Numerical simulation and experimental investigation of structural optimization of capacitance sensors for measuring steam wetness with different coaxial cylinders

Abstract

Steam wetness is an important parameter, which is difficult to measure accurately. A simulation study is performed based on the theories of electrodynamics and hydrodynamics to investigate the characteristics of wetness capacitance sensors with different coaxial cylinders, and an experimental system and two capacitance probes were designed to measure steam wetness. Using a FLUENT user defined function (UDF) code, a program to compute the electric field was compiled which can transmit the data between the electric field and the flow field. The coupling of the steam flow field and the electric field within the sensors is investigated through numerical simulation. The results show that the electric field intensity decreases from the inner electrode plate to the outer electrode plate. The electric field intensity near the inner plate increases with increasing plate thickness while the sensor length has no effect on the electric field intensity distribution in the radial direction, but the peak electric field intensity decreases with increasing sensor length. The peak electric field intensity weakens with increasing electrode separation. Comparison of the numerical simulation results and the experimental results shows that the results of the simulation are similar to those of the experiments, with the output capacitance fluctuating around a fixed value as the steam flow rate changes and increasing linearly with increasing wetness. The maximum difference between the experimental data and the numerical simulation data is 0.78nF, which is a discrepancy of 19.8%.