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

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:

$$u\frac{𝜕u}{𝜕x}+\upsilon \frac{𝜕u}{𝜕y}={\nu }_{hnf}\frac{{𝜕}^{2}u}{𝜕y^2}+\overrightarrow{g}\beta (T-T_{\infty })-\frac{{\sigma }_{hnf}{B}_0^2}{{\rho }_{hnf}}{\sin }^2(\tau )u$$

(1)

It is well known in Physics that gravity acts in the vertical direction. Therefore, Equation (1) is incorrect because the gravity term $\overrightarrow{g}\beta (T-T_{\infty })$ in Equation (1) must be zero. The incorrect gravity term from Equation (1) has been transferred to dimensionless Equation (13) in [1] as $\frac{R{a}_s}{\mathrm{Pr}}\theta$ and as $\frac{R{a}_s}{\mathrm{Pr}}\lambda f_1$ 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:

$$f(Y)=V_C+d\left(\frac{1-e^{-\delta Y}}{\gamma }\right)$$

(2)

Equation (4c) in [1] is as follows:

$$T=T_{\infty }+\gamma (T_w-T_{\infty })x$$

(3)

In a Physics equation, all terms must have the same units, and from Equation (3), it is found that the units of $\gamma$ are $m^{-1}{(length)}^{-1}$. In Equation (2), the parameters $f(Y),V_C,d,Y,\delta$ are dimensionless, whereas $\gamma$ is dimensional, and Equation (3) is incorrect.