Numerical Research On Medium-Scale Combustion Of Lean Hydrogen Gas

When severe accident happened in nuclear power plant,the temperature of fuel corium and fuel cladding in reactor vessel and spent fuel pool will increase rapidly because of insufficient cooling,then the zirconium cladding with high temperature will react fiercely with coolant and release hydrogen gas.As the amount of hydrogen gas generated is very large,the hydrogen may mix with air in the containment and auxiliary building or some confined spaces,which will threat the safety of equipment and containment integrity when the mixture ignited,so it's very important to investigate the medium-scale combustion regimesIn this paper,the hydrogen combustion research situation is introduced at first,which includes main experiments,hydrogen combustion simulation codes and it's validations against experiments.The theory on hydrogen deflagration and the state of the art on criteria of flame acceleration(FA)and deflagration to detonation(DDT)in large scale geometry are introduced.At last the hydrogen combustion simulation model used in this paper and its equations was presented.The validation of combustion simulation model is the basis for numerical research,the open THAI-HD12 and ENACCEF-RUN153 experiments are chosen as validation experiments.According to the comparison and analysis between simulation results and experimental results,the curve of pressure versus time,the heat losses,flame propagation shapes and flame propagation speed and phenomenon of flame acceleration got a good agreement with experiment.The validation case showed that the combustion model can used for hydrogen combustion simulation.The concentrations of hydrogen and ignition location have a significant influence on hydrogen combustion,according to simulation and analysis,as the concentration of hydrogen goes up,the pressurization speed,the peak pressure,the peak temperature and flame propagation speed will increase.The middle ignition location will increase combustion speed when the concentration is near high,the bottom ignition location will increase combustion speed when the concentration is near low,and the top ignition location will quench the flame when the concentration of hydrogen is too low.The obstacles is another major effect that affect hydrogen combustion,different arrangement of blocks in combustion chamber will lead to different combustion regime at the same hydrogen concentrations and ignition locations.In this paper,lean hydrogen combustion in chamber with four different obstacles arrangements are simulated and analyzed,which includes different obstacle sizes,different obstacles numbers,different obstacles location arrangement and different obstacles shape.According to analysis,the hydrogen will combust more rapidly as the blockage of obstacles increase;the number of obstacles will affect lean hydrogen combustion except very-lean hydrogen,the effect is significant when the number of obstacles is small and the effect is disappeared when the number of obstacles get large;arranging the obstacles in the middle of the chamber will improve the combustion rate of hydrogen;as the shape of obstacles get smaller and number of obstacles get larger,the combustion rate will increase and then decrease.