Experimental Study And Numerical Simulation On Oxygenation Performance Of Fine-bubble Diffusing Aeration System

The rapid development of economy and technology has triggered a series of water environmental problems,such as maken water eutrophication,black and smelly.Oxygenation is one of the important methods to solve these water environment problems.In many aeration facilities,the fine-bubble diffusing(FBD)aeration system is more and more widely used in practical engineering because of its better oxygenation performance,but there are still many problems in its application process,such as:(1)What factors do influence on the oxygenation performance of the system and how is the influence of these factors?(2)In past studies,most of them were conducted in static clean water.While in actual engineering,there were mostly flowing water containing organic substances.Therefore,there will be errors in the extrapolation of research results into the field.(3)Although consensus has been reached,the oxygen mass transfer of the FBD aeration system mainly results from the mass transfer at the bubble-water interface and the turbulent mass transfer of the free liquid surface driven by the rising bubbles.However,research on the contribution of two kinds of mass transfer to oxygenation has lacked data and theoretical support so far.(4)The test method has the disadvantages of time-consuming,labor-consuming,and limited measurement range.When extrapolated to field sites,the studies of aeration and oxygenation performance still lack scale effect.Therefore,it is more important to construct the numerical simulation technology.In response to the current problems,a FBD aeration system and the aeration test device were built indoor:(1)A large number of experimental studies have been conducted on the influence factors of internal factors,such as aeration flow rate,diameter of aerator pipe,shape of diffuser,and outer factors,such as submergence depth,flow characteristics of water,and water quality.(2)Through the laying of film at the top of the pool and the bubble filming techniques,the two oxygen mass transfer methods were tested and analyzed.(3)A finer numerical simulation of the FBD aeration system was established.The experimental results were used to determine and verify.And a series of scenarios were set up to predict the velocity field of water under different air flow rates.Combined with laboratory experiments and numerical simulation techniques,the following conclusions were obtained:(1)With the increase of the aeration flow rate,the oxygenation effect of the fine-bubble diffusion aeration system increasd.(2)The linear-type diffuser had the best oxygenation performance,followed by the C-type and the disc-type,and the worst is the S-type.(3)The aeration tube with a diameter of 25 mm x 12 mm had the highest oxygenation efficiency,rather than the commonly used 16 mm x 10 mm size aeration tube.(4)For shallow water,the oxygen mass transfer coefficient decreased with the increase of submerged water depth.(5)The oxygenation performance of smooth flowing water was better than that of static water,and it was worse than the case where there are obstacles in the flowing water to constantly produce bubbles.(6)The oxygen mass transfer coefficient and the correction coefficient showed a trend of increasing first and then decreasing with the increase of the anionic surfactant concentration.The presence of anionic surfactants reduced the average diameter of the bubbles and hindered the deformation of the bubbles.(7)The presence of the thin film reduced the oxygenation efficiency of the fine-bubble diffusion aeration system.The linear-type diffuser had a higher rate of decline than the disc-type.With the increase of the aeration flow rate,the decrease rate increased,and the submerged water depth was the opposite.(8)The number,density,Sauter average diameter,and velocity of bubbles increased linearly with the increasing aeration flow rate,but the specific surface area was the opposite.With the change in aeration flow rate,the shape of the bubble did not change and was a flat oval shape.(9)The aeration phenomenon map,flow velocity cloud map obtained by numerical simulation and the field test phenomenon were close to each other,so the effect of numerical simulation was better.The research results of this paper will provide a good reference for the green and low-carbon promotion and application of the FBD aeration system in the actual water.