Accuracy of Bubble Velocity Measurement with a Four-point Optical Fibre Probe

For the operation of high void fraction bubbly flows in bubble columns, insight in primary parameters such as bubble size, shape and velocity as well as gas volume fraction is essential. At high gas volume fractions the flow system becomes opaque, ruling out non-intrusive optical techniques. As an alternative optical fibre probes can be used, which have the advantage of low cost, simplicity of setup and easy interpretation of the results. By using four-point optical fibre probe, properties of bubbles can be studied, such as bubble velocity, bubble size, etc. However, the effect of bubble wobbling behaviour and physical properties of liquids on the accuracy of the velocity measurements has not been investigated in detail. In the present study, the performance of a four-point optical fibre probe was evaluated for five different liquids. The probe performance and causes of inaccuracies are discussed.