Shadow imaging in bubbly gas – liquid two-phase flow in porous structures

Abstract

Shadow imaging is used for the investigation of bubbly gas–liquid two-phase flow in a porous structure. The porous structure is made of Somos® WaterShed XC 11122, a clear epoxy resin used in rapid prototyping. Optical access is provided by using an aqueous solution of sodium iodide and zinc iodide having the same refractive index as the structure material (n = 1.515). Nitrogen is injected into the continuous phase at volumetric transport fractions in the range of ε˙ = 2.4 − 4.1% resulting in a hold-up of ε = 0.94 − 2.17%. The obtained images of overlapping bubble shadows are processed to measure the bubble dimensions. Therefore, a new processing sequence is developed to determine bubble dimensions from overlapping bubble shadows by ellipse fitting. The accuracy of the bubble detection and sizing routine is assessed processing synthetic images. It is shown that the developed technique is suitable for volumetric two-phase flow measurements. Important global quantities such as gas hold-up and total interfacial area can be measured with only one camera. Operation parameters for gas–liquid two-phase flows are determined to improve mass and heat transfer between the phases.