Lubricant Enhancement via Hydrodynamic and Acoustic Cavitation

Available online at www.sciencedirect.com

ScienceDirect Procedia Engineering 148 (2016) 57 – 63

4th International Conference on Process Engineering and Advanced Materials

Lubricant Enhancement via Hydrodynamic and Acoustic Cavitation Stephen Sie Kiong Kiua, Suzana Yusupa,*, Chok Vui Soonb, Taufiq Arpinb, Syahrullail Samionc a

Biomass Processing Lab, Center of Biomass and Biofules Research, MOR Green Technology, Chemical Engineering Department, Universiti Teknologi PETRONAS, Perak, Malaysia b Platinum Nanochem Sdn.Bhd Lot 15-19 & PT1409, Senawang Industrial Estate, Batu 4, Jalan Tampin, 70450, Seremban Negeri Sembilan, Malaysia. c Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia

Abstract Lubricant plays a vital role in reducing wear, friction and energy consumption in any machinery. It is mainly used in automotive, industrial, processing, and marine. Various types of lubricant were developed from time to time to meet with the market requirement. However, lubricant performance demanded by market changes as the application varies. For instance, lubricant with high thermal stability is required in drilling, which is High Temperature High Pressure (HPHT) condition. Recent studies have revealed that by adding an optimum concentration of nanoparticles into lubricant, the tribological performance of the lubricant can be improved significantly. Viscosity of lubricant is vital in terms of forming lubricating film and reduces friction. In this study, mutliwalled carbon nanotubes were added to lubricants through hydrodynamic and acoustic cavitation. The results indicated that addition of multiwalled CNT definitely improve nanofluids’ viscosity. Besides, comparison between methods of preparation showed that hydrodynamic cavitation alone yield best suspension with highest viscosity in both 25ppm and 100ppm cases. © Published by by Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license © 2016 2016The TheAuthors. Authors. Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICPEAM 2016. Peer-review under responsibility of the organizing committee of ICPEAM 2016 Keywords: Lubricant Additive; Acoustic Hydrodynamic Cavitation; Kinematic Viscosity

* Corresponding author. Tel.: +05-368-7642 E-mail address: [email protected]

1877-7058 © 2016 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 ICPEAM 2016

doi:10.1016/j.proeng.2016.06.493

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Nomenclature CNT AC HC AHC

Carbon Nanotube Acoustic Cavitation Hydrodynamic Cavitation Acoustic and Hydrodynamic Cavitation

Introduction Environmental awareness and energy conservation are arising as global issues in modern industrial production. The main cause of energy loss is through heat, which caused by friction. Specifically in the process of drilling extended-reach, excessive torque is often reported as one of the most major problems which caused by dog legs, key seats, bit balling and hole instability [1]. The conventional way to reduce wear and friction caused by mechanical movement is using mineral oil-based lubricant. Addition of nanoparticles into a base fluid, termed ‘nanofluid’ is gaining more attention due to its great potential application in many fields. Yu.et al stated in their review paper that nanofluid have wide application by citing many researches work. The main application are heat transfer intensification, mass transfer enhancement, energy applications, mechanical applications, biomedical other applications [2]. It is proven that nanofluid can enhance thermal conductivity, reduction in pumping power and better lubrication [3]. Recently, many researchers put effort in studying different combination between nanoparticles and its base fluid prior to their application interest. Some researches introduced functional group as coating on nanoparticles [4], while some synthesize their own desirable nanocomposites subjected to their targeting properties [5-6]. Among most studies on nanofluid, the commonly used nanoparticle was allotropes of carbon, such as graphene and carbon nanotubes and graphene derivative, graphene oxide. It is mainly due to their excellent electronic, optical thermal and mechanical properties [7]. Generally, nanofluid are prepared by two types of method, either single-step or two-step preparation. Single step preparation involves simultaneously making and dispersing the particles within a single process. For example, vacuum-SANSS (submerged arc nanoparticle syntheses system), microwave irradiation and phase transfer method. On the other hand, two-step method involves direct mixing of nanoparticles with base fluids followed by dispersant addition or ultrasonication to ensure well-dispersion. Research up to date stated that the two-step preparations are preferable because it is more economic and it can produce nanofluid in a large scale [2-3]. Despite a lot of studies had revealed significant improvement of base fluid properties after adding respective nanoparticles, dispersion stability still remains as a critical challenge for nanofluid, especially when it is applied in HTHP conditions. Numerous studies had shown different nanofluid prepared by respective method possess varying suspensions duration stability. Ettefaghi et.al found that dispersing fullerene in engine oil through planetary ball mill method can achieve suspension stability up to 720 hours [8]. Meanwhile, Hao et.al managed to achieve 4 months stability by surface capping calcium borate nanoparticles with oleic acid before dispersing in lubricant oil [9]. Therefore, researches are still looking for a more sophisticated method is to produce a more stable nanofluid which has longer duration for transportation and storage. Therefore, a combination of ultrasonic cavitation and hydrodynamic cavitation technique in series is proposed in this research to study the viscosity enhancement and its suspension stability. Cavitation is divided into three phases; the generation of bubbles, collapse of cavities, resulting in very high energy release that can enhance homogenization. The pressure associated with bubble collapse is high enough to cause damages towards surface wall [10]. However, a well-controlled cavitation can homogenize the dispersion of nanoparticles in the base fluid and promotes longer suspension stability. In contrast, acoustic cavitation is in smaller unit and portable. Therefore, it is generally being used for mixing chemicals in industries. In hydrodynamic cavitation, cavities are formed due to the sudden change in pressure in the flowing fluid caused by change in the flow area such as venture and orifice plate [11]. The sudden collapse induces cavities which break the base fluid molecules into smaller pieces and promotes well mixing with the added nanoparticles. Similarly,

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acoustic cavitation utilizes sound wave to induce generation and collapse of bubbles. Therefore, a combination of these two technologies is convinced to yield a more homogenize nanofluid compared to each standalone method. The main reason for a good stable suspension is to ensure that added nanoparticles does not agglomerates easily and settles down easily. In other words, the well dispersed nanoparticles must be able to sustain themselves for transportation and storage period before putting in use. Remixing before use will definitely cause inconvenient and consumes time and unnecessary cost. Currently, limited studies had been carried out to prepare nanofluid through the combination technique of ultrasonic cavitation and hydrodynamic cavitation. Therefore, it has great potential to deeper study to produce an improved stability suspension and to obtain improved viscosity lubricant. Materials and Methods 2.1 Materials The carbon nanotubes were provided by Platinum Nanochem, a local company which manufactures a range of high performance chemicals. TEM images were taken to identify the size and the type of CNT. 2.2 Lubricants Industrial lubricant oil were used in this study which provided by Platinum Nanochem. It is a high-end lubricant namely oil A which mainly used in drilling application. The density and viscosity of oil A was shown in Table 1. 2.3 Experiment apparatus The setup for the experiment was shown in Figure 1. It consists of a hydrodynamic cavitation unit, an acoustic cavitation unit, diaphragm pump, pressure gauge and a stirrer. 2.4 Experiment Procedure Six samples of CNT nanofluid were prepared in this study. Three samples of 25ppm and three samples at 100ppm CNT were prepared through AC, HC and AHC respectively. Orifice plate with an internal diameter of 1mm was used in HC unit. Each sample was circulated in HC for one hour. While for acoustic cavitation, each sample was prepared under 40 kHz (maximum) by Brandson 8510E Ultrasonicator, for one hour. For AHC, each sample underwent one hour of AC and one hour of HC. A stirrer was inserted into tank and operated continuously at 300rpm to ensure well mixing. The diaphragm pump was operated at 50Hz (maximum). 2.5 Density and Viscosity A suitable range of hydrometer was used to measure the density of oil samples. Three measurements of density were taken and their average value was taken to minimize the error. Viscosity signifies the internal friction of liquid. It has direct relation with friction but there no formula was developed yet to correlate viscosity and friction. In this study, kinematic viscosity of oil samples was studied. . Diaphragm pump

P

Hydrodynamic Cavitation Orifice plate (1mm)

AC Acoustic Cavitation in parallel Oil + nanoparticles solution + stirring

Fig. 1. Schematic diagram of experiment setup

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Stephen Sie Kiong Kiu et al. / Procedia Engineering 148 (2016) 57 – 63 Table 1. Relative density, viscosity of oil A

Type of lubricant Oil A

Relative density 1.028

Kinematic viscosity at 40oC 174.64

Kinematic viscosity at 100oC 25.09

Results and discussions 3.1 TEM images of CNT Figure 2a showed from top view that CNT samples were consists of bundles of nanotubes overlapping each other. As shown in the figure 2b, an image at 10nm was taken and it showed that the purchased CNT have multiple layers of carbon on both side. They have average length of 4.545nm. Therefore, it was multi-walled CNT.

Fig. 2. (a) TEM image of CNT at 100nm; (b) TEM image of sample CNT at 10nm

3.2 Density and kinematic viscosity Density of a fluid is defined as its mass per unit volume. In this study, density of pristine oil A and three samples of 25ppm CNT added were measured by a suitable range hydrometer at room temperature (25 oC). Generally, there is slight increase in density after addition of 25ppm CNT nanoparticles, as shown in the table 2. Kinematic viscosity of each sample was measured by using a viscometer. Density of each sample was inserted individually to viscometer before measuring its kinematic viscosity. The data obtained was tabulated in Table 2 below. Table 2. Specific gravity and kinematic viscosity of samples at 25ppm CNT Test oil Pure A A25CNTAC A25CNTHC A25CNTAHC Relative density at 25oC 1.028 1.030 1.034 1.032 Kinematic viscosity(mm2/s) 440.2 457.0 494.0 444.7 Besides, three samples of 100ppm CNT were synthesized using AC, HC and AHC and the results are shown in table 3 below. Table 3. Specific gravity and kinematic viscosity of samples at 25ppm CNT

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Test oil S.G at 25oC Kinematic viscosity(mm2/s)

Pure A 1.028 440.2

A100CNTAC 1.030 450.9

A100CNTHC 1.032 508.7

A100CNTAHC 1.032 460.9

From Figure 3 and 4, we can observe that all six samples of CNT added samples have improved viscosity compared to pure mineral A. It proved that addition of CNT definitely improve oil’s viscosity. Vasheghani et.al (2011) presented in their result that addition of α-Al2O3 and β-Al2O3 into engine oil also had proven improvement of viscosities compared to base oil in room temperature [12]. On the other hand, samples which synthesized under hydrodynamic cavitation showed highest viscosity in both 25ppm and 100ppm nanofluid relative to AC and AHC method. This is mainly due to the energy release from the bubble implosion which enhances the homogenization of nanoparticles within the oil solution. In HC, change in flow area by orifice results in very high energy release instantaneously. Some researchers agreed that hydrodynamic cavitation is more efficient in homogenizing solution alone. For example, Romain et.al (2010) concluded their result that HC was found to be very effective in producing water-in-oil emulsions when compared to a stirred batch reactor [13]. Kumar et.al (2000) studied the effect of HC on decomposition of aqueous potassium iodide solution. Their results showed that iodine liberated per unit energy input for HC is three times higher than AC [14].

Fig. 3. Comparison of kinematic viscosity at 25ppm CNT

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Fig. 4. Comparison of kinematic viscosity at 100ppm CNT However, the lower viscosity in AHC compared to HC alone had opposed the synergistic effect proposed by Braeutigam et.al (2012) [15]. .By optimizing various parameters of AHC, they proved that AHC could have a synergy of 63% based on the OH radical generation. The synergy effect was explained in the way that bulk of bubbles were generated through HC and collapsed by AC simultaneously. The only reason which the debut arises is probably due to the difference in configuration of AHC. In this study, AHC is assembled in series which each sample undergoes HC for one hour, continued by one hour of AC bath. Unlikely, Breautigam and his colleagues combined HC and AC parallel in a single unit, which an AC probe was inserted into HC unit. Theoretically, both AHC should have similar synergistic effect on viscosity improvement. However, result proved that putting HC and AC in series does a negative effect in terms of kinematic viscosity of the nanofluid. It might be due to resettlement of nanoparticles after AC, which is not identified in this study. 3.3 Suspension Stability All six samples of 25ppm and 100ppm CNT oil samples have minimum of 45 days suspension stability. There is no agglomerates been observed at the bottom of container before sending for viscosity test.. Figure 5a and 5b shows the sedimentation method to observe the height of nanoparticle sediment.

a

b

Fig. 5 Sedimentation in oil sample for (a) 25ppm CNT; (b) 100ppm CNT under HC

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4. Conclusions In conclusion, HC was found to be best methodology to prepare CNT nanofluid in terms of viscosity improvement among the three studied method. The result of both 25ppm and 100ppm CNT confirmed the finding. Indirectly, it associated to higher lubricating performance as viscosity plays important role in forming lubricating film. Besides, all three methods have minimum suspension stability of 45 days without agglomerates. Further study with different concentration and other types of nanoparticles can be implied to have deeper understanding in this topic.

Acknowledgements This work was developed thanks to the support of Biomass Processing Lab, Universiti Teknologi Petronas, technical support from Platinum Sdn.Bhd and Mechanical Department, Universiti Teknologi Malaysia.

References [1] A.Sönmez, M.V. Kök, R.Özel, Performance analysis of drilling fluid liquid lubricants, Journal of Petroleum Science and Engineering. 108 (2013) 64-73. [2] W.Yu, H.Xie, A review on nanofluids: Preparation, stability mechanisms, and applications, Journal of nanomaterials. (2012) [3] S.Mukherjee, S.Paria, Preparation and stability of nanofluids- a review, IOSR Journal of Mechanical and Civil Engineering. 9 (2013) 63-69 [4] Y.Zeng, Y.Zhou, L.Kong, T.Zhou, G.Shi, A novel composite of SiO 2 –coated graphene oxide and molecularly imprinted polymers for electrochemical sensing dopamine, Journal of Biosensors and Bioelectronics. 45 (2013) 25-33 [5] X.Li, Y.Zhao, W.Wu, J.Chen, G.Chu, H.Zou, Synthesis and characterizations of graphene-copper nanocomposites and their antifriction application, Journal of industrial and engineering chemistry. 20 (2014) 2043-2049 [6] F.Zhang, C.Hou, Q.Zhang, H.Wang, Y.Li, Graphene sheets/cobalt nanocomposites as low-cost/high performance catalysts for hydrogen generation, Journal of materials chemistry and physics. 135 (2012) 826-831 [7] X.Zhou, W.Wang, Z.Liu,. Graphene: Energy storage and conversion applications, Chapter 1-Graphene Overview, CRC Press, Taylor and Francis Group, Chicago, 2015,pp. 1-16 [8] E.Ettefaghi, A.Rashidi, H.Ahmadi, S.S.Mohtasebi, M.Pourkhalil, Thermal and rheological properties of oil-based nanofluids from different carbon nanostructures, International Communications in Heat and Mass Transfer. 48 (2013) 178-182 [9] L.Hao, J.Li,T.Ren, Preparation and tribological properties of a kind of lubricant containing calcium borate nanoparticles as additives, Industrial Lubrication and Tribology. 64/1 (2012) 16-22. [10] P.Einserberg, H.S. Preiser, A. Thiruvengadam, On the mechanisms of methods of protection cavitation damage and methods of protection, Transactions, Society of Naval Architects and Marine Engineers, Vol. 73, 1965, pp. 241-279 [11] P.R.Goagte, A.B.Pandit, Engineering design methods for cavitation reactors II: Hydrodynamic cavitation, AIChE Journal. 46 (2000) 16411649 [12] M.Vasheghani, E.Marzbanrad, C.Zamani, M.Aminy, B.Raissi, T.Ebadzadeh, H.B.Bafrooei, Effect of Al2O3 phases on the enhancement of thermal conducitivity and viscosity of nanofluids in engine oil, Heat mass transfer (2011) [13] R.S.Beuve, K.R.Morison, Enzymatic hydrolysis of canola oil with hydrodynamic cavitation, Chemical Engineering and Processing: Process Intensification. 49 (2010) 1101-1106 [14] P.S.Kumar, M.S.Kumar, A.B.Pandit, Experimental quantification of chemical effects of hydrodynamic cavitation, Chemical Engineering Science. 55 (2000) 1633-1639 [15] P.Braeutigam, M.Franke, R.Scheneider, A.Lehmann, A.Stolle, B.Ondruschka, Degradation of carbamazepine in environmentally relevant concentration in water by hydrodynamic-acoustic cavitation (HAC), Journal of water research. 46 (2012) 2469-2477

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