Measurement of the Thin Liquid Film at the Wet-Gas Outlet of the Supersonic Separator by FPC Conductance Sensor

Gas–liquid two-phase flow widely exists in the natural gas transportation industry. Accurate measurement of the liquid film is conducive to enhance the efficiency and economy of supersonic separators. Therefore, a flexible printed circuit (FPC) liquid film conductance sensor based on array arrangement is designed. First, the geometric parameters of sensors are optimized by the finite element method. The modules of electrical signal excitation and collection system based on field-programmable gate array (FPGA) are designed. A liquid film calibration device is built to calibrate the FPC sensor, the liquid film thickness is fitted through calibration experiments, and the fitting curve error is within ±5.0%. Second, to analyze the liquid film thickness and velocity at the wet-gas outlet Section of the supersonic separator, several experiments are carried out in different working conditions, and the signals of liquid film thickness are processed by time and frequency domain analysis. The results reveal that the liquid film thickness has a bimodal characteristic, where the thickness of the thin base layer is about
$70 \mu \text{m}$
, and fluctuating layer thickness is related to working conditions. The normalized energy ratio and fluctuation characteristics significantly changed under different frequency bands. At the same time, the existence of shock waves seriously influences the generation of liquid film, resulting in a decrease in the liquid film thickness seriously. Last, the cross correlation algorithm is used to analyze the liquid film velocity. The different signal transmitter and receiver electrode orders can realize the velocity measurement in different directions. The experimental results show that the liquid film velocity at the outlet of the supersonic separator maintains at 54.8–339.0 mm/s when the back pressure ranges from 0.350 to 0.717, the maximum root mean square error (RMSE) of flow direction velocity is 4.51 mm/s, and the maximum RMSE of circumferential direction velocity is 3.38 mm/s.