A new methodology to estimate the gas ascending time from underwater gas releases

Accidental subsea gas releases can pose a threat to people, equipment, and facilities since gas can be toxic or flammable at the concentrations in which the leak occurs. The accurate prediction of the behavior of the gas plume formed in the leaks can be fundamental to the development of techniques of accident prevention or, in some cases, remediation measures, avoiding the emergence of more serious consequences. Among the different ways to analyze the behavior of gas plumes formed underwater, the Computational Fluid Dynamics (CFD) tool stands out for allowing the study of plume behavior to be done in a safer, simpler, and less expensive way, if compared to experimental studies. Inspired by the accidental release of the subsea gas scenario, this work validated a CFD setup of a 2D two-phase air–water flow using the VOF method in Ansys Fluent. The use of the VOF method differs this work from other works that use a hybrid Eulerian–Lagrangian methodology to model such types of flow. In this validation, simulations with a 9 m base tank, and 7 m water depth, and 0.050, 0.100, and 0.450 m${}^3$/s gas flow were performed. The simulated data were compared to experimental results available in literature. After the validation of the setup, a study was carried out varying the size of the leak to 0.24 and 0.17 m, and the gas flow from 0.006 to 0.150 m${}^3$/s aiming to verify how some plume characteristics are affected by the changes. Finally, following the directions from literature for analyzing the ascending gas behavior, and combining it with a dimensional analysis of the data, we proposed a mathematical model for calculating the gas ascending time using only properties of the gas leak. With future modifications of the proposed methodology, we hope that soon it will be possible to simulate gas releases under more realistic conditions. Even so, the findings of this work are already a significant step forward in the study of underwater gas releases.     

非离子表面活性剂对菲在水/土壤界面间吸附行为的影响

比较研究了不同浓度非离子表面活性剂TX 10 0存在下 ,4种土壤对菲的吸附作用 .研究表明 ,TX 10 0浓度小于 2CMC时 ,有机碳含量 (foc)分别为 5 1× 10 3 mg kg、1 2 8× 10 4 mg kg的土壤对菲的吸附作用增强 ,即K d Kd 比值大于 1,且随TX 10 0浓度的增大而增大 ;foc分别为 3 31× 10 4 mg kg、6 4 8× 10 4 mg kg的土壤 ,则降低土壤对菲的吸附作用 ,即K d Kd 比值小于 1,且随TX 10 0浓度的增大而减小 .当加入的TX 10 0浓度大于 2CMC时 ,则明显降低土壤对菲的吸附作用 .菲的K d Kd 比值随土壤有机碳含量的增加而降低 ,而表观有机碳标化的吸附系数K oc 则随TX 10 0浓度的增大而减小 .影响机理由吸附态和溶解态的TX 10 0分别对菲的吸附作用和增溶作用决定 .