Nonlinear Thermopower Behaviour of N-Type Carbon Nanofibres and Their Melt Mixed Polypropylene Composites

The temperature dependent electrical conductivity σ (T) and thermopower (Seebeck coefficient) S (T) from 303.15 K (30 °C) to 373.15 K (100 °C) of an as-received commercial n-type vapour grown carbon nanofibre (CNF) powder and its melt-mixed polypropylene (PP) composite with 5 wt.% of CNFs have been analysed. At 30 °C, the σ and S of the CNF powder are ~136 S m−1 and −5.1 μV K−1, respectively, whereas its PP/CNF composite showed lower conductivities and less negative S-values of ~15 S m−1 and −3.4 μV K−1, respectively. The σ (T) of both samples presents a dσ/dT < 0 character described by the 3D variable range hopping (VRH) model. In contrast, their S (T) shows a dS/dT > 0 character, also observed in some doped multiwall carbon nanotube (MWCNT) mats with nonlinear thermopower behaviour, and explained here from the contribution of impurities in the CNF structure such as oxygen and sulphur, which cause sharply varying and localized states at approximately 0.09 eV above their Fermi energy level (EF).

Temperature-Dependent Electrical Conductivity and Thermal Radiation Effects on MHD Peristaltic Motion of Williamson Nanofluids in a Tapered Asymmetric Channel

ABSTRACTThis paper is intended for dealing with the peristaltic flow of an electrically conducting Williamson nanofluid in a tapered asymmetric channel through a porous medium with heat and mass transfer. In the current paper, temperature-dependent electrical conductivity formulation was introduced for the first time in peristaltic literature. The flow is pervaded by an oblique uniform magnetic field. The present investigation includes the influences of thermal radiation, Joule heat, viscous dissipation, Hall Current, 1st order chemical reaction, and Dofour and Soret numbers. Current problem is reformulated under the molds of low Reynolds number and long wavelength approximation. Afterwards, semi analytical solutions have been evaluated for the distributions of velocity, temperature, nanoparticle concentrations as well as longitudinal pressure gradient. Solutions can be obtained by using multi-step differential transform method (MS-DTM), a reliable and powerful technique that improve accuracy and overcome drawbacks raised in using the standard differential transform method (DTM). Detailed comparisons have been made at different values of 𝑥 through graphs by Ms-DTM. The graphically results were prepared to visualize the effects of various physical parameters of interest. The semi-analytical results had shown that, as the thermal radiation increases, the nanoparticles diameter and concentration of fluid increase (thermal radiation is a decreasing function in temperature when the temperature decreases the diameter of the nanoparticles increases i.e. the volume of nanoparticle and its concentration increases and become more effective near to tumor tissues). Consequently, it can be used as agents for radiation therapy, generate localized raises in radiation doses and selectively target tumor cells for localized damage (Radiotherapy of oncology).