Bubbly pipe flow study via refractive index matching

Abstract

A phase-Doppler light-scattering method is used to measure, nonintrusively, liquid and bubble velocities and bubble size in vertical-upwards, dispersed, bubbly pipe flow. Bubble size measurements are also obtained with a video imaging technique. Optical distortion is eliminated, by using pipe material with index of refraction equal to that of water at room temperature, in combination with an index-of-refraction-matching box. Pure-liquid velocity and turbulence intensity test-measurements performed with the incorporation of this technique compare very well with existing data in pipe flow. Measurements of bubble velocity and size at two locations along the pipe are presented with emphasis on the near wall region. The experiments have been carried out at a Reynolds number of 12086 and a volumetric flow ratio of 2.7%. Bubble velocity fluctuation properties were found to be almost uniform in the core region. Bubble mean velocity was constant within one average bubble diameter from the wall and axial velocity fluctuations peaked at approximately half that distance. Velocity distributions near the wall were non-Gaussian and skewed towards lower values. The average bubble size was found to be in the range between 1200 μm and 1400 μm with standard deviations of the order of 500 μm. Smaller bubbles were found to be in the neighborhood of the wall.