| Under serious accident such as main steam pipe rupture in nuclear power plant,there is a potential risk for radioactive iodine leak from containment to atmosphere.Due to the fatal detriment,the leak dose of radioactive iodine is limited strictly.Bubble filter which can provide considerable cross-section area and contact time between gas and liquid,has inherent advantage in decontaminating organic iodide that is difficult to filter.In this paper,experiment research,theoretical analysis and numerical simulation have been conduct in order to the performance characteristic of bubble filter and the relevant hydraulic process,and the major contents of the present research can be summarized as follow:1、The filtration process of bubble filter was analyzed theoretically and a calculation model for decontamination factor has been established on account of mass conservation.According to the calculation model,the filtration process is influenced by mass transfer resistance and chemical reaction resistance.The influences of operation parameters on decontamination factor have been studied experimentally and the influence of each parameter was analyzed by combiming the experimental results and calculation model.It suggests that in different operation parameter scopes,the parameter needed to be adjusted varies in order to improve decontamination factor.2、Based on numberical heat transfer theory and bubbling degassing characteristic,two numerical models have been established which are called as’bubble inflation filtration model’ and ’subtle bubble filtration model’ respectively.Making use of these bubbling degassing models,the influences of evaporation condition and evaporation caused phenomenon on bubbling degrassing have been analyzed.The influence mechanism of evaporation is that the methyl iodide concentration near bubble surface is According to bubble inflation model,the contribution of sensible heat to evaporation vanishes quickly in the initial stage of bubble formation.The expanding velocity due to temperature change and generated steam has negligible effect on mass transfer compared to diffusion process.Besides the amplitude of bubble diameter variance plays an inessential role in mass transfer.According to subtle bubble filtration model,the influences of bubble rise velocity,bubble diameter,steam concentration and liquid temperature on mass transfer attenuated by the steam caused by evaporation.Bubble size change and additional radial velocity have little effect on bubbling degrassing,which result from bubble temeperature decrease and evaporation.A new variable,which is called ’temperature difference ratio’,is proposed to describe the mass transfer rate weaken under different evaporation conditions.Based on Peclet number and temperature difference ratio,the calculation model for decontamination factor is improved to consider the influence resulting from evaporation.3、The bubble characteristic of multi-orifice plate has been studied by high speed photography in order to clarify the influence of structure parameters and operation parameters on the bubble characteristic including bubble coalescence,weeping and bubble detachment volume.According to experimental results,a calculation expression is proposed to calculate the bubble coalescence efficiency.An analytical model is established to study the bubble process of multi-orifice plate based on potential flow theory and the force balace acting on growing bubble.Due to the analytical model and experimental results,when bubble diameter is above 2 mm,increasing the pitch of orifice can suppress the occuration of bubble growth coalescence and weeping.Beyond that,a larger gas chamber and a higher number of opening orifice are favorable for the condition where working gas flow rate is below the transfer gas flow rate and the aeration performance is more excellent.4、Numerical simulation method is employed to study the gas holdup in non-coalescence media for a large orifice diameter and the influences of constructure parameter and operation parameter have been analyzed emphatically.According to the numerical results,the influence of bubble size on gas holdup is small enough to be ignored when bubble diameter is larger than 6 mm.In the vicinity of gas sparger,the local gas holdup distribution is in developing region in which the residence time of bubble in liquid is short and gas hold-up is small.Many influencing factors make the influence on gas holdup by changing the ratio of the height of developing region to submerged depth.Making use of numerical results and experimental results,the applicability of different classical gas holdup calculation expressions are evaluated and then a gas holdup calculation method was specified for the work condition of bubble filtration. |
