Scanning Electron Microscopy SEM

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2.2 Fourier Transform Infrared FTIR

An infrared spectrum represents a fingerprint of a specimen with absorption peaks which correlate to the frequencies of vibrations between the obligations of the atom that making up the material. In order to make an identification and requires a frequency spectrum, as the measured interferogram signal cannot be interpreted, a means of decoding the individual frequencies is required. This can be solved only through the well- known mathematical method called the Fourier transform. This transformation will be performed and solved by the computer which then presents the user with desired spectral information for analysis.

2.3 Thermal Conductivity Testing

The thermal conductivity test of the nanofluid will be taken at three different temperatures which are at 6°C, 25°C and 40°C. To obtain such temperature of the nanofluid, those three samples will be immersed in the water bath so that the temperature of the samples will maintain at desired temperature.

3. RESULTS AND DISCUSSION

The morphology of three different types of carbon nanotubes is shown in Figure 1. The nanotubes morphology are randomly entangled and highly interconnected, probably due to the van der Waal’s. Figure 1 SEM images of a CNT1, b CNT2, c CNT3 The surface areas contribute to the enhancement of physical and chemical properties of nanofluids. The properties that found to influence surface area were number of walls or diameter, impurities, and surface functionalization with hydroxyl and carboxyl groups. All images shown in Figure 1 illustrated agglomerate carbon nanotube and nanofibers, primarily with non- uniform tubular structure. The increase in diameter size will reduce the surface area. Higher surface areas are expected to provide a better media for thermal transport in nanofluid. Figure 2 shows the FTIR spectra of the CNTs. On the horizontal axis is the infrared wavelengths expressed in term of a unit called wavenumber cm -1 which represent the number of waves fit into one centimeter. The peaks in the COOH spectrum represent the functional groups that are present in the molecule. The results reveal that the CNT1 fMWNT shows the higher COOH spectrum followed by CNT2 Nanoamor, and CNT3 HHT24. The higher in the peak spectrum will enable a good dispersion of CNT in nanofluids and improve the stability of nanofluids. Figure 2 FTIR spectra of CNTs Table 2 Thermal conductivity WmK for CNT at various temperatures CNT Temperature o C 6 25 40 CNT1 0.55 0.50 0.50 CNT2 0.57 0.50 0.60 CNT3 0.58 0.60 0.60 Table 2 shows the thermal conductivity analysis for the all CNTs. CNT3 shows the higher thermal conductivity compared to others due to the decrement of diameter size in carbon nanofiber. The smallest diameter generates the best enhancement in thermal conductivity which contribute to the higher surface area.

4. CONCLUSIONS

In conclusion, the study of surface area of the selected CNT nanocarbon shows that the decrement in diameter size will attributed to the highest surface area and possesses a good thermal conductivity. The experimental studies shows that CNT3 HHT24 generates the best enhancement in thermal conductivity. High surface area of the CNT3 HHT24 offers a better media for thermal transport in nanofluids. 5. REFERENCES [1] Weitz, D. A., Huang, J. S., Lin, M. Y., and Sung, J., “Dynamics of Diffusion-Limited Kinetic Aggregation,” Phys. Rev. Lett., vol. 53, pp. 1657– 1660, 1985. [2] Meakin, P., “Aggregation Kinetics,” Phys. Scr., vol. 46, pp. 295–331, 1992. [3] J. Eapen, R. Rusconi, R. Piazza and S. Yip, “The Classical Nature of Thermal Conduction in Nanofluids”, Journal of Heat Transfer, vol. 132, no. 10, pp. 1-14, 2010. [4] Iijima.S. 2007. “Nano-carbon materials: Their Fundamentals and Various Applications including Nano-Biotechnology”. University of Wien. [5] Lin, T., Bajpai, V., Ji, T. and Dai, L., “Chemistry of Carbon Nanotubes”. Australian Journal of Chemistry, vol. 56, no. 7, pp. 635-651, 2003. 4000 3500 3000 2500 2000 1500 1000 500 10 26 13 83 16 24 34 37 Nanoamor MWCNT HHT24 Tr an sm itt an ce [a .u ] Wavenumber [cm -1 ] a b c CNT2 CNT1 CNT3 __________ © Centre for Advanced Research on Energy Thermal properties and heat transfer study of dispersed fluid with functionalized Multi-Walled Carbon Nanotube MWCNT particles F.N. Zahari 1, , M.R.H. Noor Salim 1 , I.S. Mohamad 1 , N. Abdullah 2 , S. Thiru 3 1 Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia. 2 Department of Chemistry, Centre for Foundation Studies, Universiti Pertahanan Nasional Malaysia, Kem Sungai Besi, 57000, Kuala Lumpur, Malaysia. 3 Department of Mechanical Engineering, King Abdul Aziz University - North Campus P.O. Box 80204, Jeddah 21589, Kingdom of Saudi Arabia. Corresponding e-mail: fatinbellanabilagmail.com Keywords: Thermal conductivity; MWCNT; specific heat capacity ABSTRACT – Water, ethylene glycol and engine oil are commonly used in heat exchanger applications as coolant. However, these fluids possess low thermal conductivity. The advancement in nanotechnology has enabled nano-size particles to be included in a base fluid and this is known as nanofluids. The aim of this study is to investigate the most stable and homogeneous nanofluids with different weight percentage that produced excellent result in thermal properties and heat transfer characteristics. For this study, the usage of MWCNT as nanoparticles and deionized water as based fluids with surfactant were investigated for their stability and thermal properties. Different temperature and particle volume concentration were used in this study and this will affect the thermal conductivity, viscosity and specific heat as well as the heat transfer characteristics of nanofluids. As a result, the thermal conductivity and specific heat capacity of nanofluids were increased when the temperature and particle volume concentration increased. Besides that, the viscosity of nanofluids seem to decreased when temperature was increased but not for its particle concentration.

1. INTRODUCTION

Nanofluids are a new generation of thermal fluids which have particular features that affect their behavior. One of these features is response of nanofluids to temperature difference. Nanofluids have been found to possess enhanced thermophysical properties such as thermal conductivity, thermal diffusivity, viscosity and convective heat transfer coefficients as compared to those of base fluids like oil or water. Owing to their enhanced properties as thermal transfer fluids for instance, nanofluids can be used in engineering applications ranging from use in the automotive industry to the medical arena. Besides, it also being use in power plant cooling systems as well as computers. Focused on the nanofluids thermal properties, the temperature are greatly affected their thermal properties. It increasing the thermal conductivity for nanofluid when the temperature range increased [1,5]. The results suggested the application of nanofluids as coolant for devices with high energy density where the cooling fluid works at temperature higher than room temperature. Besides that, the viscosity of nanofluids also increased with increasing MWCNT concentration and decreasing temperature [2] meanwhile the specific heat of nanofluids decreases with an increase in concentration and an increase in temperature [3]. 2. METHODOLOGY 2.1 Preparation of Nanofluids To produce nanofluids, the MWCNT particles were used in this study and deionized water DI as well as polyvinylpyrrolidone PVP were used as base fluid and surfactant respectively. The nanofluids were prepared by dispersing MWCNT nanoparticles and PVP in a base fluid. They were mixed together by using a homogenizer at a rotational speed of 10000 rpm for about 5 minutes. Each of the samples will undergo 30 minutes of intensive ultrasonication to disperse the nanoparticles. This process was conducted by using the Elmasonic S30H Ultrasonicator 50-60 kHz frequency with 280W of output power. It generates high shear forces that break particle agglomerates into single dispersed particles.

2.2 Stability Test

Each samples need to undergo stability test. As for an investigation of the stability characteristics, the sedimentation of the nanofluid samples was observed for the duration of 100 hours by visual inspection and also by using laser shot technique. The stability of the nanofluid is generally determined by penetration of the laser beam emitted from the semiconductor laser diode which will travel through the nanofluid. If the laser light can travel through the nanofluid, the samples are considered as stable nanofluids. The stable nanofluid was then used for further experimentation. The stability of nanofluid was affected by the characteristics of suspended particle and base fluids such as the particle morphology, the chemical structure of the particles and base fluid [4,6].