A Method for Inferring Local Bubble Size Distribution from the Chord Length Data Measured in a Vertical Air-Water Column

摘要

The local size distribution of bubbles in a bubbly column can be inferred from the distribution of chord lengths measured with an intrusive probe, such as conductivity or optical probe, using a statistical backward transformation. However, the shape and movement of bubbles as well as their interactions with each other and with the probe are complicated. Consequently, the chord length distribution (CLD) is complicated too, and the transforming those into the respective bubble size distributions (BSD) becomes more difficult. In this paper, a new approach, which considers separately the size distribution of several groups of bubble shapes, is proposed to overcome the difficulty. The CLDs are separated into individual modes, which characterize for the groups of uniform bubbles, by fitting methods. An analytical algorithm is derived to find the BSD of the groups, and then the overall distribution of all these groups. An investigation of the BSDs in a vertical air-water column basing on the approach is carried out. The experimental chord length data used to find the BSDs is acquired with five-sensor conductivity probes located at two different elevations L/D = 12.2 and 42.2. The influence of flow conditions, including air and liquid flow rates, on the distributions and the propagation characteristics of the bubble size along the flow channel are discussed in details. The investigation shows the improvement of the applicability of the method in determining the BSDs for complicated two-phase flow problems.