The use of large scale computer assisted tomography for the study of hydrodynamics in trickling filters

In this paper, a new experimental technique is proposed, based on X-ray tomography, allowing the analysis of the gas-liquid-solid phase distribution in trickling filters. Tomography refers to the cross-sectional imaging of an object from data collected by illuminating this object from many directions. The experimental set-up allows the scanning of transverse sections of rather large filters: up to 0.8 m diameter and 2 m height can be irradiated. Experiments were carried out both without and with liquid flow. In the absence of liquid, the reconstructed images give a view of the non-uniformity of the solid phase distribution. The images obtained are very complex because they result from the superposition of several distributions with different spatial scales. The existence of a first spatial scale is shown which allows separation of the properties belonging to the individual packing elements from those belonging to the bed scale. When liquid is flowing through the packed bed, the distribution of the liquid hold-up is clearly evidenced, despite the very low liquid film thickness.