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A cascade impactor is used when a particulate substance is moved through an opening with the use of aerosol. The impactor is used to measure the range of the substance’s reach. Cascade impactors are strictly measurement-related devices.
In addition to measuring the range of substances moved through an opening by aerosol, the impactor can also be used to determine the particle size of the distributed substance. A cascade impactor collects its samples in a graduated manner. This allows the user to identify the sizes of the substance particles as the particles are distributed from the propellant aerosol source.
When the aerosol substance is distributed into the cascade impactor, the substance enters a series of discs designed to collect solids and different particulate matter. The substance is thus collected as it passes through the disc series. Each disc is set in sequence with both the prior and the previous disc. The size of the discs is graduated as well, to properly determine the size of the particulate matter at each stage of the impactor.
There are typically ten different stages in a cascade impactor; the stages range from large to small, depending on the substance being measured. The lighter the substance, the farther it will travel into the impactor. Each disc in the impactor has its own speed in which it is used to collect the substance being passed through it. Once the discs cease to collect any amount of matter, the user is able to determine the dispersion rate of the substance propelled by the aerosol.
The function of the cascade impactor is directly relevant to its design, which consists of a powered flow chamber that contains all of the discs. Each disc within the flow chamber represents a stage of the impactor. Each stage acts as a guide for the user to determine the dispersion rate for the substance.
As the substance is distributed into the inner workings of the impactor, the discs at each stage gather any sizable particulate or amount of solid matter they are able to. This allows smaller and smaller solid particles to pass through to the next stage of the impactor. Since each disc has its own collection velocity, the flow chamber gains speed toward the end of the impactor. This allows for the collection of the finer particles all the way through to the end of the impactor.
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