Articles written in Pramana – Journal of Physics

    • Instability analysis of a streaming electrified cylindrical sheet through porous media


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      The current study deals with the influence of a uniform electric field on a cylindrical streaming sheet.This paper investigates a few representatives of porous media. These media are considered to be uniform, homogeneous and isotropic. The analysis is based on viscous potential theory, which assumes that the viscous forces affect only the interface between the fluids. The mathematical treatment is based on the normal modes analysis. For convenience, cylindrical coordinates are used. The boundary-value problem yields coupled second-order and damped differential equations with complex coefficients. These equations are combined with a single equation under the concepts of the symmetric and antisymmetric deformations. The Routh–Hurwitz criterion is adopted to govern the stability of the system. Several special cases are recovered upon appropriate data choices. The effects of various parameters on the interfacial stability are theoretically presented and illustrated graphically through some sets of figures. These parameters are the Darcy’s coefficients, basic velocities, dielectric constants, viscosity and thickness of the inner cylinder. We have found that the thickness of the inner cylinder plays a dual role on the stability picture. Also, the Darcy’s coefficient and dielectric constants have stabilising influence and the dynamic viscosity has a destabilising effect.

    • The effects of the pressure work and Hall currents in the MHD peristaltic flow of Bingham–Papanastasiou nanofluid through porous media


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      This article is concerned with the influences of the pressure work and Hall currents on the motion of a non-Newtonian nanofluid with heat and mass transfer inside a vertical symmetric channel. The fluid conforms to the Bingham–Papanastasiou model. The walls of the channel are assumed to be flexible, movable and sinusoidal. Thermal radiation, heat generation/absorption and chemical reaction are thus considered. Concerning the assumptions of the long wavelength and low Reynolds number, the resulting equations are solved by utilising the homotopy perturbation method (HPM). The succeeding complex computations are clarified for the stream flow, temperature and concentration distributions. A set of graphs is plotted to illustrate the effects of various physical parameters of the problem at hand. It is found that as the Bingham factor is increased, both axial velocity and temperature are also increased. Additionally, it is observed that the stress growth exponent has a dual influence on the axial velocity as well as the size of the trapped bolus. The behaviour of the left wall of the channel is different from that of the right wall. When the pressure work and Hall current coefficients increase, both temperature and pressure gradient decrease. The Brownian motion and thermophoresis parameters have different influence on the nanoparticle concentration distribution. Furthermore, it is shown that the heat transfer coefficient is a decreasing function in both Hall and thermal radiation parameters.

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