| Summary: | Three sensor systems measuring particle velocity in gas-solids flows have been studied. These are the microwave Doppler flow sensor, the electrostatic sensor, and the microwave sensor for correlation measurement, all utilizing different principles of operation. The Doppler sensor is based on the Doppler frequency shift observed when microwaves are backscattered by moving targets. An analysis of the process of Doppler signal generation and a computer model based on this analysis have been presented. A novel feature of this work is the implementation of partial screening of the flow field which improves the shape of the Doppler spectrum and results in a mean Doppler frequency proportional to the flow velocity and independent of the flow profile. The electrostatic sensor is based on the principle of monitoring the charge induced on metallic surfaces by charged particles moving in their neighbourhood. A theoretical analysis of the spatial performance of the sensor along with a computer model and experimental verification are presented. Principally, ring type of sensors have been examined and the streched band electrostatic sensor is introduced (SBES). The advantage gained with the introduction of the stretched band electrostatic sensor is a uniform sensitivity across the plane of the sensor. The microwave correlation sensor follows the principles of previous ultrasonic and laser correlation flovrneters. That is, "a transmitted beam penetrates the flow field, suffers modulation, and is detected by receivers placed on the other side of the flow field. An analysis of the principles has been presented and a simplified computer model has been used for system design studies. The study presented here shows that a microwave correlation sensor is viable device for measuring solids velocity. Wherever possible direct comparisons of the properties and the performance of the three sensors are made in order to draw conclusions as to which sensor is best for a specific industrial application. Engineering, environmental and safety problems which might be encountered in the practical implementation of the sensors are discussed. In addition, areas of uncertainty where further work is required are summarized.
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