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1
Content available Role of sudden application or withdrawal of magnetic field on MHD Couette flow
Jha B. K., Oni M. O.
International Journal of Applied Mechanics and Engineering
|
2019
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Vol. 24, no. 4
92--105
EN
This article investigates the impact of a sudden application or sudden withdrawal of a magnetic field on an unsteady MHD Couette flow formation in a parallel plate channel. The governing momentum equation is derived and solved exactly in Laplace domain using the Laplace transform technique with the necessary initial and boundary conditions to capture the present physical situation for the cases; sudden application or sudden withdrawal of a magnetic field. Due to the complexity of the solution obtained, the Riemann-sum approximation technique is used to transform the Laplace domain to time domain. During the course of graphical and tabular representations, results show that the Hartmann number, time and nature of application of a magnetic field play an important role in the transition from hydrodynamic to magnetohydrodynamic flow and vice-versa. Also, fluid velocity steady-state solution is independent on whether the magnetic field is fixed relative to the moving plate or to the fluid for sudden withdrawal of magnetic field. In addition, the application of a sudden magnetic field leads to a delay in the attainment of steady-state solution.
2
Content available Effect of induced magnetic field on MHD mixed convection flow in vertical microchannel
Jha B. K., Aina B.
International Journal of Applied Mechanics and Engineering
|
2017
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Vol. 22, no. 3
567--582
EN
The present work presents a theoretical investigation of an MHD mixed convection flow in a vertical microchannel formed by two electrically non-conducting infinite vertical parallel plates. The influence of an induced magnetic field arising due to motion of an electrically conducting fluid is taken into consideration. The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained for the velocity field, the induced magnetic field and the temperature field. The expressions for the induced current density and skin friction have also been obtained. The effects of various non-dimensional parameters such as rarefaction, fluid wall interaction, the Hartmann number and the magnetic Prandtl number on the velocity, the induced magnetic field, the temperature, the induced current density, and skin friction have been presented in a graphical form. It is found that the effect of the Hartmann number and magnetic Prandtl number on the induced current density is found to have a decreasing nature at the central region of the microchannel.
3
Content available Unsteady Hartmann two-phase flow: the Riemann-sum approximation approach
Jha B. K., Babila C. T., Isa S.
International Journal of Applied Mechanics and Engineering
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2016
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Vol. 21, no. 4
891--904
EN
We consider the time dependent Hartmann flow of a conducting fluid in a channel formed by two horizontal parallel plates of infinite extent, there being a layer of a non-conducting fluid between the conducting fluid and the upper channel wall. The flow formation of conducting and non-conducting fluids is coupled by equating the velocity and shear stress at the interface. The unsteady flow formation inside the channel is caused by a sudden change in the pressure gradient. The relevant partial differential equations capturing the present physical situation are transformed into ordinary differential equations using the Laplace transform technique. The ordinary differential equations are then solved analytically and the Riemann-sum approximation method is used to invert the Laplace domain into time domain. The solution obtained is validated by comparisons with the closed form solutions obtained for steady states which have been derived separately and also by the implicit finite difference method. The variation of velocity, mass flow rate and skin-friction on both plates for various physical parameters involved in the problem are reported and discussed with the help of line graphs. It was found that the effect of changes of the electric load parameter is to aid or oppose the flow as compared to the short-circuited case.
4
Content available Study of temperature of black holes in terms of Chandrasekhar limit
Mahto D., Jha B. K., Singh K.M., Ram M.
International Letters of Chemistry, Physics and Astronomy
|
2015
|
Vol. 40
43--50
EN
Stephen Hawking gave the formula for the temperature for the black holes as[wzór] . In the present research article, we have converted this formula in terms of Chandrasekhar limit [Mch] and also calculated their values for different test black holes existing in XRBs and AGN. [wzór] Kelvin.
5
Content available Role of induced magnetic field on transient natural convection flow in a vertical channel: The Riemann sum approximation approach
Jha B. K., Sani I.
International Journal of Applied Mechanics and Engineering
|
2015
|
Vol. 20, no. 1
65--85
EN
This paper investigates the role of induced magnetic field on a transient natural convection flow of an electrically conducting, incompressible and viscous fluid in a vertical channel formed by two infinite vertical parallel plates. The transient flow formation inside the channel is due to sudden asymmetric heating of Chanel walls. The time dependent momentum, energy and magnetic induction equations are solved semi-analytically using the Laplace transform technique along with the Riemann-sum approximation method. The solutions obtained are validated by comparisons with the closed form solutions obtained for the steady states which hale been derived separately and also by the implicit finite difference method. Graphical results for the temperature, velocity, induced magnetic field, current density, and skin-friction based on the semi-analytical solutions are presented and discussed.
6
Content available Unsteady/steady natural convection flow of reactive viscous fluid in a vertical annulus
Jha B. K., Samaila A. K., Ajibade A. O.
International Journal of Applied Mechanics and Engineering
|
2013
|
Vol. 18, no. 1
73--83
EN
This paper presents both analytical and numerical analyses of a fully developed unsteady/steady natural convection flow of a reactive viscous fluid in an open ended vertical annulus. Analytical expressions for velocity, temperature, skin-friction and rate of heat transfer are obtained after simplifying and solving the governing differential equations with reasonable approximations. The interesting result found in this study is that an increase in non-dimensional time (t) , increases both temperature and velocity profiles until a steady-state value is attained. Subsequent results obtained by numerical calculations show excellent agreement with analytical results.
7
Content available Unsteady hydromagnetic Couette flow due to ramped motion of one of the porous plates
Jha B. K., Jibril H. M.
International Journal of Applied Mechanics and Engineering
|
2013
|
Vol. 18, no. 4
1039--1056
EN
An unsteady flow formation in Couette motion of an electrically conducting fluid subject to transverse magnetic field has been analyzed in the presence of suction/injection through the porous plates when one of the porous plates is in ramped motion. It is assumed that the porous plates are uniformly permeable and the fluid is entering the flow region through one of the porous plates at same rate as it is leaving through the other porous plate. The resulting boundary value problem has been solved exactly under the assumption of a negligible induced magnetic field, external electric field and pressure gradient. Unified closed form expressions for the velocity field and skin-friction corresponding to the case of a magnetic field fixed relative to the fluid or to the moving porous plate have been presented. In order to highlight the impact of the ramp motion of the porous plate on the fluid flow, it has also been compared with Couette flow between porous plates when one of the porous plates has been set into an impulsive motion.
8
Content available remote Time dependent MHD Couette flow due to ramped motion of one of the boundaries
Jha B. K., Jibril H. M.
International Journal of Applied Mechanics and Engineering
|
2012
|
Vol. 17, no. 2
383-399
EN
The effects of a transverse magnetic field on the Couette flow of an electrically conducting fluid between two infinite parallel plates have been discussed when one of the plates has been set into ramped motion. Under the assumption of a negligible induced magnetic field and applied magnetic field being fixed relative to the fluid or moving plate, the governing momentum equation has been solved exactly. The expressions for velocity field and skin-friction have been presented. The transient features of velocity and skin-friction have been discussed for different values of the Hartmann number. It is seen that the velocity field and skin-friction increases with an increase of the Hartman number when the magnetic field is fixed with respect to the moving plate while the result is just reverse when it is fixed with respect to the fluid.
9
Content available remote Time dependent natural convection Couette flow of heat generating/absorbing fluid: accelerated motion
Jha B. K., Ajibade A. O.
International Journal of Applied Mechanics and Engineering
|
2010
|
Vol. 15, no 4
1083-1100
EN
The unsteady Couette flow in a channel formed by two vertical parallel plates is investigated in the presence of internal heat generation/absorption. The flow is set up due to time dependent motion of one of the plates coupled with asymmetric heating of the infinite vertical parallel plates. Analytical solutions of the resulting partial differential equations are obtained using the Laplace transforms technique. The numerical values obtained from the analytical expressions for temperature, velocity, Nusselt number, skin-friction and mass flux are presented graphically to study the flow behaviour in the presence of the governing parameters. It is interesting to note that in the absence of convection currents (Gr=0) the flow is dependent only on the motion of one of the channel plates. The influence of the heat generation/absorption parameter on the rate of heat transfer on one plate is the exact opposite of the influence on the other plate while its influence on the skin-friction is identical on both plates. In the presence of external cooling, the mass flux diverges as time increases, while it converges to zero in the case of external heating.
10
Content available remote Hydromagnetic flow due to ramped motion of the boundary
Jha B. K., Jibril H. M.
International Journal of Applied Mechanics and Engineering
|
2010
|
Vol. 15, no 4
1101-1109
EN
The unsteady flow of a viscous, incompressible and electrically conducting fluid subject to a uniform transverse magnetic field near a horizontal plate having ramped motion is considered. A unified closed form analytical solutions have been obtained for the velocity field and the skin-friction corresponding to the cases of a magnetic field fixed relative to the fluid or the moving boundary. Under the assumption of a negligible induced magnetic field, the governing momentum equation has been solved exactly by using the Laplace-transform technique. The flow formation near ramped motion of the plate has also been compared with the flow formation near a plate having constant motion (impulsive motion). It is observed that velocity of the fluid in the case of ramped motion of the plate is always less than that of the flow induced by impulsive motion of the plate.
11
Content available remote Inverse Laplace transforms using convolution integral
Jha B. K., Ajibade A. O.
International Journal of Applied Mechanics and Engineering
|
2008
|
Vol. 13, no 4
1119-1123
EN
In the present article, the convolution theorem is used to obtain the inverse Laplace-transforms of some Laplace-transforms functions. Although the inverse Laplace-transforms of these functions are available in the works of Abramowitz and Stegun (1965), Carlslaw and Jaeger (1952), Churchill (1972), Miles (1971) and Özisik (1980), they require integration of complementary-error-function for computational purposes. The results presented in this article are directly applicable in many branches of science where time-dependent initial and boundary conditions are frequently occurring.
12
Content available remote Transient free-convective flow in a vertical channel due to symmetric heating
Jha B. K., Singh A. K., Takhar H. S.
International Journal of Applied Mechanics and Engineering
|
2003
|
Vol. 8, no 3
497-502
EN
This paper presents a closed form solution for a transient free convective flow of a viscous and incompressible fluid in a vertical channel due to symmetric heating of channel walls. The Laplace transform technique has been used to obtain the expression for the velocity and temperature fields by solving the governing differential equations. The influence of the physical parameters on the velocity field, skin-friction, rate of heat transfer and volumetric flux of the fluid are carefully analysed. A correlation between the steady state time and the Prandtl number has been developed. It is observed that the nature of correlation is linear when the Prandtl number is greater than one while cubic for the Prandtl number is less than one.
13
Content available remote Transient natural convection in a vertical channel
Paul T., Jha B. K., Singh A. K.
International Journal of Applied Mechanics and Engineering
|
2001
|
Vol. 6, no 4
913-922
EN
This paper describes a theoretical analysis of transient motion of a viscous incompressible fluid in a vertical channel. The motion of the fluid is caused by the buoyancy force arising from the temperature gradient as a result of constant heat flux at one wall and an adiabatic condition on the other wall. Expressions for the velocity and temperature fields are derived with the help of the Laplace transform technique. The influence of the various parameters is extensively discussed with the help of graphs. It has been observed that the temperature is not influenced by the presence of an adiabatic condition on the other plate for large values of the Prandtl number.
14
Content available remote Transient free-convective flow in a vertical channel with heat sinks
Jha B. K.
International Journal of Applied Mechanics and Engineering
|
2001
|
Vol. 6, no 2
279-286
EN
This paper investigates analytically heat sinks effect on transient free convective flow in a vertical channel. Laplace transform technique has been used to solve the governing momentum and energy equations. The expressions for velocity field, temperature field, skin-friction and rate of heat transfer have been obtained in closed form for two different cases. The influence of heat sinks and time parameter on velocity, temperature, skin-friction and rate of heat transfer is extensively discussed.
15
Mass transfer effects on unsteady free convection Couette flow
Takhar H. S., Jha B. K.
Applied Mechanics and Engineering
|
1998
|
Vol. 3, no 1
163-169
EN
In the present paper, mass transfer effect on the unsteady free-convective flow of an incompressible viscous fluid between two vertical parallel plates is discussed for impulsive start of one of the plate. Expressions for velocity, temperature and concentration are obtained by the Laplace transform technique. The influence of the Prandtl number (Pr), Schmidt number (Sc) and time parameter (t) on velocity field and skin-friction are discussed extensively.
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