Research On Bubbling Characteristics Of The Multi-orifice Plate

When sever accident occurred,filtered containment venting system can reduce the risk of leaking the radioactive material into environment dramatically.As a kind of wet filter which possesses large heat capacity and dusk capacity,high reliability etc.,bubble filter has the ability of filtering the radioactive gas which is difficult to decontaminate such as methyl iodide and has been applied in filtered containment venting system.The multi-orifice plate is the key component of bubble filter,which has many advantages: simplicity of construction,lack of mechanically operated parts,low energy input requirements and similarity.In this work,a set of visual experiments have been conducted.Refer to the experimental results,a theoretical model describing the bubbling characteristic of multi-phase plate is proposed which is employed to guide engineering design.This paper focuses on bubble coalescence,weeping phenomenon and bubble detachment volume,all of which play an important influence on the aeration performance of gas sparger.The studied independent variables are component of two types,the structure parameters of multi-orifice plate including orifice diameter,the pitch of orifices,the number of open orifices,plate thickness,gas chamber volume and condition etc.and the operation parameters including gas flow rate,solution temperature,the submersed depth of gas sparger and so on.According to the results of visual experiments,the bubble coalescence behaviors near gas sparger have been classified.A reasonable statistic method for coalescence efficiency is proposed based on the types of bubble coalescence.Bubble coalescence increases obviously as gas flow rate increases or the pitch of orifices decreases.The number increase of open orifices strengthens the perturbation near gas sparger which suppresses bubble coalescence.The suppressing effects resulted from various additives have significant differences from each other.The solution containing volatile solute possesses the strongest suppressing effect.Ca number and Bo number are employed to define ‘coalescence time' and coalescence efficiency and coalescence time possesses logarithmic relation.A calculation expression is obtained by making use of the experimental results.The duration of weeping is no more than 30 min.When weeping ended up,the gas chamber is full of liquid where the bubbling of multiply orifices is suppressed and the aeration performance of gas sparger becomes worse.Bubble coalescence has a significant influence on weeping rate.The coalescence efficiency increases with decreasing the pitch of orifices which leads to the increase of weeping rate.When the submerged depth of multi-orifice plate is over 1cm,the submerged depth has little effect on weeping rate.The variation relation of weeping rate with gas flow rate,the number of open orifice and plate thickness is not monotonous.The weeping rate first increases and then decreases as one of these three parameters increases.Bubble detachment volume depends on the pressure variation of gas chamber which is determined by the relative relation between gas chamber volume and gas flow rate.When the pressure variation of gas chamber belongs to constant pressure region,bubble detachment volume is free from gas flow rate.But when the pressure variation of gas chamber belongs to transition region,bubble detachment volume increases with gas flow rate.There is a transformational gas flow rate acting as the boundary between constant pressure region and transition region.This transformational gas flow rate increases as the number of open orifices increases.In this paper,a calculation expression for coalescence efficiency and a theoretical model describing bubbling and weeping are proposed.Making use of the calculation expression and theoretical model,bubble coalescence and weeping phenomenon can be avoided effectively and the pressure variation of gas chamber belongs to constant pressure region.