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Show In a first set of calculations, a uniform effective temperature Tgl = 26000 F (1700 K) and an effective emissivity of €gl = 0.88 were used for the whole glass surface. The value used for fgl corresponds to the greys hemispherical emissivity of a transparent glass sheet with infinite optical thickness and a refrac tIve index of 1.7 (Ref. 11). The second set of calculations was carried out by calculating effective temperatures of the glass surface with help of a simple heat conduction model into the glass. It is assumed that temperatures of the glass are uniform (2410oF = 1600 K) in a horizontal plane located at a certain vertical distance into the bath. A uniform effective ratio of conductance to thickness of the glass layer was then determined so, that the area-weighted effective glass surface temperature was 1700 K (2600F). The surface emissivity used in this approach was again €gl = 0.88. It is believed, that use of a uniform value for glass surface temperatures simulates closer conditions for a transparent glass, where as the second way to calculate boundary conditions, is more representative for a darker glass. Both approaches are certainly very approximate. However, it has to be pointed out, that predictions of relative performance changes for the air and 02-system can still be accurate provided similar incident heat flux distributions at the glass bath can be achieved in the 02-system by appropriate burner selection, placement and operation. INPUT DESCRIPTION AND CASE DEFINITIONS Furnace Description 'Il,,,- glass f urnace investigated in this study is d.e :;igned for a pull rate of 350 TPD. The furnace is cross-fired and is currently operated with natural gas using regeneratively heated air as oxidizer. A horizontal cross-section of the furnace is shown in Fig. 3. The furnace is 27.2 ft (8.28 m) wide and 49.6 ft (15.11 m) long. The distance between glass surface and crown is 8.7 ft (2.64 m). Each of the five ports of each furnace side is equipped with two pipe burners with 2.3" nozzle diameters. The burners point from each port side at an angle of 47 degrees relative to the port axis and produce five long flames which extend over the whole furnace width. The time between a switch of the burners of one side to the opposite side is 30 min. oxy-fuel Burner The Linde "A" Burner, patented by Union Carbide Industrial :- Gases Inc., was chosen for the oxy-fuel firing cases. The burner -"~offers high momentum low £ l ame temperature characteristics 8 |
