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Show UTILIZATION OF A NUMERICAL MODEL FOR THE DESIGN OF A GAS IMMERSION TUBE Marc Perrin, Philippe Lievoux Gaz de France Research and Development Division Paris, France PRESENTATION OF THE APPLICATION RATIONAL UTILIZATION OF ENERGY - The rational utilization of energy has become an economic necessity. As regards the utilization of gas fuels in high temperature industrial furnaces, the complexity of the aerothermal phenomena to be modelized requires the use of large scale computer resources. Only those applications with a high added value (propulsion units, large luminous flames ••• ) make use of these calculation methods. New heating equipment in the metallurgy industry was therefore developed using empirical and experimental procedures. However, the cost of the tests that had systematically to be carried out in order to improve the equipment and define a product range grew very high, and the phenomena involved were not well understood. For this reason GAZ DE FRANCE decided to collaborate with the research scientists of the CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE (U.A. nO 230 in ROUEN) to gain assistance in the application of recent research work. The studies resulted in the development of a computer program comprising three two-dimensional models. It is used to determine flow and the heat transfers (convection and radiation) which accompany this flow. THE APPLICATION PRESENTED - The first application that was chosen is a gas immersion tube to be used to maintain at melting point a bath of molten zinc for the galvanization of steel parts. It is illustrated in Figure 1. The equipment is comprised of a high velocity selfrecuperative burner which injects the combustion products at high speed into a recirculating tube. The depression created by the jet draws in, through the free space between the burner and the tube, a portion of the combustion products returning to the recuperator after heat exchange with the ceramic shell. It is this phenomenon which is known as "recirculation". The shell is directly immersed in the zinc bath. This heating method will be used to modernize the ceramic tank galva- 127 Roland Borghi, Michel Gonzalez Centre National de la Recherche Scientifique U.A.n° 230 Rouen, France nization furnaces heated by a radiant roof. The objective is to improve the combustion efficiency and to decrease the heat gradient in the bath. A decrease in metal loss through oxidation should also be achieved as the combustion products will no longer be in contact with the zinc. Burner protection High-velocity metal burner Recirculating tube • Air and fuel input ~ Circulation of combustion products Fig. 1 - Diagram of single-ended immersion tube THE NUMERICAL METHOD THE EQUATIONS OF THE PROBLEM - The system to be solved is that constituted by the unsteady two-dimensional equations of conservation of : - mass : (1 ) op 0_ --+--p u~ ot ox~ o |