Homogenizers – Working Principle, Use and Scale-Up
Homogenizers are a type of mixers, which apply mechanical forces to blend, emulsify, disperse, and dissolve liquid-liquid and solid-liquid systems. Depending on the homogenizer model rotational shear, nozzles or high-power ultrasound are used to create the required forces to disintegrate and break up solid particles as well as liquid droplets. Learn more about homogenizer devices and their applications in research and production!
What is a Homogenizer?
A homogenizer is a class of mixing devices, which is designed to break particles, both solid and liquid, into a uniform mixture. Homogenizers are available as laboratory, bench-top and, industrial equipment used for various applications in research and industry. Typical application of homogenizer include the mixing and disintegration of various materials, including particles, pigments, chemicals, plants, food, cells, tissues, amongst others.
Overview over Various Homogenizer Types
Various homogenizer types are commercially available for the use in bench-top and industrial large-scale production. However the rotor/stator (colloid) mixers, high pressure homogenizers, and ultrasonic homogenizers are the most widely used models.
Impeller or blade mixers have a spinning blade, which rotates at high speed at the bottom of the mixing vessel thereby combining various materials into a homogeneous mixture.
As the name of the rotor/stator mixer already implies, a rotor/stator mixer has a rotor and a stator component. The rotor is a metal shaft that rotates at high speeds within the stator. The stator is the metal part that remains stationary. The rotation of the rotor creates a suction effect that moves the solid-liquid material between the stator and rotor, where the solids are reduced to smaller particle size.
The working principle of the high-pressure homogenizer (HPH) is based on the use of a high-pressure pump and a valve (nozzle, orifice), which makes the equipment large, heavy, and expensive. The processed slurry is forced with high flow velocity through a small orifice, which reduces particle size as particles require a certain small size in order to pass through the valve. Especially when processing solids, HPHs are prone to clogging.
Ultrasonic homogenizers use the high-shear forces generated by acoustic cavitation, which gives them various advantages over other homogenizing techniques. The working principle and benefits of ultrasonic homogenization are presented below.
High-Power Ultrasound as Homogenizing Force
An ultrasonic homogenizer uses high-intensity ultrasonic vibrations and cavitation to create very intense shear forces and can be therefore called a super-intense high-shear mixer. The secret behind the super-intense high-shear forces is acoustic cavitation, which is generated by high-power ultrasound waves. An ultrasonic homogenizer has a generator, which is the power supply and control unit, and a transducer. The transducer contains piezo-electric ceramics. These piezo-electric ceramics convert the electric energy into oscillation, since the piezoelectric crystals change their size and shape when voltage is applied. When the frequency of the electronic oscillator is equal to the natural frequency of the piezoelectric quartz, resonance occurs. Under resonance conditions, the quartz produces longitudinal ultrasonic waves of large amplitude.
The generated ultrasound waves are then coupled via the ultrasonic probe (sonotrode / horn) into the process medium. The amplitude at the ultrasonic probe determines intensity of ultrasound waves, which are transmitted into the liquid or slurry. The ultrasonic waves generate alternating high-pressure and low-pressure cycles in liquid media. During the low-pressure cycle, high-intensity ultrasonic waves produce small vacuum bubbles in the liquid. During the high-pressure cycle, small vacuum bubbles collapse destructively. This phenomenon is called cavitation. Implosion of cavitation bubbles may also generate liquid jets with a high speed of up to 280 m/s, resulting in powerful shear forces. The shear forces break the particles, cause inter-particle collision and disrupt droplets and cells mechanically, promoting at the same time a highly efficient mass transfer. These cavitational forces produce uniform and homogeneous dispersions, emulsions and suspensions and are also known to promote chemical reactions (so-called sonochemistry).
Ultrasonic Homogenizers – Advantages
Ultrasonic homogenizers are superior, when it comes to the production of solid-liquid (so-called slurries) and liquid-liquid suspensions and solutions. Since ultrasonicators use the working principle of ultrasonic cavitation, the material should be wet or in a wet phase, since cavitation only occurs in liquid. This means an ultrasonicator would not be very efficient in mixing a dry powder, but as soon as the powder gets wetted, sonication is the most efficient method for blending. Ultrasonic homogenizers are well known to reliably mix, blend and disperse even pastes and highly viscous materials. The extraordinarily intense forces caused by the implosion of cavitation bubbles creates not only very powerful high-shear forces but also locally confined high temperatures and pressures as well as respective differentials. These combination of physical forces disrupt particles to much smaller sizes than a conventional homogenizer. Therefore, ultrasonic homogenizers are the preferred equipment for the reliable production of nano-sized emulsions and dispersions.
- excellent efficiency
- capable to deliver highly focused energy
- superior results in micron and nano
- for micron- and nano-sized emulsions and dispersions
- any volume from mL to tons/hr
- batch and inline
- for single pass and recirculation
- precise process control
- simple operation
- easy cleaning
- low maintenance
Applications of Ultrasonic Homogenizers
Ultrasonic homogenizers are widely used in laboratory and industrial facilities to homogenize solid-liquid and liquid-liquid suspensions, reduce particle size, disrupt and extract biological material, intensify chemical reactions and dissolve soluble compounds.
Emulsification is the process of blending two or more immiscible liquids together in order to prepare a stable or semistable mixture. In general, these two liquids consist of an oil phase and an aqueous (water) phase. To stabilize the mixture of the different liquid phases, an emulsifier (surfactant / co-surfactant) are added. The droplet size of an emulsion plays a crucial role when it comes to the functionality and stability of an emulsion. Since power-ultrasound creates sonomechanical forces, which break up droplets und reduce them to minute droplets, sonication is a very popular method for the production of micron- and nano-emulsions. Ultrasonic homogenizers are a reliable tool for the production of O/W and W/O emulsions, inverse emulsions, double emulsions (O/W/O, W/O/W), mini-emulsions as well as Pickering emulsions. Based on this flexibility and the reliable emulsifying capacity, ultrasonic homogenizers (sometimes also called ultrasonic emulsifiers when used for emulsification) are used e.g., in the chemical, food, pharmaceutical, and fuel industry to produce long-term stable emulsions.
Click on the following links to learn more about nano-emulsions, and Pickering emulsions!
Ultrasonic homogenizers are very efficacious when particle agglomerates, aggregates and even primary particles must be reliably reduced in size. The advantage of ultrasonic homogenizers is their capability to mill particles down to smaller and more uniform particles sizes, whether micron- or nano-particles are targeted as process result. Cavitational shear forces and liquid streams accelerate particles so that they collide with each other. This is known as interparticle collision. The particles themselves act as milling medium, which avoids contamination by grinding beads and the subsequent separation process, which is necessary when conventional bead mills are used. Since the particle clash by interparticle collision at very high speeds of up to 280m/sec, extraordinarily high forces apply to the particles, which therefore shatter into minute fractions. Friction and erosion give those particle fragments a polished surface and uniformly shaped form. The combination of shear forces and interparticle collision give ultrasonic homogenization and dispersion the advantageous edge delivering highly homogeneous colloidal suspensions and dispersions!
The picture sequence below depicts the cavitational forces of ultrasound on graphite flakes.
Dispersion and Homogenization of Nanomaterials
For both, emulsions and dispersions, the preparation of nano-sized mixtures is a challenging task. Most conventional homogenization and blending techniques such as blade mixers, bead mills, high-pressure homogenizers and other mixers are capable to produce micron-sized particles, but they cannot reliably break droplets and solids down to nano-size. This is mostly due to insufficient intensity. For instance, blade mixers do not provide enough shear for breaking particles to nano-size. Bead mills, another type of homogenizer, cannot mill solids uniformly to a finer particle size than the beads (grinding media) itself. Conventional grinding beads have an average size between 1,500 mm – 35,000 mm. Another problem is the contamination by wear and tear of the milling medium. Since ultrasonicators provide extraordinarily high, yet precisely controllable shear forces, ultrasound cavitation is the preferred technique for the reliable production of nano-dispersion and nano-emulsions in lab (R&D), pilot, and industrial setups.
Scale-Up of Ultrasonic Homogenizing Processes
When scaling up from a laboratory ultrasonic homogenizer to a pilot ultrasonicator, and from a pilot system to a full-scale production ultrasonic homogenizer, the scale-up can be applied completely linear! All important process parameters such as amplitude, pressure, temperature and processing time are kept constant, only the surface area of the ultrasonic probe and the ultrasonicator as energetic agitator of the probe are scaled to larger, more powerful units. The linear scalability of ultrasonic homogenization processes allows to obtain in large production the same high-quality results as in lab and pilot settings.
Find the Most Suitable Ultrasonic Homogenizer for Your Process!
Hielscher Ultrasonics is your long-time experienced partner for ultrasonic homogenizers. All Hielscher ultrasonicators are designed, manufactured and tested in our headquarter in Germany before we ship them to our customers worldwide. Hielscher ultrasonic homogenizers are high-quality devices charcterized by constant high-performance, reliability, robustness, and user-friendliness. Technical sophistication of the ultrasonic homogenization technology give the users of Hielscher equipment competitive advantages, which make them to the market-leader in their industry. With the broad product range from lab and bench-top homogenizers, pilot systems and full-industrial ultrasonic homogenizers for commercial productions, Hielscher has the ideal ultrasonic mixing system for your requirements. The manifold accessories allow for the ideal ultrasonic homogenizer setup – matching individual needs.
Tell us your process requirements and specifications – we will gladly recommend you the most suitable and efficient ultrasonic homogenizer for your application!
High-Efficiency with Ultrasonic Homogenizers
Due to extraordinary process efficiency, reasonable investment costs, very high energy-efficiency and low labour and maintenance costs, Hielscher ultrasonic homogenizers outcompete conventional homogenizing techniques and achieves a fast RoI (Return on Investment). Often, an ultrasonic homogenizer is amortized within a few months.
High-Power Ultrasound for Industrial Homogenization
The amplitude is the most important process parameter in ultrasound-driven homogenization processes. All Hielscher ultrasonicators allow the precise control over the amplitude. Depending on the process target, a lower amplitude can be set for milder processing conditions or a high amplitude is chosen for more destructive dispersion results. Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available.
Low Maintenance Requirements for Ultrasonic Homogenizers
Ultrasonic homogenizers are not only easy to clean since the sonotrode and reactor are the only components which are wet parts and get in contact with the processed material. Sonotrode (also known as ultrasonic horn or probe) and reactor are made from titanium and stainless steel, respectively and have clean geometries without orifices or dead corners.
The only part which is subject to wear and tear is the ultrasonic probe, which can be replaced without significant disruption to the operation. The sonotrode of a lab ultrasonicator is changed within approx. 10 min, whilst the change of a sonotrode of an industrial ultrasonic homogenizer may take approx. 30-45 min.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
|Batch Volume||Flow Rate||Recommended Devices|
|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|
|0.3 to 60L||0.6 to 12L/min||UIP6000hdT|
|n.a.||10 to 100L/min||UIP16000|
|n.a.||larger||cluster of UIP16000|
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Literature / References
- Karl A. Kusters, Sotiris E. Pratsinis, Steven G. Thoma, Douglas M. Smith (1994): Energy-size reduction laws for ultrasonic fragmentation. Powder Technology, Volume 80, Issue 3, 1994. 253-263.
- Ahmed Taha, Eman Ahmed, Amr Ismaiel, Muthupandian Ashokkumar, Xiaoyun Xu, Siyi Pan, Hao Hu (2020): Ultrasonic emulsification: An overview on the preparation of different emulsifiers-stabilized emulsions. Trends in Food Science & Technology Vol. 105, 2020. 363-377.
- Seyed Mohammad Mohsen Modarres-Gheisari, Roghayeh Gavagsaz-Ghoachani, Massoud Malaki, Pedram Safarpour, Majid Zandi (2019): Ultrasonic nano-emulsification – A review. Ultrasonics Sonochemistry Vol. 52, 2019. 88-105.
- Brad W. Zeiger; Kenneth S. Suslick (2011): Sonofragmentation of Molecular Crystals. J. Am. Chem. Soc. 2011, 133, 37, 14530–14533.