High-speed liquid film sensor for two-phase flows with high spatial resolution based on electrical conductance

摘要

A sensor is presented, that allows high-speed measurements of two-phase film flows. The sensor consists of electrodes flush to the wall, that measure the electrical conductance in a liquid film. This sensor has a time resolution of 10 kHz and 64 × 16 measuring points, with a spatial resolution of 3.12 mm2 and a maximum film thickness range of 0.8 mm. The shape of the sensor electrodes is optimized by calculating the potential field of the liquid film. The calculated sensor characteristic is compared with experimental data received by imposing static liquid films of known thickness on top of the sensor. Further dynamic measurements of co-current air-water flow in a horizontal channel have been conducted. The statistical analysis concerning film thickness distribution and flow patterns is generally in agreement with literature. The high time and spatial resolution allows a wave analysis over a wide range of wavelengths and wave velocities. By using a continuous wavelet transform, a significant amount of additional information has been retrieved, particularly in regard to ripple waves. Preliminary experiments show the ability of the sensor to detect droplet deposition onto the liquid film. An autoregressive filter has been applied to separate droplet impacts from periodic wavy structures.