Comment on Magnetohydrodynamic non-Darcy mixed convection heat transfer from a vertical heated plate embedded in a porous medium with variable porosity, by Dulal Pal

In the above paper the author treats the boundary layer flow along a vertical flat plate, immersed in a Darcy Brinkman Forchheimer porous medium. The porosity and the permeability of the porous medium are variable across the boundary layer. In addition a magnetic field with constant strength is applied normal to the plate. The fluid temperature at the plate is constant and different from that of the ambient fluid. This temperature difference creates a buoyancy force and the flow is characterized as mixed convection. The partial differential equations of the boundary layer flow are transformed into ordinary differential equations and subsequently are solved with the Runge-Kutta Fehlberg method. The results are presented in two tables and 11 figures.Comment: 4 page

Comment on "Three papers published by Subhas Abel and his co-workers in International Journal of Non-Linear Mechanics and International Journal of Thermal Sciences

The above paper concerns the boundary layer flow of a visco-elastic fluid along a stretching sheet immersed in a porous medium. The plate temperature is different from that of the ambient medium and the fluid viscosity is a function of temperature while the other fluid properties are assumed to be constant. The boundary layer equations are transformed into ordinary ones and subsequently are solved using the shooting method with Runge-Kutta integration algorithm. However, there are two fundamental errors in this paper which are presented below.Comment: Comment on "Three papers published by Subhas Abel and his co-workers in International Journal of Non-Linear Mechanics and International Journal of Thermal Science

Comment on Influence of convective boundary condition on double diffusive mixed convection from a permeable vertical surface, by P.M. Patil, E. Momoniat, S. Roy, International Journal of Heat and Mass Transfer, 70 (2014) 313-321

In the above paper the authors treat the boundary layer flow along a stationary, vertical, permeable, flat plate within a vertical free stream. Fluid is sucked or injected through the vertical plate. The fluid species concentration at the plate is constant and different from that of the ambient fluid. It is also assumed that the plate is heated by convection from another fluid with constant temperature with a constant heat transfer coefficient. The temperature and species concentration difference between the plate and the ambient fluid creates buoyancy forces and the flow is characterized as mixed convection. The partial differential equations of the boundary layer flow (Eqs. 1-4 in their paper) are transformed and subsequently are solved numerically using an implicit finite difference scheme in combination with a quasi-linearization technique. The quasi-linearization technique is a Newton-Raphson method. The results are presented in 12 figures

Comment on "The effect of variable viscosity on the flow and heat transfer on a continuous stretching surface"

The problem of forced convection along an isothermal, constantly moving plate is a classical problem of fluid mechanics that has been solved for the first time in 1961 by Sakiadis (1961). Thereafter, many solutions have been obtained for different aspects of this class of boundary layer problems. Solutions have been appeared including mass transfer, varying plate velocity, varying plate temperature, fluid injection and fluid suction at the plate. The work by Hassanien (1997) belongs to the above class of problems, including a linearly varying velocity and the variation of fluid viscosity with temperature. The author obtained similarity solutions considering that viscosity varies as an inverse function of temperature. However, the Prandtl number, which is a function of viscosity, has been considered constant across the boundary layer. It has been already confirmed in the literature that the assumption of constant Prandtl number leads to unrealistic results (Pantokratoras, 2004, 2005). The objective of the present paper is to obtain results considering both viscosity and Prandtl number variable across the boundary layer. The differences of the two methods are very large in some cases.Comment: Comment on A. Hassanien [ ZAMM, 1997, Vol. 77, pp. 876-880

Comment on Conjugate heat transfer of mixed convection for viscoelastic fluid past a stretching sheet, by Hsiao and Chen, Mathematical Problems in Engineering

Comment on Conjugate heat transfer of mixed convection for viscoelastic fluid past a stretching sheet, by Kai-Long Hsiao and Guan-Bang Chen, Mathematical Problems in Engineering, Volume 2007, article 17058, 21 pagesComment: 4 page

Comment on "Similarity analysis in magnetohydrodynamics: effects of Hall and ion-slip currents on free convection flow and mass transfer of a gas past a semi-infinite vertical plate," A.A. Megahed, S.R. Komy, A.A. Afify

Comment on Similarity analysis in magnetohydrodynamics:effects of Hall and ion-slip currents on free convection flow and mass transfer of a gas past a semi-infinite vertical plate, A.A. Megahed, S.R. Komy, A.A. Afify [Acta Mechanica 151, 185-194 (2001)] In the above paper is investigated the boundary layer flow of an electrically conducting fluid over a vertical, stationary plate placed in a calm fluid. The effects of Hall and ion-slip currents are taken into account. The boundary layer equations are transformed into ordinary ones using a scaling group of transformations and subsequently are solved numerically. However, there are two fundamental errors in the above paper which are presented below.Comment: 4 page

Comment on "The effect of variable viscosity on mixed convection heat transfer along a vertical moving surface" by M. Ali

The problem of forced convection along an isothermal moving plate is a classical problem of fluid mechanics that has been solved for the first time in 1961 by Sakiadis (1961). It appears that the first work concerning mixed convection along a moving plate is that of Moutsoglou and Chen (1980). Thereafter, many solutions have been obtained for different aspects of this class of boundary layer problems. In the previous works the fluid properties have been assumed constant. Ali (2006) in a recent paper treated, for the first time, the mixed convection problem with variable viscosity. He used the local similarity method to solve this problem but there are doubts about the validity of his results. For that reason we resolved the above problem with the direct numerical solution of the boundary layer equations without any transformation.Comment: comment on M. Ali [International Journal of Thermal Sciences, 2006, Vol. 45, pp. 60-69

Comment on Effects of transverse magnetic field on mixed convection in wall plume of power-law fluids, by Gorla, Lee, Nakamura and Pop, IJES, 1993

Comment on Effects of transverse magnetic field on mixed convection in wall plume of power-law fluids, by Rama Subba Reddy Gorla, Jin Kook Lee, Shoichiro Nakamura and Ioan Pop [International Journal of Engineering Science, 31 (1993) 1035-1045]. In the above paper the authors treat the boundary layer mixed convection flow of a power-law fluid along a vertical adiabatic surface in a transverse magnetic field with a steady thermal source at the leading edge. The governing non-similar equations are solved by means of a novel finite difference scheme. However, there are two fundamental errors in this paper and the presented results do not have any practical value.Comment: 3 page

A new kind of boundary layer flow due to Lorentz forces

In this paper we present a new kind of boundary layer flow produced by an electromagnetic Lorentz force which acts parallel to the plate in an electrically conductive fluid. The plate is motionless and the ambient fluid stagnant. This flow is equivalent to the classical free convective flow along a vertical plate. The boundary layer equations are transformed to non-dimensional form and a new dimensionless number is introduced which is equivalent to the Grashof number. The transformed boundary layer equations are solved with the finite difference method and the presented results include values of the friction coefficient and velocity profiles.Comment: 11 pages, 4 figure

Comment on "Chebyshev finite difference method for the effects of variable viscosity and variable thermal conductivity on heat transfer to a micro-polar fluid from a non-isothemal stretching sheet with suction and blowing," by S.N. Odda and A.M. Farhan

In the paper [Chaos, Solitons & Fractals, 2006, vol. 30, pp. 851-858]the authors treat the boundary layer flow of a micropolar fluid along a horizontal flat plate with blowing or suction. The fluid viscosity and thermal conductivity are assumed functions of temperature. The boundary layer equations are transformed into ordinary ones and subsequently are solved using the Chebyshev finite difference method. However, there are some deficiencies and errors in this paper.Comment: 2 pages, comment on S.N. Odda and A.M. Farhan [Chaos, Solitons & Fractals, 2006, vol. 30, pp. 851-858