Sub-cooled and flashing liquid jets and droplet dispersion II. Scaled experiments and derivation of droplet size correlations

This paper describes the results of the first stage of Phase III of a Joint Industry Project (JIP) on liquid jets and two-phase droplet dispersion. This stage included scaled experiments for water, gasoline, and cyclohexane for a range of superheats and nozzles with different aspect ratios. Additional experiments for butane and propane were conducted as a validation exercise and are discussed in the companion paper. Moreover this paper provides recommendations for atomisation correlations in the regimes of mechanical break-up, transition to flashing, and fully flashing. The objectives of this scaled experimental programme are to : (i) provide confidence in the previously proposed modelling methodology (Phase II) across a broad range of initial conditions (ii) update the models’ correlations to generalise further its applicability (iii) recommend further model improvements. Development of new correlations for Sauter Mean Droplet diameter (SMD) and droplet size distribution is based on a best fit of the current scaled experimental data. The new data endorses the previous tri-functional Phase II approach including regimes for mechanical break-up, transition to flashing, and fully flashing, which is hence updated in the new Phase III SMD model. Considerable effort is devoted to capturing the full droplet size range under low-superheat conditions. Also, new enhancements in PDA technology were adopted to enable better quality data under high-superheat conditions. The priority recommendation for further model improvement is better characterisation of the poor quality releases under low-superheat conditions, where this work indicates that extremely broad droplet size distributions are likely. A companion paper (Part I) presents a more general overview of the dispersion problem, implementation of the correlations and subsequent performance against both the current scaled experiments and additional large-scale butane experiments.     

Two-phase jet releases,droplet dispersion and rainout I. Overview and model validation

Many accidents involve two-phase releases of hazardous chemicals into the atmosphere. This paper describes the results of the fourth phase of a Joint Industry Project (JIP) on liquid jets and two-phase droplet dispersion. The objective of Phase IV of the JIP was to generate experimental rainout data for non-flashing experiments, and to develop recommendations for the best methodology to predict rainout [total rainout mass and its spatial distribution (‘distributed’ rainout)].Phase IV of the JIP first included rainout experiments by the UK Health and Safety Laboratory (HSL) for sub-cooled releases of water and xylene with a range of orifice sizes and stagnation pressures. See the companion paper II for further details. Secondly model validation was carried out by DNV Software for these experiments using different correlations for the initial droplet size (Sauter Mean Diameter, SMD), i.e. the CCPS SMD correlation and the Phase III JIP SMD correlation. The validation includes flow rates, droplet size, distributed rainout and cloud temperature drop. Subsequently validation was considered for a wider range of experiments from the literature (sub-cooled and superheated releases) for both SMD and total rainout. Adopted rainout methods comprised both methods including explicit modelling of the droplets (using an extended version of Phast dispersion model UDM), as well as more simple methods based on rainout correlations without droplet modelling. Recommendations are made for the most accurate droplet size and rainout modelling. A modified CCPS UDM droplet size correlation has been shown to agree best against experimental rainout data.     

Two-phase jet releases,droplet dispersion and rainout,II. Rainout experiments

This paper describes the results of the first experimental stage of Phase IV of a Joint Industry Project (JIP) on liquid jets and two-phase droplet dispersion. The objective of this stage of the JIP was to generate experimental rainout data for non-flashing water and xylene experiments. See the overview companion paper I for a wider overview of the problem, model implementation and associated model validation.A range of orifice sizes (2.5 and 5 mm) and stagnation pressures (4–16 barg) were applied. Measurements included flow rate, initial droplet size, plume concentrations/temperatures for a range of downstream locations, and distributed rainout.Instead of the Phase Doppler Anemometry method used for droplet size measurements earlier in the JIP, a photographic technique was applied in an attempt to include measurement of the larger (non-spherical) droplets. This enabled a more accurate evaluation of the initial droplet size distribution and a much clearer understanding of the droplet morphology. The results showed that the droplet behaviour in the jet is more complex than had been anticipated with the mass distribution dominated by a very small number of large non-spherical droplets. Consequently a large number of spray images were required to evaluate an accurate size distribution.Distributed rainout was measured by weighing the amount of rainout in trays positioned along the jet direction. The rainout results showed a good degree of repeatability and internal consistency. They indicated that an increasing proportion of the released material did not rainout for increasing pressure. Rainout distance also increased with increasing pressure. Evaporation of the liquid was confirmed by temperature measurements, which showed the effect of evaporative cooling.Xylene concentration measurements (up to 1%) were carried out using a direct reading photoionization detector calibrated for xylene (measuring vapour only). For a limited dataset, the accuracy of these measurements was estimated by means of comparison against an alternative more time-consuming concentration method (xylene absorption onto a charcoal filter; measuring both vapour and liquid). The concentration measurements displayed several consistent qualitative features. For example, at a given downstream distance, the peak concentration increases with increasing pressure and nozzle diameter and the vertical height at which the peak is achieved increases. The cross-stream profiles displayed a consistent tendency to increased concentration at the edge of the jet, and the reason for this has not been established.Finally recommendations are provided for potential future work.     

B／S模式下基于角色的权限管理系统设计与实现

结合基于角色的访问控制的原理,实现了一个基于Struts框架B/S模式的权限管理系统.该系统围绕用户、角色、功能、单位等基本定义以及它们之间的关系进行模块编码,实现了灵活、实用的基于角色的权限管理功能,达到了页面级别的权限控制.利用Struts配置文件,隐藏了系统的文件结构,提高了系统安全性.同时利用过滤器技术,通过重载Filter接口,可有效拦截直接在IE的地址栏中输入内部页面地址的访问.实际应用表明,该系统具有很好的可扩展性和通用性.     

An integrated quantitative hazard analysis method for natural gas jet release from underground gas storage caverns in salt rock. I: Models and validation

It is very important and necessary to perform quantitative hazard analysis for possible accidental leakage from an underground gas storage cavern in salt rock. An integrated quantitative hazard analysis method for natural gas jet release from salt caverns is presented in this paper, which was constituted by a revised model for gas leakage rate calculation, a consequence analysis and a model of probability assessment for harm. The presented method was validated by comparing the analytical results with the data collected from the real accidents (including the leakage, jet fire, fireball and vapor cloud explosion). It is indicated that the proposed method was more accurate than the TNT equivalence method for vapor cloud explosion and gave more reasonable results when applied to the consequence analysis for the thermal radiation from jet fire and fireball.     

The development of a more risk-sensitive and flexible airport safety area strategy: Part I. The development of an improved accident frequency model

This two-part paper presents the development of an improved airport risk assessment methodology aimed at assessing risks related to aircraft accidents at and in the vicinity of airports and managing airport safety areas (ASAs) as a risk mitigation measure. The improved methodology is more quantitative, risk-sensitive, flexible and transparent than standard risk assessment approaches. As such, it contributes to the implementation of Safety Management Systems at airports, as stipulated by the International Civil Aviation Organisation.The first part of the paper presents the methodological advances made in the development of accident frequency models; namely the building of a single comprehensive database of all relevant accident types, the collection and use of normal operations data in quantifying the criticality of a series of risk factors, and modelling accident frequency using multivariate logistic regression. The resulting models have better goodness-of-fit, sensitivity and specificity than standard risk assessment methodologies.