Modelling ultrasonic cavitation onset in spiral-wound reverse osmosis modules

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A model was developed to predict the onset of inertial cavitation within a spiral-wound reverse osmosis module sonicated along its axis from within its pressure vessel. The aim was to investigate the scalability of ultrasonic antifouling for reverse osmosis applications. The model employs a one-dimensional discretization to represent the module feed channel, calculating each element's pressure, flow rate, permeate flux, and sonication intensity. The Blake threshold assesses whether the pressure amplitude at each element is sufficient to produce inertial cavitation. When applied with parameters from a typical small-scale reverse osmosis module, the model identified a linear relationship between inlet pressure and inertial cavitation onset location, with a constant inlet flow rate and sonication power. With a sonication power of 120 W and a flow rate of 8.796 × 10−5 m3 s−1, the model predicted that inertial cavitation could be induced throughout the reverse osmosis module with inlet pressures ranging from 335 kPa to 355 kPa. While these pressures may be inefficient from a permeate production standpoint compared to standard operating pressure, they could be produced temporarily as part of a regular membrane cleaning operation. The model estimates the system's power consumption during cleaning to be 134.8 W, approximately equal to the estimated system energy requirements under recommended operating conditions of 134.3 W. This suggests that this technology could integrate effectively with existing reverse osmosis systems.