Moisture-Independent Measurement of Solid Concentration in Gas–Solid Flows Using Dual-Frequency Dipole Antennas

In gas–solid two-phase flow, the accuracy of solid concentration measurement is significantly affected by the unknown and varying moisture content in the solid phase, particularly when the used method is sensitive to the moisture content. To address this issue, a new method that uses a novel microwave transmission sensor working at two frequencies and a novel decoupling method is proposed to achieve moisture-independent solid concentration measurement. A dual-frequency resonant printed dipole antenna is designed using the finite element simulation method, and the microwave transmission sensor, which can work at two frequencies, is formed by two dipole antennas. A simple and effective decoupling method is proposed to extract moisture content from dual-frequency phase shift information, enabling solid concentration measurement. The flow structures of roping flow with varying solid concentrations and moisture contents are used to verify the proposed method. Experimental results demonstrate that the dual-frequency phase shifts of the microwave transmission sensor are both sensitive to the solid concentration and moisture content. Therefore, only relying on the phase shift information from a single frequency cannot accurately measure solid concentration under conditions of varying moisture content. The decoupling method proposed in this study, based on dual-frequency phase shift information, can accurately determine moisture content. Consequently, it enables solid concentration measurement in gas–solid flows with relative errors within ±5% under conditions of varying moisture content.