Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications

Transcription

1 J. Chem. Eng. Chem. Res. Vol. 2, No. 5, 2015, pp Received: April 16, 2015; Published: May 25, 2015 Journal of Chemical Engineering and Chemistry Research Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications Ismat Zerin Luna 1, Sarwaruddin Chowdhury 1, Mohammad Abdul Gafur 2, Nuruzzaman Khan 1 and Ruhul A. Khan 3 1. Department of Applied Chemistry and Chemical Engineering, Faculty of Engineering and Technology, University of Dhaka, Dhaka-1000, Bangladesh 2. Pilot Plant and Process Development Center (PP & PDC), Bangladesh Council of Scientific and Industrial Research, Dhaka-1205, Bangladesh 3. Institute of Radiation and Polymer Technology, Bangladesh Atomic Energy Commission, Savar, Dhaka, Bangladesh Corresponding author: Ruhul A. Khan (dr.ruhul_khan@yahoo.com) Abstract: In the present study CuO-PVA nanofluids were prepared using two-step technique. Copper oxide nanoparticles (CuO-NPs) were prepared via chemical precipitation method. Different nanofluid samples at different volume concentrations (0.05, 0.1 and 0.2%) were prepared by dispersing CuO NPs in 4 wt% PVA solution using ultrasonication and magnetic stirring. X-ray diffraction (XRD) pattern of CuO-NPs showed that prepared sample was highly pure, crystalline and nanosized. Using Thermogravimetric analysis (TGA) and differential thermal analysis (DTA), thermal stability and weight loss of the CuO NPs were studied. The Fourier Transform Infra-Red (FT-IR) spectroscopy showed the interaction between PVA solution and CuO-NPs. The Ultra Violet Visible (UV-VIS) absorption spectra revealed the presence of CuO with characteristic λ max at around 280 nm. Experimental result showed that with increase in concentration of nanofluid the value of absorbance also increased. Relative stability of CuO-PVA nanofluid upon static duration was also investigated by this method. From the viscosity data it was found that the viscosity of nanofluids increases with an increase in concentration and decreases with an increase in temperature. Key words: CuO-PVA nanofluid, TG-DTA, FTIR, UV-visible absorption spectroscopy, viscosity. 1. Introduction Fluids are generally used as a cooling medium in many industrial applications. The enhancement of the heat transfer behavior of these fluids is very important in many sector. Nanofluids are a new class of fluids dispersing nanometer-sized materials or nanoparticles in base fluids. Nanofluids can be defined as nanoscale colloidal suspensions containing condensed nanomaterials. They are two-phase systems with one phase (solid phase) in another (liquid phase). Nanofluids have been found to possess enhanced thermal and physical properties such as thermal conductivity, thermal diffusivity, viscosity, and convective heat transfer coefficients. Nanofluids are using in many fields such as microelectronics, transportation, manufacturing, heating, and cooling [1-3]. The suspensions of solid particles in liquids provide useful advantages in industrial fluid systems. Thermal conductivity of a liquid can be increased by dispersing solid particles with higher thermal conductivity [4, 5]. Nanofluid is a new kind of heat transfer medium, containing nanoparticles having dimensions in nano range (1-100 nm) which are uniformly and stably distributed in a base fluid like water, ethylene glycol,

2 608 Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications polyvinyl pyrrolidone, polyvinyl alcohol, oil and lubricants, etc. It has been observed that nanofluids exhibit superior thermal properties as compared to the conventional fluids [5-7]. Nanofluids possess smaller particle size and large surface-volume ratio which increase the stability of the suspensions [8]. Nanofluids have superior heat transfer capabilities as the suspended nanoparticles increase the thermal conductivity of the fluids. Moreover, the chaotic movement of nanoparticles increases fluctuation and turbulence of the fluids, which accelerates the energy exchange process [9]. Many industrial processes require the transfer of heat energy. The intensification of heating or cooling system in an industrial process may save energy, increase thermal rating, reduce process time and extend the working life of equipment. The evolution of high performance thermal systems for heat transfer improvement gains much interest nowadays. For almost two decades, nanofluids have been considered for applications as advanced heat transfer fluids [10]. Generally metals, metal oxides and nanotubes are used in the preparation of nanofluids to enhance the thermal conductivity of the nanofluid by increasing conduction and convection coefficients [10, 11]. Compared to other metal oxides oxides of copper have high thermal conductivity [12, 13]. Copper oxide nanofluid shows reduced weight loss, enhanced thermal stability and thermal conductivity when compared to other fluids [14]. Preparation of stable nanofluids is of great importance in the area of nanofluid research and its application. Nanofluids can be prepared either by one-step method [15] or by two-step method [13]. In this study CuO-PVA nanofluid was prepared by two-step method. The objectives of this study were to prepare CuO-PVA nanofluids by an effective and economic method, and to investigate the characteristics of the nanofluids. The main aim of this study was to prepare CuO-PVA nanofluid having good heat transfer properties suitable for thermal engineering applications. 2. Experimental 2.1 Chemical Reagents Copper (II) chloride dihydrate was collected from Merck, India. Sodium hydroxide (99%) pellets were collected from Lobha Chemie. Polyvinyl alcohol (PVA) powder was collected from Jiangsu, China. Analytical reagent grade chemicals were used in the experiment and they were used without further purification. Distilled water and deionized water were used throughout the experiment for preparing solutions and washing purposes. 2.2 Preparation of Samples In this study CuO-PVA nanofluids were prepared using two-step technique [16-18]. At first, CuO-NPs were prepared via chemical precipitation method by following the procedure applied by Pandey et al. [18]. Then the nanofluids of 0.05 to 0.2 volume percent were prepared by dispersing different quantity of CuO nanoparticles in base fluid (Table 1). PVA solution (4.0 weight percent) was used as a base fluid in this study (Fig. 1). The nanofluids were sonicated continuously for 1 hour using a probe sonicator to disperse the nanoparticles uniformly. Following this, the nanofluids of different volume concentrations were stirred continuously for 3-4 hours using magnetic stirrer to obtain uniform dispersion of nanoparticles in base fluid. 2.3 Characterization X-ray diffraction (XRD) was carried out to analyze the phase and estimate the crystallite size of CuO NPs using X-ray diffractometer (XRD, Bruker D8 Advance, Germany) with nm Cu-Kα radiation source in Table 1 Weights of CuO NPs required in preparing the nanofluids of different volume concentrations. Weights of CuO nanoparticles (mg) Volume concentrations of nanofluids (vol %)

3 Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications C. 3. Results and Discussion 3.1 X-Ray Diffraction (XRD) Studies Fig. 1 (a) 4 wt% PVA solution; (b) 0.05%, (c) 0.1% and (d) 0.2% CuO-PVA nanofluids. the 2θ range from 20 to 80 (40 KV, 40 ma, step size 0.020, scan rate 0.50 min -1 ). The XRD pattern with diffraction intensity versus 2θ was recorded. FTIR spectroscopy of CuO NPs, PVA solution and CuO-PVA nanofluid were taken in (with Perkin Elmer 1650, USA) in order to understand the chemical and structural nature of the samples, and also the interactions between the species.tg/dta curves of CuO NPs were recorded by an equipment TG-DTG-DTA (Perkin-Elmer Diamond Thermal Analyzer-TG/DTA, USA) to determine the thermal stability at temperatures up to 1000 C and weight loss or gain due to decomposition, oxidation, or dehydration. The sample was heated from 30 to 1000 C with a heating rate of 20 C/min. The proper utilization of the potential of nanofluids depends on their stability. Absorption spectra of CuO NPs and CuO-PVA nanofluids were obtained using a UV-visible spectrophotometer (Shimadzu UV-1601, Japan) to investigate the stability of nanofluids. The viscosity of nanofluids is of great importance as the application of nanofluids is always affiliated with their flow. Viscosity of CuO-PVA nanofluids was measured using rotational viscometer (HAAKE Viscotester 550 Rotational Viscometer) by keeping only the shear stress variable and the shear rate constant. Effect of temperature on the viscosity of the nanofluids was studied at temperatures 25, 50 and Fig. 2 represents XRD patterns of CuO NPs along with the standard tenorite (CuO). This XRD pattern is almost completely matched with the monoclinic phase of CuO (tenorite) nanoparticles. No characteristic peaks any other phases were observed. The intensities and positions of peaks were in good agreement with that of reported values [19]. The present experimental result was also found to be in harmony with the reported [20] diffraction patterns of CuO-NPs. The average crystallite size of CuO NPs is nm. 3.2 Thermal Properties The thermo-gravimetric/differential thermal analysis (TG/DTA) profile for the CuO-NPs is shown in Fig. 3. The weight loss of CuO-NPs observed between the temperatures C is about 7%. This weight loss is mainly due to vaporization of water content in the sample. No significant weight loss is observed in the range of C indicating no oxidation behavior of the copper oxide NPs in this temperature range. Above the 800 C weight loss is 4.2%, it may be due to oxygen loss [14, 21]. From TGA analysis the total weight loss is about 11.2%. The TG-DTA results suggest that CuO is thermally highly stable in C temperature range and it has negligible weight loss when compared to bulk sample of CuO. The DTA curve shows that there are two endothermic peaks at about 794 and 931 C which indicates about the possibility of phase change in the sample at those temperatures. Melting started at around 790 C. The DTG curve of CuO NPs depicts one dominant peak at 212 C where the maximum degradation rate was mg/min. A similar results were reported by Arpana et al. [22].

4 610 Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications Fig. 2 XRD pattern of CuO NPs. The vertical lines ( ) indicate the position and relative intensity of JCPDS card file diffraction peaks for the monoclinic phase. Fig. 3 The thermal spectrum (TG/DTA)of the CuO-NPs.

5 Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications Fourier Transform Infra-Red (FT-IR) Analysis Fig. 4(a) shows FTIR spectra of CuO NPs. The broad absorption peak at around 3, cm -1 is caused by the adsorbed water molecules. Since the nano crystalline materials possess a high surface to volume ratio, they can absorb moisture. Radhakrishnan and Beena also found similar peak at 3,434 cm -1 in the FTIR spectra of CuO NPs [20]. The two infrared absorption peaks show the vibrational modes of CuO NPs in the range of cm -1. The peaks are observed at cm -1 and cm -1, respectively. The peak at cm -1 should be due to stretching of CuO [23]. The peaks at cm -1 and cm -1 indicate the formation of the CuO NPs. These two peaks support the presence of monoclinic phase. Padil and Černík observed two peaks at 525 cm -1 and 580 cm -1 in the FTIR spectra of CuO-NPs which nearly matches with our results [24]. FTIR spectra of PVA solution indicates a wide and intense band at 3, cm -1 verifying the existence of hydroxyl groups (O-H) shown in Fig. 4(b). The PVA solution also shows two characteristic bands at 2, cm -1 and 2, cm -1 for the presence of asymmetric and symmetric -CH 2 -stretching, respectively. Symmetric stretching of carboxylate anion (-COO-) represents an absorption band at 1, cm -1. The FTIR spectra of PVA solution obtained in this study is in good accordance with published FTIR spectra of PVA solution [25-27]. From Fig. 4(c), it is observed that the peaks obtained for CuO-PVA nanofluid is all the same to that of PVA solution. As the concentration of CuO NPs in the PVA solution is very low, there is no any significant bonding between them. Therefore, only peaks for PVA solution are predominantin region cm -1. Shifting in the absorption bands of nanofluid does not occur which indicates the existence of onlyphysical interaction between CuO and PVA solution [17]. Fig. 4 The FT-IR spectra of (a) CuO-NPs, (b) PVA solution and (c) CuO-PVA nanofluid.

6 612 Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications 3.4 Ultra Violet Visible (UV-VIS) Spectroscopy The UV-VIS absorption spectra of CuO nanoparticles and CuO-PVA nanofluids at different concentrations are depicted in Fig. 5. Figure shows absorption band in UV region with λ max around 280 nm for all samples, which proves the existence of CuO nanoparticles [28]. From the figure it is also observed that with increase in concentration the value of absorbance also increases, as the concentration of nanofluid has a linear relation with absorbance [29]. The UV-VIS spectrum method also is used to investigate the relative stability of CuO-PVA nanofluid. If the nanofluid is kept aside for a couple of days, the suspension of CuO nanoparticles in the base fluid will be decreased. From Fig. 6 it is found that as the static duration is prolonged, the the absorbance value of 0.2% CuO nanofluid is reduced because the particles begin to flocculate slightly [12]. Similar results are found for the nanofluids of other concentrations. 3.5 Viscosity The effect of concentration of CuO nanoparticles on the viscosity of the PVA solution (base fluid) at 25 C is shown in Fig. 7. It was found that the viscosity of nanofluids is substantially higher than that of the base fluid. It is also observed thatthe viscosity of the nanofluid with lower concentration is lower than those of nanofluids with higher concentrations [30]. Fig. 8 shows the influence of temperature on viscosity of 0.2% CuO-water nanofluid. It is observed that the viscosity of nanofluid at 50 C is lower than that obtained at 25 C. At 75 C the viscosity of nanofluid is lowest. Therefore, viscosity of nanofluid decreases with increase in temperature [31]. 4. Conclusions CuO nanoparticle prepared via chemical precipitation method was highly cryslalline, pure and nanosized. CuO-PVA nanofluids of different concentrations were successfully prepared by two-step technique.tg/dta profile showed that CuO NPs is thermally stable upto 1000 C and shows a minimum weight loss. FTIR spectra of nanofluid indicated only the physical interaction between CuO and PVA. Fig. 5 UV-visible absorption spectra of CuO nanoparticles and CuO-PVA nanofluids of different concentrations.

7 Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications 613 Fig. 6 UV-visible absorption spectra of 0.2% CuO-PVA nanofluid after different static durations. Fig. 7 Change of viscosity with respect of concentration of nanofluids at 25 C. UV-visible absorption spectroscopy confirmed the presence of CuO NPs in the nanofluid. From this method it was also observed that the absorbance value of nanofluid was reduced with the increase in the static duration. The experimental results about the viscosity of naofluids showed that viscosity increased with increase in concentration and decrease in temperature. CuO-PVA nanofluid prepared in this study is suitable for engineering applications such as convective heat transfer and fluid flow. It can be used successfully for heat transfer management systems in industrial applications. Acknowledgments The authors are thankful to Centre for Advanced Research in Sciences (CARS), University of Dhaka for providing additional research facilities. References Fig. 8 Influence of temperature on viscosity of 0.2% CuO-water nanofluid. [1] K.S. Meenakshi, P.J. Sudhan, Preparation and characterization of copper oxide-water based nanofluids by one step method for heat transfer applications, Chemical Science Transactions 4 (1) (2015) [2] R. Manimaran, K. Palaniradja, N. Alagumurthi, S. Sendhilnathan, J. Hussain, Preparation and characterization of copper oxide nanofluid for heat transfer applications, Application of Nanoscience 4 (2014)

8 614 Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications [3] D. Li, W.J. Xie, W.J. Fang, Preparation and properties of copper-oil-based nanofluids, Nanoscale Research Letters 6 (2011) [4] Y.Xuan, Q. Li, Investigation on convective heat transfer and flow features of nanofluids, Journal of Heat transfer 125 (2003) [5] X. Wang, A.S. Mujumdar, Heat transfer characteristics of nanofluids: A review. International Journal of Thermal Sciences 46 (2007) [6] S. Choi, Z. Zhang, W. Yu, F. Lockwood, E. Grulke, Anomalous thermal conductivity enhancement in nanotube suspensions, Applied Physics Letters 79 (2001) [7] H. Xie, M. Fujii, X. Zhang, Effect of interfacial nanolayer on the effective thermal conductivity of nanoparticle-fluid mixture, International Journal of Heat and Mass Transfer 48 (2005) [8] K. Rajan, S. Srivastava, B. Pitchumani, B. Mohanty, Simulation of gas-solid heat transfer during pneumatic conveying: Use of multiple gas inlets along the duct, International Communications in Heat and Mass Transfer 33 (2006) [9] L. Godson, B. Raja, L.D. Mohan, S. Wongwises, Enhancement of heat transfer using nanofluids An overview, Renewable and Sustainable Energy Reviews 14 (2010) [10] P. Sivashanmugam, Application of nanofluids in heat transfer, in: S.N. Kazi (Ed.), An Overview of Heat Transfer, INTECH Publications, Croatia, Chapter 14, 2012, pp [11] M. Jalal, H. Meisami, M. Pouyagohar, Experimental study of CuO/water nanofluid effect on convective heat transfer of a heat sink, MiddleEast Journal of Scientific Research 13 (2013) [12] H. Chang, Y. Wu, X. Chen, M. Kao, Fabrication of Cu based nanofluid with superior dispersion, National Taipei University of Technology Journal 5 (2000) [13] A.G. Nasibulin, P.P. Ahonen, O. Richard, E.I. Kauppinen, I.S. Altman, Copper and copper oxide nanoparticle formation by chemical vapor nucleation from copper (II) acetylacetonate, Journal of Nanoparticle Research 3 (2001) [14] G.K. Murugalakshmi, N. Selvakumar, Experimental studies of thermal transport in heat transfer fluids using infrared thermography, International Journal of Innovative Research in Science, Engineering and Technology 3 (2014) [15] C.S. Jwo, T.P. Teng, H.A. Chang, A simple model to estimate thermal conductivity of fluid with acicular nanoparticles, Journal of Alloys and Compounds 434 (2007) [16] J. Eastman, S. Choi, S. Li, W. Yu, L. Thompson, Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles, Applied Physics Letters 78 (2001) [17] D. Anandan, K. Rajan, Synthesis and stability of cupric oxide-based nanofluid: A novel coolant for efficient cooling, Asian Journal of Scientific Research 5 (2012) [18] V. Pandey, G. Mishra, S. Verma, M. Wan, R. Yadav, Synthesis and ultrasonic investigations of CuO-PVA nanofluid, Materials Sciences and Applications 3 (2012) [19] International Centre for Diffraction Data (ICDD), Joint Committee on Powder Diffraction Standards, Diffraction Data File No , 2000, pp [20] A.A. Radhakrishnan, B.B. Beena, Structural and optical absorption analysis of CuO nanoparticles, Indian Journal of Advances in Chemical Science 2 (2014) [21] A. Ortiz, L. Shaw, X-ray diffraction analysis of a severely plastically deformed aluminum alloy, Acta Materialia 52 (2004) [22] Y. Aparna, K. Rao, P.S. Subbarao, Synthesis and characterization of CuO nano particles by novel sol-gel method, in: 2nd International Conference on Environment Science and Biotechnology, 2012, pp [23] K. Karthik, J.N. Victor, M. Kanagaraj, S. Arumugam, Temperature-dependent magnetic anomalies of CuO nanoparticles, Solid State Communications 151 (2011) [24] V.V.T. Padil, M. Černík, Green synthesis of copper oxide nanoparticles using gum karaya as a biotemplate and their antibacterial application, International Journal of Nano Medicine 8 (2013) [25] T. Wang, M. Turhan, S. Gunasekaran, Selected properties of ph sensitive, biodegradable chitosan-poly (vinyl alcohol) hydrogel, Polymer International 53 (2004) [26] N. Labidi, A. Djebaili, Studies of the mechanism of polyvinyl alcohol adsorption on the calcite/water interface in the presence of sodium oleate, Journal of Minerals and Materials Characterization and Engineering 7 (2008) [27] W. Jabbar, N. Habubi, S. Chiad, Optical characterization of silver doped poly (vinyl alcohol) films, Journalof Arkansas Academy of Science 64 (2010) [28] N. Topnani, S. Kushwaha, T. Athar, Wet synthesis of copper oxide nanopowder, International Journal of Green Nanotechnology: Materials Science & Engineering 1 (2010) [29] A. Ghadimi, R. Saidur, H. Metselar, A review of nanofluid stability properties and characterization in

9 Preparation and Characterization of CuO-PVA Nanofluids for Heat Transfer Applications 615 stationary conditions, International Journal of Heat and Mass Transfer 54 (2011) [30] S. Murshed, K. Leong, C. Yang, Investigations of thermal conductivity and viscosity of nanofluids, International Journal of Thermal Sciences 47 (2008) [31] M. Kole, T. Dey, Thermal conductivity and viscosity of Al 2 O 3 nanofluid based on car engine coolant, Journal of Physics D: Applied Physics 43 (2010)