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Comment on ‘Effects of thermal radiation and slip mechanism on mixed convection flow of Williamson nanofluid over an inclined stretching cylinder' (Commun. Theor. Phys. 71 1405–15)

  • Asterios Pantokratoras
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  • School of Engineering, Democritus University of Thrace, 67100 Xanthi, Greece

Received date: 2021-09-21

  Revised date: 2022-03-15

  Accepted date: 2022-05-16

  Online published: 2022-07-01

Copyright

© 2022 Institute of Theoretical Physics CAS, Chinese Physical Society and IOP Publishing

Abstract

Some errors exist in the above paper.

Cite this article

Asterios Pantokratoras . Comment on ‘Effects of thermal radiation and slip mechanism on mixed convection flow of Williamson nanofluid over an inclined stretching cylinder' (Commun. Theor. Phys. 71 1405–15)[J]. Communications in Theoretical Physics, 2022 , 74(7) : 075008 . DOI: 10.1088/1572-9494/ac6fc6

The momentum equation (2) in [1] is as follows
$\begin{eqnarray}\begin{array}{l}\displaystyle \frac{\partial w}{\partial t}+u\displaystyle \frac{\partial w}{\partial r}+w\displaystyle \frac{\partial w}{\partial z}=\displaystyle \frac{\nu }{r}\displaystyle \frac{\partial w}{\partial r}\\ \times \,\left[{\beta }^{* }+\left(1-{\beta }^{\#}\right){\left(1-{\rm{\Gamma }}\displaystyle \frac{\partial w}{\partial r}\right)}^{-1}\right]\\ +\,\nu \displaystyle \frac{{\partial }^{2}w}{\partial {r}^{2}}\left[{\beta }^{* }+\left(1-{\beta }^{* }\right){\left(1-{\rm{\Gamma }}\displaystyle \frac{\partial w}{\partial r}\right)}^{-1}\right]\\ +\,\nu {\rm{\Gamma }}\displaystyle \frac{\partial w}{\partial r}\displaystyle \frac{{\partial }^{2}w}{\partial {r}^{2}}\left[\left(1-{\beta }^{* }\right){\left(1-{\rm{\Gamma }}\displaystyle \frac{\partial w}{\partial r}\right)}^{-2}\right]\\ +\,\left[-\displaystyle \frac{({\rho }_{p}-\rho )(C-{C}_{\infty })}{\rho }+(1-{C}_{\infty })(T-{T}_{\infty })\lambda \right]\\ -\,\displaystyle \frac{\sigma {B}_{0}^{2}}{\rho }w.\end{array}\end{eqnarray}$

First error

The units of concentration C are kg m−3 (Nomenclature) whereas the pure number 1 is dimensionless. In Physics it is not allowed to add quantities with different units and the term $(1-{C}_{\infty })$ is wrong.

Second error

In the term $(T-{T}_{\infty })\lambda $ appears the parameter $\lambda $ which is dimensionless. However equation (1) is dimensional and this is irrational.

Third error

From figure 1 in [1] it is seen that gravity is present. However there is no gravity term in equation (1).

Fourth error

The mixed convection parameter is defined as follows in [1]
$\begin{eqnarray}\lambda =\displaystyle \frac{\beta g(1-{C}_{\infty })(T-{T}_{\infty })}{z{W}_{0}^{2}}.\end{eqnarray}$
The units of concentration C are kg m−3 (Nomenclature) whereas the pure number 1 is dimensionless. Therefore the term $(1-{C}_{\infty })$ is wrong and the equation (2) is wrong.

Fifth error

For the same reason the buoyancy ratio parameter in [1]
$\begin{eqnarray}{N}_{r}=\displaystyle \frac{({\rho }_{p}-\rho ){C}_{\infty }}{\beta \rho (1-{C}_{\infty })({\rm{T}}-{{\rm{T}}}_{\infty })}\end{eqnarray}$
is wrong. In addition the appearance of dimensionless heat generation parameter $\beta $ in equation (3) is irrational.

Sixth error

The dimensionless Brownian parameter is defined as follows in [1]
$\begin{eqnarray}Nb=\displaystyle \frac{\tau {D}_{B}{C}_{\infty }}{\nu },\end{eqnarray}$
where ${D}_{B}({{\rm{m}}}^{2}\,{{\rm{s}}}^{-1})$ is the Brownian diffusion coefficient and $\nu ({{\rm{m}}}^{2}\,{{\rm{s}}}^{-1})$ is the fluid kinematic viscosity. From equation (4) it is found that the units of $Nb$ are $\mathrm{kg}\,{{\rm{m}}}^{-3}.$ Therefore equation (4) is wrong.

Seventh error

In the energy equation (3) in [1] appears the term
$\begin{eqnarray}\left[{D}_{B}\displaystyle \frac{\partial C}{\partial r}\displaystyle \frac{\partial T}{\partial r}+\displaystyle \frac{{D}_{T}}{{T}_{\infty }}{\left(\displaystyle \frac{\partial T}{\partial r}\right)}^{2}\right].\end{eqnarray}$
The units of the term ${D}_{B}\tfrac{\partial C}{\partial r}\tfrac{\partial T}{\partial r}$ are $\mathrm{kg}\,\mathrm{Kelvin}\,{{\rm{m}}}^{-3}\,{{\rm{s}}}^{-1}$ whereas the units of the term $\tfrac{{{D}}_{{T}}}{{{T}}_{\infty }}{\left(\tfrac{\partial {T}}{\partial {r}}\right)}^{2}$ are $\mathrm{Kelvin}\,{{\rm{s}}}^{-1}.$ Therefore the term (5) is wrong.

Eighth error

Equation (5) in [1] and the above figure 1 in [1] appears the equation
$\begin{eqnarray}{{D}}_{{B}}\displaystyle \frac{\partial {C}}{\partial {r}}+\displaystyle \frac{{{D}}_{{T}}}{{{T}}_{\infty }}\displaystyle \frac{\partial {T}}{\partial {r}}=0.\end{eqnarray}$
The units of the term ${D}_{B}\tfrac{\partial C}{\partial r}$ are kg m−2 s−1 whereas the units of the term $\tfrac{{{D}}_{{T}}}{{{T}}_{\infty }}\tfrac{\partial {T}}{\partial {r}}$ are ${\rm{m}}\,{{\rm{s}}}^{-1}.$ Therefore the term (6) is wrong.
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Khan M Hamid A Hashim 2019 Effects of thermal radiation and slip mechanism on mixed convection flow of williamson nanofluid over an inclined stretching cylinder Commun. Theor. Phys. 71 1405 1415

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