Experimental study of void fraction behaviour in vertical bubbly gas-liquid flow using conductivity and measurements

The void fraction is an important variable in describing gas-liquid two-phase flows, since it is required to predict the heat and mass transfer coefficients and the pressure drop and is an indicator of the flow regime. The contrast in conductivity between water and air is one way to measure the void fraction in gas-liquid flow. This project has examined use of the ring conductivity electrodes to measuring the void fraction in an up-flow bubble column. The conductivity method has potential to be a low cost, safe and accurate method of measuring local void fractions in pipes and other process engineering mass transfer devices. In this project, the void fraction was measured in an air-water system by using conductivity in a 2" pipe equipped with two ring electrodes. Further gas hold-up experiments were conducted in the annular channel formed between 2" and a 4" pipe, using a system of four pairs of electrodes. The data obtained from the experiments agreed fairly well with the Maxwell and Burggeman theories which relate the dimensionless conductance to the void fraction. The measured void fractions were correlated using the drift-flux model, as proposed by Zuber and Findlay. Significant differences were observed between the void fraction measurements obtained for the annular channel and for an empty pipe, when operated at the same gas superficial velocity.