Unsteady numerical simulation of circulation and heat transfer in a glass melting tank

Various numerical simulations are currently available for the representation of flow and heat transfer in glass melts. Increasing computer performance allows 3D complex simulation coupled with electrical boosting, flame radiation heat transfer, chemical reaction, bubbling, etc. We present the numerical results of unsteady modeling of glass flow and heat transfer in the glass melting tank. The use of finite-element spatial discretization decreases the total number of degrees of freedom required to achieve acceptable accuracy, while efficient integration schemes (implicit predictor-corrector) lead to time step sizes which reduce the number of solutions even for studies of long term duration. First, different variations on the TC21 test-case (modification of the pull rate, thermal boundary profiles) are performed. This reference situation was selected by the 21st Technical Committee of the International Commission on Glass. Following this, a reduced-scale mixed electrical-fuel furnace is studied, allowing the modeling of unsteady boosting heat transfer. Finally an unsteady advection-diffusion problem is solved to represent the mixing of two different types of glasses. The interest in unsteady modeling is two-fold: (1) the accurate time evolution of flow and temperature sheds light on the structure and stability of the flow related to a given set of physical properties and boundary conditions; and (2) the transient solution gives reproducible and inexpensive information for the definition of a control process. The main result of this study is the clear distinction between kinematic and thermal time constants and the feasibility of direct exchanges between unsteady simulation and control models.