Inhibition Of Hydrogen's Explosion Limits

At present,the most frequently used gas – as filling gas of aerostats – is helium,which is very hard to manufacture and extremely expensive.Meanwhile,hydrogen is much easier to manufacture and its market price is only one eighth of helium's,plus hydrogen has the smallest density.Naturally,hydrogen seems like the most ideal option of substitutes for helium.However,what restrained hydrogen from large-scale application is the fact that hydrogen is highly flammable and explosive.Hydrogen has a very low minimum ignition energy?about0.02mJ?and a very wide range of explosion limits?4% – 75%?.To replace helium with hydrogen as filling gas of aerostats,the explosion limits of hydrogen must be inhibited.After analyzing the main factors that can influence the explosion limits of hydrogen,a decision was made that adding inhibitors into hydrogen to inhibit its explosion limits.And theoretical researches on the mechanisms of different materials' inhibition effect on hydrogen's flammability,leads to the choices of inhibitors.Then researchers established the test platform for explosion limits of the “inhibitor-hydrogen” mixture in air,and analysis of experimental data is key to the safe usage of hydrogen.The mechanisms of different materials' inhibition effect on hydrogen's flammability basically includes two ways – physical thermodynamics and chemical reaction kinetics.Inert gases' inhibition effect is mainly through the former one,while non-flammable halogenated alkane gases' and flammable unsaturated hydrocarbon gases' impact is mostly through the latter one.Eventually,this thesis chose three different inert gases?He,N₂ and CO₂?,four different non-flammable halogenated alkane gases?CHF₃,CHClF₂,CH₂FCF₃ and C₂HF₅?and some mixtures of these two kinds as candidate inhibitors.The test results show that,out of the previous three inert gases,CO₂ has a best inhibition effect because of its comparatively largest heat capacity.Generally,non-flammable halogenated alkanes can inhibit hydrogen'sflammability much more effectively than inert gases.And the inhibition efficiency of binary mixtures varies with different concentration ratios of the two components.Following the review of experimental data in different groups,a regulation was found out that with the same number of carbon atoms,the inhibition effectiveness of different halogenated alkanes is directly related to the reaction rate between them and active center radicals of combustion chain reaction.What's more,an appropriate method is used to evaluate the explosion limits of ternary mixture consisting of two different non-flammable inhibitors and hydrogen,and the precision turns out very acceptable.Because hydrogen is the lightest gas,adding inhibitors into it will definitely cost some buoyancy.Under the premise of controlling buoyancy loss,it's important to obtain the best inhibition effect as possible.After comparing the explosion limits of mixtures that are made up of inhibitor and hydrogen at highest mixing ratio?under a certain ratio of buoyancy loss?,CHF₃ is the best inhibitor for hydrogen among all the inhibitors brought up in the thesis.When a 20-percent-limit of buoyancy loss is required,the range of explosion limits of the CHF₃–H₂mixture can be narrowed down to 5.39% – 58.12%.