Dynamic Superficial Dielectric Constant Models and Void Fraction Prediction by Microwave Resonant Cavity for Gas Liquid Flow

In the investigation of nonuniform flow measurement utilizing microwave technologies, both the dielectric properties and phase fraction of the flow are crucial factors. This study introduces a new concept of dynamic superficial dielectric constant (DSDC) to characterize the variations in dielectric constant of the fluids, thereby facilitating the development of a method to measure void fraction in air-water flows. A detection technique employing a microwave resonant cavity (MRC) was implemented, and experiments were conducted for various air-water flow void fractions using an MRC sensor under pressures ranging from 0.3 to 0.9 MPa and superficial gas velocities from 5 to 12 m/s. The experimental results demonstrated that the void fraction of the air-water flow significantly affects the resonant frequency, while the pressure and superficial gas velocity have no direct impact. Furthermore, DSDC models were constructed and assessed based on the MRC sensor data. The proposed methodology, when applied to void fraction measurement in stratified and annular flows, yielded an accuracy within ±5% for approximately 91% and 95% of tested samples, respectively. The introduced concept, method, and DSDC model offer a novel, feasible, and precise measurement system capable of characterizing the dielectric properties and estimating phase fractions in nonuniform flow fields.