Multi-phase flow measurements in powder processing

This paper describes recent advances in the design and application of a number of promising techniques that employ non-intrusive transducers to enable the interrogation of multi-phase particulate systems. Most of these techniques are based on electrical sensing methods which have the particular advantages of being non-hazardous, high speed, low cost, and utilise reliable solid-state devices that can operate independently of the opacity of the particulate dispersion. Consequently, it is possible to acquire data on phase concentration, velocity, mass flow and spatial distribution in fast-moving process pipelines or vessels by relating the data obtained from several transducers simultaneously. The principle of measurement techniques based on capacitance, impedance, ultrasonics, electrodynamics and pressure transducers are reviewed and then illustrated for specific powder processing applications involving (i) analysis of solid/liquid sedimentation processes, (ii) pneumatic conveying, (iii) slurry transport in pipelines and (iv) imaging of solid/gas, solid/liquid and liquid emulsions in real time. The limitations and future uses of such instrumentation for powder and materials handling operations are discussed.