*2.4. Discretization Error*

In order to evaluate the accuracy of the numerical model, the influence of the meshing method on the results was evaluated. Ten different discretization grids were analyzed—all of them consist of structured and polygonal elements. Two examples of the tested meshes are presented in Figure 4.

**Figure 4.** Examples of discretization mesh located 0.5 m above the furnace bogie level consisting of (**a**) 875,119 and (**b**) 533,386 elements.

The volume average temperature of the load (ALT) was chosen for an indicator of the discretization error. Case 1 was simulated using the same model settings and the same time step sizes, and the obtained results of ALT after 2 h of the process were compared (Figure 5). The black point on the chart marks the mesh used for performing the calculations for cases 1–9.

**Figure 5.** Convergence study results—volume average load temperature after 2 h of the heat treatment for different discretization meshes.

One can see that enhancing the grid resolution keeps the values of ALT within the 2 K range, what appears to be an acceptable value of error, i.e., less than 2% when compared to the value change of average load temperature (ΔALT).
