Vortex based hydrodynamic cavitation reactors offer various advantages like early inception, less erosion and higher cavitational yield. No systematic modelling efforts have been reported to interpret the cavitation performance of these vortex based devices for cavitation. It is essential to develop a modelling framework for describing performance of cavitation reactors. We have addressed this need in the present work. A comprehensive modelling framework comprising three layers: per-pass performance models (overall process), computational fluid dynamics models (flow on reactor scale) and cavity dynamics models (cavity scale) is developed. The approach and computational models were evaluated using the experimental data on treatment of acetone-contaminated water. The presented models were successful in describing the experimental data using initial cavity size as an adjustable parameter. Efforts were made to quantify optimum operating conditions and scale-up. The developed approach, models and results will provide useful design guidelines for pollutant degradation using vortex based cavitation reactors. It will also provide a sound and useful basis for comprehensive multiscale modelling of hydrodynamic cavitation reactors.

Hydrodynamic cavitation is being increasingly pursued for the development of an intensified and compact wastewater-treatment process. Experimental data on the degradation of water contaminated with three commonly used solvents (acetone; ethyl acetate, EA; and isopropyl alcohol, IPA) using vortex-based cavitation devices are presented. The influence of operating flow or pressure drop across cavitation devices (150 to 300 kPa), operating temperatures (20 to 45 °C), concentrations of pollutant (1000 to 50 000 ppm), and scales of the cavitation reactor (with a scaling-up factor of 4, maintaining the geometric similarity) has been reported. A new reaction-engineering model based on the number of passes through the cavitation device was developed to interpret degradation behavior. The model provides a convenient way to estimate the per-pass degradation factor from batch experiments and allows its extension to continuous processes and to more-sophisticated models for estimating the generation of hydroxyl radicals. The model showed excellent agreement with experimental data. The per-pass degradation factor exhibited a maxima with respect to pressure drop (200–250 kPa) across cavitation devices. Aeration was found to improve degradation performance up to 1 vvm ([L/min]gas/L liquid]). The initial concentrations of acetone (1000 to 50 000 ppm) and IPA (1000 to 22 000 ppm) were found to have a negligible effect on degradation performance. The per-pass degradation factor for EA was 1.5 and 4 times that of acetone and IPA, respectively. The effect of two scales (nominal capacities of the small- and large-scale devices used were 0.3 and 1.2 m3/h, respectively) was investigated for the first time, and it was found that the per-pass degradation factor decreased with scale. The presented model and experimental data provide new insights into the application of hydrodynamic cavitation for wastewater treatment and provide a basis for further work on the scaling-up of hydrodynamic cavitation devices. The results will be useful to researchers as well as practicing engineers interested in harnessing hydrodynamic cavitation for water treatment.

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Hydrodynamic cavitation (HC) is being increasingly used for a wide range of applications including wastewater treatment. No systematic comparison of pollutant degradation performance of different HC devices is available. In this work, for the first time: a basis for comparing performance of HC devices and a systematic comparison of pollutant degradation performance of five different types of HC devices based on linear and swirling flows is presented. 2,4-Dichloroaniline (DCA) was selected as a model pollutant in water as it contains multiple functional groups on an aromatic ring. Experiments were performed at two values of pressure drop across HC devices (100 and 200 kPa) at a constant initial concentration (35 ppm), pH (7), and temperature (18 °C) for five types of HC devices, namely orifice, venturi, orifice with swirl, venturi with swirl, and vortex diode. The pollutant degradation was interpreted by a per-pass degradation factor approach. The study demonstrated that five different types of cavitation devices performed similar to each other when these devices were designed to exhibit a similar pressure drop versus flow rate curve. It was conclusively shown that swirl does not suppress degradation performance while offering advantages on shielding device walls from collapsing cavities. This is an important and new result which will be useful for selecting and designing cavitation devices. Pollutant degradation data for geometrically similar vortex diodes of two smaller scales showed significantly higher degradation performance. The number of passes required for ∼10% degradation for the devices with a nominal capacity of 1, 5, and 20 LPM were 15, 100, and 1200 passes, respectively. The presented experimental data from these seven devices will be useful for evaluating computational models and hopefully stimulate further development of predictive computational models in this challenging area.

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