Numerical Analysis of the Heating Zone of a Container Glass Annealing Furnace: Effect of Circulation Fan Speed on the Heating Effectiveness of the Furnace

Annealing is a heat treatment process commonly carried out in a continuous annealing furnace. While radiative heat transfer is the primary mode of heat transfer in annealing, convective heat transfer also makes a noteworthy contribution. In this numerical study, the effect of the circulation fan flow rate on the heating characteristics of the heating zone of a continuous glass bottle annealing furnace was studied. Heat transfer process is solved by modeling the convection inside the furnace and conduction in the solid glass in separate solvers and by coupling these solvers including radiation in an iterative scheme. The radiation heat transfer between the furnace walls and glass bottles is solved using an in-house developed graphic accelerated Monte Carlo ray tracing algorithm-based model. The glass bottle rows are included as porous zones in the furnace. The flow blockage due to the bottles and convective heat transfer between the bottles and furnace air are calculated using the average flow conditions inside each porous zone. Results clearly show the effect of the circulation fan volumetric flow rate on the shares of the radiative and convective heating mechanisms in the process. Increasing the volumetric flow rate enhances the convective heat transfer rate on the glass which results in lower furnace wall temperatures and it also leads to a considerably more uniform temperature distribution within the glass bottles at the zone outlet. The increased uniformity in the glass temperatures implies a reduction in the soaking zone length which would reduce the investment and operational cost of the furnace.