Ventilation theory and dispersion modelling applied to hazardous area classification

Critical formulae given in the current Explosive Atmospheres Hazardous Area Classification Standard IEC 60079-10-1 (2008) [BS EN 60079-10-1, 2009] to determine the expected gas cloud volume which is used to determine area classification do not have any scientific justification. The standard does allow the alternative use of Computational Fluid Dynamics (CFD) methods, which serve to compound the concern with these formulae: the predicted volume of the gas cloud from CFD models being several orders of magnitude smaller than that given by the formulae in question. To resolve such major discrepancies, replacement of the current formulae with a scientifically validated approach is proposed. Integral models of dispersion and ventilation have been used routinely for many years in the analysis of major hazards in the chemical industry. This paper presents an adaptation of these models to determine the expected volume of a gas cloud arising from a release of gas from a pressurised source. A very simple integral jet model is presented for outdoor dispersion, extended to the case of indoor dispersion, from which the volume of the gas cloud is derived. The single free parameter, an entrainment coefficient, is fixed by comparison with data on a free jet, and then predictions of the model are compared with CFD calculations (which themselves have been validated against experimental data) for dispersion within an enclosed volume. The results of this simple integral model are seen to agree very well with the CFD predictions. The methodology presented here is therefore proposed as a scientifically validated approach to Hazardous Area Classification.     

多孔喷头射流特性的实验研究

在没有密度分层的容泄水体条件下,对某污水排海工程多孔喷头的射流特性进行了实验研究。文中介绍了不同排污流量和环境流速条件下,多孔喷头附近的流速场和污水场特性;并对出流平均稀释度作了分析。最后,还对该喷头周围的冲淤形态进行了探讨.文中所得的结果对实际排污系统的设计和进一步研究有一定的参考价值。      

宽间距立式电除尘器的研究

在 1m×1m×21m的水槽底部安装模型喷口形成水平周向射流,在没有浮力的情况下试验研究流速和水深对射流扩散的影响,结果表明射流近区稀释度基本随着流速的增加而线性增加,在大多数情况下,稀释度也随着水深的增加而增加。