화학공학소재연구정보센터
International Journal of Heat and Mass Transfer, Vol.38, No.12, 2183-2193, 1995
An Analysis of Freeze-Up Phenomena During Gas Atomization of Metals
A numerical model is developed to describe the flow and heat transfer behavior of molten metals during flow in the delivery tube in gas atomization and spray deposition. Numerical simulations for Al, Cu, Mg, Ni. Ti and W melt are conducted to investigate the influence of processing parameters and material properties on the minimum melt superheat that is necessary to prevent the tube from premature solidification during delivery of the molten metal prior to atomization. Processing maps are developed to provide direct insight into the complex relationship among the minimum melt superheat, processing parameters and material properties. A quantitative correlation is obtained by means of a regression analysis of the numerical results, which Facilitates application of the numerical model. The calculated results demonstrate that For the materials studied, the minimum melt superheat ranges from 0.005T(m) to 0.19T(m), depending on processing parameters and material properties. The dependence can be expressed using a correlation derived from the regression analysis such as [GRAPHICS] Increasing the overpressure can effectively decrease the minimum melt superheat, especially for a large tube-length : diameter ratio and for materials possessing low densities. This effect diminishes with increasing overpressure. The minimum melt superheat can also be decreased by reducing the tube length : diameter ratio, by selecting a smooth delivery tube with low thermal conductivity and thick tube wall, and/or by enhancing the ambient gas temperature. Materials with high thermal conductivity, high thermal capacity and/or large density allow a small melt superheat to prevent the delivery tube from freeze-up, while materials with high melting temperature and/or high viscosity require a large melt superheat.