Laser doppler anemometry measurements in gas‐solid flows

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Abstract
Laser Doppler Anemometry (LDA) was used for the simultaneous measurement of the gas and particle velocities in a gas‐solid, two‐phase flow. The flow configuration consists of an air jet at ambient temperature in which a spherical glass powder of a mean particle diameter of 97.0 or 13.7 μm was injected from one side using a secondary air jet. Both principal and secondary jets were also seeded with talcum powder with a mean particle diameter of about 1 μm which served as a tracer.The probability density distribution function (PDF) of the LDA output showed two distinct peaks corresponding to the particle and gas velocities. As the particles were accelerated by the flow, the slip velocity between the gas and the particles decreased causing the gap between these two peaks to narrow. The measured mean particle velocity profiles were in agreement with the predictions of a theoretical model.The objectives of the present investigation was to obtain experimental data on the dependence of the particle trajectories and their mean velocities on the injection conditions in a free jet stream. The principal question, however, was whether such data could be obtained using Laser Doppler Anemometry (LDA). In other words, whether LDA could be effectively used in two‐phase flow systems for the simultaneous measurement of the gas and particle velocities? Obviously, the answer to this last question can affect far beyond this particular study and more than justified the effort for this detailed investigation. It should be pointed out that, while LDA has been known for sometime, and the necessary equipments for an LDA system are available on a commercial bases, relatively little attention has been given to its application to other than single‐phase, fluid‐flow measurements.

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