Design and Evaluation of Carbon Nanotube Based Nanofluids for Heat Transfer Applications
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Design and Evaluation of Carbon Nanotube Based Nanofluids for Heat Transfer Applications Sathya P. Singh1, Nader Nikkam1, Morteza Ghanbarpour2, Muhammet S. Toprak1*, M. Muhammed1 and Rahmatollah Khodabandeh2 1 Department of Materials and Nano Physics, KTH-Royal Institute of Technology, SE-16440 Kista, Stockholm, Sweden. 2 Department of Energy Technology, KTH-Royal Institute of Technology, SE-100 44 Stockholm, Sweden. ABSTRACT The present work investigates the fabrication, thermal conductivity (TC) and rheological properties of water based carbon nanotubes (CNTs) nanofluids (NFs) prepared using a two-step method. As-received (AR) CNTs heated and the effect of heat treatment was studied using X-ray diffraction and thermogravimetric analysis. The AR-CNTs and heat-treated CNTs (HT-CNTs) were dispersed with varying concentration of surface modifiers Gum Arabic (GA) and TritonX100 (TX) respectively. It was found that heat treatment of CNTs effectively improved the TC and influenced rheological properties of NFs. Scanning electron microscopy analysis revealed TX modified NFs showed better dispersion ability compared to GA. Surface modification of the CNTs was confirmed by Fourier Transformation Infrared (FTIR) analysis. Zeta potential measurement showed the stability region for GA modified NFs in the pH range of 5-11, whereas pH was between 9.5-10 for TX NFs. The concentration of surface modifier plays an extensive role on both TC and rheological behavior of NFs. A maximum TC enhancement of 10% with increases in viscosity around 2% for TX based HT-CNTs NFs was measured. Finally comparison of experimental TC results with the predicted values obtained from a model demonstrated inadequacy of the predictive model for CNT NFs system. INTRODUCTION Heat transfer technologies are being focused on the development of highly efficient and new hybrid materials for effective heat transfer or cooling system. Demand for thermal management in various industries such as microelectronics, combustion engines, boilers, power transformers, space and defense cannot be met by the conventional heat exchange fluids, like water and ethylene glycol due to their limited heat transfer performance. Nanofluids, as the term coined by Choi [1], in which a small amount of nanoparticles added into base fluids, showed promising heat transfer performance over conventional heat exchange fluids. CNTs possess high electrical and thermal conductivity, which makes them an attractive candidate for NFs for heat transfer applications. CNTs cannot be dispersed in water directly due to their hydrophobic surface. Therefore, selecting suitable surface modifier with the optimized concentration plays an important role in fabrications of stable CNT based NFs. To develop an effective CNTs NFs, we focused on the improvement of the quality of ARCNTs by heat treatment. Then two different surface modifiers, Gum arabic (GA) and triton X100 (TX), were used based on their binding ability with graphitic structures on the CNTs and
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stabilize them in water. TX is a surfactant ha
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