108
M. Feng et al.
Symmetry Plane. On the symmetry plane, the adiabatic boundary condition for
Eq. (9.1) is adopted and can be expressed as Eq. (9.12):
q t = 0.
(9.12)
9.3.4 Solution Method
According to Fig. 9.2 in Sect. 9.3.1, the calculation geometry was created and meshed
with hexahedral grid using Gambit 2.3 software. A dense mesh was used in the surface
zone to guarantee the computational efficiency and simulation accuracy. The oxide
scale growth and the thermal resistance models were inputted using user-defined
functions based on fluent software. At certain time step, on based of the slab surfaces
temperature resulted at the previous time step, the oxide scale thickness and thermal
resistance was solved by use of the oxide scale growth model. And then, the heat
conduction equation was solved on base of the slab surfaces temperature resulted at
current time step. The above process was repeated at each location in the furnace.
The residual of energy convergence was set to 10
–6 . The time step was set to 30 s.
9.4 Results and Discussion
9.4.1 Growth of Oxide Scale
The thermal resistance, which is caused by the oxide scale on the surfaces of the slab,
is a significant factor to affect the comprehensive heat transfer coefficient between
the surroundings and the slab’s surfaces. The thickness of the oxide scale might
determine the thermal resistance value. Thus, it is worth investigating that the variation regularity of the oxide scale thickness during the reheating process. Figure 9.3
shows the varying of average scale thickness on the upper and lower surface of the
slab during the reheating process. It can be seen that the highest temperature zone
of the slab is located at the intersecting point of the three surfaces, i.e. the front
surface, the upper surface and the end surface. we take this point as investigated
object. Figure 9.4 shows the varying of scale thickness and temperature of the investigated point during the reheating process. That as seen in Figs. 9.3 and 9.4, the
surfaces temperature of the slab and the resident time in the high temperature zone
in the furnace might be important factors for the oxide scale formation rate. When
the temperature is lower than 833 K, the oxide scale formation rate is very small. So
even prolonging the resident time here, the oxide scale will not become very thick.
But, when the temperature is very high, it will increase rapidly with resident time.
M. Feng et al.
Symmetry Plane. On the symmetry plane, the adiabatic boundary condition for
Eq. (9.1) is adopted and can be expressed as Eq. (9.12):
q t = 0.
(9.12)
9.3.4 Solution Method
According to Fig. 9.2 in Sect. 9.3.1, the calculation geometry was created and meshed
with hexahedral grid using Gambit 2.3 software. A dense mesh was used in the surface
zone to guarantee the computational efficiency and simulation accuracy. The oxide
scale growth and the thermal resistance models were inputted using user-defined
functions based on fluent software. At certain time step, on based of the slab surfaces
temperature resulted at the previous time step, the oxide scale thickness and thermal
resistance was solved by use of the oxide scale growth model. And then, the heat
conduction equation was solved on base of the slab surfaces temperature resulted at
current time step. The above process was repeated at each location in the furnace.
The residual of energy convergence was set to 10
–6 . The time step was set to 30 s.
9.4 Results and Discussion
9.4.1 Growth of Oxide Scale
The thermal resistance, which is caused by the oxide scale on the surfaces of the slab,
is a significant factor to affect the comprehensive heat transfer coefficient between
the surroundings and the slab’s surfaces. The thickness of the oxide scale might
determine the thermal resistance value. Thus, it is worth investigating that the variation regularity of the oxide scale thickness during the reheating process. Figure 9.3
shows the varying of average scale thickness on the upper and lower surface of the
slab during the reheating process. It can be seen that the highest temperature zone
of the slab is located at the intersecting point of the three surfaces, i.e. the front
surface, the upper surface and the end surface. we take this point as investigated
object. Figure 9.4 shows the varying of scale thickness and temperature of the investigated point during the reheating process. That as seen in Figs. 9.3 and 9.4, the
surfaces temperature of the slab and the resident time in the high temperature zone
in the furnace might be important factors for the oxide scale formation rate. When
the temperature is lower than 833 K, the oxide scale formation rate is very small. So
even prolonging the resident time here, the oxide scale will not become very thick.
But, when the temperature is very high, it will increase rapidly with resident time.