Articles written in Pramana – Journal of Physics

    • Observation of floating potential asymmetry in the edge plasma of the SINP tokamak

      Krishnendu Bhattacharyya N R Ray

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      Edge plasma properties in a tokamak is an interesting subject of study from the view point of confinement and stability of tokamak plasma. The edge plasma of SINP-tokamak has been investigated using specially designed Langmuir probes. We have observed a poloidal asymmetry of floating potentials, particularly the top-bottom floating potential differences are quite noticeable, which in turn produces a vertical electric field (Ev). This Ev remains throughout the discharge but changes its direction at certain point of time which seems to depend on applied vertical magnetic field (Bv).

    • Soret and Dufour effects on MHD boundary layer flow of non-Newtonian Carreau fluid with mixed convective heat and mass transfer over a moving vertical plate


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      In this analysis, the mixed convection boundary layer MHD flow of non-Newtonian Carreau fluid subjected to Soret and Dufour effects over a moving vertical plate is studied. The governing flow equations are converted into a set of non-linear ordinary differential equations using suitable transformations. For numerical computations, bvp4c in MATLAB package is used to solve the resulting equations. Impacts of various involved parameters, such as Weissenberg number, power-law index, magnetic parameter, thermal buoyancy parameter, solutal buoyancy parameter, thermal radiation, Dufour number, Soret number and reaction rate parameter, on velocity, temperature and concentration are shown through figures. Also, the local skin-friction coefficient, local Nusselt number and local Sherwood number are calculated and shown graphically and in tabular form for different parameters. Some important facts are revealed during the investigation. The temperature and concentration show decreasing trends with increasing values of power-law index, whereas velocity shows reverse trend and these trends are more prominent for larger values of Weissenberg number. For stronger magnetic field, velocity decreases, while the temperature and concentration increase. It was also found that for shear thinning fluid the drag coefficient exhibits an increasing character when Weissenberg number increases, but for shear thickening fluid the drag coefficient shows the contrary nature. For small values of Dufour number, heat transfer rate enhances with increasing Soret number, but for higher values of Dufour number it slightly dies down with Soret number and the mass transfer rate reacts oppositely. In addition, due to increasing chemical reaction rate, the concentration and velocity decrease.

    • Impact of metal oxide nanoparticles on unsteady stagnation point flow of the hybrid base fluid along a flat surface


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      This paper deals with a detailed investigation of the effects of various metal oxide nanoparticles on unsteady stagnation point flow of a hybrid base fluid impinging on a flat surface. The ‘single-phase’ nanofluid model, i.e., the Tiwari and Das model, is considered for the study. We consider water and ethylene glycol in 1:1 ratio as the base fluid and four different types of metal oxides, namely, CuO, TiO$_2$, ZnO and MgO as the nanoparticles. Using similarity transformations, the conservation equations are transformed into self-similar ordinary differential equations. Dual and unique similarity solutions are obtained for certain set of values of parameters. The analysis explores many important findings. Dual self-similar solutions exist up to a certain critical value of the decelerating unsteady parameter and the critical value is independent of the type of metal oxide nanoparticles considered. The strongest surface drag force is observed for the nanofluid with CuO nanoparticles, while the weakest is for the nanofluid with MgO nanoparticles. The heat transfer rate is highest for the nanofluid with CuO nanoparticles and lowest for the nanofluid with TiO$_2$ nanoparticles. Also, the boundary layer is thickest for the nanofluid with MgO nanoparticles.

    • Entropy generation analysis of Falkner–Skan flow of Maxwell nanofluid in porous medium with temperature-dependent viscosity


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      Entropy generation analysis in steady two-dimensional, viscous, incompressible forced convective Falkner–Skan flow of Maxwell nanofluid over a static wedge embedded in a porous medium with temperature-dependent viscosity is examined. The Buongiorno’s model has been utilised, to get the flow governing higher-order coupled nonlinear partial differential equations (PDEs) from mass, momentum, energy and concentration conservations. Suitable transformations have been done to convert governing PDEs into the coupled non-linear ODEs along with no-slip boundary conditions, which are then solved using the MATLAB programme bvp4c. The influences of diverse flow governing parameters on various flow properties and quantities of physical interest are displayed in graphical mode and discussed. It is found that entropy generation reduces only with Eckert number (Ec), while more entropy is generated for pressure gradient parameter $(m)$, local Deborah number ($\beta$), variable viscosity parameter ($\delta$) and permeability parameter ($K$). Entropy generation due to heat transfer irreversibility is prominent with increase in $m$ and $\delta$, but it is not so for other parameters. The drag force on the wedge surface become stronger with $\beta$ and $m$, but it reduces with $\delta$. Rates of heat transfer and mass transfer enhance with $m$ and $\delta$. In addition, surface drag force and heat transfer rate diminish with Brownian motion parameter ($Nb$) and thermophoresis parameter ($Nt$).

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