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Ring Tribo pair material of Hermetically Sealed Compressors
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ScienceDirect Materials Today: Proceedings 16 (2019) 488–495
www.materialstoday.com/proceedings
ICAMMAS17
Effect of Biodegradable Refrigeration oil on the Tribological Behaviour of Liner/Ring Tribo pair material of Hermetically Sealed Compressors P. Vithyaa, G. Sriramb, S. Arumugamc* a,b,c,
Department of Mechanical Engineering, Sri Chandrasekharendra Saraswathi Viswa Mahavidyalaya University, Enathur, Kanchipuram-631561, India.
Abstract An improvement in co-efficient of performance (COP) of a vapour compression refrigeration (VCR) system is largely depends upon the work of compression which in turn rely on the quality of lubricants. Further the compatibility of cylinder liner/piston ring tribo pair material of a hermetically sealed compressor is another vital aspect to consider during the development of refrigeration oil. The base oil, which has been used for the formulation of refrigeration oil, is derived from petroleum products. However the depletion of petroleum reserves, uncertainty in crude oil prices, energy demand and increased environmental awareness has promoted the crucial requirement to synthesize refrigeration oil from environmentally friendly energy resources. The present investigation is intended to formulate a rapeseed oil based trimethylolpropane tri ester as biodegradable refrigeration oil with good thermo-oxidative stability and cold flow behaviour via chemical modifications. Thermo gravimetric Analysis (TGA) and Differential Thermal Analyses (DTA) were performed to study the thermo-oxidative stability of biodegradable refrigeration oil. This investigation is also addressing the issue of the tribological behaviour of cylinder liner/piston ring material of a hermetically sealed compressor in VCR system under the influence of biodegradable refrigeration oil and synthetic refrigeration oil (ISO 68 grade-POE oil) using a pin-on-disc tribometer. The surface morphology analysis of tested pin materials was also carried out using scanning electron microscope. The tribological experiments were carried out in accordance with ASTM G99. Under similar experimental conditions, biodegradable refrigeration oil exhibited good friction reduction behaviour and inferior wear reduction behaviour as compared to synthetic refrigeration oil. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advances in Materials, Manufacturing and Applied Sciences. Keywords: Hermetically Sealed Compressor; Refrigeration oil; Vapour compression refrigeration; Pin-on-disc tribometer; wear
1. Introduction The usage of the refrigerators and the air conditioners has increased every year due to their demand. Main issues of the refrigeration system are energy consumption and the environmental impact of refrigerants.
* Corresponding author. Tel.: 91 99946 99223; E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advances in Materials, Manufacturing and Applied Sciences.
P. Vithya et al. / Materials Today: Proceedings 16 (2019) 488–495
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The compressor is the major power consuming part of the refrigeration system. The widely used type in refrigeration system is the reciprocating compressor for domestic and commercial applications. The refrigeration oils used in the refrigeration compressors are to lubricate the moving parts and its bearings. The lubricants incorporated in the refrigeration systems are of classified into mineral oil and synthetic oil which originated from the petroleum-based products. The synthetic lubricants are an alternative to mineral oil for the HFC refrigerants. Over the past few decades, raising demand for clear operating equipments and awareness towards the green environment led to turn the lubrication system into bio-based environment friendly in various applications. Bio lubricant has advantages such as higher lubricity, lower volatility, higher viscosity index, non-toxic, biodegradable and eco friendly. Quinchia et al [1] found that the esters derived from the vegetable oil possess better low temperature behaviour. kodali [2] reported the high oxidation stability of the polyolester oil owing to the nonappearance of hydrogen atom in beta location and positioning of carbon in the quaternary centre. Wang et al [3] formulated the bio lubricant through the transesterification of fatty acid tri ester from waste cooking oil with TMP using KOH as a catalyst. The obtained final product yield was 85.7%. They found a considerable elevation in the oxidation stability due to the additives in trimethylpropane fatty acid Tri ester. Physio-chemical properties match with the standard ISOVG32. Syaima et al [4] synthesized bio lubricant from palm oil by using hydrolysis and non - catalytic esterification. They suggested that the bio lubricant formed have the potential to be chosen as industrial lubricant for commercial purpose. A detailed study of the bio lubricant synthesis for diesel engine with high oxidation stability and increased cold flow behavior through epoxidation followed by hydroxylation and esterification process discussed by Arumugam and Sriram [5]. They extended their work to focus on friction and wear aspects of piston ring and cylinder liner on both synthetic and bio lubricant using HFRR and concluded that bio lubricant shows 23% lesser coefficient of friction and 12% higher wear compared with synthetic lubricant. Long et al [6] prepared pentaerythritol polyolester from jatropha oil via chemical modification of hydrolysis and esterification exhibit high decomposition temperature 3590 C is an evidence for bio lubricant’s potential. Zulkiflia et al [7] studied the tribological properties of trimethylolpropane ester bio lubricant from palm oil through transesterification process with added TiO2 nanoparticles using four ball machine tribometer shows inclusion of TiO2 nanoparticles at 160 kg reduces the coefficient of friction by 15% and the wear scar diameter by 11% respectively as compared without TiO2 nanoparticles. Yashvir Singh [8] investigated the friction and wear characteristics of Pongamia oil added biolubricant 15, 30 and 50% (v/v) with the base lubricant using pin-on-disc tribometer. They reported that the Pongamia oil added bio-lubricant PB 15 performs well in terms of coefficient of friction and wear. Krishna Sabareesh et al [9] investigated the performance improvement of a vapour compression refrigeration system on various concentrations on TiO2 nanoparticles in the mineral oil, found that the 0.01% volume fraction shows the optimum result, further analyzed the tribological properties of nanolubricant using pin on disc tribometer and reported that the reduction in the friction and wear characteristics for 0.01 volume fraction. A number of research works are carried using bio lubricant as an alternative to synthetic lubricant for Engine oil and transformer oil applications. Similarly, lots of research work is focused on the performance improvement of vapour compression refrigeration system by using synthetic lubricant with nanoparticles as additives. However, less work has been carried out on using bio lubricant as Refrigeration oil. Hence the present work synthesized the bio degradable refrigeration oil from rapeseed oil using transesterification with trimethylolpropane through chemical modification in order to find out the lubrication characteristics suitability as refrigeration oil for hermetically sealed reciprocating compressor. Furthermore, tribological study has been evaluated for checking the compatibility of the formulated bio degradable refrigeration oil and synthetic refrigeration oil using a Pin on disc Tribometer.
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2. Experimental 2.1. Materials The raw rapeseed oil, which has chosen as base oil for the conversion of bio degradable refrigeration oil was procured from the local dealer. Sodium hydroxide, dilute sulphuric acid, xylene, Nitrogen gas was procured from Sri Balaji Scientifics, Secunderabad. Trimethylolpropane (99% pure) was procured from M/s. Sigma Aldrich US. 2.2. Synthesis of Bio degradable Refrigeration oil The formulation of bio degradable refrigeration oil for the vapour compression refrigeration system of refrigeration compressors was carried out by the transesterification of fatty acid methyl ester from rapeseed oil with Trimethylolpropane. The bio degradable refrigeration oil from raw rapeseed oil was synthesized in two stages that is synthesis of rapeseed oil methyl ester in one stage followed by the synthesis of Trimethylolpropane tri ester of rapeseed oil in on next stage. The detailed procedure for the transesterification process, followed by purification process is adopted from Hiekel et al [10]. The methyl ester of rapeseed oil was produced by transesterification process with measured quantity of rapeseed oil and sodium hydroxide was mechanically stirred for 1 hour maintaining the temperature at 800C - 900 C until the complete disappearance of triglyceride. This course of the reaction is monitored by thin layer chromatography and the reaction mixture cooled and neutralized by diluting sulphuric acid. Further the synthesis of bio degradable refrigeration oil was carried out by the three necked reaction flask equipped with a thermometer, condenser and dean stark separator. Trimethylolpropane with known quantity was first loaded and the xylene was introduced as a catalyst. The rapeseed oil methyl ester was introduced during the reaction process at 1350C-1400C. The mixture was distilled at 1100C-1150C under the reduced pressure of 2-3mm of Hg to remove the xylene catalyst as shown in Fig.2. After the completion of reaction process, the mixture was distilled at 110C0-1150C under the reduced pressure of 2-3mm of Hg to remove the xylene catalyst. The final product of TMP ester obtained as a yield of 95%. 2.3 Tribological Study The effect of bio degradable refrigeration oil and ISO 68 grade POE oil on the lubrication properties were experimentally elucidated using Pin on Disc Tribometer [supplied by M/s DUCOM Instruments Pvt. Ltd]. The pin on disc tribometer was used to check the compatibility between the newly formulated refrigeration oil and ISO 68 grade-POE oil and cylinder liner/piston ring tribo pair materials. As the experiments were intended for pretending the tribological cross section cylinder liner/piston ring tribo pair of a hermetically sealed reciprocating compressor, the disc was made out of compressor cylinder liner material SAE J431 grade grey cast iron, heat treated to raise the hardness value up to 60HRC. Table.1. Experimental conditions of pin on disc tribometer
_____________________________________________________________________________________________ Normal load N
Rotational Speed rpm
Sliding distance m
Wear track diameter mm
__________________________________________________________________________________________________________________ 98 400 1000 50 -100 ___________________________________________________________________________________________________________________
The pins were made out of piston ring material FG 150 grade grey lamellar graphite cast iron of hardness 210 BHN. The separate pin and disc were used to performing the tribological study of ISO 68 grade-POE oil and bio degradable refrigeration oil. The tribological tests were carried out in accordance with ASTM G99 standards and experimental conditions were presented in Table1.
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After the completion of the test, the pins were examined using SEM to analyze the surface morphology behaviour under the influence of the bio degradable refrigeration oil and ISO 68 grade-POE oil. 3.
Results and Discussion
3.1.1. Analysis of physio-chemical properties The viscosity is significant property of oil related to the temperature and has a greater influence in heat generation. The viscosity of oil is directly correlated to the load and energy consumption of a refrigeration compressor. The kinematic viscosities of bio degradable refrigeration oil and synthetic refrigeration oil (ISO 68 grade POE oil) were determined using ASTM D-445. This viscosity of the bio degradable refrigeration oil at 400 C and 1000 C was 38.5 and 10.15cst. Table.3 shows the physio-chemical properties of raw rapeseed oil, ISO 68 grade POE oil and bio degradable refrigeration oil. The ASTM D-2270 standard was followed to find out the viscosity index (VI). The viscosity index obtained was extremely superior to the reported values of Phani et al [11]. The viscosity index of the bio lubricant is higher than the pure synthetic POE oil due to the higher molecular weight and by the chemical nature. The viscosity of the NPG and TMP esters synthesized at 40°C was 13.5 – 37.6 cst and it should possess higher viscosity index more than 200 as stated by Gryglewicz et al [12]. The pour point is the temperature of the lubricant remains in a fluid state that is ability to pour. The lower pour point is the critical characteristic of the lubricant under the cold operating temperatures. The pour point of both the oils was measured using ASTM D-97 method. The bio degradable refrigeration oil was a pour point of -60 C. This is significant with the studies by Cermak et al [13], which stated that the formation of a complex chain and branched oils have lower pour point. The action of forming macro crystalline structures of decrement in temperatures by the cause of stacking of bend in the triglyceride backbone responsible for confine of ease of liquid flow agreed with the fact with Kleinova [14]. Table.3. Tested properties of raw rapeseed oil, ISO 68 grade POE oil and bio degradable refrigeration oil
_____________________________________________________________________________________________ Properties
Standard
Raw rapeseed oil
Synthetic refrigeration oil
Bio degradable refrigeration oil
___________________________________________________________________________ 35
68
38.5
Viscosity@100 ˚C(cst) ASTM D445
Viscosity @ 40˚C(cst)
ASTM D445
8
9.3
10.15
Viscosity Index
ASTM D2270
212
114
266
Flash Point (˚C)
ASTM D92
320
270
220
Pour Point (˚C)
ASTM D97
-39
-11
-6
Density (kg/m3)
ASTM D1298
922
980
907.2
Amber
Brownish red
Colour
-
Brownish yellow
_________________________________________________________________________________________ 3.1.2. Thermo oxidative stability Analysis using TGA/DTA An oxidative property of lubricants is of prime importance to evaluate the thermal stability and to foresee actual lubricant life time exposed in high temperature and other extreme conditions. Excellent resistance to degradation means that it inhibits oxidation and reduces sludge and varnish. Thermo gravimetric analysis was incorporated to study the thermal stability of the lubricant and to detect the changes in weight in relation to changes in temperature. Changes in weight are a result of the rupture and formation of various physical and chemical bonds at elevated temperatures that lead to evolution of volatile products or the formation of heavier reaction products. The TGA thermal curve indicates a weight loss occurred with 20.18 mg sample of synthetic and bio degradable refrigeration oil by heating from 1000C to 7000C @ 10°C/min in nitrogen atmosphere with a purge rate of 20 ml/min was analyzed as shown in Fig.1 and Fig.2.
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Fig.(1) & (2) TGA Thermograms of synthetic ISO 68 grade POE oil and bio degradable refrigeration oil
Fig.(3) and (4) DTA analysis of synthetic ISO 68 grade POE oil and bio degradable refrigeration oil
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The bistage weight loss of 96% ended at 3920C for synthetic lubricant whereas 94% weight loss ended at 4790C for bio lubricant due to the evaporation of hydrocarbons shows that bio lubricant was more stable than the synthetic lubricant. This phenomenon can be associated with a broad endothermic peak centered at about 336.550C in DTA curve for the synthetic ISO 68 grade POE oil and bio degradable refrigeration oil as 438.100C due to the recombination of hydrocarbon free radicals as shown in the Fig.3 and Fig.4. Further the tristage weight loss ended at 5820C for bio degradable refrigeration oil under air. The complete degradation and decomposition was observed at higher temperatures of 7000C as shown in the Fig.2.The results were well agreed and extremely superior with Vinu et al [15]. 3.2
Tribological Investigation of bio degradable refrigeration oil
Friction is the property related directly with resistance energy, which lead to heat conversion. The Tribological characteristics of the compressor material under the influence of bio lubricant were found using a pin on disc Tribometer.
Fig. (5),(6) and (7) Coefficient of friction, Friction Force and Wear vs sliding distance
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Fig.5 and Fig.6 illustrates the friction coefficient and frictional force variations with respect to sliding distance. The results show that the friction coefficient of bio degradable refrigeration oil was considerably 20% lower than that of synthetic lubricant. The indicated reduced friction coefficient is due to the high polar functional groups of carboxylic acids and ester in the bio lubricant acts as a covering agent developing a film layer between the material surfaces of the cylinder liner/piston ring that reduces the direct contact of mating surface in any case. Thus the bio degradable refrigeration oil enhances the adsorption rates of the metal surfaces due to its chemical nature of increasing chain lengths and polarity in the structure improves the lubrication characteristics and plays a role as an anti friction agent. In the investigation of frictional force, the average value obtained for bio degradable refrigeration oil was 5 N was lower than the average frictional force of the synthetic lubricant. Fig.7 explains the variations of wear behaviour with respect to a sliding distance. The experimental results showed that the lubrication regime that occurred was boundary lubrication whereas the main wear mechanisms were abrasive and the adhesive wear.
Fig.8. SEM images of tested pin for (a) Synthetic ISO 68 grade POE oil (b) Bio degradable refrigeration oil
The bio degradable refrigeration oil has higher wear than ISO 68 grade POE oil due to the fatty acid present in the vegetable oil have a tendency to cause the metallic surface chemical attack that create non reactive detergents. Also for the reason, synthetic refrigeration oil was formulated with anti wear, anti-detergent and anti-foam agents, which leads to an increase in performance of the lubricant at low temperatures. Thus the inclusion of anti-wear additives will increase the performance correlated to the wear characteristics. Chemical modification of triacylglycerols structures has great potential in achieving broad temperature range stability as well as excellent wear and friction characteristics. Fig.8 (a) and 8(b) shows the scanning electron microscope image of the pin surface under the influence of the synthetic ISO 68 grade POE oil and bio degradable refrigeration oil at 200x magnification. The pin surface was examined through SEM micrographs to investigate the wear behaviour. The pin surface come into the contact of the disc surface, the abrasive type of wear crop up due to the development of the grooves in the sliding direction of motion, subsequently wear debris and pores are formed in the case of bio degradable refrigeration oil. The formation of furrows originated shows that the deformation raised with respect to increased load. On the other hand, smooth surface with inferior wear behaviour appeared in the case synthetic refrigeration oil. Conclusions The purpose of the research is to produce bio degradable refrigeration oil for refrigeration systems and the following conclusion was made in this present study.
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Bio degradable refrigeration oil (Trimethylolpropane Tri ester) from rapeseed oil with high thermo oxidative stability was formulated for vapour compression refrigeration system. The Physio-chemical properties met the requirements of the synthetic refrigeration ISO 68 grade POE oil except that of pour point. The effect of bio degradable refrigeration oil on the tribological properties shows better compatibility between the newly formulated refrigeration oil and ISO 68 grade-POE oil and cylinder liner/piston ring tribo pair materials. The friction coefficient found to be 20% lesser for the bio degradable refrigeration oil in comparison with the synthetic refrigeration ISO 68 grade POE oil owing to the presence of high polar functional groups of carboxylic acids and ester in the bio lubricant. In case of wear characteristics, higher wear behaviour occurred in the bio degradable refrigeration oil in contrast to the synthetic refrigeration oil showed that the certainty of inclusion of additives related to the anti-wear characteristics. This investigation gives an innovative alternative approach for the refrigeration oil derived from the vegetable oil for the refrigeration system. An extended research process is necessary to examine the wear reduction in the bio degradable refrigeration oil is planned by the authors in the future studies. References [1]. L.A. Quinchia, M.A. Delgado, J.M. Franco, H.A. Spikes, C. Gallegos, Ind. Crops Prod 37, (2012) 383–388. [2]. D.R. Kodali, Ind. Lubrication and Tribology 54, 4 (2002), 165–170. [3]. Erpei Wanga, Xiang Maa, Shuze Tang, Rian Yan, Yong Wang, William, W. Riley, J.T.Martin, Biomass and Bio energy, (2014) 1-8. [4]. M.T.S.Syaima, K.H. Ong, Ishenny Mohd Noora, M.I.M.Zamratul, S.A.Brahima, M.M. Hafizul, Renew. Sustainable Energy Rev 44(2015), 669–675 [5]. S. Arumugam, G. Sriram, J Engineering Tribology 227, 1, (2012) 3–15. [6]. Can Liu, Jing Liu, Lanqing Ma, Long Rong, J.Chemistry, (2014) 1-6. [7]. N.W.M. Zulkiflia, M.A. Kalam, H.H. Masjukia, R. Yunus, Procedia Engineering 68, (2013) 152 – 157. [8]. Yashvir Singh, Int. J. Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering 10(7), (2016) 12681274. [9]. R. Krishna Sabareesh, N. Gobinath,V. Sajith, S. Das, C.B. Sobhan, Int. J. Refrigeration 35(7), (2012) 1989-1996. [10].Ebtisam K. Heikal, M.S. Elmelawy, Salah A. Khalil, N.M. Elbasuny, Egyptian J. Petroleum 03, (2016)1-13. [11].S.K. Phani, Ind. Crops and Products 50, (2013) 95– 103. [12].S. Gryglewicz, W. Piechocki, G. Gryglewicz, Bio resource Technology 87, (2003) 35–39. [13].S.C. Cermak, T.A. Isbell, Ind. Crops and Products18, (2003) 183-196. [14].A. Kleinova, P. Fodran, L. Brnc alova, J. Cvengros, Bio mass Bio energy 32, (2008) 366–371. [15].Anand Kumar Tripathi, Ravikrishnan Vinu, Lubricants 3, 54-79.
ScienceDirect Materials Today: Proceedings 16 (2019) 488–495
www.materialstoday.com/proceedings
ICAMMAS17
Effect of Biodegradable Refrigeration oil on the Tribological Behaviour of Liner/Ring Tribo pair material of Hermetically Sealed Compressors P. Vithyaa, G. Sriramb, S. Arumugamc* a,b,c,
Department of Mechanical Engineering, Sri Chandrasekharendra Saraswathi Viswa Mahavidyalaya University, Enathur, Kanchipuram-631561, India.
Abstract An improvement in co-efficient of performance (COP) of a vapour compression refrigeration (VCR) system is largely depends upon the work of compression which in turn rely on the quality of lubricants. Further the compatibility of cylinder liner/piston ring tribo pair material of a hermetically sealed compressor is another vital aspect to consider during the development of refrigeration oil. The base oil, which has been used for the formulation of refrigeration oil, is derived from petroleum products. However the depletion of petroleum reserves, uncertainty in crude oil prices, energy demand and increased environmental awareness has promoted the crucial requirement to synthesize refrigeration oil from environmentally friendly energy resources. The present investigation is intended to formulate a rapeseed oil based trimethylolpropane tri ester as biodegradable refrigeration oil with good thermo-oxidative stability and cold flow behaviour via chemical modifications. Thermo gravimetric Analysis (TGA) and Differential Thermal Analyses (DTA) were performed to study the thermo-oxidative stability of biodegradable refrigeration oil. This investigation is also addressing the issue of the tribological behaviour of cylinder liner/piston ring material of a hermetically sealed compressor in VCR system under the influence of biodegradable refrigeration oil and synthetic refrigeration oil (ISO 68 grade-POE oil) using a pin-on-disc tribometer. The surface morphology analysis of tested pin materials was also carried out using scanning electron microscope. The tribological experiments were carried out in accordance with ASTM G99. Under similar experimental conditions, biodegradable refrigeration oil exhibited good friction reduction behaviour and inferior wear reduction behaviour as compared to synthetic refrigeration oil. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advances in Materials, Manufacturing and Applied Sciences. Keywords: Hermetically Sealed Compressor; Refrigeration oil; Vapour compression refrigeration; Pin-on-disc tribometer; wear
1. Introduction The usage of the refrigerators and the air conditioners has increased every year due to their demand. Main issues of the refrigeration system are energy consumption and the environmental impact of refrigerants.
* Corresponding author. Tel.: 91 99946 99223; E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advances in Materials, Manufacturing and Applied Sciences.
P. Vithya et al. / Materials Today: Proceedings 16 (2019) 488–495
489
The compressor is the major power consuming part of the refrigeration system. The widely used type in refrigeration system is the reciprocating compressor for domestic and commercial applications. The refrigeration oils used in the refrigeration compressors are to lubricate the moving parts and its bearings. The lubricants incorporated in the refrigeration systems are of classified into mineral oil and synthetic oil which originated from the petroleum-based products. The synthetic lubricants are an alternative to mineral oil for the HFC refrigerants. Over the past few decades, raising demand for clear operating equipments and awareness towards the green environment led to turn the lubrication system into bio-based environment friendly in various applications. Bio lubricant has advantages such as higher lubricity, lower volatility, higher viscosity index, non-toxic, biodegradable and eco friendly. Quinchia et al [1] found that the esters derived from the vegetable oil possess better low temperature behaviour. kodali [2] reported the high oxidation stability of the polyolester oil owing to the nonappearance of hydrogen atom in beta location and positioning of carbon in the quaternary centre. Wang et al [3] formulated the bio lubricant through the transesterification of fatty acid tri ester from waste cooking oil with TMP using KOH as a catalyst. The obtained final product yield was 85.7%. They found a considerable elevation in the oxidation stability due to the additives in trimethylpropane fatty acid Tri ester. Physio-chemical properties match with the standard ISOVG32. Syaima et al [4] synthesized bio lubricant from palm oil by using hydrolysis and non - catalytic esterification. They suggested that the bio lubricant formed have the potential to be chosen as industrial lubricant for commercial purpose. A detailed study of the bio lubricant synthesis for diesel engine with high oxidation stability and increased cold flow behavior through epoxidation followed by hydroxylation and esterification process discussed by Arumugam and Sriram [5]. They extended their work to focus on friction and wear aspects of piston ring and cylinder liner on both synthetic and bio lubricant using HFRR and concluded that bio lubricant shows 23% lesser coefficient of friction and 12% higher wear compared with synthetic lubricant. Long et al [6] prepared pentaerythritol polyolester from jatropha oil via chemical modification of hydrolysis and esterification exhibit high decomposition temperature 3590 C is an evidence for bio lubricant’s potential. Zulkiflia et al [7] studied the tribological properties of trimethylolpropane ester bio lubricant from palm oil through transesterification process with added TiO2 nanoparticles using four ball machine tribometer shows inclusion of TiO2 nanoparticles at 160 kg reduces the coefficient of friction by 15% and the wear scar diameter by 11% respectively as compared without TiO2 nanoparticles. Yashvir Singh [8] investigated the friction and wear characteristics of Pongamia oil added biolubricant 15, 30 and 50% (v/v) with the base lubricant using pin-on-disc tribometer. They reported that the Pongamia oil added bio-lubricant PB 15 performs well in terms of coefficient of friction and wear. Krishna Sabareesh et al [9] investigated the performance improvement of a vapour compression refrigeration system on various concentrations on TiO2 nanoparticles in the mineral oil, found that the 0.01% volume fraction shows the optimum result, further analyzed the tribological properties of nanolubricant using pin on disc tribometer and reported that the reduction in the friction and wear characteristics for 0.01 volume fraction. A number of research works are carried using bio lubricant as an alternative to synthetic lubricant for Engine oil and transformer oil applications. Similarly, lots of research work is focused on the performance improvement of vapour compression refrigeration system by using synthetic lubricant with nanoparticles as additives. However, less work has been carried out on using bio lubricant as Refrigeration oil. Hence the present work synthesized the bio degradable refrigeration oil from rapeseed oil using transesterification with trimethylolpropane through chemical modification in order to find out the lubrication characteristics suitability as refrigeration oil for hermetically sealed reciprocating compressor. Furthermore, tribological study has been evaluated for checking the compatibility of the formulated bio degradable refrigeration oil and synthetic refrigeration oil using a Pin on disc Tribometer.
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2. Experimental 2.1. Materials The raw rapeseed oil, which has chosen as base oil for the conversion of bio degradable refrigeration oil was procured from the local dealer. Sodium hydroxide, dilute sulphuric acid, xylene, Nitrogen gas was procured from Sri Balaji Scientifics, Secunderabad. Trimethylolpropane (99% pure) was procured from M/s. Sigma Aldrich US. 2.2. Synthesis of Bio degradable Refrigeration oil The formulation of bio degradable refrigeration oil for the vapour compression refrigeration system of refrigeration compressors was carried out by the transesterification of fatty acid methyl ester from rapeseed oil with Trimethylolpropane. The bio degradable refrigeration oil from raw rapeseed oil was synthesized in two stages that is synthesis of rapeseed oil methyl ester in one stage followed by the synthesis of Trimethylolpropane tri ester of rapeseed oil in on next stage. The detailed procedure for the transesterification process, followed by purification process is adopted from Hiekel et al [10]. The methyl ester of rapeseed oil was produced by transesterification process with measured quantity of rapeseed oil and sodium hydroxide was mechanically stirred for 1 hour maintaining the temperature at 800C - 900 C until the complete disappearance of triglyceride. This course of the reaction is monitored by thin layer chromatography and the reaction mixture cooled and neutralized by diluting sulphuric acid. Further the synthesis of bio degradable refrigeration oil was carried out by the three necked reaction flask equipped with a thermometer, condenser and dean stark separator. Trimethylolpropane with known quantity was first loaded and the xylene was introduced as a catalyst. The rapeseed oil methyl ester was introduced during the reaction process at 1350C-1400C. The mixture was distilled at 1100C-1150C under the reduced pressure of 2-3mm of Hg to remove the xylene catalyst as shown in Fig.2. After the completion of reaction process, the mixture was distilled at 110C0-1150C under the reduced pressure of 2-3mm of Hg to remove the xylene catalyst. The final product of TMP ester obtained as a yield of 95%. 2.3 Tribological Study The effect of bio degradable refrigeration oil and ISO 68 grade POE oil on the lubrication properties were experimentally elucidated using Pin on Disc Tribometer [supplied by M/s DUCOM Instruments Pvt. Ltd]. The pin on disc tribometer was used to check the compatibility between the newly formulated refrigeration oil and ISO 68 grade-POE oil and cylinder liner/piston ring tribo pair materials. As the experiments were intended for pretending the tribological cross section cylinder liner/piston ring tribo pair of a hermetically sealed reciprocating compressor, the disc was made out of compressor cylinder liner material SAE J431 grade grey cast iron, heat treated to raise the hardness value up to 60HRC. Table.1. Experimental conditions of pin on disc tribometer
_____________________________________________________________________________________________ Normal load N
Rotational Speed rpm
Sliding distance m
Wear track diameter mm
__________________________________________________________________________________________________________________ 98 400 1000 50 -100 ___________________________________________________________________________________________________________________
The pins were made out of piston ring material FG 150 grade grey lamellar graphite cast iron of hardness 210 BHN. The separate pin and disc were used to performing the tribological study of ISO 68 grade-POE oil and bio degradable refrigeration oil. The tribological tests were carried out in accordance with ASTM G99 standards and experimental conditions were presented in Table1.
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After the completion of the test, the pins were examined using SEM to analyze the surface morphology behaviour under the influence of the bio degradable refrigeration oil and ISO 68 grade-POE oil. 3.
Results and Discussion
3.1.1. Analysis of physio-chemical properties The viscosity is significant property of oil related to the temperature and has a greater influence in heat generation. The viscosity of oil is directly correlated to the load and energy consumption of a refrigeration compressor. The kinematic viscosities of bio degradable refrigeration oil and synthetic refrigeration oil (ISO 68 grade POE oil) were determined using ASTM D-445. This viscosity of the bio degradable refrigeration oil at 400 C and 1000 C was 38.5 and 10.15cst. Table.3 shows the physio-chemical properties of raw rapeseed oil, ISO 68 grade POE oil and bio degradable refrigeration oil. The ASTM D-2270 standard was followed to find out the viscosity index (VI). The viscosity index obtained was extremely superior to the reported values of Phani et al [11]. The viscosity index of the bio lubricant is higher than the pure synthetic POE oil due to the higher molecular weight and by the chemical nature. The viscosity of the NPG and TMP esters synthesized at 40°C was 13.5 – 37.6 cst and it should possess higher viscosity index more than 200 as stated by Gryglewicz et al [12]. The pour point is the temperature of the lubricant remains in a fluid state that is ability to pour. The lower pour point is the critical characteristic of the lubricant under the cold operating temperatures. The pour point of both the oils was measured using ASTM D-97 method. The bio degradable refrigeration oil was a pour point of -60 C. This is significant with the studies by Cermak et al [13], which stated that the formation of a complex chain and branched oils have lower pour point. The action of forming macro crystalline structures of decrement in temperatures by the cause of stacking of bend in the triglyceride backbone responsible for confine of ease of liquid flow agreed with the fact with Kleinova [14]. Table.3. Tested properties of raw rapeseed oil, ISO 68 grade POE oil and bio degradable refrigeration oil
_____________________________________________________________________________________________ Properties
Standard
Raw rapeseed oil
Synthetic refrigeration oil
Bio degradable refrigeration oil
___________________________________________________________________________ 35
68
38.5
Viscosity@100 ˚C(cst) ASTM D445
Viscosity @ 40˚C(cst)
ASTM D445
8
9.3
10.15
Viscosity Index
ASTM D2270
212
114
266
Flash Point (˚C)
ASTM D92
320
270
220
Pour Point (˚C)
ASTM D97
-39
-11
-6
Density (kg/m3)
ASTM D1298
922
980
907.2
Amber
Brownish red
Colour
-
Brownish yellow
_________________________________________________________________________________________ 3.1.2. Thermo oxidative stability Analysis using TGA/DTA An oxidative property of lubricants is of prime importance to evaluate the thermal stability and to foresee actual lubricant life time exposed in high temperature and other extreme conditions. Excellent resistance to degradation means that it inhibits oxidation and reduces sludge and varnish. Thermo gravimetric analysis was incorporated to study the thermal stability of the lubricant and to detect the changes in weight in relation to changes in temperature. Changes in weight are a result of the rupture and formation of various physical and chemical bonds at elevated temperatures that lead to evolution of volatile products or the formation of heavier reaction products. The TGA thermal curve indicates a weight loss occurred with 20.18 mg sample of synthetic and bio degradable refrigeration oil by heating from 1000C to 7000C @ 10°C/min in nitrogen atmosphere with a purge rate of 20 ml/min was analyzed as shown in Fig.1 and Fig.2.
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Fig.(1) & (2) TGA Thermograms of synthetic ISO 68 grade POE oil and bio degradable refrigeration oil
Fig.(3) and (4) DTA analysis of synthetic ISO 68 grade POE oil and bio degradable refrigeration oil
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The bistage weight loss of 96% ended at 3920C for synthetic lubricant whereas 94% weight loss ended at 4790C for bio lubricant due to the evaporation of hydrocarbons shows that bio lubricant was more stable than the synthetic lubricant. This phenomenon can be associated with a broad endothermic peak centered at about 336.550C in DTA curve for the synthetic ISO 68 grade POE oil and bio degradable refrigeration oil as 438.100C due to the recombination of hydrocarbon free radicals as shown in the Fig.3 and Fig.4. Further the tristage weight loss ended at 5820C for bio degradable refrigeration oil under air. The complete degradation and decomposition was observed at higher temperatures of 7000C as shown in the Fig.2.The results were well agreed and extremely superior with Vinu et al [15]. 3.2
Tribological Investigation of bio degradable refrigeration oil
Friction is the property related directly with resistance energy, which lead to heat conversion. The Tribological characteristics of the compressor material under the influence of bio lubricant were found using a pin on disc Tribometer.
Fig. (5),(6) and (7) Coefficient of friction, Friction Force and Wear vs sliding distance
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Fig.5 and Fig.6 illustrates the friction coefficient and frictional force variations with respect to sliding distance. The results show that the friction coefficient of bio degradable refrigeration oil was considerably 20% lower than that of synthetic lubricant. The indicated reduced friction coefficient is due to the high polar functional groups of carboxylic acids and ester in the bio lubricant acts as a covering agent developing a film layer between the material surfaces of the cylinder liner/piston ring that reduces the direct contact of mating surface in any case. Thus the bio degradable refrigeration oil enhances the adsorption rates of the metal surfaces due to its chemical nature of increasing chain lengths and polarity in the structure improves the lubrication characteristics and plays a role as an anti friction agent. In the investigation of frictional force, the average value obtained for bio degradable refrigeration oil was 5 N was lower than the average frictional force of the synthetic lubricant. Fig.7 explains the variations of wear behaviour with respect to a sliding distance. The experimental results showed that the lubrication regime that occurred was boundary lubrication whereas the main wear mechanisms were abrasive and the adhesive wear.
Fig.8. SEM images of tested pin for (a) Synthetic ISO 68 grade POE oil (b) Bio degradable refrigeration oil
The bio degradable refrigeration oil has higher wear than ISO 68 grade POE oil due to the fatty acid present in the vegetable oil have a tendency to cause the metallic surface chemical attack that create non reactive detergents. Also for the reason, synthetic refrigeration oil was formulated with anti wear, anti-detergent and anti-foam agents, which leads to an increase in performance of the lubricant at low temperatures. Thus the inclusion of anti-wear additives will increase the performance correlated to the wear characteristics. Chemical modification of triacylglycerols structures has great potential in achieving broad temperature range stability as well as excellent wear and friction characteristics. Fig.8 (a) and 8(b) shows the scanning electron microscope image of the pin surface under the influence of the synthetic ISO 68 grade POE oil and bio degradable refrigeration oil at 200x magnification. The pin surface was examined through SEM micrographs to investigate the wear behaviour. The pin surface come into the contact of the disc surface, the abrasive type of wear crop up due to the development of the grooves in the sliding direction of motion, subsequently wear debris and pores are formed in the case of bio degradable refrigeration oil. The formation of furrows originated shows that the deformation raised with respect to increased load. On the other hand, smooth surface with inferior wear behaviour appeared in the case synthetic refrigeration oil. Conclusions The purpose of the research is to produce bio degradable refrigeration oil for refrigeration systems and the following conclusion was made in this present study.
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Bio degradable refrigeration oil (Trimethylolpropane Tri ester) from rapeseed oil with high thermo oxidative stability was formulated for vapour compression refrigeration system. The Physio-chemical properties met the requirements of the synthetic refrigeration ISO 68 grade POE oil except that of pour point. The effect of bio degradable refrigeration oil on the tribological properties shows better compatibility between the newly formulated refrigeration oil and ISO 68 grade-POE oil and cylinder liner/piston ring tribo pair materials. The friction coefficient found to be 20% lesser for the bio degradable refrigeration oil in comparison with the synthetic refrigeration ISO 68 grade POE oil owing to the presence of high polar functional groups of carboxylic acids and ester in the bio lubricant. In case of wear characteristics, higher wear behaviour occurred in the bio degradable refrigeration oil in contrast to the synthetic refrigeration oil showed that the certainty of inclusion of additives related to the anti-wear characteristics. This investigation gives an innovative alternative approach for the refrigeration oil derived from the vegetable oil for the refrigeration system. An extended research process is necessary to examine the wear reduction in the bio degradable refrigeration oil is planned by the authors in the future studies. References [1]. L.A. Quinchia, M.A. Delgado, J.M. Franco, H.A. Spikes, C. Gallegos, Ind. Crops Prod 37, (2012) 383–388. [2]. D.R. Kodali, Ind. Lubrication and Tribology 54, 4 (2002), 165–170. [3]. Erpei Wanga, Xiang Maa, Shuze Tang, Rian Yan, Yong Wang, William, W. Riley, J.T.Martin, Biomass and Bio energy, (2014) 1-8. [4]. M.T.S.Syaima, K.H. Ong, Ishenny Mohd Noora, M.I.M.Zamratul, S.A.Brahima, M.M. Hafizul, Renew. Sustainable Energy Rev 44(2015), 669–675 [5]. S. Arumugam, G. Sriram, J Engineering Tribology 227, 1, (2012) 3–15. [6]. Can Liu, Jing Liu, Lanqing Ma, Long Rong, J.Chemistry, (2014) 1-6. [7]. N.W.M. Zulkiflia, M.A. Kalam, H.H. Masjukia, R. Yunus, Procedia Engineering 68, (2013) 152 – 157. [8]. Yashvir Singh, Int. J. Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering 10(7), (2016) 12681274. [9]. R. Krishna Sabareesh, N. Gobinath,V. Sajith, S. Das, C.B. Sobhan, Int. J. Refrigeration 35(7), (2012) 1989-1996. [10].Ebtisam K. Heikal, M.S. Elmelawy, Salah A. Khalil, N.M. Elbasuny, Egyptian J. Petroleum 03, (2016)1-13. [11].S.K. Phani, Ind. Crops and Products 50, (2013) 95– 103. [12].S. Gryglewicz, W. Piechocki, G. Gryglewicz, Bio resource Technology 87, (2003) 35–39. [13].S.C. Cermak, T.A. Isbell, Ind. Crops and Products18, (2003) 183-196. [14].A. Kleinova, P. Fodran, L. Brnc alova, J. Cvengros, Bio mass Bio energy 32, (2008) 366–371. [15].Anand Kumar Tripathi, Ravikrishnan Vinu, Lubricants 3, 54-79.