Numerical Simulation And Optimization On Coupled Multi-field In A Tilting-type Aluminum Holding Furnace

The uniformity of temperature field in tilting-type aluminum holding furnace (shorted for aluminum holding furnace) is significant to the quality and productivity of the aluminum (or its alloy) ingots. So the uniform temperature field and reasonable heating schedule are helpful for improving the product quality, productivity and the energy efficiency. Moleing the temperature field gives scientific references for controlling the working conditions and prolonging the longevity of the furnace, and has guidance meaning to design, reform furnace equipment, and optimize the schedule parameters.The main conclusions and innovations of the paper are as follow:1) Numerical model for aluminum holding furnace has been built up based on FLUENT code combined with user defined program. The simulation of combustion, fluid-solid coupled heat transfer, and the gas stirring process in porous plug have been achieved for the first time, the flow field and temperature field in the combustion chamber as well as in the molten aluminum zone have been obtained.2) The computational results of the furnace have been analyzed, and the characteristic of temperature distribution has been obtained. The maximum combustion temperature is 1850K, the average temperature of molten aluminum is 1158K, and the maximum temperature difference in the melt zone is found to be about 250K. The difference in temperature of the whole molten aluminum space is less than 3K in the condition of gas stirring, and the high temperature zone is a small area. According as the measured data, the average error of calculative temperature of combustion space is 7%, and molten aluminum is 12.5%.3) The influences of operating parameters on the maximum combustion temperature and the average temperature of molten aluminum have been investigated in deep. The results show that the average temperature of molten aluminum increases 15℃ while the temperature of combustion-supporting air increases 50℃; the increasing rate of temperature is 7℃/(Nm3·h-1) which can be manipulated by the flux of natural gas; the optimal air excess ratio is between 1.25 and 1.30; the stirring effect is more intense, and the whole temperature of molten aluminum is more uniform while the flux of stirring gas increases.4) The optimized schedule of furnace has been made for the first time, and the optimal thermal system of the furnace has been obtained. The variation tendencies of average temperature of molten aluminum in different manipulations were calculated. The increasing rates of temperature 1.65℃·min-1 and the decreasing rates of temperature are 0.53℃·min-1 and 3.30℃·min-1, respectively, when burners were ignited for 40 minutes, burners were closed for 30 minutes and the door was opened for 10 minutes. Taking optimization of a real thermal process into account, the intermittent calefaction mode is superior to the continuous. Adopting high temperature of combustion air and relative large excess air ratio is an appropriate combustion mode which is reasonable and economical relatively.