Comments On 'perturbation Analysis Of Radiative Effect On free Convection Flows In Porous Medium In The Presence of Pressure Work And Viscous Dissipation', By a.m. Rashad [commun Nonlinear Sci numer Simul 2009; 14:140-153]

摘要

The above paper concerns the boundary layer flow of a Newtonian fluid in a porous medium. The effects of thermal radiation, permeability of the porous medium, pressure stress work and viscous dissipation have been included in the analysis. Four different vertical flows have been investigated: isothermal surface, uniform heat flux surface, adiabatic surface and plane plume. The boundary layer equations are transformed into ordinary ones and subsequently are solved numerically using a perturbation method. However, there are two errors in the above paper, one of them been fundamental. They are presented below: (1) The characteristics of the variation of velocity, temperature or any other substance transported inside a boundary layer are well established and known taking into account that the classical german book on boundary layer theory was first published in 1950 by Schlichting. Velocity and temperature profiles approach the ambient fluid conditions asymptotically. Asymptotically means that the velocity and temperature gradient at large distance from the plate is zero. Some velocity and temperature profiles that approach the ambient conditions correctly (asymptotically) in a boundary layer flow are shown in Arpaci and Larsen [3, p. 154], Cebeci and Bradshaw [5, p. 42], Kakac and Yener [7, p. 47], Bejan [4, p. 43], Incropera and DeWitt [6, p. 290], Oosthuizen and Naylor [11, p. 62], Schlichting and Gersten [12, p. 215, 265 and 281] and White [13, p. 80].