Comment on Khan et al. Impact of Irregular Heat Sink/Source on the Wall Jet Flow and Heat Transfer in a Porous Medium Induced by a Nanofluid with Slip and Buoyancy Effects. Symmetry 2022, 14, 2212

Asterios Pantokratoras

doi:10.3390/sym17081181

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

Symmetry2025, 17(8), 1181;https://doi.org/10.3390/sym17081181

This article belongs to the Section Engineering and Materials

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Abstract

Many errors exist in the above paper.

First Error

In Equation (10) in [1], the dimensionless similarity variable

ξ

is presented as follows:

ξ = {(α_{f}^{2} x^{3})}^{- 1 / 4} y

(1)

where

α_{f} (m^{2} \sec^{- 1})

is the fluid thermal diffusivity and

x, y (m)

are the Cartesian coordinates. From Equation (1), it is found that the units of

ξ

are

m^{- 3 / 4} \sec^{1 / 2}

and the parameter

ξ

is dimensional and wrong.

Second Error

In Equation (10) in [1], the stream function

ψ

is presented as follows:

ψ = {(α_{f}^{2} x)}^{1 / 4} F (ξ)

(2)

where

F (ξ)

is a dimensionless function. From Equation (2), it is found that the units of

ψ

are

m^{5 / 4} \sec^{- 1 / 2}

instead of

m^{2} \sec^{- 1}

.

Third Error

In Equation (11) in [1], the following equation is presented:

u = \frac{4}{\sqrt{x}} F' (ξ)

(3)

where

u (m \sec^{- 1})

is the fluid velocity. Equation (3) is wrong because the units of the LHS are

m \sec^{- 1}

, whereas the units of the RHS are

m^{- 1 / 2}

. In a physics equation, all terms must have the same units.

Fourth Error

In Equation (11) in [1], the following equation is presented:

υ = - \sqrt{α_{f}} x^{- 3 / 4} (F (ξ) - 3 ξ F' (ξ))

(4)

where

υ (m \sec^{- 1})

is the fluid velocity. Equation (4) is wrong because the units of the LHS are

m \sec^{- 1}

, whereas the units of the RHS are

m^{1 / 4} \sec^{- 1 / 2}

.

Fifth Error

The dimensionless mixed convection parameter is as follows:

λ = \frac{g β_{f} T_{0}}{4}

(5)

where

g (m s e c^{- 2})

is the gravity acceleration,

β_{f} (K e l v i n^{- 1})

is the thermal expansion coefficient and

T_{0} (m^{2} K e l v i n)

. From Equation (5), it is found that the units of

λ

are

m^{3} \sec^{- 2}

.

Sixth Error

In Equations (5), (13) and (14) in [1], the term

e^{ξ}

appears. In mathematics,

e^{x}

with x dimensional is meaningless. Taking into account that

ξ (m^{- 3 / 4} \sec^{1 / 2})

is dimensional, Equations (5), (13) and (14) in [1] are wrong.

Seventh Error

In the dimensionless Equation (15) in [1], the velocity slip parameter

Σ_{a} = \frac{A μ_{f}}{\sqrt{α_{f}}}

appears. The parameter A is included in

γ_{1} (x) = A x^{3 / 4}

and the parameter

γ_{1} (x)

is included in Equation (4) in [1]. From these equations, it is found that the units of

Σ_{a}

are

m^{- 3 / 4} \sec^{1 / 2}

. Therefore Equation (15) in [1] is wrong because in a dimensionless equation, all terms must be dimensionless.

Eighth Error

Below Equation (12) in [1], the parameter

K_{a} = \frac{ν_{f} ε_{a}^{2}}{K_{0}}

appears. However the parameter

K_{0}

is unknown.

Conflicts of Interest

The author declares no conflicts of interest.

Reference

Khan, U.; Zaib, A.; Ishak, A.; Elattar, S.; Eldin, S.M.; Raizah, Z.; Waini, I.; Waqas, M. Impact of Irregular Heat Sink/Source on the Wall Jet Flow and Heat Transfer in a Porous Medium Induced by a Nanofluid with Slip and Buoyancy Effects. Symmetry 2022, 14, 2212. [Google Scholar] [CrossRef]

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© 2025 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Comment on Khan et al. Impact of Irregular Heat Sink/Source on the Wall Jet Flow and Heat Transfer in a Porous Medium Induced by a Nanofluid with Slip and Buoyancy Effects. Symmetry 2022, 14, 2212

Abstract

Conflicts of Interest

Reference

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