Measurement of Solid Concentration in Gas–Solid Flows Using a Microwave Resonant Cavity Sensor

Gas–solid flows with nonuniform phase distribution and varying moisture often exist in the industrial process. Its solid concentration measurement is an important and challenging research field, and new effective measurement methods are needed. In this study, a novel method using the microwave resonant cavity sensor is proposed to measure solid concentration of gas–solid two-phase flow with varying moisture. The sensor is developed from a cylindrical resonant cavity with open ends, and the orthogonal experiment is carried out using simulation method to determine the resonant mode and optimize the sensor configuration. Afterward, experiments are conducted to evaluate the performance of the designed sensor and the proposed method. The sensor has a high and nearly constant sensitivity to the solid concentration and its output is almost not affected by the nonuniform phase distribution. The varying moisture brings effect to solid concentration measurement when the proposed sensor is used. To solve this problem, the new parameter named normalized resonant frequency is defined to reduce this influence, and finally, the solid concentration measurement is achieved.

I. Introduction

Gas–Solid flows with nonuniform phase distribution and varying moisture are often encountered in the actual industrial processes. For example, in order to convey coal powder in steel industry, pneumatic conveying technology is used and gas–solid flows exist in this process. Accurate measurement of the solid concentration is crucial for the monitoring and control of these industrial processes. Because of the nonuniform distribution of solid phase, it is difficult to measure solid concentration. Moreover, when solid moisture varies and its value is unknown, it will bring new challenge to achieve the solid concentration measurement when the used method is affected by solid moisture [1].