Tubular Ultrasonic Emulsifier/Disperser

Industrial  Tubular Ultrasonic Reactor(Flow-Type)

Ultrasonic Cavitation

The propagation of ultrasound through a medium is achieved via pressure waves, which induce vibrational motion in molecules. These vibrations cause the molecular structure of the medium to alternately compress and expand, with this time-varying pressure continuously changing.

Consequently, the distance between molecules changes as they vibrate around their average positions. If the ultrasonic intensity in the liquid increases beyond a certain point, a critical threshold is reached where the intermolecular cohesive forces can no longer maintain the integrity of the molecular structure.

When the bubble volume reaches a point where it can no longer absorb energy, they collapse violently during the high-pressure cycle. This phenomenon is known as "cavitation."

The high collapse temperatures and energetic particle collisions lead to thermal radiation. It is estimated that the temperature inside a collapsing bubble can reach up to 5000 Kelvin, with pressures exceeding 1000 atmospheres.

Ultrasound finds applications in numerous physical, chemical, and biological processes. Emulsification and dispersion are two examples of physical processes.

Emulsification is the process of mixing two or more immiscible liquids, resulting in a heterogeneous system where at least one immiscible liquid is uniformly dispersed as droplets within another liquid.

At the interface between the two liquids, bubbles rupture or collapse near this interface, leading to disruption and achieving highly efficient mixing. Emulsions produced ultrasonically are often more stable than those generated by conventional methods and require fewer (or even no) surfactants.

This is because ultrasound can be fully controlled and adapted through the selection of amplitude, pressure, and temperature.

The dispersion phenomenon is caused by minute turbulences resulting from pressure fluctuations and cavitation. Investigations into different materials have shown that ultrasound offers significant advantages compared to other techniques. It is particularly effective for small particles ranging from several nanometers to a few micrometers, where ultrasonic cavitation efficiently breaks up agglomerates, aggregates, and even primary particles.

When using ultrasound for grinding high-concentration batches, the fluid jets generated by ultrasonic cavitation cause particles to collide with each other at speeds of up to 1000 kilometers per hour.

This breaks the van der Waals forces in agglomerates and can even disrupt primary particles. Larger particles undergo surface erosion (via cavitation collapse in the surrounding liquid) or size reduction (due to particle collision splitting or collapse of cavitation bubbles formed on the surface).

For each specific application and process, there is an optimal set of parameters. The most important among these are amplitude, pressure, temperature, and viscosity.

The oscillation amplitude describes how the surface of the acoustic waveguide moves within a specific time (e.g., 1/20,000 of a second at 20 kHz). A larger amplitude results in a higher rate of pressure drop and rise per oscillation cycle. Additionally, the volumetric displacement per oscillation increases, leading to a larger cavitation volume (bubble size and/or quantity). When applied to dispersion systems, a larger amplitude is more destructive to solid particles.

Higher pressure induces cavitation at temperatures near or above the boiling point. It also enhances the intensity of the shock waves, which is related to the difference between the static pressure inside the bubble and the vapor pressure. Since the power and intensity of ultrasound change rapidly with pressure, using a constant pressure pump is more appropriate. When supplying liquid to the flow cell, the pump should be capable of handling the specific liquid flow rate at the appropriate pressure.

High temperatures help break strong solute-solvent matrix interactions. However, on the other hand, cavitation is better achieved at lower temperatures when the ultrasonic generator's power remains constant. This is because as the solvent temperature increases, its vapor pressure also rises, meaning more solvent vapor fills the cavitation bubbles, making their collapse less violent. Thus, the ultrasonic effect becomes weaker than expected.

Viscosity is a qualitative measure of molecular interactions within a liquid. Higher viscosity indicates stronger attractive forces between molecules.

Product Applications

Cosmetics

• Preparation of Carrier Systems: Nanoemulsions, Liposomes, Multiple Emulsions

• Finished Product Dispersion: Sunscreen Powders, Creams

• Microbead and Microcapsule Preparation: Cosmetic Oil Beads, Fragrance/Flavor Encapsulation

Biopharmaceuticals

• Pharmaceutical Formulation Synthesis: Liposomes, Nanoemulsion Formulations, PLGA, Nanocrystals

• Microbial Extraction and Cell Disruption: Microalgae Extraction, Yeast Cell Disruption

Fine Chemicals

• Nanomaterial Synthesis: Ceramic Powders, Precious Metal Catalysts, IVD Microspheres, Perovskites, Zinc Oxide, Cerium Oxide, Calcium Carbonate, Layered Double Hydroxides, Hydroxyapatite

• Powder Slurry Dispersion: Polishing Slurries, Electrode Pastes, Battery Separator Powders, Carbon Nanotubes

Food & Health Products

• Mixing and Dispersion: Applied to renewable diesel and bio-jet fuel, ultrasonic extraction technology for edible oils, ultrasonic extraction of extra virgin olive oil (Note: duplicate line in original removed in translation), Heme, Probiotics, Baijiu (Chinese liquor), Melatonin Encapsulation

• Microbead and Microcapsule Preparation