Nitrogen-doped carbon nanotubes for heat transfer applications
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Nitrogen-doped carbon nanotubes for heat transfer applications Enhancement of conduction and convection properties of water/N-CNT nanofluid Mohammad Bazmi1,2 • Saeed Askari2,3 • Ebrahim Ghasemy2 • Alimorad Rashidi2
•
Ehsanollah Ettefaghi2
Received: 13 August 2018 / Accepted: 10 January 2019 Akade´miai Kiado´, Budapest, Hungary 2019
Abstract In this research, it is aimed to enhance the heat transfer properties of the carbon nanotubes through nitrogen doping. To this end, nitrogen-doped multiwall carbon nanotubes (N-CNTs) were synthesized via chemical vapor deposition method. For supplying carbon and nitrogen during the synthesis of N-CNTs, camphor and urea were used, respectively, at 1000 C over Co–Mo/MgO nanocatalyst in a hydrogen atmosphere. N-CNTs with three different nitrogen loadings of 0.56, 0.98, and 1.38 mass% were synthesized, after which, water/N-CNT nanofluids of these three samples with concentrations of 0.1, 0.2, and 0.5 mass% were prepared. To obtain a stable nanofluid, N-CNTs were functionalized by nitric acid followed by stabilizing in water by employing the ultrasonic bath. Investigation on the stability of the samples showed a high stability level for the prepared water/N-CNT nanofluids in which the zeta potential of - 43.5 mV was obtained for the best sample. Also for studying the heat transfer properties, the thermal conductivity in the range of 0.1–0.5 mass% and convection heat transfer coefficients of nanofluids in the range of 0.1–0.5 mass%, and Reynolds number in the range of 4000–9000 were evaluated. The results showed 32.7% enhancement of the convection heat transfer coefficients at Reynolds number of 8676 and 27% increase in the thermal conductivity at 0.5 mass% and 30 C. Keywords Nitrogen-doped carbon nanotubes Nanofluid Rheological properties Thermal conductivity Heat transfer
Introduction Heat transfer in various mechanical systems is an energyconsuming factor. Generally, in these systems, an intermediate fluid is used for heat transfer. Therefore, any solutions which can enhance the thermophysical properties of heat transfer fluids would reduce the energy consumption of the mechanical systems [1, 2]. One of the main solutions which have been developed in recent decades for & Alimorad Rashidi [email protected] 1
Faculty of Chemical Engineering, Amirkabir University of Technology, Hafez Ave, P.O. Box 15875-4413, Tehran, Iran
2
Nanotechnology Research Center, Research Institute of Petroleum Industry (RIPI), P.O. Box: 14665-1998, Tehran, Iran
3
Chemical Engineering Department, Sharif University of Technology, Azadi Ave., P.O. Box 11155-9567, Tehran, Iran
solving this problem is using the nanoparticles for preparing heat transfer nanofluids. In fact, micrometer particles were the subject of several investigations; however, because of the large sizes of particles, high-pressure drops, rapid sedimentation, and damages to the equipment’s wall, using these kinds of particles were unpractical and ineffective [3, 4]. Accordingly, due to unique properties of the nanoparticle
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