Hayat et al. (2019) analyzed flow of stagnation point using Carreau fluid in the existence of homogeneous–heterogeneous reactions. In their analysis, Hayat et al. (2019) presented the energy equation (Eq. (5) in the paper) as:

$$ u\frac{\partial T}{\partial x} + v\frac{\partial T}{\partial y} = \frac{k}{{\rho c_{p} }}\frac{{\partial^{2} T}}{{\partial y^{2} }} - \frac{1}{{(\rho c)_{f} }}\frac{{16\sigma^{*} }}{{3m^{*} }}\frac{\partial }{\partial y}\left( {T^{3} \frac{\partial T}{\partial y}} \right) + \frac{{Q_{0} (T - T_{\infty } )}}{{\rho c_{p} }} $$
(1)

From Eq. (1), every term on RHS must have the units of K s−1. Thus, we have

$$ [{\text{Q}}_{0} /\uprho{\text{c}}_{\text{p}} ] = {\text{s}}^{ - 1} $$

Also, Hayat et al. (2019) defined the heat generation/absorption parameter (γ1) (below Eq. (22) in the paper) as:

$$ \gamma_{1} = \frac{{Q_{0} }}{{\rho c_{p} U_{0} }} $$
(2)

Hayat et al. (2019) defined the velocity, Uw as:

$$ U_{w} = U_{0} (x + b_{1} )^{m} $$
(3)

From Eq. (3), the U0 units are

$$ [{\text{U}}_{0} ] = {\text{m}}^{{1 - {\text{m}}}} {\text{s}}^{ - 1} $$

Thus, we can find the units of γ1 in Eq. (2) as:

$$ [\upgamma_{1} ] = ({\text{s}}^{ - 1} ) /({\text{m}}^{{1 - {\text{m}}}} {\text{s}}^{ - 1} ) = {\text{m}}^{{{\text{m}} - 1}} $$

From the above, the heat generation/absorption parameter (γ1) is dimensionless only if the parameter (m) = 1 that means constant surface thickness. However, Hayat et al. (2019) used m < 1 such as m = 0.5 in their 1st and 2nd tables (shape with increasing thickness). For the motion kind, m = 0.5 represents decelerated motion. Furthermore, Hayat et al. (2019) used m > 1 such as m = 1.5 in their 1st table (shape with decreasing thickness). For the motion kind, m = 1.5 represents accelerated motion.

Therefore, the heat generation/absorption parameter (γ1) is dimensional not dimensionless as Hayat et al. (2019) claim.