氢气泄漏过程的理论模型计算及CFD模拟

Integral model and CFD simulations for hydrogen leaks

采用Fluent数值模型虽然可以较为准确地预测氢气泄漏后的扩散和运动规律,但是建模及计算时间较长。提出一种新型理论模型,可以在很短时间内预测氢气泄漏的扩散和运动规律,适用于应急处理。为了探究理论模型的准确性,还建立了二维和三维的CFD模型进行计算。对不同尺寸泄漏口的水平和竖直方向的两种射流进行了研究,计算了氢气泄漏时射流轮廓及摩尔分数分布,预测了基于可燃极限计算的储罐周围的安全区域。比较了氢气射流的理论模型和CFD模型计算结果,并且与前人的实验结果做了比较,吻合度很好。研究还发现Froude数较高的射流是动量控制的射流;而较低情况下有射流很强的浮升力效应,氢气的摩尔分数下降速率加快。

With increasing concerns for environmental and pollution problems the world is currently facing,hydrogen is being widely used to reduce our dependence on imported oil and to reduce pollution from vehicles.Hydrogen is the lightest gas and very diffusive.It easily leaks from storage tanks and disperses into the air.Fluent can accurately predict the concentration fields and flammability contours for hydrogen leaks,but building the model and running simulations both take much time.The integral model presented here can very quickly compute the trajectory of the hydrogen jet and the hydrogen concentration decay along the jet trajectory,hence it can be used to deal with emergencies.This study compares the integral and CFD models for low pressure,slow leaks with previous experimental data and then uses these models to predict safety zones around tanks based on the flammability limits of various expected size leaks for both horizontal and vertical leaks.The results show that the hydrogen molar concentration decay rate curve for Frden=500 is almost linear,indicating that this is a momentum dominated jet.The decay curve for Frden=50 is strongly influenced by the buoyancy induced entrainment so the hydrogen concentration decays much faster with the hydrogen concentration reaching the 4% molar concentration,the flammability limit,by S/D equal to about 130,which would be less than 30 cm.The lengths of the jets in both the horizontal and vertical directions predicted by the integral model are proportional to the orifice diameter.The CFD model is also used to predict the jet profiles for a variety of conditions for both 2D axisymmetric and 3D jets.The jet profiles predicted by the CFD model are compared with the integral model results for a vertical jet with Frden=268 and an orifice diameter of 1.905 mm.The 4% flammability limit predicted by the CFD model is slightly larger than that predicted by the integral model.The centerline molar concentration profiles predicted by the 2D and 3D models agree well with the experimental data.The three-dimensional CFD model is then used to predict the jet profiles for horizontal jets.The centerline molar concentration predicted by the 3D model for Frden=100 and a 1.9 mm diameter orifice show that the flammability envelope extends less than 0.5 m from the orifice and to a height of less than 0.4 m.The centerline molar concentration for Frden=100 and a 1.9 mm diameter orifice show that the flammability envelope extends 0.8 m from the orifice and is almost horizontal since such a large Froude number gives a momentum dominated jet.