Defect and Diffusion Forum Vol. 409

Abstract: Heat transport processes through radiation in a dissipative flow of Al₂O₃ and CuO oil-based nanofluids has been discussed. The equations modeling the flow has been transformed using similarity variables into coupled nonlinear higher order ordinary differential equations. These equations are solved by employing the fourth order Runge-Kutta algorithm and a shooting technique. The results for the embedded parameters were tabulated and depicted graphically. The study revealed that oil-based nanofluid of CuO has a better rate of heat transfer than Al₂O₃ oil-based nanofluid with increased radiation. Thus, the study concluded that CuO oil-based nanofluid has a superior heat transfer characteristic and thus preferred for radiation hardening.

Abstract: The time-dependent hydromagnetic boundary layer flow across a vertical surface with internal heat regeneration in porous media is investigated. The flow problem has been modelled mathematically in partial differential equations along with appropriate defined boundary conditions. These equations were expressed in dimensionless form using suitable similarity variables. The resulting dimensionless equations along with the conditions defined at the boundaries are solved by means of the Laplace transform methods. Results of the study are graphically illustrated for various quantities of practical importance. It was concluded that time positively influence the flow as a reduced skin friction coefficient was observed. Furthermore, the magnetic parameter, the radiation parameter, the heat absorption parameter and the permeability of the porous media can be used to influence the characteristics of a flow in porous media.

Abstract: Two-phase flows are widely encountered in many natural phenomena and industrial processes. The presence of one or more interfaces between the two phases presents a major difficulty which makes the modeling and the simulation of this type of flow complex. This work consists in performing a three-dimensional numerical simulation of a two-phase Hydrogen-Water flow inside a horizontal cylindrical channel. The results are obtained in the form of velocity contours, enthalpy and pressures.

Abstract: The present work is conducted for studying the natural convection in a circular enclosure that contains three equal-sized cylinders in tandem arrangement. The outer cylinder has a cold surface and the enclosure internals have hot surfaces. The relation between the density of the fluid and the temperature is treated by the Boussinesq approximation. The fluid used for the investigation is Newtonian and incompressible. The results present the roles of some non-dimensional parameters (Rayleigh (Ra) and Prandtl (Pr) numbers) on the buoyancy-driven flow and the convective heat transfer. The obtained results revealed an intensification of the v-velocity component in the annular space and an enhancement in the heat transfer rates with the rise of Rayleigh number.

Abstract: Numerical simulations were performed to study the pertinent parameters of natural convection in annular space. The studied geometry consists of two semi-circular cylinders of hot walls confined in cold cavity of circular cross-sectional form. The simulations were done by solving numerically the governing equations via the commercial software ANSYS-CFX. The results showed that this new form of inner cylinders is suitable for insulating applications. The pertinent parameters were selected for this work were: Prandtl number (Pr = 0.71 to 1000) and Rayleigh number (Ra = 10³, 10⁴ and 10⁵).

Abstract: The study is concerned with the effects of slip velocity on a non-uniform rotating electroosmotic flow in a micro-channel. Electroosmotic driven fluid flow is obtained by the application of a potential electric field which describes the nonlinear Poisson-Boltzmann equation. The external electric potential is applied along the x and y directions which provides the necessary driving force for the electroosmotic flow. Two semi analytical techniques were employed to obtain the solution of the nonlinear Poisson-Boltzmann equation. The first method incorporates the complex normalized function into the Laplace transform and the second method is the combination of the Laplace transform and D’Alembert technique. Further, the complex normalized function became difficult to invert in closed form, hence we resort to the use of numerical procedure based on the Stehfest's algorithm. The graphical solutions to the axial velocities on both x and y components have been obtained and analyzed for the effects of the slip parameter and the amplitude of oscillation of the micro-channel walls. The solutions show that the rotating electroosmotic flow profile and the flow rate greatly depend on time, rotating parameter and the electrokinetic width. The results also indicate that the applied electric field and the electroosmotic force, play vital role on the velocity distribution in the micro-channel. The fact is that the solutions obtained in this study synthesize most of the solutions available in the previous studies. Finally, this study will be relevant in biological applications particularly in pumping mechanism to help transport substances within different parts of the systems.

Abstract: The onset of convection in a horizontal nanofluid layer of finite depth is a subject that can never be over-emphasized as it plays a significant role in controlling the transport phenomenon within a nanofluidic medium. This body of knowledge led to a doubtful report in 2014 by Nield and Kuznetsov concerning some obtained equations and established results. However, the accuracy of the thermal stability characteristics is strongly dependent on the used model as well as the employed methodological procedure. In this report, countable models are suggested as a better improvement of the aforementioned analysis. Either mathematical or technical point of view, it is worth concluding that the approximate analytical results elaborated by Nield and Kuznetsov can be improved properly by using the models presented herein.

Abstract: An analysis of nonlinear mixed convection transport of hydromagnetic Casson nanofluid over a nonlinear stretching sheet near a stagnation point is deliberated in this study. The flow is confined in a porous device in the presence of thermophoresis, Ohmic heating, non-uniform heat source with temperature-dependent thermal conductivity associated with haphazard motion of tiny particles. The transport equations are translated from nonlinear partial differential equations into ordinary ones via similarity transformation technique and subsequently tackled with shooting method coupled with Runge-Kutta Fehlberg algorithm. The significant contributions of the embedded parameters on the dimensionless quantities are graphically depicted and deliberated while the numerical results strongly agree with related published studies in the limiting conditions. It is found that a rise in the magnitude of Casson fluid parameter decelerates the fluid flow while enhancing the viscous drag and thermal profiles. The inclusion of the nonlinear convection term aids fluid flow whereas heat transfer reduces with growth in the thermophoresis and Brownian motion terms.

Abstract: The present work deals with the numerical investigation of forced convection flow and heat transfer in a finned concentric annulus. The outer cylinder is axially finned while the rotating inner cylinder has a smooth surface. Our research focus on the impact of the fin inclination angle on heat transfer enhancement in rotating annular channels. Tests were carried out for different geometrical configurations using fins with inclined angle (α = 30°, 60°, 90° and 120°). Numerical study is based on effective Reynolds number and Taylor number. The results obtained using the code ANSYS-Fluent with SST k-ω turbulence model show a good agreement between the experimental and the numerical results. In the presence of rotational flow (Ta = 1.14 × 10⁶), the results indicate that α =120° is the optimal case which improves significantly the heat and mass transfer inside the finned channel.