Development of a numerically efficient CFD model to predict transient temperature distribution of mother tubes moving translative and rotative through a gas fired furnace

In this work the heating of mother tubes in a walking beam type reheating furnace has been investigated. The tubes are heated prior to further processing into seamless tubes in a downstream stretch reducing mill. In contrast to previous works, the heating of hollow geometries moving through the furnace is considered. The main difference to existing works is the movement of the tubes in a combination of translational and rotational movement. The tubes rest on walking beams in loading bays and perform a rotational movement when passing through the furnace. The walking beams are not water cooled so that they reach the gas temperature inside the furnace. Due to these effects, it is to be expected that the influence of the skid system on tube heating is low. The model used in this work is based on two separate simulations: a steady state simulation characterizing the gas-phase combustion, and a transient simulation considering the heating of the tubes. This approach minimizes the computing power required, which is thus significantly lower than that for a full transient model. The steady state combustion simulation has been performed using the steady flamelet model (SFM). The advantage of the SFM compared to other models is the low computational effort and allows a detailed CH4 chemical mechanism, the skeletal25 to be used. The discrete ordinates model was used to solve the radiative transfer equations. To validate the model, the results of the steady state simulation are compared to process data, revealing a good agreement. A test tube, equipped with several thermocouples, provided a statement about the heating characteristic of the tubes. The data of the test tube and pyrometer measurement have been compared to the transient heating simulation, also constituting good agreements.