Here is the most complete guide on the internet about
You will learn:
This chapter details the fundamental concepts of centrifuges, explaining their design, construction, and the core principles behind their operation.
A centrifuge is an essential scientific tool employed to separate fluids, gases, or liquids based on varying densities. This separation occurs when the material-filled container is spun rapidly, creating centrifugal forces that propel denser substances towards the container's bottom.
A laboratory centrifuge employs centrifugal force, generated by a rotating rotor mechanism, to segregate materials of varying particle sizes within a solution or suspension. This apparatus commonly finds use in pharmaceutical, food testing, environmental protection, and chemical analysis.
Centrifuges are crafted with an eye on design and user-friendly features, including adjustable speed and temperature controls for greater usability. A typical laboratory centrifuge comprises the following components:
Rotors are categorized into angular and horizontal, each designed for different speed and capacity needs. Horizontal rotors face more resistance than angular ones, making them ideal for larger volume separations rather than high-speed tasks.
Centrifuge rotors, whether angular or horizontal, facilitate separation at high speeds but are generally used for lower capacities. Horizontal rotors offer more resistance, more suitable for handling larger volumes than rapid separations.
The driving system features a motor, drive shaft, and damping unit. The motor is powered by AC electricity, operating a sealed and lubricated shaft. The damping system reduces force impact, vibration, and noise, ensuring smooth functioning.
Managed by a microcomputer with a touch interface and digital display, the control system allows operators to adjust spin speed and centrifugal force, with options to save these settings for repeat experiments.
The refrigeration setup utilizes a sealed Copeland Compressor unit with distinct circuits for both cooling and heating control functions.
Security elements include protections for current, temperature, speed, balance, and door cover, ensuring safe operations.
Particles in a solution separate based on density, with denser particles settling at the bottom, while lighter ones float to the top. A significant difference in densities accelerates this separation. When density differences are minimal, applying enhanced centrifugal force alongside gravity facilitates effective separation.
Operating a centrifuge involves spinning an object around a fixed axis, applying a perpendicular force. Through sedimentation, the centrifuge creates centripetal acceleration to propel denser materials to the container’s edges. Meanwhile, lighter substances collect towards the center. In laboratory conditions, samples in tubes show denser particles at the bottom with lighter ones settling above.
Centrifuges use sedimentation, combining gravitational and centrifugal forces, to sort substances by density. Techniques like isopycnic separation, pelleting, density gradient, and phase separation are employed. Among these, pelleting is most prevalent, concentrating particulate matter at the bottom as a pellet, separate from the supernatant. Chemicals are often partitioned into a solvent from an aqueous matrix during this process.
Ultrafiltration employs a membrane to separate, purify, and concentrate molecules. Isopycnic centrifugation relies on sedimentation equilibrium to align particles with isodense solutions, specifying forces in gravity units rather than RPM for precision.
Choosing the right laboratory centrifuge is an investment that requires careful consideration of the following attributes:
This defines the centrifuge’s spinning prowess and force. Relative centrifugal force (RCF) is pivotal, dictating the applied force on container contents. Many centrifuges operate up to 14,000 RPM and generate an RCF of 18,624.
Centrifuge models come with specific sets of rotors and attachments, considering:
The selected centrifuge should provide rotors compatible with intended vessels, available in necessary sizes.
Centrifuge models offer rotors in fixed-angle or swing-out styles, with some including additional types like vertical, PCR strip, and microlite rotors.
It’s crucial to assess if the centrifuge achieves the desired RCF.
Centrifuges may function at room temperature or feature cooling mechanics capable of reducing temperatures to -10°C or -20°C.
Centrifuges incorporate several safety systems to safeguard users and environments. These include:
This function securely locks the lid during usage, avoiding unintentional exposure.
Monitors the centrifuge’s balance, discontinuing operation if excessive vibration occurs, ensuring safety and stability.
The design prevents biohazard spills or leaks during operation.
Detects the rotor type and restricts operations within safe speed limits.
When situating a centrifuge, its vibration necessitates stable placement. Additionally, being a source of noise, the unit should be placed where sound is minimized.
All centrifuges consist of two primary components: the rotor assembly and an electric motor. The rotor assembly is responsible for creating the spin and movement transfer, while the motor converts electrical energy into mechanical and kinetic forms.
This chapter will cover the various classes and types of centrifuges.
Centrifuges are generally categorized into two main types: low-speed centrifuges and high-speed centrifuges.
Standard low-speed centrifuges are commonly used in laboratories for routine sedimentation of heavy particles. They typically operate at speeds ranging from 4,000 to 5,000 RPM and usually function at room temperature, with limited temperature control options. These centrifuges are equipped with two types of rotors: fixed-angle rotors and swinging bucket rotors. A typical application for low-speed centrifuges is the sedimentation of red blood cells, where they are concentrated into pellets, and the supernatant is then separated by decanting.
High-speed centrifuges are employed in more advanced biochemical applications, where higher speeds and temperatures are necessary for effective sedimentation.
High-speed centrifuges can reach speeds of up to 15,000 to 20,000 RPM. Operators carefully manage both the temperature and speed to meet the specific needs of sensitive biological samples. These centrifuges typically use three types of rotors: fixed-angle rotors, swinging bucket rotors, and vertical rotors.
The various types of centrifuges include:
A solid wall basket centrifuge makes use of centrifugal force to promote the separation of liquids or solids. The slurry feed is brought into the rotating basket and it is made to accelerate to the basket speed. Any rather large solids or contaminants are pulled away radically from the liquid due to the centrifugal force and they collect along the inner wall of the basket.
The purified liquid accumulates along the interior surfaces and eventually spills over the edge, where it is then collected and allowed to exit through a gravity-fed outlet. This cycle persists until the basket is free of solids and requires emptying.
This centrifugation method allows for the processing of large volumes at high centrifugal forces without the hassle of filling numerous centrifuge tubes or frequently starting and stopping the rotors. With this approach, you'll either need to collect the supernatant or remove the pellet that has formed.
Continuous centrifuges feature brief path lengths to reduce the time needed for pelleting. This design ensures efficient solid separation and allows for a swift flow of material through the rotor. Additionally, these centrifuges have large capacities, which eliminates the need for frequent starts and stops, unlike traditional rotors. This efficiency minimizes sample handling and reduces delays caused by rotor acceleration and deceleration.
Common uses for continuous flow rotors include the following:
The continuous flow rotor is most effective when the sedimentation coefficient of the particles to be collected exceeds 50 s. With its high pelleting efficiency, this rotor separates solid material from the liquid medium more rapidly compared to swinging bucket or fixed angle rotors. It is particularly suited for samples with a solid-to-liquid ratio of 5 – 10%. For ratios above 15%, the efficiency of these rotors is even greater.
When it comes to separating solid or liquid mixtures with a very high solid content, the decanter centrifuge is the best choice. The finely distributed solid particles are separated out of the suspension by very strong centrifugal forces. Decanters thereby play a pivotal role in a wide variety of industries worldwide. They are optimally adapted for a specific application and the applications range from dewatering of sludge to the classification of or wet classification of solids.
A decanter is a type of sedimentation vessel mounted on a rotating axis. Heavier solid particles migrate to the base of the tank due to gravity, accumulating as sediment. In contrast, a centrifuge separates solid and liquid phases using centrifugal force. The higher density solids are forced to the bottom of the centrifuge bowl, forming a sediment along the inner walls. The centrifugal force can be up to 3000 times greater than the force of gravity, compared to the standard 1g of gravitational force.
Another type of centrifuge is the high-capacity, high-speed centrifuge. This substantial machine is floor-mounted and is typically used in laboratories that handle large volumes on a daily basis. It features a program memory capable of storing around 100 protocols and includes automatic rotor recognition. Additionally, it comes with acceleration and deceleration ramps, a spin pulse function, and lockable castors for safety. This centrifuge operates based on generating a specific centrifugal force while also considering gravitational force. The sedimentation rate is influenced by the applied centrifugal force, which acts radially outward, and depends on the following factors:
Industrial centrifuges play a crucial role in dewatering and classifying within the global mineral processing sector. They are employed to separate solids from liquids across various industrial materials. These centrifuges are highly effective for processing a diverse array of minerals and ores, including coal, copper, and other valuable metals.
Industrial centrifuges are generally divided into two primary categories: sedimentation and filtration centrifuges. Sedimentation centrifuges utilize centrifugal force to separate solids from liquids, whereas filtration centrifuges apply force to push a liquid through a filtration medium.
Examples of industrial processes that utilize centrifugation include:
This laboratory centrifuge is designed for experiments that require particle separation through centrifugal force. It separates particles based on factors such as density, size, shape, or viscosity by applying an artificial gravitational force.
Particles with higher densities or larger sizes migrate towards the bottom of the centrifuge (sedimentation), whereas those with lower densities or smaller sizes are pushed outward from the axis of rotation. This method is commonly used to separate cells, cellular components, tiny virus particles, and precipitated proteins.
The oil centrifuge is also referred to as a centrifugal oil filter since it is used in areas where oils need to be filtered. The dirty lube oil circulates from the machine into the centrifuge oil filter. The oil is then pressure driven through the filter into a bowl. The bowl is then spun at very high speeds of up to 5 000 rpm to up to 8 000 rpm with respect to the oil inlet pump pressure. The resultant gravitational force draws any particles to the exteriors of the bowl walls while the clean purified oil passes back into the machine for usage. Soot and other contaminants are repeatedly removed during regular operation of the engine.
It is important to understand that the oil filter does not use a barrier-type filtration method. Instead, it does not depend on filtration media to remove particles contaminating hydraulic or lubricant oil.
Peeler centrifuges are batch-type units featuring perforated bowls with cloth filters. During operation, liquids are spun at high speeds, causing solids to accumulate on the filter cloth and form cakes. The cakes are then dried through a spinning process. Once dried, peeler knives scrape off the cakes, and any remaining residual material, known as heel, is removed. The scraper's position is adjusted, and high-pressure nitrogen is employed to clear the residual material.
A horizontal peeler centrifuge operates as a continuous flow filtration system and can be set to either automatic or manual control modes.
The inverting filter centrifuge is designed to fully expel cake material without leaving any residual heel. Like horizontal peeler centrifuges, it features a rotating drum. However, instead of using peeler knives to remove the cake, the material is pushed out through the bottom of the drum. This pushing action is so thorough that it inverts the filter cloth, effectively clearing any remaining residue and eliminating the need for mechanical cleaning.
This method ensures the highest level of product purity and is ideal for handling challenging filtration processes and situations where minimizing operator contact with the product is crucial.
Solid bowl vertical centrifuges are designed for clarification by using centrifugal force to separate mixed materials. The slurry is introduced into the spinning bowl, and as the bowl’s speed increases, the centrifugal forces drive the dense, solid particles against the interior walls of the bowl, leaving the liquid phase separated.
Because solid bowl vertical centrifuges lack openings for continuous discharge, they require periodic maintenance to remove accumulated solids. This is done during the scrape cycle. Consequently, these centrifuges are not suitable for continuous flow operations as they must be halted and emptied at intervals.
Pusher centrifuges, also known as horizontal basket centrifuges, are equipped with metal screening sheets or slotted sieves and utilize a hydraulic piston. These centrifuges filter liquids to form filter cakes, with the hydraulic piston providing an oscillating pushing motion to either move the cakes out of the bowl or wash them away. They are designed for continuous operation and are particularly effective for handling large volumes of solids where high purity and low residual moisture are required.
In a pusher centrifuge, the basket generates centrifugal force to separate solids from the slurry. A hydraulically driven piston, which rotates with the basket, pushes the solids out with each forward stroke. Solids accumulate on the basket’s screen, while liquids pass through the metal screen or slotted sieve.
This chapter will explore the various applications and advantages of centrifuges.
Centrifugation encompasses a broad range of laboratory and industrial applications. This process is used to separate particles in a solution based on their viscosity, shape, size, and density. Some of the common uses of centrifuges are outlined in this section.
Centrifugation can separate mixtures of two immiscible liquids by exploiting their density differences. It is also employed in analyzing macromolecules and their hydrodynamic properties. Additionally, it is used to fractionate various subcellular organelles and analyze membranes. Specialized centrifuges are used to purify mammalian microcells.
In chalk production, centrifugation is used to remove water from the chalk (dewatering). Similarly, the process is employed to produce skimmed milk by separating the fat from regular milk. The centrifuge effectively separates the fat, resulting in milk with reduced fat content.
Another practical application of centrifugation is in the stabilization and dewatering of wine. During the aging process, wine is processed in a centrifuge to enhance its stability and improve its quality. Additionally, centrifugation is utilized in forensic chemistry to analyze complex samples such as blood, DNA, urine, and other substances that are difficult to detect.
In recent times, centrifugation has increasingly dominated the commercial dewatering market. The following are some of the key advantages of using centrifuges.
Although centrifuges are highly useful, they do have their share of significant drawbacks.
When considering the purchase of a centrifuge, it is important to evaluate several factors to ensure you choose the right device for your needs.
The rotor speed is an important factor to consider, as it determines the level of centrifugal force. If your work demands very high centrifugal forces, you should look for a centrifuge that offers high revolutions per minute (RPM).
The centrifuge should offer programmable settings, allowing it to operate automatically without the need for manual adjustments or constant supervision.
An ideal centrifuge should be equipped with sensors to detect rotor imbalances, preventing spillage and disruptions during the separation process.
The buyer should also consider the type of display required, such as Liquid Crystal Display (LCD), AMOLED, or QLED, and ensure it meets their specific needs.
Considering the overall dimensions of the device is crucial based on its intended use. Industrial centrifuges can be as wide as 5 meters, while medical centrifuges may be as compact as 30 centimeters.
The weight of the centrifuge is another important factor. Some scientific centrifuges are compact and lightweight, whereas others can weigh up to 200 kg.
The required operating voltage depends on the centrifuge’s location. Some areas use a 240V residential plug, while others require higher voltages for industrial applications. Large industrial centrifuges necessitate more voltage and are unsuitable for residential settings.
Centrifuges with high power consumption need a reliable and robust energy source to operate effectively without interruption.
Before selecting a centrifuge, it’s essential to understand the specific tasks it needs to perform. Different centrifuges are designed for various purposes; some are suited for lighter tasks, such as those in pharmaceuticals, while others are built for more demanding industrial applications.
Floor standing centrifuges are designed for high-speed and high-capacity operations, often reaching speeds of up to 150,000 rpm and generating forces up to 300,000N.
Benchtop centrifuges are compact and portable, typically suited for smaller-scale operations. Examples of these are provided below.
Micro centrifuges are intended for small volume tubes, offering relatively low speeds and forces. Some can handle both high and low temperatures, though many only provide one type of temperature control.
Multipurpose centrifuges are versatile, providing a range of options and capabilities for various tasks.
A centrifuge is a scientific device that is used to separate fluids, gasses or liquids based on the density of the subject. The separation is acquired by spinning a container with the material at a very high speed. The resultant forces created will then push out the heavier materials to the extreme outside of the container.
In summary, centrifuges are very important devices that help us in our day to day lives as they can be used in various walks of life. Ranging from laboratories, pharmaceuticals, biology and chemical technology experiments, mining, and industrial processes. There are also many different types of centrifuges with different capabilities. These centrifuges, though important, do come in with a notable number of drawbacks that need to be considered. They have a wide range of specifications that need to be considered before acquiring one.
A water filtering system is a mechanism that is designed to remove solid particles, tiny or large, from inside a liquid through the use of a filter medium that only allows the liquid to pass but restricts solid particles...
Liquid filters are equipment used to separate suspended solids from a fluid stream. A physical barrier, called the filter medium, is a prerequisite in the filtration process in which the liquid passes through and where the solids are retained...
Air filters are devices used to remove airborne particles, pollutants, and microorganisms hazardous to health and the ecosystem. In industrial facilities, air filters preserve the quality of products and materials and protect critical equipment from damage...
A HEPA filter is a high efficiency pleated air filter capable of capturing extremely small particulate matter down to particles that are the size of a micron (µ), or a micrometer, which is 1/1000th of a meter...
An air dryer is a system or piece of equipment that is used to remove moisture present in the air, particularly compressed air. Ambient air typically has a relative humidity of around 30 to 50%. Compressing air packs higher quantities of moisture in a small volume...
A dryer is a machine that reduces the moisture content of bulk solids, manufactured parts, and other valuable materials. It is a complex system consisting of a drying chamber, heaters, materials handling equipment, forced convection equipment...
An altitude chamber is a test chamber that is designed to simulate the altitude, vacuum, and temperature of environmental conditions at heights that match the flight patterns of all forms of aircraft, from commercial to military...
A climate chamber is an enclosed space that provides a controlled set of circumstances for testing the impact of various environmental and climatic conditions on industrial goods, commercial products, electronic devices, materials, and biological matter...
A cold room is a temperature controlled environment that is capable, through refrigeration, to create conditions for storage, experimentation, and preservation of foods, equipment, and medical supplies. The types of cold rooms are...
An environmental chamber is an enclosure used to test the effects of a variety of conditions on a product, component, part, or assembly. These highly technical pieces of equipment are capable of simulating the types of conditions a product may face while in use...
A humidity chamber is a mechanism that examines how products react when exposed to variations in humidity. This type of environmental testing is used by manufacturers to test the various parameters of their products in the harshest of conditions...
Stability chambers and rooms are climate-controlled environments that provide stable conditions for testing and storage. These specialized environmental chambers offer a precise, raised temperature or humidity to ascertain whether a...
A temperature chamber is a controlled environment capable of producing conditions that a product will encounter during its use. These highly controlled technical tools are able to produce the types of hazards, uses, and atmospheres a product may endure...
A test chamber is a managed and controlled environment used to test the endurance, stability, and practicality of equipment, products, and chemicals. They are a controlled enclosure that mimics the effects of environmental conditions that a product may encounter during its usage...
Thermal shock chambers are climatic chambers for thermal shock testing that are utilized to put the material to serious shocks. This is accomplished through the repeated and sudden passage to low temperature areas from...
A vacuum chamber removes air and pressure from a confined enclosure to test the effects of a vacuum on parts, materials, components, and assemblies. It can also be used to test the performance of applications for manufacturing operations...
The purpose of an environmental testing chamber is to examine the effects of a variety of climactic, physical, and other unique conditions on a product. They are designed to create environments that a product may encounter during its use...