Measurement of liquid films thickness in a condensing and re-evaporating environment using attenuation of near infrared light

A novel technique developed to measure liquid film thickness up to 2 mm was tested under thermodynamic conditions encountered in containment during severe accident scenario. The tests were performed in the thermal-hydraulic facility LINX located at PSI (Villigen, Switzerland), a 10 m3 pressure vessel with precise control of the boundary conditions. In the experiments, liquid films were created on a temperature controlled wall placed in the center of the vessel. Selected tests involving condensation and evaporation on film with steady state conditions are presented. In each test, sequences of thickness mappings were recorded with an image size of 246 × 180 pixels, a projected pixel size of 0.63 mm and a frame rate of 250 fps. Uncertainty on the film thickness was estimated to 35 μm absolute over the entire measurement range based upon current calibration. Large and small structure can be observed spatially but also temporally through extracted local signal. Average and fluctuating part of the film thickness are presented and discussed for four tests where the controlled wall temperature and bulk composition were varied. Strong time-correlation in the signal was observed for rivulets whose formation is enhanced by an increase of the wall temperature.