Application of CFD in vacuum dezincing process

Most lead bullion is refined by pyrometallurgical methods - this involves a serics of processes that remove the antimony (softening) silver (Parkes process), zinc (vacuum dezincing) and if need be, bismuth (Betterton-Kroll process). The first step, softening, removes the antimony, arsenic and tin by air oxidation in a furnace or by the Harris process. Next, in the Parkes process, zinc is added to the melt to remove the silver and gold. Insoluble zinc, silver and gold compounds are skimmed off from the melt surface. Excess zinc added during desilvering is removed from lead bullion using one of ghree methods: * Vacuum dezincing; * Chlorine dezincing; or * Harris dezincing. The present study concentrates on the Vacuum dezincing process for lead refining. The main aims of the research are to develop mathematical model(s), using Computational Fluid Dyanmics (CFD) a Surface Averaged Model (SAM), to predict the process behaviour under various operating conditions, thus providing detailed information of the process - insight into its reaction to changes of key operating parameters. Finally, the model will be used to optimise the process in terms of initial feed concentration, temperature, vacuum height cooling rate, etc.

Fatal impact? The effects of emotional arousal and weapon presence on police officers' memories for a simulated crime

Purpose. (1) To investigate the effects of emotional arousal and weapon presence on the completeness and accuracy of police officers' memories; and (2) to better simulate the experience of witnessing a shooting and providing testimony. Methods. A firearms training simulator was used to present 70 experienced police officers with either a shooting or a domestic dispute scenario containing no weapons. Arousal was measured using both self-report and physiological indices. Recall for event details was tested after a 10-minute delay using a structured interview. Identification accuracy was assessed with a photographic line-up. Results. Self-report measures confirmed that the shooting induced greater arousal than did the other scenario. Overall, officers' memories for the event were less complete, but more accurate, when they had witnessed the shooting. The recall and line-up data did not support a weapon focus effect. Conclusions. Police officers' recall performance can be affected both qualitatively and quantitatively by witnessing an arousing event such as a shooting.