A conductivity-based sensor for the measurement of liquid film thickness and surface wetting in structured packing columns

This work introduces a sensor designed to study the wetting performance, i.e. non-wetted, partially wetted, and fully wetted channels, in a structured packing column along with their corresponding film thicknesses on the packing sheets. A numerical approach was followed to optimize the shape of the sensor electrodes in order to achieve both sufficient dynamic range for film thickness measurements and high spatial resolution. For this purpose, COMSOL Multiphysics® was used to simulate the potential field distribution in liquid films of different thicknesses. The sensor was fabricated as a thin and flexible printed circuit board (PCB) strip, making it easy to bond it to the surface of the packing sheets. Performance measurements were conducted by forming static liquid films with defined thicknesses on a sensor in a single-strip experimental setup, and the data obtained from these measurements were then used to calibrate the sensor and to validate the numerical model. The sensor detects wetted and non-wetted areas based on the electrical conductivity of the liquid phase and can measure liquid films with thicknesses of up to 1.7 mm. Subsequently, it was bonded to the corrugated sheets of Mellapak 250Y® to study the wetting performance in a packed column and to measure local film thicknesses. The liquid flow distribution and average film thickness were investigated for both an upright vertical column and a tilted column, and then compared to determine the impact of inclination on wetting performance.