The numerical model for predicting the flow and temperature fields of the melt in holding furnace with porous brick purging system were set up using Euler-Lagrange approach. In this model, bubbles coalescence and disintegration were ignored based on the dimensionless analysis, and the bubble size was assumed to be obedient to Rosin-Rammler distribution with a mean size of 0.6 mm. The results show that on reference operating condition, during the heating and agitation process, melt mixes well in the furnace, and the melt velocity increases with the increase of gas flux. Holding the melt for 30 min causes the max temperature in the bulk melt to increase to 60 K. After holding the heat, the agitation processing restarts, and it takes 10 min for the stratified melt to retrieve the homogeneous temperature field when the gas flux is 10 L/min, which shows deficient alloying and degassing in the melt. With the increase of gas flux from 10 to 20, 30 and 40 L/min, the necessary recovery time decreases from 10 to 6, 5 and 4 min gradually, which shows the improvement of the stirring efficiency. Depending on the processing purposes, for both good degassing performance and gas saving, proper operating strategy and parameters (gas flux, primarily) could be adjusted.
For acquiring the details in aluminum holding furnace with bottom porous brick purging system, efforts were performed to try to find out the potential optimal operation schemes. By adopting transient analysis scheme and constant boundary temperature, combustion in the furnace was investigated numerically using computational fluid dynamics (CFD). The predicted gas temperature shows good agreement with the measured results, and the predicted energy distribution of the furnace is consistent with that obtained from energy balance experiment, which confirms the reliability of the numerical solution. The results show that as the fuel−air mixture temperature rises up from 300 K to 500 K, the energy utilization of the furnace could increase from 34.55% to 37.14%. However, as the excess air coefficient increases from 1.0 to 1.4, energy utilization drops from 34.55% to 29.56%. Increasing the combustion temperature is the most effective way to improve the energy efficiency of the furnace. High reactant temperature and medium excess air coefficient are recommended for high operation performance, and keeping the furnace jamb sealed well for avoiding leakage has to be emphasized.
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