A Droplet-Based Image Velocimetry Technique for the Measurement of Liquid Velocity Fields in Two-Phase Water-Oil Dispersion Flows

Resumo

by Rafael Franklin Lázaro de Cerqueira, William Monte Verde, Jorge Luiz Biazussi, Rodolfo Marcilli Perissinotto, Marcelo Souza de Castro, Antonio Carlos Bannwart, published at EPTT-2022.

Abstract

The present work describes a measurement technique to estimate the continuous liquid velocity fields in twophase water-oil dispersion flows. A transparent pump prototype made of acrylic was firstly developed and installed to enable the use of flow visualization and optical measurement techniques. Then, in the experiments, water droplets were injected into the impeller channels of the centrifugal pump, where a mineral oil with a viscosity of µo = 18.0 cP was used as the continuous phase. The two-phase water-oil dispersion flow was then filmed with a high-speed camera, and the water droplets were black-dyed for a better contrast with the white background. When injecting the water drops, breakage events were frequently observed due to turbulence and shear effects, resulting in the birth of small droplets with a size in the range from 100 µm to 500 µm. The occurrence of small water droplets in combination with the viscous continuous oil phase meant that those droplets could be assumed as tracer particles from the continuous phase. Therefore, by computing the
small water droplet velocities, it is possible to estimate the velocity field of the continuous oil phase within an acceptable error margin. This is the main idea of the technique presented in this work, which does not require the addition of intrusive tracer particles, and thus can be seen as a cheap and simple alternative to PIV in two-phase dispersions with continuous viscous phases. After a series of image processing steps, the small water droplets in the range from 100 µm to 500 µm are identified, and the PTV technique computes their instantaneous velocity. In order to assess the method capabilities, the PTV ensemble-averaged liquid flow rate is compared against experimental values from a Coriolis flowmeter installed in the experimental setup. The technique is then applied to study the flow within a pump impeller, resulting in similar flow patterns found in the literature for studies using LDV and PIV studies.

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