• Mahesh Kumar

      Articles written in Pramana – Journal of Physics

    • Bianchi Type-IX viscous fluid cosmological model in general relativity

      Raj Bali Mahesh Kumar Yadav

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      Bianchi Type-IX viscous fluid cosmological model is investigated. To get a deterministic model, we have assumed the conditiona = bm(m is a constant) between metric potentials andηθ whereη is the coefficient of shear viscosity andθ the scalar of expansion in the model. The coefficient of bulk viscosity (ς) is taken as constant. The physical and geometrical aspects of the model are also discussed.

    • Performance evaluation of self-breakdown-based single-gap plasma cathode electron gun

      Niraj Kumar Nalini Pareek Udit Narayan Pal Deepak Kumar Verma Jitendra Prajapati Mahesh Kumar Bharat Lal Meena Ram Prakash

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      This paper presents the experimental studies on self-breakdown-based single-gap plasma cathode electron (PCE) gun (5–20 kV/50–160 A) in argon, gas atmosphere and its performance evaluation based on particle-in-cell (PIC) simulation code `OOPIC-Pro’.The PCE-Gun works in conducting phase (low energy, high current) of pseudospark discharge. It produces an intense electron beam, which can propagate more than 200 mm in the drift space region without external magnetic field. The profile of this beam in the drift space region at different breakdown conditions (i.e., gas pressures and applied voltages) has been studied and the experimental results are compared with simulated values. It is demonstrated that ∼30% beam current is lost during the propagation possibly due to space charge neutralization and collisions with neutral particles and walls.

    • Transient entropy analysis of the magnetohydrodynamics flow of a Jeffrey fluid past an isothermal vertical flat plate


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      This study presents the analysis of entropy generation concept for unsteady magnetohydrodynamics Jeffrey fluid flow over a semi-infinite vertical flat plate. This physical problem is constituted by transient coupled highly nonlinear equations and is evaluated numerically by using an implicit scheme. The average values of wall shear stress and Nusselt number, entropy generation number and Jeffrey fluid-flow variables are analysed for distinct values of physical parameters at both transient and steady states. The results show that the time needed for achieving a steady state pertaining to the temperature and velocity gets augmented with the increased values of Jeffrey fluid parameter. The results also specify that the entropy generation number increases with the increasing values of Jeffrey fluid parameter, group parameter and Grashof number while the opposite trend is seen for the magnetic parameter.

    • Study of entropy generation in transient hydromagnetic flow of couple stress fluid due to heat and mass transfer from a radiative vertical cylinder


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      Radiative–convective flow studies find wide range of applications in furnace design, solar fans, photochemical reactors, turbid water bodies, etc. The present article focusses on unsteady radiative–convective hydromagnetic couple stress fluid (CSF) flow from a vertical cylinder using the thermodynamic concept. The obtained governing equations of the present model are resolved by a well-organised numerical scheme. The unsteady nature of friction, entropy, coefficients of heat and mass transfer (HMT) along with the time-independent state pattern of flow-field profiles, are shown graphically for distinct values of governing radiation parameter, magnetic parameter, concentration parameter, and constant parameter to display important aspects of the solution. To analyse the HMT process in a 2D domain, Bejans flow visualisation is considered along with isotherms, streamlines, andisoconcentration lines. The Bejans HMT flow visualisation shows that the heat and mass function contours are denser in the foremost verge of the hot surface of the cylinder compared to other contours. The result indicatesthat the entropy generation (EG) parameter increases with decreasing values of radiation and magnetic parameters. Also, the entropy parameter increases for increasing values of concentration parameter or constant parameter.

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