关键词: 氢气泄漏, 理论模型, CFD, Froude数, 射流

Abstract: 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 Fr_den=500 is almost linear,indicating that this is a momentum dominated jet.The decay curve for Fr_den=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 Fr_den=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 Fr_den=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 Fr_den=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.

Key words: hydrogen leak, integral model, CFD, Froude number, jet