When ultrasonic homogeizers are are used for applications such as mixing, dispersing and emulsifying, the objective is to reduce small particles or droplets in a liquid or slurry to improve uniformity and stability of the mixture. These particles (disperse phase) can be either solids or liquids. A reduction in the mean diameter of the particles increases the number of individual particles. This leads to a reduction of the average particle distance and increases the particle surface area. The graphic (click for larger view) shows the correlation between individual particle diameter and total surface area. Surface area and average particle distance can influence the rheology of a liquid.
If there is a difference in specific gravity between the particles and the liquid, the homogeneity of the mixture can influence the stability of the dispersion. If the particle size is similar for the majority of the particles, the tendency to agglomerate during settling or rising reduces, because the similar particles have a similar speed of rising or settling.
The most common mechanism for homogenization is high pressure homogenization. There, liquid is pressed at high pressure (approx. 2000 barg) through a homogenizing valve. When passing the valve, the liquid undergoes a short (approx. 50 microsec.) high-pressure low-pressure cycle.
While this mechanism works well for small, soft particles, such as fat globules in milk, it has its limitations when used for dispersions of hard and abrasive materials, such as pigments, polishing media or metal oxides, or fibrous and stringy materials, such as fruit purees, algae or sludge. This is due to the high liquid speeds (up to 120mtr/sec) and because of the small orifices of the valves used. As the abrasive material passes the pumps and the valve orifice, it causes wear. This reduces the efficiency and life time of the pump and of the valve.
- Ultrasonic homogenizers produce small particles / droplets and a narrow distribution curve.
- Ultrasonic homogenizers can handle high solid concentrations.
- Ultrasonic homogenizers prepare stable suspensions, dispersions and emulsions.
- Ultrasonic homogenizers are precisely controllable as the important process parameters (e.g. amplitude, power, time, temperature and pressure) can be influenced and adjusted.
- Ultrasonic homogenizers are very effective, energy-efficient, user-friendly and safe to operate.
Ultrasonic homogenizers are very efficient for the reduction of soft and hard particles. The homogenization is based on cavitation. When liquids are exposed to intense ultrasonication, sound waves propagate through the liquid causing alternating high-pressure and low-pressure cycles (approx. 20000 cycles/sec.). During the low-pressure cycle, high-intensity small vacuum bubbles are created in the liquid, as the liquid vapor pressure is attained.
When the bubbles reach a certain size, they collapse violently during a high-pressure cycle. During this implosion very high pressures and high speed liquid jets are generated locally. The resulting currents and turbulences disrupt particle agglomerates and lead to violent collisions between individual particles.
One major advantage of ultrasonic homogenizers is the low number of wetted and moving parts. This reduces frictional wear and cleaning time. There are only two wetted parts: The sonotrode and the flow cell. Both have simple geometries and no small or hidden orifices.
Another advantage is the exact control over the operational parameters influencing the cavitation. Hielscher ultrasonic homogenizers can be used at oscillation amplitudes from approx. 1 to 200 micron. The liquid pressure can range from 0 to approx. 500psig. As amplitude and pressure are the most influential parameters, the wide operational range of each parameter allows for very gentle to very destructive processing.
Ultrasonic Tissue Homogenizers
Besides the preparation of dispersions and emulsions, ultrasonic homogenizers are firmly established in biotechnology, cellular and molecular biology, and life science for cell lysis and fractionation, tissue disruption, the extraction of intracellular compounds as well as the shearing of DNA, RNA, and chromatin. Ultrasonic homogenizers are available for sample preparation of tiny volumes (0,1mL) up to very large volumes for industrial processes (e.g. extraction of bioactive compounds for supplement manufacturing).
In order to disrupt tissue with an ultrasonic homogenizer, an isotonic buffer solution is used to stop osmotic damage. Hielscher ultrasonic homogenizers come with a temperature sensor and temperature control setting, which allow to keep the samples in a well-controlled temperature range.
Hielscher produces ultrasonic homogenizers for the homogenization of any sample volume for batch or inline processing. Laboratory ultrasonic homogenizers can be used for volumes from 1.5mL to approx. 2L. Ultrasonic industrial homogenizers are used for the process development and production of batches from 0.5 to approx 2000L or flow rates from 0.1L to 20m³ per hour.
The table below, indicates general device recommendations depending on the batch volume or flow rate to be processed. Click at the device type to get more information on each ultrasonic homogenizer.
|Batch Volume||Flow Rate||Recommended Devices|
|0.5 to 1.5mL||n.a.||VialTweeter|
|1 to 500mL||10 to 200mL/min||UP100H|
|10 to 2000mL||20 to 400mL/min||UP200Ht, UP400St|
|0.1 to 20L||0.2 to 4L/min||UIP2000hdT|
|10 to 100L||2 to 10L/min||UIP4000hdT|
|n.a.||10 to 100L/min||UIP16000|
|n.a.||larger||cluster of UIP16000|
Ultrasonic Homogenizers for High Performance Applications
Hielscher ultrasonic homogenizers are the work horse for mixing and homogenization. Ultrasonic lab homogenizers are compact and a reliable tool for the efficient and rapid dispersing and emulsifying of small and medium samples. Hielscher’s industrial ultrasonic homogenizers are efficacious and outperform traditional homogenization techniques such as high pressure homogenizers or bead mills. Hielscher industrial homogenizers can deliver very high amplitudes and are thereby exceptionally powerful when it comes to mixing, dispersing and milling processes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available. The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.
Our customers are satisfied by the outstanding robustness and reliability of Hielscher Ultrasonics’ homogenizers. The installation in fields of heavy-duty application, demanding environments and 24/7 operation ensure efficient and economical processing. Ultrasonic process intensification reduces processing time and achieves better results, i.e. higher quality, higher yields, innovative products.
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Facts Worth Knowing
Applications of Ultrasonic Probe-Type Homogenizers
The field of applications, where ultrasonic probe homogenizers are successfully used, covers manifold processes in various industries. the most prominent applications of ultrasonicators include the preparation of suspensions, dispersions and emulsions, wet-milling of micron- and nano-particles, dissolving powders and tablets, production of extracts from botanicals, cell lysis, the extraction and subsequent shearing of DNA, RNA and chromatin, protein extraction, the encapsulation of APIs in liposomes, and sonochemical reactions, where powerful ultrasound waves are used to initiate and accelerate rections (sono-catalysis, sono-synthesis), to increase mass transfer and to switch reaction pathways.