In this study, the thermoelectric properties of the (6, 3) two sided-closed single-walled boron nitride nanotubes are investigated. To examine the effect of the impurity on the thermoelectric properties, carbon atom is replaced instead of boron and nitrogen atoms at the center, left and right the nanotube. The energy range is selected as -5.5 to 5.5 eV and temperatures is considered as 200, 300, 500, 700, 900, 1100 and 1300K. Investigations show that with increasing temperature and creating impurity, the bandgap of the nanotube significantly reduces. The greatest reduction in the bandgap and the least reduction in the height of the peaks is related to the temperature of 1300 K, in which the carbon atom is replaced instead of nitrogen atom in the center of the nanotube. By increasing temperature, the number of peaks decreases, the mobility of electrons and holes increases and their localization decreases. Also, results show that the largest Seebeck coefficient is related to the temperature of 1300 K and in the case of carbon impurity instead of boron atom at the left side of the nanotube. The magnitude of the maximum of Seebeck coefficient is about 500μV/K. Besides, the minimum amount of Seebeck coefficient is about -600 μV/K, which is related to carbon impurity instead of boron at the center of (6.3) TSC-SWBNNT. The largest thermal conductivity is equal to 5.1 nW/K which is related to the pure (6, 3) TSC-SWBNNT at the energy of - 4.3eV. The thermal conductivity values are in the nano (10-9) range, which is small amounts. Studies demonstration that the highest amount of ZT is equal to 1.65 which is related to the impurity of carbon atom instead of boron on the right side of the (6.3) TSC-SWBNNT at the temperature of 1300 K. This value occurs at the energy of -5.2 eV. As the values of ZT are larger than 1, especially at high temperatures, one can conclude that (6, 3) TSC-SWBNNTs is suitable selection as a thermoelectric material. پرونده مقاله

In this study, the fullerenes have been inserted into water base-fluid to investigate the atomic and thermal behavior of nanofluid and hybridnanofluid as heat transfer fluid. This choice derives from low cast and high thermal stability of this nanostructure. Our computational results from Molecular Dynamics (MD) simulations indicate that the addition of nanoparticles with 4% atomic ratio produced an appreciable effect on the nanofluid. The maximum value of density, velocity, and temperature profile have reached to 0.029 atom/cubic angstrom, 0.005 angstrom/ps, and 321 centigrade degree. Its thermal conductivity would increase to 0.82 W/m.K. Heat flux reached to 2019 kW/m2 after t= 10 ns. Also, the aggregation phenomenon detected after t= 5.84 ns. This hybridnanofluid has been used to enhance the energy efficiency of the heat exchangers at high temperature for the nuclear industry applications for the first time. Numerically, by the temperature increase of nanofluid structure to 625.15 K, thermal power of nanofluid reached to 3881 MW. The thermal performance of hybridnanofluid can be improved by more than 30% by adding concentration of fullerene and doped fullerene at 4 vol%. پرونده مقاله

Vacancies occur naturally in all crystalline materials. A vacancy is a point defect in a crystal in which an atom is removed at one of the lattice sites. The defect could be imported during the synthesis of the material or be added by defect engineering. In this paper by employing the density functional theory as well as the non-equilibrium Green’s function approach, the structure and electronic properties of the perfect and defected BN nanosheet would be obtained and compared. In addition to the influence of the vacancy defect position, the effect of removed atom type is also studied. For this purpose, the defect is considered at the centre, left, and right-hand sides of the nanosheet. It is seen that the electric current changes by changing the position of the vacancy defect and the type of removed atoms. This can be related to the electronic structures of BN nanosheets. In addition, the transmission and conductance of the defected BN nanosheets continuously change by changing the bias voltage. The obtained results can benefit the design and implementation of BN nanosheets in nanoelectronic systems and devices. پرونده مقاله