Study On Bubble Size And Mass Transfer Performance Of New Venturi Bubble Geneartors

Compared with macro bubbles（>1000μm）,micro bubbles（1～1000μm）have the advantages of small size,large specific surface area,long residence time,fast dissolution rate,good surface adsorption,etc.,and are widely used in wastewater treatment,aquaculture,mineral flotation,molten salt nuclear reactor and other fields.In the field of petrochemical industry,the formation of microbubbles can increase the mass transfer area between gas and liquid phase,improve the mass transfer rate,and realize process strengthening.Venturi bubble generator relies on the high-speed liquid jet generated by the smaller throat to shear the broken gas,which is a relatively common microbubble generation equipment.In view of the shortcomings of Venturi bubble generator,such as large bubble size and high energy consumption,this thesis constructs and designs a new type of Venturi bubble generator through structural innovation research,in order to reduce bubble size,reduce pressure drop energy consumption and improve mass transfer rate.In this thesis,two types of new Venturi bubble generators（swirl-type Venturi bubble generators,double swirl-type bubble generators）are designed to optimize the structure.In N₂-water system,the influence of liquid flow rate,gas flow rate and structural parameters on the Sauter mean bubble size of bubble generators was explored by high-speed visualization method,and the pressure drop of bubble generators was measured.The Sauter mean bubble size and pressure drop of different types of bubble generator are compared to determine the optimal structure.On this basis,in the air-water system,the liquid phase volume mass transfer coefficient of bubble generators was measured by the dynamic dissolved oxygen method,and the comprehensive liquid phase volume mass transfer coefficient was calculated to further investigate the mass transfer performance of the optimal structure.The main research results are as follows:1.The Sauter mean bubble size decreases with the increase of liquid flow and increases with the increase of gas flow.Swirl-type Venturi has swirling wake,Sauter mean bubble size of this structure is 104.1%～224.6%of that of swirl-type Venturi with vortex breaking baffle.With d_th=16.3 mm,the Sauter mean bubble size in swirl-type Venturi with vortex breaking baffle which is a better structure are 36.0%～63.2%of those in typical Venturi.In the double swirl-type bubble generator,the reverse swirl structure eliminates the swirl wake,Sauter mean bubble size is 54.8%～98.3%of that of the same swirl structure,and the radial dispersion width is larger.2.The liquid volume mass transfer coefficient increases with the increase of liquid flow rate and gas flow rate.Among the typical Venturi,swirl-type Venturi and swirl-type Venturi with vortex breaking baffle,the swirl-type Venturi with vortex breaking baffle has the best mass transfer effect,and the smaller the throat diameter,the higher the liquid phase volume mass transfer coefficient.In the double swirl-type bubble generator,the volume mass transfer coefficient of the reverse swirl structure is 109.9%～127.6%of that of the same swirl structure,and the mass transfer effect is better.3.Among the typical Venturi bubble generator,swirl-type venturi bubble generator with vortex breaking baffle,and double swirl-type bubble generator,swirl-type venturi bubble generator with vortex breaking baffle has the lowest pressure drop,and the comprehensive liquid volume mass transfer coefficient increases by 8.7%～157.2%compared with typical Venturi,and the energy consumption cost is the lowest.Compared with Venturi bubble generator,double swirl bubble generator can reduce the pressure drop energy consumption and increase the comprehensive liquid volume mass transfer coefficient by 32.9%～68.7%under the condition that Sauter mean bubble size is the same.