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Centrifuges separate suspended material from a mixture by rotating containers at high speeds, using centrifugal force to push denser material against the walls. They are used in labs, medical facilities, and industries, and can separate solids from fluid suspension media. Different substances separate in order of density, forming distinct layers at the bottom of the tube. Centrifuges are also used in wastewater management, the oil industry, sugar and milk processing, and to expose people to extreme forces in a controlled environment.
Centrifuges are machines used in laboratories, medical facilities and industries to separate suspended material from the media with which they are mixed. This is done by rotating the closed containers of the mixture very quickly around a fixed and central point. The centrifugal force generated by this motion pushes the denser material in suspension against the walls of the container, effectively separating it from the solution. These devices are used to separate solids from fluid suspension media; for example, they are an essential medical tool for separating plasma from blood samples.
How do they work
The fundamental principle of the operation of the centrifuge is the centrifugal force. If a half-full bucket of water is spun in a fast circle, overhead and then back to the ground, the centrifugal force created by the bucket’s rotation pushes the water to the bottom. This is what keeps the water in the bucket even when it’s upside down.
Most centrifuges harness this force in a similar way and consist of a casing with a lid and a driven central rotor. The rotor has a row of holes around its circumference into which containers, typically test tubes, of solution are placed. Once the lid of the machine is closed and the centrifuge is turned on, the rotor spins at high speed. As with the bucket experiment, centrifugal force causes any matter in the solution denser than the liquid to be forced against the outer walls of the tubes, separating it from the fluid in the process.
Once the cycle is finished, the centrifuge is progressively slowed down and stopped to avoid any turbulence which could cause the solution to mix. This slowdown period also allows all separated material to drop to the bottom of the tube. Once the rotor has stopped, the tube can be removed and the samples processed.
In some cases, a centrifuge may have a screen at one end, allowing liquids to pass through while solids remain trapped inside the tube. Others may hold the pipes at a fixed angle or allow them to swing as they spin. The position of the tube and the speed of rotation of the centrifuge may vary depending on the type of solution to be separated.
Density separation
Any number of suspended materials can be separated from a suspension in this way. Each different substance will separate in order of density, forming distinct layers at the bottom of the tube when the machine is stopped. This is known as the settling principle. For example, a blood sample placed in a centrifuge for an adequate cycle length will break down completely with heavier blood cells pooling at the bottom and lighter blood plasma at the top. This is especially useful for identifying all components of unknown solutions.
other uses
Centrifuge devices are not only used in laboratories; they see extensive use in wastewater management, the oil industry, and even sugar and milk processing. Typically, medical and scientific laboratory centrifuges are small tabletop devices. The industrial machines used to separate the magnetite sludge from the process water in a coal-fired power plant, on the other hand, can be very large.
The gas-fired centrifuges used in the uranium enrichment process have specially designed vessels that include a strategically placed internal scoop. When spun, this scoop collects the desirable uranium-235 isotope while the heavier 238 isotope collects on the container walls. This is, however, a much longer process than slurry separation, often requiring several thousand cycles to achieve.
Large centrifuges are also used to expose people to extreme forces in a controlled environment. The outward force created by such a large machine can be used to simulate the massive gravitational forces (G-forces) that an astronaut or fighter pilot might experience when traveling at very high speeds. Geotechnical modeling is another area where centrifuges are used to simulate gravitational stresses in prototypes.
