Table of contents 1 Why is particle size important?
NUMBER VS. VOLUME DISTRIBUTION
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| NUMBER VS. VOLUME DISTRIBUTION
The easiest way to understand a number distribution is to consider measuring particles using a microscope. The observer assigns a size value to each particle inspected. This approach builds a number distribution—each particle has equal weighting once the final distribution is calculated. As an example, consider the nine particles shown in Figure 6. Three particles are 1µm, three are 2µm, and three are 3µm in size (diameter). Building a number distribution for these particles will generate the result shown in Figure 7, where each particle size accounts for one third of the total. If this same result were converted to a volume distribution, the result would appear as shown in Figure 8 where 75% of the total volume comes from the 3µm particles, and less than 3% comes from the 1µm particles. When presented as a volume distribution it becomes more obvious that the majority of the total particle mass or volume comes from the 3µm particles. Nothing changes between the left and right graph except for the basis of the distribution calculation. Particle size result interpretation: number vs. volume distributions 30 25 20 15 10 5 0 1µm 2µm 3µm 70 60 50 40 30 20 10 0 1µm 2µm 3µm Another way to visualize the difference between number and volume distributions is supplied courtesy of the City of San Diego Environmental Laboratory. In this case beans are used as the particle system. Figure 9 shows a population where there are 13 beans in each of three size classes, equal on a number basis. Figure 10 shows these beans placed in volumetric cylinders where it becomes apparent that the larger beans represent a much larger total volume than the smaller ones. Figure 11 shows a population of beans where it may not be intuitively obvious, but there is an equal volume of each size, despite the wide range of numbers present. It becomes apparent in Figure 12 when the beans are placed in volumetric cylinders that each volumes are equal. tải về 7.54 Mb. Chia sẻ với bạn bè của bạn:
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