Sonochemical Effect Induced by Hydrodynamic Cavitation

13 Materials, Safety, and Product Quality

The same collapse events that generate useful chemistry can damage equipment. Erosion is concentrated where bubbles collapse near a wall, particularly in abrupt recovery regions, downstream jet impingement zones, and narrow rotor stator gaps. Erosion changes geometry, pressure drop, and chemical performance over time. Released metal can contaminate product and may catalyze peroxide chemistry, creating an apparent increase in radical yield that is actually a wear artifact. Replaceable inserts, hard coatings, geometry that moves collapse away from walls, and routine metal analysis should be considered part of the chemical reactor design [1-2,36,52].

Organic liquid service adds flammability, vapor, static electricity, and peroxide hazards. The microscopic hot spot does not raise the entire liquid to ignition temperature, but cavitation can generate off gas, aerosols, and reactive intermediates. Systems handling fuels, solvents, hydrogen, oxygen enrichment, ozone, or concentrated peroxide require inerting or controlled gas composition, bonding and grounding, ventilation, compatible seals, pressure relief, and hazardous area electrical classification. Materials must be compatible with both the parent liquid and cavitation generated oxidants.

Table 13.1. Principal hazards and engineering controls

Hazard	Mechanism	Potential consequence	Control strategy
Cavitation erosion	Microjets and shock loading at walls	Leak, geometry drift, metal contamination	Move collapse off wall, use replaceable liners, inspect and monitor metals
Overpressure	Blocked outlet, gas expansion, thermal rise	Rupture or seal failure	Relief valve, interlocks, rated piping, pressure transmitters
Flammable vapor	Organic vapor and off gas release	Fire or explosion	Closed system, inerting, ventilation, gas detection, classified equipment
Oxidizer exposure	Ozone, peroxide, persulfate, oxygen enrichment	Fire acceleration, burns, seal degradation	Compatible materials, staged dosing, residual monitoring
Noise and vibration	Bubble collapse and rotating equipment	Worker exposure and fatigue failure	Enclosure, isolation, acoustic survey, balancing
Aerosol generation	Gas disengagement and turbulent tank return	Exposure or product loss	Demister, closed vent, condenser, negative pressure
Biological aerosol	Treatment of pathogen containing liquids	Operator exposure	Closed loop, disinfection, filtered vent, PPE
Hot surfaces and bulk heating	Pump inefficiency and recirculation	Thermal degradation or burn	Heat exchanger, temperature interlock, insulation
Nanomaterial release	Particle synthesis or catalyst processing	Inhalation and environmental exposure	Closed handling, filtration, containment, waste plan
Unexpected byproducts	Radical and halogen chemistry	Toxicity or product quality failure	Transformation product analysis, quench, process limits