The present work is devoted to investigate the effect of thermal radiation on fully developed flow of micropolar fluid flowing between the two infinite parallel porous vertical plates in the presence of transverse magnetic field. The fluid is considered to be a gray, absorbing-emitting but non-scattering medium, and the Cogley-Vincent-Gilles formulation is adopted to simulate the radiation component of heat transfer. The rigid plates are assumed to exchange the heat with an external fluid by convection. The governing equations are solved numerically by Crank-Nicolson implicit finite difference method. The effect of various physical parameters such as transient, Hartmann number, micropolar parameter, radiation parameter, Prandtl number, Biot number and Reynolds number on the velocity and temperature field are discussed graphically. The important finding of the present work is that the temperature of the fluid is reduced by applying thermal radiation. Further, the results obtained under the limiting conditions were found to be in good agreement with the existing one.Ó 2014 Production and hosting by Elsevier B.V. on behalf of Ain Shams University.
An analysis is performed to study the influence of local thermal non-equilibrium (LTNE) on unsteady MHD laminar boundary layer flow of viscous, incompressible fluid over a vertical stretching plate embedded in a sparsely packed porous medium in the presence of heat generation/absorption. The flow in the porous medium is governed by Brinkman-Forchheimer extended Darcy model. A uniform heat source or sink is presented in the solid phase. By applying similarity analysis, the governing partial differential equations are transformed into a set of time dependent non-linear coupled ordinary differential equations and they are solved numerically by Runge-Kutta Fehlberg method along with shooting technique. The obtained results are displayed graphically to illustrate the influence of different physical parameters on the velocity, temperature profile and heat transfer rate for both fluid and solid phases. Moreover, the numerical results obtained in this study are compared with the existing literature in the case of LTE and found that they are in good agreement.
We present a transformative route to obtain mass-producible helical slow-wave structures for operation in beam−wave interaction devices at THz frequencies. The approach relies on guided self-assembly of conductive nanomembranes. Our work coordinates simulations of cold helices (i.e., helices with no electron beam) and hot helices (i.e., helices that interact with an electron beam). The theoretical study determines electromagnetic fields, current distributions, and beam− wave interaction in a parameter space that has not been explored before. These parameters include microscale diameter, pitch, tape width, and nanoscale surface finish. Parametric simulations show that beam−wave interaction devices based on selfassembled and electroplated helices will potentially provide gain-bandwidth products higher than 2 dBTHz at 1 THz. Informed by the simulation results, we fabricate prototype helices for operation as slow-wave structures at THz frequencies, using metal nanomembranes. Single and intertwined double helices, as well as helices with one or two chiralities, are obtained by selfassembly of stressed metal bilayers. The nanomembrane stiffness and built-in stress control the diameter of the helices. The inplane geometry of the nanomembrane determines the pitch, the chirality, and the formation of single vs intertwined double helices.
The current study is made to analyze the impact of local thermal nonequilibrium (LTNE) on the steady, incompressible, and viscous Ostwald-de-Waele nano-liquid over a rotating disk in a porous medium with the various power law index, due to many remarkable applications, such as aeronautical systems, rotating machineries, air cleaning machineries, electrical power-generating systems, heat exchangers, gas turbines, centrifugal pumps. To describe the modeling of the nano-liquid, Brownian movement and thermophoresis are employed with the passive control boundaries. Three temperature model is adopted to distinguish the temperature among the fluid, particle, and solid. The governing transport equations have been converted to a system of nonlinear coupled ordinary differential equations by employing von Karman transformation. Numerical results of the flow and heat and transfer characteristics of the fluid, particle, and solid are obtained by applying Runge–Kutta–Fehlberg method (RKF) together with the shooting technique. The numerical results in the present work are compared with the published results for the case of thermal equilibrium and found that they are in good agreement. It is observed that the temperature profile significantly varies with the fluid-particle, fluid-solid interphase heat transfer coefficients and the modified thermal capacity ratios.
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