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Hydrodynamic cavitation is a widely utilized method for generating nanobubbles through mechanical means. The process operates on the principle that when a liquid flows through a narrow restriction — such as a venturi tube, orifice plate, rotating impeller, or high-shear mixer — the local pressure drops below the liquid's vapor pressure. This sudden drop in vapor pressure leads to the formation of vapor cavities or bubbles, a phenomenon known as cavitation. 

As these bubbles collapse under high shear conditions, they fragment into nanoscale bubbles, resulting in the formation of stable nanobubbles within the liquid.

This technique typically employs equipment such as venturi tubes, orifice plates, high-shear mixers, and rotating impellers to induce the necessary pressure differentials and shear forces.

Hydrodynamic cavitation is particularly effective in breaking down larger gas bubbles into nanobubbles, owing to the intense shear and pressure gradients generated during bubble collapse. 

Its simplicity and scalability make it a preferred approach in several industrial applications, including wastewater treatment, agricultural irrigation systems, and aquaculture operations.

Electrochemical (Electrolysis-Based) Nanobubble Generation

The electrochemical method generates nanobubbles through the process of water electrolysis. 

When an electrical current is applied across an electrolysis cell equipped with inert electrodes — typically platinum (Pt) or titanium (Ti) — water molecules are split into hydrogen and oxygen gases. 

These gases form nanobubbles on the surfaces of the electrodes, which then disperse uniformly into the surrounding liquid.

This technique requires a direct current (DC) power supply and an electrolysis cell designed for stability and efficiency. One of the key advantages of this method is the ability to precisely control the type of gas produced and the distribution of bubble sizes. Additionally, it enables the direct and efficient production of high-density nanobubbles within the liquid medium.

Electrochemical nanobubble generation is widely used in applications where purity and precision are critical. These include biomedical treatments, surface cleaning in semiconductor and pharmaceutical manufacturing, and hydrogen production for energy and fuel cell technologies.

Pressurized Gas–Liquid Mixing (Gas Supersaturation Method)

The pressurized gas–liquid mixing method, also known as gas supersaturation, produces nanobubbles by first dissolving gas into a liquid under elevated pressure. When the pressurized liquid is subsequently released through a controlled depressurization process, the sudden drop in pressure induces the nucleation of nanobubbles within the fluid.

This method typically employs a high-pressure saturator or tank, a precision pressure control valve, and a diffuser or sparger to facilitate uniform gas dispersion. By carefully regulating these components, operators can achieve consistent nanobubble formation and precise control over gas dosing — particularly for oxygen (O₂), hydrogen (H₂), or carbon dioxide (CO₂).

This approach is particularly advantageous for applications that require stable and targeted gas delivery. Common uses include enhancing oxygen transfer in biological systems—such as plant root zones and microbial environments—as well as improving separation efficiency in flotation systems used in wastewater treatment and mineral processing.

Membrane Sparging Using Nanoporous Membranes

The membrane sparging method utilizes nanoporous membranes to generate nanobubbles by forcing gas through extremely small pores into a liquid medium. As gas is introduced into the system, it passes through a hydrophobic membrane with nanoscale pore sizes, which restricts the formation of larger bubbles. This results in the controlled release of gas in the form of uniformly sized nanobubbles on the downstream side of the membrane.

The system typically consists of a gas feed source and a hydrophobic nanoporous membrane designed to maintain pressure differentials and prevent wetting. The pore size and membrane material are critical to ensuring the generation of nanobubbles rather than microbubbles.

This technique is particularly effective for applications requiring high precision and minimal bubble size variation. It is commonly used in semiconductor manufacturing for surface cleaning processes, as well as in chemical reactions where fine gas dispersion is essential for enhancing mass transfer and reaction efficiency.

Ultrasonic (Acoustic Cavitation) Nanobubble Generation

Ultrasonic or acoustic cavitation generates nanobubbles by subjecting a liquid to high-frequency sound waves, typically in the range of 20-kHz. to 40 kHz. These ultrasonic waves create alternating high- and low-pressure zones within the liquid, leading to the formation of vapor cavities. The rapid collapse and rebound of these cavities produce intense localized forces that fragment the gas pockets into micro- and nanobubbles.

The process utilizes ultrasonic transducers or sonicator baths to deliver controlled acoustic energy into the fluid. Key parameters influencing bubble formation include the frequency and power of the ultrasound, as well as the temperature and viscosity of the liquid medium.

Ultrasonic nanobubble generation is employed in applications that benefit from enhanced gas–liquid interactions and precise bubble control. Common use cases include targeted drug delivery systems, emulsification in pharmaceutical and food processing, and the sterilization of water through physical disruption of microbial membranes.