For coarse granular materials such as sand, granulated sugar and alumina, that have
poor air retention properties, the relationship will generally be similar to that of material
type B. With these materials a minimum conveying air velocity of about 13–16 m/s
is usually required to convey the material. These materials are not usually capable of
being conveyed in any mode other than suspension flow with conventional pneumatic
conveying systems. There is, therefore, little change in value of the minimum conveying
air velocity that can be used to convey the material. Maximum values of solids
loading ratio that can be achieved are generally quite low. A typical maximum value is
about 15 but this can be as high as 30 if the pressure gradient is very high.
For very permeable materials conveying air velocities can also be very low, but
solids loading ratios are also very low, with a typical maximum value of about 30. This
is because the air flows readily through the interstices between the particles. For dilute
phase conveying a minimum velocity similar to that for type B materials is required.
At this point in time data on minimum conveying relationships of the type shown in
Figure 8.1 can only be obtained reliably from actual conveying trials with the material.
The means by which this data can be obtained is considered in Chapter 11.
For coarse granular materials such as sand, granulated sugar and alumina, that havepoor air retention properties, the relationship will generally be similar to that of materialtype B. With these materials a minimum conveying air velocity of about 13–16 m/sis usually required to convey the material. These materials are not usually capable ofbeing conveyed in any mode other than suspension flow with conventional pneumaticconveying systems. There is, therefore, little change in value of the minimum conveyingair velocity that can be used to convey the material. Maximum values of solidsloading ratio that can be achieved are generally quite low. A typical maximum value isabout 15 but this can be as high as 30 if the pressure gradient is very high.For very permeable materials conveying air velocities can also be very low, butsolids loading ratios are also very low, with a typical maximum value of about 30. Thisis because the air flows readily through the interstices between the particles. For dilutephase conveying a minimum velocity similar to that for type B materials is required.At this point in time data on minimum conveying relationships of the type shown inFigure 8.1 can only be obtained reliably from actual conveying trials with the material.The means by which this data can be obtained is considered in Chapter 11.
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