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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.

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 pages

The concept of boundary layer flow, introduced in 1904 by Prandtl, is a popular field in Fluid Mechanics for engineers, physicists and mathematicians. In the classical Blasius boundary layer flow the transverse (normal) velocity reaches a finite value and remains constant in the free stream. If this finite vertical speed will be added to the free stream speed the resulting velocity in the free stream will be greater than the original velocity upstream of the plate which is irrational. This phenomenon has been marked and discussed in many Fluid Mechanics textbooks without a satisfactory explanation. In the present work we present a definite explanation by solving the complete Navier-Stokes equations. It is found that the real ambient transverse velocity is zero and not finite as it is predicted by the boundary layer theory. The same is valid in the classical free convection flow along a vertical isothermal plate., Comment: 11 pages, 5 figures

In the above paper the author treats the boundary layer flow of an electrically conducting, non-Newtonian fluid along a vertical plate embedded in a Darcy-Brinkman-Forchheimer porous medium. The fluid is under the action of a constant transverse magnetic field and the radiation is taken into account in the energy equation. The boundary layer equations are transformed into ordinary ones and subsequently are solved numerically. However, there is a fundamental error in this paper which is presented below, Comment: 3 pages

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 pages, Comment: 4 pages

Comment on Group method analysis of magneto-elastico-viscous flow along a semi-infinite flat plate with heat transfer,Helal and Abd-el-Malek, Journal of Computational and Applied Mathematics 173 (2005) 199-210. In the above paper the authors treat the boundary layer flow of a elasto- viscous liquid along an infinite plate in the presence of a transverse magnetic field. The plate temperature is higher than the ambient fluid temperature. The boundary layer equations are transformed into ordinary ones using the group theory and subsequently are solved numerically. Velocity, temperature, shear stress and heat transfer profiles are presented for values of magnetic parameter M=0, 0.5 and 1. This is an interesting work but there are some fundamental errors which are presented below., Comment: 6 pages, 1 figure

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 pages

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 pages

In the above paper the authors treat the natural convection boundary layer flow in a Darcy-Brinkman-Forchheimer porous medium. In the energy equation the radiation effect has been taken into account. A two-parameter perturbation method is used for the solution of the equations. The first order results are presented in tables and figures. This is an interesting work but there are some weak points which are presented below, Comment: 4 pages, 1 figure

Comment on six papers published by M.A. El-Hakiem and his co-workers in International Communications in Heat and Mass Transfer, Journal of Magnetism and Magnetic Materials and Heat and Mass Transfer, Comment: Comment on six papers published by M.A. El-Hakiem and his co-workers in International Communications in Heat and Mass Transfer, Journal of Magnetism and Magnetic Materials and Heat and Mass Transfer

Comments on six papers published by S.P. Anjali Devi and R. Kandasamy in Heat and Mass Transfer, ZAMM, Mechanics Research Communications, International Communications in Heat and Mass Transfer, Communications in Numerical Methods in Engineering, Journal of Computational and Applied Mechanics In conclusion all the above papers are of very low quality, written without care and are partly or completely wrong., Comment: Comments on six papers published by S.P. Anjali Devi and R. Kandasamy in Heat and Mass Transfer, ZAMM, Mechanics Research Communications, International Communications in Heat and Mass Transfer, Communications in Numerical Methods in Engineering, Journal of Computational and Applied Mechanics

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 Sciences

In the above paper an analysis has been carried out to obtain results in the Couette flow of a Newtonian fluid with viscous dissipation and temperature dependent viscosity. The fluid viscosity is an exponential function of temperature. Exact analytical solutions are obtained for the calculation of velocity and temperature. However, there are some fundamental errors in this paper which are presented herein., Comment: Comment on K.S. Adegbie and F.I. Alao [Journal of Mathematics and Statistics, 2007, Volume 3, pp. 12-14]

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 figures

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]

In the above paper by Bechtel, Cai, Rooney and Wang, Physics of Fluids, 2004, 16, 3955-3974 six different theories of a Newtonian viscous fluid are investigated and compared, namely, the theory of a compressible Newtonian fluid, and five constitutive limits of this theory: the incompressible theory, the limit where density changes only due to changes in temperature, the limit where density changes only with changes in entropy, the limit where pressure is a function only of temperature, and the limit of pressure a function only of entropy. The six theories are compared through their ability to model two test problems: (i) steady flow between moving parallel isothermal planes separated by a fixed distance with no pressure gradient in the flow direction (Couette flow), and (ii) steady flow between stationary isothermal parallel planes with a pressure gradient (Poiseuille flow). The authors found, among other, that the incompressible theory admits solutions to these problems of the plane Couette/Poiseuille flow form: a single nonzero velocity component in a direction parallel to the bounding planes, and velocity and temperature varying only in the direction perpendicular to the planes., Comment: Comment on S. Bechtel, M. Cai, F. Rooney and Q. Wang [Physics of Fluids, 2004, Vol. 16, pp. 3955-3974]

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]

In the above paper [Chaos, Solitons & Fractals, 13 (2002) 1843-1850] the author treats the boundary layer flow along a vertical isothermal plate of an electrically conducting fluid. The plate lies in a vertical free stream of constant velocity $u_\infty$, constant temperature $T_\infty$ and constant mass concentration $C_\infty$. The plate moves vertically with a velocity which is a linear function of distance $x$ ($u_w=cx$). A transverse magnetic field with constant strength $B_0$ is imposed on the flow. The boundary layer equations are integrated numerically. However, there is a fundamental error in this paper and the presented results do not have any practical value., Comment: comment on A.Y. Ghaly [Chaos, Solitons & Fractals, 13 (2002) 1843-1850]and on A.Y. Ghaly and M.A. Seddeek [Chaos, Solitons and Fractals, 19, 2004, pp. 61-70]

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]