Measurement of void fraction in dispersed bubbly flow containing micro-bubbles with the constant electric current method

摘要

Void fraction is one of the dominant parameters of gas-liquid two-phase flow in industrial equipment. An electric sensing method based on the difference in electric conductivity and permittivity between liquid and gas is one of the online measurement methods of void faction. However, the previous constant electric current method is not applicable to dispersed bubbly flow because bubbles are dispersed in three dimensions. In the present study, the new constant electric current method available to the three dimensional dispersed bubbly flow with tiny bubbles (micro-bubbles) is developed. The proposed method to estimate the void fraction is based on Maxwell's theory and polarization of tiny bubbles. The method makes it possible to measure the void fraction of three dimensional dispersed bubbly flow. It is experimentally clarified that the present proposed method with the constant electric current method can be applicable to measure the void fraction of three dimensional bubbly flow more accurately than the previous constant electric current method. It is also clarified that Maxwell's theory and the present proposed method with polarization are compatible with the drift flux model although void fraction estimated with the previous method is higher than the drift flux model for three dimensional dispersed bubbly flow.