Comment on "MHD-mixed convection flow in a lid-driven trapezoidal cavity under uniformly/non-uniformly heated bottom wall" 1. Comments Javed et al. (2017) performed a numerical investigation of MHD-mixed convection heat transfer inside a lid-driven trapezoidal cavity with uniform or non-uniform heating conditions. During their simulation, they varied the governing dimensionless parameters such as Rayleigh number (Ra) and Prandtl number (Pr). For a mixed convective problem, the associated heat and fluid flow characteristics due to the combined effect of natural and forced convection mechanisms are mathematically described by the combination of two crucial governing parameters, namely, Grashof number (Gr ¼ Ra/Pr, which signifies the dominance of natural convection) and Reynolds number (Re, which indicates the dominance of forced convection). Hence, the characteristic parameter for mixed convection heat transfer is called the Richardson number (Ri ¼ Gr/Re 2 ), which should be 0.1 # Ri # 10 within the mixed convection regime (Lukose and Basak, 2021). Forced convection becomes dominant when Ri > 0.1, while the dominance of natural convection takes into play at Ri > 10. When Ri ¼ 1, it is commonly known as pure mixed convection (Rahman et al., 2010; Hasib et al., 2015). Unfortunately, Javed et al. (2017) did not consider either Richardson or Reynolds number in their investigation while performing an extensive analysis of the mixed convection problem.They also mentioned that they varied the Hartmann number within 50 # Ha # 1,000 to show the MHD effect but presented all results only at Ha ¼ 50. Besides, they mentioned the investigated range of the Prandtl number twice in their paper as 0.026 # Pr # 100 and 0.026 # Pr # 1,000, respectively, but only considered Pr ¼ 0.026 and 10. Javed et al. (2017) considered a lid-driven trapezoidal cavity in their problem, where the top lid was moving at a fixed speed U 0 . Hence, they mentioned the velocity boundary condition of the top wall as u(x, L, where L is the height of the trapezoidal enclosure) ¼ U 0 in equation (5) of their paper, which represents the sliding motion of the lid in the positive x-direction. However, while drawing the schematic diagram of their problem [see Figure 1(a)], they showed the direction of the lid movement in the negative x-direction, which was wrong as per the boundary condition described in equation ( 5). Moreover, they neither showed the size of the base wall of the trapezoidal chamber in Figure 1(a) nor mentioned it anywhere in their paper. By analyzing Figure 9 of Javed et al. (2017), it can be confirmed that the base length of the trapezoidal cavity was L. The corrected physical domain is now shown in Figure 1(b), along with the corrected direction of the lid movement. In the caption of Figure 1 of Javed et al. (2017), it was mentioned that f ¼ 0°represented the square cavity, where f was the inclination angle of the side walls. However, the physical models developed using the physical dimensions of three different cases (f ¼ 0°, 30°and 45°) do n...
