Homogenizer: Parts, Types, and Functions

Homogenizer is an efficient industrial or laboratory equipment that breaks solid and liquid particles into uniform and consistent mixtures. It is also known as a cell lysor, dispenser, high shear mixer, rotor stator homogenizer, or sonicator. It was invented in the early 1900s by Auguste Gaulin for homogenizing milk. The primary purpose of a homogenizer is to reduce particles or globules to sizes of 0.2 to 2 microns and blend them to create stable dispersion and emulsion. Similarly, homogenizer can help perform processes like shredding, wetting, dissolving, emulsifying, extraction, precipitation, and cell rupture.

Main Components of Homogenizer

The major components of a homogenizer are; the pump, homogenizing valve, breaker ring, tension spring, and valve seat.

Homogenizing valve: It is a significant component in the homogenization process. It may be of different shapes and sizes. Based on the number of valves used, homogenizers are of two types; single-stage homogenizers (uses a single valve) and two-stage homogenizers (uses two valves).

Valve seat: Both homogenizing valve and seat form the opening of the homogenizer.

Breaker ring: The valve consists of a breaker ring. The fluid passing through the opening formed by the valve and seat strikes perpendicularly on the breaker ring inner wall. As a result, size reduction of the larger particles or globules into finer forms takes place.

Tension spring: It helps to hold the valve at adjustable tension. As the fluid pressure comes against the valve, it rises a few thousand inches; as a resulting in the formation of the orifice. 

Homogenizing pumps: It imparts the desired pressure required for homogenization.

Principle 

The working principle of the homogenizer is based on the conversion of large globules or coarse particles into fine globules or particles by passing them under high pressure through a narrow orifice. Thus, the product formed has a high degree of uniformity and stability. In a homogenizer, homogenizing action occurs by the combined effect of three major physical principles; shearing, turbulence, and cavitation.

Shearing 

The shearing effect is accomplished by large particles when it is caught between the fluid layer of different velocities. Thus, a generated force known as shear force breaks the large particles into smaller sizes.

Turbulence

It occurs when fluid experiences high velocity. The high velocity generates irregular motion within the fluid. Irregular motion in a fluid results from the conversion of kinetic energy into internal energy in the form of eddy currents and some heat. The eddy current developed helps to convert larger particles into finer sizes.

Cavitation 

Cavitation occurs when there is a significant drop in pressure in the fluid. In a homogenizer, a pump that lies upstream of homogenizing valve helps to introduce high pressure within the fluid. The force of the fluid converts into kinetic energy when it passes to the valve. When enough pressure drops, cavities forms from the vapor as vapor pressure exceeds the absolute pressure inside the homogenizer. Once these cavities collapse, shock waves release that are responsible for breaking particles in the mixture.

Types of Homogenizer

There are different types of homogenizers. Each type has advantages and drawbacks; these make them suitable for a particular application. These include; high-pressure homogenizers, mechanical homogenizers, and ultrasonic homogenizers. 

High-pressure homogenizer

• It is one of the most common and versatile homogenizing equipment and consists of two main parts; a high-pressure pump and a homogenization valve.
• A high-pressure pump is a positive displacement pump that forces liquid into the valve area at high pressure. The pressure developed by the pump depends on the fluid type. But most operate at around 8,000 to 40,000 psi (550 to 2750 bars).
• A homogenization valve comprises a seat, valve, and impact ring.
• When the product is forced through the adjustable gap, its velocity rises massively and strikes the impact ring. This sudden change in energy causes shear, turbulence, and cavitation formation resulting in size reduction and uniform dispersion of particles.

Mechanical homogenizer

The mechanical homogenizer uses tearing caused by moving parts as the primary energy source. The most popular homogenizer types include colloid mill, rotor-stator homogenizer, bead mill, and blade type homogenizer.

Colloid mill

• The homogenizer composed of a conical rotor and stator separated by a small clearance.
• The high rotating speed of the rotor results in a rapid amount of shearing and turbulence within the fluid that breaks large particles into finer forms.

Rotor-stator homogenizer

• Its rotor-stator assembly is sometimes called a mixing head, generator, or probe.
• Fluid flow between the shear gap or the region between the rotor tip and stator gap.
• Inside the shear gap, fluid flowing with high differentials and turbulence is present that produces high shear rates that break larger particles into finer forms.

Bead mill

• Also known as ball mills, it uses beads for mechanically grinding and breaking large particles dispersed in the premix fluid.
• Beads are loaded inside the container along with the contact with the premix fluid. The agitation occurs by internal rotating components such as paddles and blades, or by centrifugally spinning the container at high speed.

Blade type homogenizer

• This homogenizer uses blades as its rotor.
• The Shearing effect is developed only by the high-speed rotation of the blade.

Ultrasonic homogenizer

• Also known as sonicators or sonic disruptors, they work based on the ultrasonic cavitation physical principle.
• Cavitation is created by alternating rarefaction and compression periods at ultrasonic frequencies.
• It comprises of three parts; generator, transducer, and probe.
• The generator receives electrical power and converts it into a suitable form for energizing the transducer at the desired frequency. The transducer converts electrical current supplied by a generator into ultrasonic vibration. Similarly, the probe is the part that comes in contact with the premix fluid, one end of the probe connected to the transducer causes it to vibrate, and the probe’s vibration on transmission to the premix fluid leads to the development of cavitation. 
• The probe sizes vary on the basis of companies like the Fisher Scientific™ Model 120 Sonic Dismembrator provides three probe sizes for processing 0.2-50 ml volumes. 

Functions or uses of homogenizer

Homogenizers have wide application in pharmaceuticals, food and beverage production, agriculture products production, chemical processing, and laboratory testing. Besides its use in producing emulsions and suspension, homogenizer also performs other functions, including;

1. It helps in microbial inactivation by finely breaking the cell structure of dispersed microorganisms. Therefore, it helps to increase the shelf life of food in food industries.
2. It helps in cell fractionation, in which a cell ruptures, but its internal component remains the same. Thus produced intact internal parts are used for making agricultural and pharmaceuticals bioproducts.
3. High-pressure homogenization can modify the structure of enzymes. By adjusting pressure, enzymes can be targeted for activation or deactivation process, which is applicable in beverages and liquor production.
4. It also helps extract high-value compounds such as polyphenols, flavonoids, lycopene, etc.

Differences between homogenizer and mixer

Although the homogenizer and mixer have the same function of mixing substances, there exist some differences between them which are as follows;

Homogenizer	Mixer
Homogenizer works by specific cooperation of the rotor and stator, the rotor rotates at high speed and steadily to obtain homogeneity.	Mixer works by rotating the blade at the bottom of the mixing cup at high speed.
It uses various methods of mixing and provides thorough mixing.	It uses traditional mixing method that results in simple mixing.
It’s general use is in tissue dispersion in biotechnology, sample preparation, and enzyme treatment in the food industry.	It is generally used to mix a variety of fruits and vegetables.
There is a shearing and refining effect to obtain homogeneity in the mixture.	There is no shearing and refining effect, only simple mixing is carried out.
It requires high power consumption and high maintenance cost.	It requires low power consumption and low maintenance cost.

References

• Aldridge WN, Emery RC and Street BW. A tissue homogenizer. Biochem J, 1960. 77: 326-327. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1204988/pdf/biochemj01007-0120.pdf
• Homogenizers. Dairy Processing Handbook. Retrieved on 1st september 2022. Retrieved from https://dairyprocessinghandbook.tetrapak.com/chapter/homogenizers
• The field of homogenizing. PRO SCIENTIFIC. Retrieved on 31st August 2022. Retrieved from https://proscientific.com/the-field-of-homogenizing
• Wet grinding mill and mixing machine. ELE Dispersers & Bead mills. Retrieved on 30th August, 2022.Retrieved from https://www.ele-mix.com/homogenizer/