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Comment

# Comment on Vishalakshi et al. MHD Hybrid Nanofluid Flow over a Stretching/Shrinking Sheet with Skin Friction: Effects of Radiation and Mass Transpiration. Magnetochemistry 2023, 9, 118

by
Asterios Pantokratoras
School of Engineering, Democritus University of Thrace, 67100 Xanthi, Greece
Magnetochemistry 2024, 10(4), 26; https://doi.org/10.3390/magnetochemistry10040026
Submission received: 8 January 2024 / Accepted: 7 April 2024 / Published: 11 April 2024

## 1. First Error

In Figure 1, in [1], it is clearly shown that the x-axis is horizontal and the y-axis is vertical. The horizontal(u) momentum Equation (2) in [1] is as follows:
$u 𝜕 u 𝜕 x + υ 𝜕 u 𝜕 y = ν h n f 𝜕 2 u 𝜕 y 2 + g → β ( T − T ∞ ) − σ h n f B 0 2 ρ h n f sin 2 ( τ ) u$
It is well known in Physics that gravity acts in the vertical direction. Therefore, Equation (1) is incorrect because the gravity term $g → β ( T − T ∞ )$ in Equation (1) must be zero. The incorrect gravity term from Equation (1) has been transferred to dimensionless Equation (13) in [1] as $R a s Pr θ$ and as $R a s Pr λ f 1$ in Equation (17) in [1], and these equations are incorrect. Two papers with the same error have been criticized in [2,3].

## 2. Second Error

Equation (20) in [1] is as follows:
$f ( Y ) = V C + d 1 − e − δ Y γ$
Equation (4c) in [1] is as follows:
$T = T ∞ + γ ( T w − T ∞ ) x$
In a Physics equation, all terms must have the same units, and from Equation (3), it is found that the units of $γ$ are $m − 1 ( l e n g t h ) − 1$. In Equation (2), the parameters $f ( Y ) , V C , d , Y , δ$ are dimensionless, whereas $γ$ is dimensional, and Equation (3) is incorrect.

## Conflicts of Interest

The authors declare no conflicts of interest.

## References

1. Vishalakshi, A.B.; Mahesh, R.; Mahabaleshwar, U.S.; Rao, A.K.; Pérez, L.M.; Laroze, D. MHD Hybrid Nanofluid Flow over a Stretching/Shrinking Sheet with Skin Friction: Effects of Radiation and Mass Transpiration. Magnetochemistry 2023, 9, 118. [Google Scholar] [CrossRef]
2. Pantokratoras, A. Discussion on “Higher Order Chemical Reaction and Radiation Effects on Magnetohydrodynamic Flow of a Maxwell Nanofluid with Cattaneo–Christov Heat Flux Model Over a Stretching Sheet in a Porous Medium” (Reddy Vinodkumar, M. and Lakshminarayana, P., 2022, ASME J. Fluids Eng., 144(4), p.041204). ASME J. Fluids Eng. 2023, 145, 125501. [Google Scholar]
3. Pantokratoras, A. Comment on the paper “Shape effect of nanosize particles in unsteady mixed convection flow of nanofluid over disk with entropy generation”. Proc. IMechE Part E J. Process Mech. Eng. 2019, 233, 147–148. [Google Scholar] [CrossRef]
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## Share and Cite

MDPI and ACS Style

Pantokratoras, A. Comment on Vishalakshi et al. MHD Hybrid Nanofluid Flow over a Stretching/Shrinking Sheet with Skin Friction: Effects of Radiation and Mass Transpiration. Magnetochemistry 2023, 9, 118. Magnetochemistry 2024, 10, 26. https://doi.org/10.3390/magnetochemistry10040026

AMA Style

Pantokratoras A. Comment on Vishalakshi et al. MHD Hybrid Nanofluid Flow over a Stretching/Shrinking Sheet with Skin Friction: Effects of Radiation and Mass Transpiration. Magnetochemistry 2023, 9, 118. Magnetochemistry. 2024; 10(4):26. https://doi.org/10.3390/magnetochemistry10040026

Chicago/Turabian Style

Pantokratoras, Asterios. 2024. "Comment on Vishalakshi et al. MHD Hybrid Nanofluid Flow over a Stretching/Shrinking Sheet with Skin Friction: Effects of Radiation and Mass Transpiration. Magnetochemistry 2023, 9, 118" Magnetochemistry 10, no. 4: 26. https://doi.org/10.3390/magnetochemistry10040026

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