International Journal of Chemical Engineering
Volume 2017 (2017), Article ID 8925828, 2 pages
https://doi.org/10.1155/2017/8925828

Letter to the Editor

Comment on “Heat and Mass Transfer Effect on MHD Flow of a Viscoelastic Fluid through a Porous Medium Bounded by an Oscillating Porous Plate in Slip Flow Regime”

Asterios Pantokratoras

School of Engineering, Democritus University of Thrace, 67100 Xanthi, Greece

Correspondence should be addressed to Asterios Pantokratoras; apantokr@civil.duth.gr

Received 21 November 2016; Accepted 1 March 2017; Published 30 May 2017

Academic Editor: Evangelos Tsotsas

Copyright © 2017 Asterios Pantokratoras. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The present comment concerns some doubtful results included in the above paper.

In the paper [1], the momentum equation includes the term . This term is not correct. The correct form is . The transformed dimensionless momentum equation is as follows ( in [1]):

The above equation is not correct. The correct form is

The nondimensional porosity parameter is defined as follows ( in [1]):

where is the porous medium permeability, is a reference velocity, and is the fluid kinematic viscosity. The units of porous medium permeability are

The units of velocity are

The units of fluid kinematic viscosity are

Therefore the units of are

This means that the porous medium parameter is dimensional not dimensionless as the author claims.

The magnetic parameter is defined as follows ( in [1]):

The above definition is not correct. For the above dimensionless momentum equation (2) to be correct, the magnetic parameter must be defined as

However, all calculation and results by Sahoo [1] are based on the wrong definition of ((8) of the present work).

In Figure of Sahoo [1] the effect of parameters ,  , and   on nondimensional velocity is presented. Comparing the cases ,  , , and ,  ,  , it is seen that the greater mass Grashof number corresponds to greater velocity; that is, as the mass Grashof number increases the velocity increases too. Comparing the cases ,  ,   and ,  ,  , it is seen that the greater thermal Grashof number corresponds to smaller velocity; that is, as the thermal Grashof number increases the velocity decreases. This is irrational because the mass Grashof number and the thermal Grashof number are two positive nondimensional parameters on the right hand side of (2) and both act in the same way. When they grow the velocity increases and when they decrease the velocity decreases (both terms ,   in (2) are positive). This means that the velocity profiles for the cases ,  ,   and ,  ,   in Figure are not correct. This also means that the conclusion (iii) saying “The velocity of the flow field decreases due to the increase in the thermal Grashof number” is not correct.

Conflicts of Interest

The author declares that there are no conflicts of interest.

References

S. N. Sahoo, “Heat and mass transfer effect on mhd flow of a viscoelastic fluid through a porous medium bounded by an oscillating porous plate in slip flow regime,” International Journal of Chemical Engineering, vol. 2013, Article ID 380679, 8 pages, 2013.