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The effects of fluctuating temperature on Darcy-Forchheimer flow of oil-based nanofluid with activation energy and velocity slip has been analyzed. Similarity transformation was used to transform the governing partial differential equations into coupled nonlinear ordinary differential equations and solved numerically with the aid of the fourth order Runge-Kutta algorithm with a shooting technique. Results for the embedded parameters controlling the flow dynamics have been tabulated and illustrated graphically. The slip velocity parameter was found to enhance the Nusselt number but depleted both the skin friction coefficient and Sherwood number while the local inertial was noted to increase both the skin friction coefficient and Sherwood number but diminishes the Nusselt number. These results indicate that the velocity slip parameter and local inertial coefficient can be used to control flow characteristics in industrial and engineering systems.

In this current paper, an investigation has been conducted on the magnetohydrodynamic boundary layer flow of non-Newtonian Casson fluids on magnetized sheet with an exponentially stretching sheet. The similarity approach has been used to transform the governing models for Casson fluid to ordinary differential equations. We presented numerical results for momentum, energy and concentration equation parameters. Effects of the magnetized sheet and varying all the emerged parameters on the flow of Casson fluid with respect to the friction between the fluid and the surface, temperature and concentration are presented in tables. As a result of the induced magnetization of the sheet, the thickness of the thermal boundary layer has been enhanced. This behaviour brings a considerable reduction to the heat transfer. The induced magnetized sheet has a similar influence on the skin friction, Nusselt number and the Sherwood number. We however proposed incorporation of magnetized surfaces in MHD flows for controlling the flow rate of the fluid and heat transfer characteristics.

The novel effect of direct current generation by carbon nanotubes with hot electron injection which may arise due to an electromagnetic radiation with commensurate frequencies has been theoretically investigated using the semiclassical Boltzmann kinetic equation with relaxation time assumed constant. The nonlinearity of the current voltage characteristics and the chiral effects have been considered. We note that the direct current is a result of the strong nonprabolicity of the energy of the carbon nanotubes for the case where it Bloch oscillates. It is shown that the novel expression for the direct current generation strongly and significantly dependence on the hot electron injection rate, which leads to strong oscillatory behavior and the shift of the regions of absolute negative conductivity from low to higher dimensionless amplitude β values with increasing injection rate. We predict that carbon nanotubes with hot electron injection may be useful for generation of direct current.

The effect of variable heat source on viscoelastic fluid of CuO-oil based nanofluid over a porous nonlinear stretching surface is analyzed. The problem was modelled in the form of partial differential equations and transformed into a coupled fourth order ordinary differential equations by similarity techniques. It was further reduced to a system of first order ordinary differential equations and solved numerically using the fourth order Runge-Kutta algorithm with a shooting method. The results for various controlling parameters have been tabulated and the flow profiles graphically illustrated. The study revealed that the viscoelastic parameter has a decreasing effect on the magnitude of both the skin friction coefficient and the rate of heat transfer from the surface. It enhanced the momentum boundary layer thickness whilst adversely affecting the thermal boundary layer thickness.

The combined effect of variable viscosity and thermal conductivity on dissipative flow of oil-based nanofluid over a permeable vertical plate with suction has been studied. The governing partial differential equations have been transformed into a coupled third-order ordinary differential equations using similarity techniques. The resulting third-order ordinary differential equations were then reduced into a system of first-order ordinary differential equations and solved numerically using the fourth-order Runge-Kutta algorithm with a shooting method. The results revealed that both viscosity and thermal conductivities of CuO oil-based nanofluid enhances the intensity of the skin friction coefficient and the rate of heat transfer at the surface of the plate. Furthermore, the thermal boundary layer thickness is weakened by the viscosity of CuO oil-based nanofluid, the Prandtl number, the suction parameter, the permeability of the medium and the thermal Grashof number

The combined effect of suction and thermal conductivity on the boundary layer flow of oil–based nanofluid over a porous stretching surface has been investigated. Similarity techniques were employed in transforming the governing partial differential equations into a coupled third order ordinary differential equations. The higher third order ordinary differential equations were then reduced into a system of first order ordinary differential equations and solved numerically using the fourth order Runge-Kutta algorithm with a shooting method. The results were presented in tabular and graphically forms for various controlling parameters. It was found that increasing the thermal conductivities of the base fluid (oil) and nanoparticle size (CuO) of the nanofluid did not affect the velocity boundary layer thickness but depreciates with suction and permeability. The suction parameter and thermal conductivity of the base fluid also made the thermal boundary layer thinner.

Hot electrons injection in carbon nanotubes (CNTs ) where in addition to applied dc field ($\mathbf{E}$), there exist simultaneously a quasi-static ac electric field (i.e. when the frequency $\omega$ of ac field is much less than the scattering frequency $v$ ($\omega\ll v$ or $\omega\tau\ll 1$, $v =\tau^{-1}$, where $\tau$ is relaxation time) is considered. The investigation is done theoritically by solving semiclassical Boltzmann transport equation with and without the presence of the hot electrons source to derive the current densities. Plots of the normalized current density versus dc field ($\mathbf{E}$) applied along the axis of the CNTs in the presence and absence of hot electrons reveal ohmic conductivity initially and finally negative differential conductivity (NDC) provided $\omega\tau\ll 1$ (i.e. quasi- static case). With strong enough axial injection of the hot electrons , there is a switch from NDC to positive differential conductivity (PDC) about $\mathbf{E} \geq 75 kV/cm$ and $\mathbf{E} \geq 140 kV/cm$ for a zigzag CNT and an armchair CNT respectively. Thus, the most important tough problem for NDC region which is the space charge instabilities can be suppressed due to the switch from the NDC behaviour to the PDC behaviour predicting a potential generation of terahertz radiations whose applications are relevance in current-day technology, industry, and research.

The influence of thermophoretic transport of Al2O3 nanoparticles on heat and mass transfer in viscoelastic flow of oil-based nanofluid past porous exponentially stretching surface with activation energy has been examined. Similarity technique was employed to transform the governing partial differential equations into a coupled fourth-order ordinary differential equations which were reduced to a system of first-order ordinary differential equations and then solved numerically using the fourth-order Runge-Kutta algorithm with a shooting method. The results for various controlling parameters were tabulated and graphically illustrated. It was found that the thermophoretic transport of Al2O3 nanoparticles did not affect the rate of flow and heat transfer at the surface but it affected the rate of mass transfer of the nanofluid which decayed the solutal boundary layer thickness. This study also revealed that activation energy retards the rate of mass transfer which causes a thickening of the solutal boundary layer.

We report on a theoretical investigation of a direct current generation in carbon nanotubes (CNTs) that are stimulated axially by terahertz (THz) field. We consider the kinetic approach based on the semiclassical Boltzmann’s transport equation with constant relaxation time approximation, together with the energy spectrum of an electron in the tight-binding approximation. Our results indicate that for strong THz-fields, there is simultaneous generation of DC current in the axial and circumferential directions of the CNTs, even at room temperature. We found that a THz-field can induce a negative conductivity in the CNTs that leads to the THz field induced DC current. For varying amplitude of the THz-field, the current density decreases rapidly and modulates around zero with interval of negative conductivity. The interval decreases with increasing the amplitude of the THz-field. We show that the THz-field can cause fast switching from a zero DC current to a finite DC current due to the quasi-ballistic transport, and that electron scattering is a necessary condition for switching.