Hydrodynamic Cavitation in Emulsification and Homogenization

5 Equipment and Process Configurations

5.1 Static constriction devices

Static devices create a pressure decrease without moving internal parts. Orifices provide abrupt contraction and expansion, strong jets, and compact construction. Venturis provide smoother acceleration and pressure recovery. Cone, baffle, and nozzle devices offer additional control of the low pressure region and collapse location. Studies show that throat geometry, recovery profile, and cavitation number definition must be assessed together because nominal pressure drop alone does not identify the active breakup field [5–8,19,31,33–35].

Table 6. Hydrodynamic cavitation device families for emulsification and homogenization.

Device family	Cavitation generation mechanism	Principal control variables	Strengths	Limitations
Orifice plate	Jet and vena contracta pressure decrease	Hole number, diameter, area ratio, edge, pressure drop	Simple, low cost, replaceable insert	Clogging, erosion, abrupt recovery, broad residence time distribution
Circular Venturi	Smooth acceleration through a throat	Throat diameter, convergent/divergent angles, length, backpressure	Good throughput, controlled recovery	Larger footprint, geometry sensitive cavitation location
Slit Venturi	Planar acceleration and shear	Slit width, height, aspect ratio, pressure	High pass rate and strong planar deformation	Narrow slit can be sensitive to solids and fouling
Cone or bluff body	Separated cavity behind body	Cone angle, blockage, channel diameter, backpressure	Visual access and controllable attached cavity	Supercavitation can reduce discrete collapse events
Vortex device	Low pressure swirling core	Inlet number, chamber aspect ratio, outlet, pressure drop	Open passages, cavitation away from walls, modular	Performance sensitive to swirl stability and droplet trajectory
Liquid whistle or jet device	Jet oscillation, impact, and cavitation	Jet velocity, resonator geometry, backpressure	Compact and effective for recirculation	Acoustic and erosion behavior can be geometry dependent
Rotor stator cavitator	Periodic cavities and high relative velocity	Rotor speed, gap, holes or grooves, flow, backpressure	Independent speed control and strong combined shear	Moving seals, mechanical complexity, heat, wear

Figure 8. Drawings of controlled flow cavitation devices illustrating inline flow passages and cavitation generating geometries [36].

The Kozyuk patent family illustrates the controlled flow principle: a pressurized stream passes a cavitation generator, cavities form in the low pressure region, and collapse occurs as pressure recovers downstream [36]. The generator shape and recovery chamber are selected to control the bubble field rather than merely maximize pressure loss.

5.2 Vortex based devices

Vortex cavitation devices use tangential inlets to create a rotating flow and low pressure axial core. Cavitation can occur in the bulk fluid away from the wall, which may reduce erosion. The open chamber and millimetre scale clearances are also favorable for streams containing suspended solids or moderate viscosity. Recent studies have varied chamber aspect ratio, inlet number, outlet geometry, scale, and parallel arrangement. An aspect ratio near six was reported as favorable in one design study, while other experiments found that vortex stabilizers and multiple inlets could improve cavitation activity and energy performance, especially at low pressure drop [19,29].

Figure 9. Representative vortex diode cavitation geometry showing a tangential inlet and axial outlet arrangement used to establish a low pressure swirling core [37].

Vortex geometry must be evaluated by both vapor generation and droplet trajectory. A large cavitation region does not guarantee effective emulsification if the dispersed phase bypasses it. This is one reason that CFD models increasingly track water, oil, and vapor phases together and then couple the predicted flow to a PBM [25,29].

5.3 Dynamic rotor stator and rotary cavitation devices

Dynamic devices generate alternating low and high pressure regions by moving cavities, holes, grooves, or blades past a stator. Rotational speed provides a control variable that can be adjusted separately from flow and backpressure. Visualization and CFD of a rotational hydrodynamic cavitation reactor show that hole diameter, hole height, and conical bottom length alter vapor exchange, cavitation area, and vortex intensity [31]. The engineering tradeoff is the addition of seals, bearings, rotor balance, tip speed limits, mechanical heating, and wear.

Figure 10. Rotor hydrodynamic cavitation apparatus with perforated or structured rotating elements and stationary housing [38].

Figure 11. Rotor stator hydrodynamic cavitation concept. Rotation provides an independent variable that can be adjusted separately from flow and backpressure [9].

5.4 Patented food and emulsion process configurations

Patents illustrate how cavitation equipment is integrated into staged industrial processes. The food emulsion patent family represented in Figure 12 uses hydrodynamic cavitation within a controlled process sequence to produce an oil in water food product. Patent examples also cover vortex diodes, inline controlled flow devices, rotor cavitators, and newer hydrodynamic cavitation mixers [36–41]. Patent drawings are useful for identifying process architecture, but performance claims should be confirmed by independent testing with the intended formulation.

Figure 12. Representative process schemes from a food emulsion patent family that incorporates hydrodynamic cavitation into preparation and phase management steps [39].

5.5 Process integration and production configurations

Commercial implementation usually takes one of three forms: a single pass inline unit, a recirculation loop, or several identical modules operated in parallel. Selection depends on residence time tolerance, validated local cavitation conditions, cleaning strategy, and required turndown. Supplier data can support mechanical design, but product specific droplet size distribution, temperature, chemistry, and wear must be established by pilot testing [42–44].

Figure 13. Industrial integration patterns for hydrodynamic cavitation: single pass, recirculation, and parallel scale out [9].

Production installation normally includes a feed or recirculation tank, pump, cavitation reactor, upstream and downstream pressure measurement, flow measurement, backpressure valve, heat exchanger, sampling point, and route for single pass discharge or recirculation. For sanitary products, drainability, elastomer compatibility, surface finish, clean in place velocity, dead leg control, and validated cleaning are as important as cavitation intensity.