Numerical Modeling of a Walking-Beam Type Slab Reheating Furnace
Date Issued
2008
Date
2008
Author(s)
Hsieh, Chia-Tsung
Abstract
In the present study, a three-dimensional simulation is performed for the turbulent reactive flow and radiactive heat transfer in the walking-beam type slab reheating furnace by STAR-CD software. The study employs the high-Reynolds-number k-ε turbulence model based on Favre-averaged governing equations. The pre-assumed PDF model associated with the fast chemistry assumption and a single diffusivity is used to account for turbulent combustion. The absorption coefficient of the gases mixture is calculated by WSGGM (weighted-sum-of-gray-gases model). The discrete ordinates radiation model is adopted to calculate the radiactive heat transfer. The geometric model takes care of all components of the furnace, including the burners, the walking beam system with skid buttons, the slab, the dam, the down-take, etc. The part 1 of the study, the surface temperature of the slab is prescribed via experimental measurements and the furnace wall is assumed adiabatic. The turbulent reactive flow is thus simulated. The part 2 of the study, the temperature distributions of the slab and the gas mixture are obtained through a coupled calculation. The slab is modeled as a laminar flow having a very high viscosity and thus moving at a nearly constant speed. No radiation is concerned within the slab. The temperature distributions of the slab and the gas mixture are obtained through a coupled calculation. And the part 3 of the study, a solution for improving the skid mark by varying either the distance between two static beams or the height of the skid buttons is targeted. To obtain a steady solution, the walking beams are assumed fixed in the furnace.he simulation results agree with the measurements very well. The difference between the predicted heating efficiency and the measured one of the furnace is only 6%. The prediction errors at six temperature-monitored points are all under 10%, except the one in the lower heating zone which appears to be 13%. The measured surface temperatures of the slab were used as boundary conditions and the flow field of the reheating furnace can be obtained. However, the measured temperature will affect the result of calculations. When coupled calculations are executed in the part 2 of the study, the surface temperature can be obtained simultaneously. Except for the upper surface temperature, all the other simulation results agree with the measurements very well. ost of all, the influence of the walking beam system on the skid marks is thoroughly explored. The simulation results show that the radiative shielding by the static beams is the main cause of the skid mark. The heat loss through the skid button to the cooling system worsens the skid mark. A parametric study then shows by shifting the static beams inward in the soaking zone, the skid mark gets even worse due to an enhanced radiative shielding on the lower surface of the slab in between the two static beams; the skid mark on the opposite can be improved by shifting the static beams outward in the soaking zone. Another parametric study shows the skid mark can also be improved by increasing the height of the skid button.
Subjects
slab
reheating furnace
radiative shielding
skidmark
Type
thesis
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