Experimental setup to study the influence of the drop size distribution and dispersed-phase load on the dense-packed zone formation in a vertical separator

Coalescence-inhibited biphasic solvent systems tend to form a higher dense-packed zone (DPZ) in liquid-liquid gravity separators, which can lead to flooding of the apparatus, and thus, to a shutdown of the separation process. DPZ formation in coalescence-inhibited solvent systems has not been studied in detail at technical scale, and the effects of key parameters on DPZ height remain unclear. This work presents an experimental setup for detailed DPZ investigations in a liquid-liquid vertical separator. The setup enables independent variation of dispersed-phase load and droplet size distribution while providing direct optical access to DPZ behaviour. The setup also includes a method for measuring the local hold-up for individual sections of the DPZ. First results obtained for a coalescence-inhibited butyl acetate–water system with calcium chloride demonstrate regions during vertical separator operation, including DPZ formation, steady state, and DPZ decay. Measured local hold-up profiles inside the DPZ show a pronounced dependence on the drop size distribution, reflecting the influence of local circulation and rearrangement of droplets and vertical structuring inside the DPZ. The presented setup provides a controlled and reproducible experimental framework for a systematic analysis of the DPZ and enables the generation of experimental data for validation and further model development of liquid–liquid gravity separators.