The Digital Image Analysis Technique For The Determination Of Bubble Size Distribution In Liquid Phase

Gas liquid two-phase system has been widely used in chemical,food,medicine,energy,environmental engineering and other industrial processes.Mass transfer and reaction efficiency can be improved by increasing the gas-liquid interfacial area under certain conditions.However,it is difficult to determinate gas-liquid interfacial area accurately.Quantifying the bubble size distribution is a reasonable way to measure gas-liquid interfacial area.Presently,there are many kinds of methods to measure gas-liquid interfacial area,including Phase Doppler Analysis technique(PDA),Interferometric Particle Imaging(IPI),Capillary Suction Probe technique(CSP)and.Among them,PDA and IPI are more complex and difficult to operate,CSP may disturb the formation and movement of bubbles by changing the flow field in the system.Therefore,Digital Image Analysis technique(DIA)is employed in measuring the bubble size distribution in the gas-liquid system.Firstly,air and water are used as gas-liquid system.The images of the bubbles at a range of superficial gas velocities are recorded by using a high speed camera with lighting emitting diode(LED)as a light source.Then,the images are preprocessed and converted into binary images by employing Matlab.Thus,the perimeters and the areas as the factors of the roundness are extracted to classify the bubbles into overlapping and solitary bubbles.The solitary bubbles are separated to prevent the software segmenting them mistakenly.And the overlapping bubbles are segmented into the solitary bubbles by using an improved watershed algorithm(IWA)based on the topological theory.Finally,the size distribution of all the bubbles at different gas velocities is achieved by the use of the formula.The gas hold-up and gas-liquid interfacial area are then calculated in terms of the size distribution.In order to check the accuracy of the result,the calculated gas hold-up and actual gas hold-up was compared and the error of them was graphically expressed.The result showed that the error is less than 10%at 1.2?1.8 cm · s-1,and the resulting interfacial area is 9.8?16.7 m2 · m-3.Based on the study of bubble size distribution influenced by gas velocity,this work further analyzes the influence of liquid surface tension and viscosity on the bubble size distribution.It shows that the gas-liquid interfacial area increases by 37.3?46.9%when the surface tension decreases from 72 mN · m-1 to 60 mN · m-1,and by 7.2?16.0%when the surface tension decreases from 60 mN · m-1 to 49 mN · m-1 at 1.2-2.0 cm · s-1.The gas-liquid interfacial area increases by 9.9?20.4%when the viscosity decreases from 16.6 mPas to 6.2 mPas,and by 7.1?21.4%when the viscosity decreases from 6.2 mPas to 3.6 mPas at 1.2?2.0 cm · s-1.