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M. Feng et al.
furnace exit, therefore the transient heat behavior of the steel slab in the reheating
furnace has attracted a great deal of interest [4–6]. In general case, the reheating
furnace is filled with high temperature oxidizing gas. During reheating process, the
steel slab surfaces are exposed to the high temperature oxidizing gas environment,
therefore, a layer of iron oxide will be generated on the slab surfaces and become
more and more noticeable over time. In particular, when the steel slab moves to the
heating zone and the soaking zone, it will become more serious. The oxide scale
has poor thermal conductivity, large specific heat and less surface emission rate
compared to steel slab, so the formation and growth of oxide scale may affect the
heat transfer characteristics of the steel slab. For these reasons, it is quite important to
accurately predict the heat transfer behavior of steel slab with growth of oxide scale
throughout heating process. Numerical simulation is an effective method for solving
problems of heat transfer in complex geometries. Over the past decades, a number of
studies have been conducted employing numerical simulation to analyze the heating
behavior of the steel slabs in the reheating furnace [7–11], but these studies rarely
involve the problem of slab oxidation. In 2003, Chen et al. [12] presented a kinetic
model for high temperature oxidation of carbon steels in oxidizing gas. Then, Jang
et al. [13] predicted the heat flux distribution within the furnace and the temperature
distribution in the slab throughout a walking-beam type reheating furnace process by
use of the kinetic model. Subsequently, Dubey et al. [14] also studied three dimensional transient heat conduction within steel slab considering the growth of oxide
scale on the slab surface during reheating on base of this model. The results show
that the kinetic model of steel oxidation by Chen et al. is a great help to predict the
heat transfer behavior of slab with growth of oxide scale throughout heating process.
But, their computational procedures are too complex because of the geometric model
including the oxide scale thickness.
In this wok, on base of the kinetic model of steel oxidation by Chen et al., the
transient heat behavior and the temperature distribution in the slab throughout the
reheating process in a pusher type furnace by considering growing oxide layer have
been studied. But, the geometric model is not including the oxide scale thickness, the
oxide scale growth and the thermal resistance models has been considered using a submodel. In addition, the heating exchange between the steel slabs and its surroundings,
including the hot combustion gases, the furnace wall, the skids, and the gas convection
heat transfer, etc., has also been considered in the simulation. Our research objective
is to provide reference for the design and operation of the reheating furnaces.
9.2 Geometry and Mathematical Model
The pusher type reheating furnace modeled in this paper is shown in Fig. 9.1. This
furnace has about 32 m in length and 5.6 m in width, and the highest/lowest furnace
roof is about 3.5/1.2 m inside. There are three zones in the reheating furnace as shown
in Fig. 9.1a: preheating, heating, and soaking zones. The water-cooled beam and
partition wall is located between the heating zone and soaking zone in the furnace.
M. Feng et al.
furnace exit, therefore the transient heat behavior of the steel slab in the reheating
furnace has attracted a great deal of interest [4–6]. In general case, the reheating
furnace is filled with high temperature oxidizing gas. During reheating process, the
steel slab surfaces are exposed to the high temperature oxidizing gas environment,
therefore, a layer of iron oxide will be generated on the slab surfaces and become
more and more noticeable over time. In particular, when the steel slab moves to the
heating zone and the soaking zone, it will become more serious. The oxide scale
has poor thermal conductivity, large specific heat and less surface emission rate
compared to steel slab, so the formation and growth of oxide scale may affect the
heat transfer characteristics of the steel slab. For these reasons, it is quite important to
accurately predict the heat transfer behavior of steel slab with growth of oxide scale
throughout heating process. Numerical simulation is an effective method for solving
problems of heat transfer in complex geometries. Over the past decades, a number of
studies have been conducted employing numerical simulation to analyze the heating
behavior of the steel slabs in the reheating furnace [7–11], but these studies rarely
involve the problem of slab oxidation. In 2003, Chen et al. [12] presented a kinetic
model for high temperature oxidation of carbon steels in oxidizing gas. Then, Jang
et al. [13] predicted the heat flux distribution within the furnace and the temperature
distribution in the slab throughout a walking-beam type reheating furnace process by
use of the kinetic model. Subsequently, Dubey et al. [14] also studied three dimensional transient heat conduction within steel slab considering the growth of oxide
scale on the slab surface during reheating on base of this model. The results show
that the kinetic model of steel oxidation by Chen et al. is a great help to predict the
heat transfer behavior of slab with growth of oxide scale throughout heating process.
But, their computational procedures are too complex because of the geometric model
including the oxide scale thickness.
In this wok, on base of the kinetic model of steel oxidation by Chen et al., the
transient heat behavior and the temperature distribution in the slab throughout the
reheating process in a pusher type furnace by considering growing oxide layer have
been studied. But, the geometric model is not including the oxide scale thickness, the
oxide scale growth and the thermal resistance models has been considered using a submodel. In addition, the heating exchange between the steel slabs and its surroundings,
including the hot combustion gases, the furnace wall, the skids, and the gas convection
heat transfer, etc., has also been considered in the simulation. Our research objective
is to provide reference for the design and operation of the reheating furnaces.
9.2 Geometry and Mathematical Model
The pusher type reheating furnace modeled in this paper is shown in Fig. 9.1. This
furnace has about 32 m in length and 5.6 m in width, and the highest/lowest furnace
roof is about 3.5/1.2 m inside. There are three zones in the reheating furnace as shown
in Fig. 9.1a: preheating, heating, and soaking zones. The water-cooled beam and
partition wall is located between the heating zone and soaking zone in the furnace.