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Particles in Water Properties and Processes - Chpater 2

Kích thước hạt và các tài sản liên quan 2.1 Kích cỡ và hình dạng "Hạt" trong nước có thể có kích thước từ vài nano mét (đại phân tử) cho đến kích thước mm (hạt cát). Hạt tự nhiên cũng có nhiều hình dạng, bao gồm các thanh, tấm, và các lĩnh vực, với nhiều biến thể ở giữa, mà làm cho một phương pháp điều trị của kích thước hạt khó khăn. Thảo luận là bao la đơn giản nếu các hạt được coi là hình cầu. Trong trường hợp này, chỉ có một kích thước tham số là cần. | chapter two Particle size and related properties 2.1 Particle size and shape Particles in water may range in size from a few nanometers macromolecules up to millimeter dimensions sand grains . Natural particles also have various shapes including rods plates and spheres with many variations in between which make a treatment of particle size difficult. The discussion is vastly simplified if the particles are considered to be spherical. In this case only one size parameter is needed the diameter and hydrodynamic properties are much more easily treated. Of course nonspher-ical particles are of great importance in natural waters and some way of characterizing them is essential. A common concept is that of the equivalent sphere based on a chosen property of the particles. For instance an irregular particle has a certain surface area and the equivalent sphere could be chosen as that having the same surface area. The surface area of a sphere with diameter d is just nd2. So if the surface area of the nonspherical particle is known the equivalent spherical diameter can easily be calculated. For an object of a given volume the sphere has the minimum surface area and so the volume or mass of a given particle must be equal to or less than that of the equivalent sphere. Another common definition of equivalent spherical diameter is based on sedimentation velocity. See Section 2.3.3 . In this case from the sedimentation velocity and density of a particle the diameter of a sphere of the same material that would settle at the same rate can be calculated. This is sometimes called the Stokes equivalent diameter. In what follows we mainly will deal with the properties of spherical particles which makes the discussion much simpler. Although real particles are usually not spherical their behavior can often be approximated in terms of equivalent spheres. 9 2006 by Taylor Francis Group LLC 10 Particles in Water Properties and Processes 2.2 Particle size distributions 2.2.1 General Only in