerants (R510A, R600a, and R134a) were selected and their performances in vapour compression refrigeration were investigated and analyzed. These are natural, ch lorine free refrigerants; therefore they are not harmful to the ozone layer and global warming. So me of the properties and environment impact of the selected environmental friendly refrigerants are as tabulated below. Table 1 Some properties and environmental impacts of selected alternative refrigerants Physical and environmental characteristic of selected refrigerants Properties R134a R600a R510A Molecular weight (kg/kmol) 102.000 58.120 47.240 Critical temperature ( o C) 101.300 134.660 128.100 Critical pressure (Mpa) 4.0069 3.630 5.120 Density 225.500 268.560 Boiling point ( o C) -26.07 -11.75 -34.40 ODP 0 0 0 GWP 1300 3 3 2.2. Experimental set-up The system was incorporated with two pressure gauges with accuracy of ± 0.5kPa at the inlet and outlet of the compressor for measuring the suction and discharge pressures. The temperature of the refrigerant at four diffe rent points was measured with digita l thermocouples with accuracy of ± 0.1 o C. The energy consumption of the refrigeration system was measured with energy meter with accuracy of ± 0.2kWh. Data were co llected at diffe rent evaporator temperatures and the following performance para meters were obtained using equations 1 to 7: refrige rating effect (Q evap), compressor work input (Wc), condenser heat load (Qcond) Coeffic ient of Performance (COP), Vo lu metric Cooling Capacity (VCC) and pressure ratio (Pr). C. 2.3. Analysis of the heat transfer in the refrigeration system 2.3.1. Evaporator The heat absorbed by the refrigerant in the evaporator or refrigerating effect (Qevap, kJ/kg) is expressed as: 1 4 ( ) evap Q h h  (1) where, 1 h = specific enthalpy of refrigerant at the outlet of evaporator (kJ/kg); and 4 h = specific enthalpy of refrigerant at the inlet of evaporator (kJ/kg). 2.3.2. Compressor The isentropic work input to compressor (Ks/S) is expressed as: 2 1 ( ) cs r W M h h  (2) where h2 is the enthalpy of refrigerant at the outlet of compressor (kJ/Kg) Proceedings of Engineering and Technology Innovation, vol. 8, 2018, pp. 32 - 39 Copyright © TAETI 34 The actual compressor work (W e, kJ/S) is given as / c cs W W ns (3) where ns is the isentropic efficiency 2.3.3. Condenser The heat rejected by the condenser (QcondkJ/S) to the atmosphere is given as 2 3 ( ) cond r Q M h h  (4) where h3is the enthalpy of refrigerant at the outlet of condenser (kJ/Kg) 2.3.4. Capillary Tube In the capillary tube the enthalpy remains constant (isenthalpy process), therefore, 3 4 h h (5) Fro m the first law of thermodynamic point of view, the measure of performance of the refrigeration cycle is the coefficient of performance (COP) and is the refrigerating effect produced per unit of work required it is expressed as: / evap c COP Q W (6) The volumet ric cooling capacity ( Vcc , kJ/ m3) is the re frigerating effect per unit volu me flow rate at the in let to the compressor. It is expressed as / cc evap r S V Q m V (7) where Vs is the specific volume at inlet to the compressor (m 3 /kg) Compressor pressure ratio (Pr) is given as: / r dis sue P P P (8) where, dis P = re frigerant vapour pressure at the compressor discharge (kN/ m2) and dis P = refrigerant vapour pressure at the compressor section (kN/m 2 ). 2.4. Retrofit procedures The e xisting refrigerat ing system used was designed to work with R134a refrigerants need to be retrofitted to use Hydrocarbon refrigerants (R600a and R510A). The specific caution o f the refrigerator is shown in Tab le 4. Retrofitting means the modification of an e xisting refrigeration system, which was designed to operate on R134a refrige rant so that it can safely and effectively operate on Hydrocarbon refrigerants. This is to ensure that existing equipment operates until the end of its economic life . R600a and R510A, wh ich is wide ly accepted as a substitute for R134a in refrigeration systems, is not a "drop-in" replacement for R134a 2.5. Baseline test The refrigerator was tested using R134a as the baseline and performance data prior to retrofit were obtained. The system was evacuated with the he lp of a Blue VA C vacuum pump to re move the non -condensable particle fro m the system. The system was charged with the help of manifold gauge. The pressure gauge and thermocouples were connected to the system. The system was instrumented with two pressure gauges with accuracy of + 0.5kPa at the inlet and outlet of the compressor for measuring the suction and discharge pressures. Proceedings of Engineering and Technology Innovation, vol. 8, 2018, pp. 32 - 39 Copyright © TAETI 35 2.6. Charging of refrigerant Charging is the process of adding refrigerant to refrigeration system. The system may be charged with the refrigerant through the high or lo w sides. When charging is done on the high side, the refrigerant is introduced in liquid form but when charging in lo w side, the re frigerant is introduced in vapour form in order to prevent possible da mage to the co mp ressor. Norma lly it is more convenient to add refrigerant to system through the low side on small units or when sma ll a mounts are to be added to large systems. The low side method of charging refrigerant into the system was employed in this work. WS - 150 Digital charging scale was used to charge the system. Th is is an automatic d igital charging system that can charge the desired amount accurately. The charging system c onsists of platform, a processing LCD, an electronic controlled valve and charging line hose. The refrigerant cylinder is placed on the platform which measures the weight and also acts as a control panel. One charg ing hose is connected with the outlet of t he cylinder and in let of the electronic valve and another one is connected with the outlet of electronic valve and inlet of the service port. Using this charging system, R600a and R510A were charged and tested one after the other. The systems being charged with R600a and R510A require a sma ller charge size than those using R134a. As reco mmended by [10], the charge of R600a and R510A was 90 percent by we ight of the original R134a charge with the optimized capillary tube system. Fig. 1 Schematic diagram of the existing refrigerator Table 2 The specification of the refrigerator Specifications Value Freezer capacity (litres) 130 Fresh food compartment capacity (litres) 320 Power rating (W) 60 Current rating (A) 0.60 Voltage (V) 220 Frequency (Hz) 50 No of door 1 Refrigerant type R 134a Freezer dimension Width : 43 mm, diameter :500 mm and height :830mm 3. Results The performance comparison of the investigated refrigerants (R600a, R510A and R134a) in the retrofitted vapour compression refrigerating system was carried out and the enthalpies of the system at various evaporating temperatures and pressures were obtained using refrigerant datab ase software known as REFPROP [11]. The performance para meters obtained using hydrocarbon refrigerants (R600a and R510a) in the system were analysed and compared with those obtained using the baseline refrigerant (R134a ). The results of effects of the evaporating te mperature on condenser heat load (Qcond), volu metric Condenser Evaporator Capillary tube Compressor Receiver Dryer-filter 2 1 3 4 Proceedings of Engineering and Technology Innovation, vol. 8, 2018, pp. 32 - 39 Copyright © TAETI 36 cooling capacity (Vcc) Coeffic ient of performance (COP), Refrigerat ing effect (Qevap) distance temperature (Tdis) and compressor work in put (Wc) are investigated. Table 3 The system enthalpies at varying evaporating temperature for R600a Evaporating temperature Enthalpy (KJ/kg) ( o C) h1 h2 h3 -28 519.92 582.21 223.15 -29 518.44 591.71 227.87 -30 516.96 599.93 234.94 -32 514.08 604.92 244.49 -33 512.62 609.96 258.98 Table 4 The system enthalpies at varying evaporating temperature for R510A Evaporating temperature Enthalpy (KJ/kg) ( o C) h1 h2 h3 -26 476.36 528.12 89.46 -28 473.71 532.36 94.12 -30 471.08 535.22 106 -32 468.46 539.52 113.14 -34 465.84 546.76 122.76 Table 5 The system enthalpy at varying evaporating temperature for R134a Evaporating temperature Enthalpy (KJ/kg) ( o C) h1 h2 h3 -25 386.9 422.08 227.47 -27 385.39 428.73 230.3 -29 383.88 430.39 234.55 -30 383.11 432.07 237.42 -32 381.61 433.75 241.72 4. Discussion 4.1. Effect of evaporating temperature on discharge pressure The variations of the discharge pressure as a function of the evaporating temperature for the three r efrigerants are shown in Fig. 2. As shown in the figure, the discharge pressure reduces as the evaporating temperature increases. R510A has the lowest pressure with average pressure of 13.40% lo wer than that of R134a. Ho wever, R134a e xh ibited significantly high pressure as compared to R510A and R600a . The pressure of R510A was very close to that of R600a. Re frigerant with low pressure is desirable in the system because the higher the pressure the weightier must be the equipment accessories and parts . 4.2. Effect of evaporating temperature on pressure ratio Fig. 2 Variation of vapour pressure varying evaporator temperatures for R134a, R600a and R510A Fig. 3 Variation of pressure ratio with varying evaporator temperatures for R134a, R600a and R510A 0 2 4 6 8 10 12 -34 -29 -24 v a p o u r p re s s u re k J /k N Evap oration Temp erature (oC) R600a R510A R134a - 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 -34 -29 -24 P r a ti o Evap oration Temp erature (oC) R600a R510A R134a Proceedings of Engineering and Technology Innovation, vol. 8, 2018, pp. 32 - 39 Copyright © TAETI 37 Fig. 3 shows the variation of pressure ratio with varying evaporating te mperature for R600a, R510A and R134a. The figure shows that the pressure ratio decreases with increase in evaporating te mperature. The three re frigerants followed thes e similar trends. As reflected in the figure, the pressure ratios of R134a a re higher than those o f R510A and R600a. Average pressure ratios obtained using R510A and R600a in the system were 6.2 and 4.2% lowe r than that of R134a respectively. Therefore, same comp ressor is usable for both R510A and R600a, while a slightly heavy compressor for the same c apacity will be needed for R134a. 4.3. Effect of evaporating temperature on condenser heat load The function of the condenser is to re move heat of the vapour refrigerant discharged from the compressor. Heat is added to the refrigerant during evaporation in the evaporator by the compressor during the work o f co mpression. The heat fro m the refrige rant is moved by transferring heat to the wall of the condenser tu bes and then fro m the tubes to the condensing mediu m. The variat ions of the condenser heat load against evaporating temperature a re presented in Figure 4 for the three refrigerants. The figure shows that the condenser heat load increases as the evaporating temperature increases. Also, in the figure, R134a has the highest mean heat load. The average heat loads of R510A and R600a were 23.3 and 16.90% lower than that of R134a respectively. If the te mperature of the evaporator increases, the work of co mpression increases. As work of co mpressor increases the heat added to the refrigerant during co mpression increases so the condenser requires more heat to remove. Fig. 4 Variation of condenser heat load with varying evaporator temperatures for R134a, R600a and R510A 4.4. Effect of evaporating temperature on coefficient of Performance Fig. 5 Variation of coefficient of performance (COP) with varying evaporator temperatures for R134a, R600a and R510A - 1.00 2.00 3.00 4.00 5.00 6.00 7.00 -34 -32 -30 -28 -26 -24 C o p Evap oration Temp erature (oC) R134a R510A R600a Proceedings of Engineering and Technology Innovation, vol. 8, 2018, pp. 32 - 39 Copyright © TAETI 38 Fig. 5 shows the variat ion of coefficient of performance (COP) with varying evaporator te mperature for the three refrigerants. As shown in this figure, the COP increases as evaporator temperature decreases. The COP is the ratio of the refrigerating e ffect to the co mp ressor work. The increase in evaporating te mpe rature increases the refrigerating effect and decreases the compressor work, therefore increases the COP of the refrigerat ion system. The COP of R510A is the highest with average values of 14.6 and 13.7% higher than those of R134a and R600a respectively. 4.5. Effect of evaporating temperature on refrigerating effect The refrigerating effect is the ma in purposes of the refrigeration system. The liquid re frigerant at the low pressure side enters the evaporator. As the liquid refrigerant passes through the evaporator coil, it continually absorbs latent heat of vapourization at constant temperature through the coil wa lls, fro m the mediu m being cooled and turn to vapour refr igerant. The refrigerat ing effect is the difference between the enthalpies of the refrigerant in the inlet and the outlet of the evapo rator. The variation of re frigerating effect with the inlet evaporating temperature is shown in Fig. 6. Fro m the figure it is evident that the refrigerating e ffect increases as the evaporating temperature increases. R134a has the lowest mean refrigerating effect. Average re frigerating effect obtained for R510A and R600a were 26.0 and 16.5% higher than that of R134a, respectively. Fig. 6 Variation of refrigerating effect with varying evaporator temperatures for R134a, R600a and R510 5. Conclusion Hydrocarbons are environmentally friendly. They have zero ozone Dep letion Potential (ODP) and negligible Globa l Warming Potential (GW P). Hydrocarbon is cheaper than the R134a wh ich is being used in the refrigerator at present. Hydrocarbon is also easily av ailable. In this work the performances of three ozone friendly refrigerants, one hydro fluorocarbon (R134a) and two hydrocarbons (R510A and R600a) in a retrofitted e xisting vapour compression refrigeration system were investigated experimentally and compared. Based on the results obtained, the following conclusions are drawn: (1) The coefficient of performance obtained for the two hydrocarbon refrigerants (R510a and R600a) were higher than that of baseline refrigerant (R134a) (2) The average pressure of R510A and R600a are 13.4% and 10.2% lower than that of R134a respectively. (3) The average compression work for R134a was 18.7% higher than that of R510A and R600a respectively. (4) The average pressure ratio of R134a is higher than those of R510A and R600a by 4.2 and 6.2%, respectively. (5) The condenser heat load increases as the evaporator temperature increases. R134a has the highest mean load. The mean heat load rates of R510A and R600a were 16.9 and 23.3% lower than that of R134a respectively Generally, the t wo hydrocarbon refrigerants performed better than R134a and they can be used as retrofit substitutes for R134a in e xisting vapour compression refrigerating systems. The best performance was obtained from the use of R510A in the system. - 50.00 100.00 150.00 200.00 250.00 300.00 350.00 400.00 -34 -32 -30 -28 -26 -24 R e fr ig e ra ti n g E ff e c t (k J /k g ) Evap oration Temp erature (oC) R134a R510A R600a Proceedings of Engineering and Technology Innovation, vol. 8, 2018, pp. 32 - 39 Copyright © TAETI 39 References [1] R. Kumar and R. Shekhar, “Performance analysis of vapour compression refrigeration system by using Azeotrops,” International Journal for Scientific Research & Development, vol. 3, no. 4, pp. 255-267, 2015. [2] F. Bill, and L. Duncan. “Chlorofluorocarbons (CFCs),” The Gale Encyclopedia of Science, http://link.galegroup.com/ap ps/doc/CV2644030480/SCIC?u=a lbertak 12&xid=c 35ecbf6, February 2018. [3] B. O. Bolaji, A. O. Akintaro, O. J. Alamu, and T. M. A. Olayanju, “Design and performance evaluation of a cooler refrigerating system working with ozone friendly refrigerant,” The Open Thermodynamics Journal, vol. 6, no. 1, pp. 25- 32, 2012. [4] A. B. Agrawal and V. Shrivastana, “ Retrofitting of vapour compression refrigeration trainer by an eco-friendly refrigerant,” Indian Journal of Science and Technology, vol. 3, no. 4, pp. 455-458, April 2010. [5] Y. Kim, K. S. Chang, and H. Kim, “Thermodynamic performance analysis of vapour compression system using alternative refrigerants based on a cycle simulation program,” Journal of Industrial Engineering Chemicals. vol. 13, no. 5, pp. 674-686, 2007. [6] J. Fernandez-Seara, F. J. Uhia, R. Diz, and J. A. Dopazo, “Vapour condensation of R22 retrofit substitutes, R417A, R422A and R422D on CuNi turbo C tubes,” International Journal of Refrigeration, vol. 33, no. 1, pp. 148-157, 2010. [7] B. O. Bolaji, M. A. Akintunde, and T. O. Falade, “Comparative analysis of performance of Three-Ozone friends HFC refrigerants in a vapour compressor refrigerator,” Journal of Sustainable Energy and Environment, vol. 2, pp. 61-64, 2011. [8] D. Del Col, M. Azzolin, S. Bortolin, and C. Zilio, “Two phase pressure drop and condensation heat transfer of R32/R1234ze (E) non-azeotropic mixtures inside a single microchannel,” Science and Technology for the Built Environment, vol. 21, no. 5, pp. 595-606, June 2015. [9] B. O. Bolaji and Z. Huan, “Thermodynamic analysis of hydrocarbon refrigerants in a sub-cooling refrigeration system,” Journal of Engineering Research, vol. 1, no. 1, pp. 317-3333, June 2013. [10] Bitzer, Refrigerant Report, Bitzer International, www.bitzer.de, February 2018. [11] E. W. Lemmon, M. O. Mclinden, and M. L. Huber, “NIST reference fluids thermodynamic and transport properties REFPROP 7.0,” National Institute of Standards and Technology Standard Reference Database, vol. 7, 2002. http://www.bitzer.de/