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2.2 Fluidised BedsA bed of sand can be expanded to have many properties similar to a liquid by continuously adding a fluid. The process is known as fluidisation; where R. H. Perry and D. W. Green highlight that particle sizes between 1 μm and 60 mm in diameter can be fluidised depending on the velocity of the liquid or gas [Per97]13. The method has historically been used in a wide range of applications, for instance in chemical reactions where homogeneous non-catalytic reaction uses fluidisation to ensure temperature control and mixing gases. Such procedure may be carried out for oxidation of gaseous fuels [Per97]13. Fluidising a dense seabed will enable the sand to behave as a fluid and thereby an object will either sink into it or, if already embedded, be easily removed depending on the characteristics of the object. Fluidising solid particles is only possible if the fluid added is travelling at a velocity high enough to suspend the weight of the solid bed. This is the minimum fluidising velocity. If using gas, or if the solid particles are very small when using a liquid, then this velocity may be calculated using the following equations [Per97]13.  (2-1)
Where:  (2-3)
 (2-4)
See page (v) for explanation of the notifications. When the velocity of the liquid or gas travelling through the bed is very low, the particles remain stationary. At this point there will be a pressure drop found using the Ergun equation, which covers the full range of flow rates. It assumes however viscous- and kinetic energy losses are additive [McC93]14. The Ergun equation is shown in equation (2-5) where it may be noticed that first part is dependent on viscosity and second part on density of the fluid.  (2-5)
 (2-6)
 (2-7)
See page (v) for notifications. Ergun equation can be re-arranged to find the minimum fluidisation velocity when the bed of sand is fluidised with a fluid and the grain size of the sand is too big to use the formula stated by R. H. Perry and D. W. Green. The derivation is found in Appendix A, where the final equation is (2-8) for Reynolds number < 1 [McC93]14. Details of new notifications are on page (v).  (2.8)
The change of minimum fluidisation velocity depending on particle diameter for air is seen in Graph 1 for a range of pressure flow rates. Once fluidised, the pressure will remain constant, however bed height should increase as the flow of the fluid is increasing. The bed height will not decrease until the flow rate is reduced, and at this point, the pressure should still be unchanged [McC93]14. 
Graph 1 Minimum fluidisation velocity with air at 20° and 1 atm from [McC93]14 Directory: shs shs -> Stonelaw Mathematics Department Green Course Revision Sheets Block E shs -> Core Classes Offered by Department Indicates ncaa clearinghouse Approved Core Class english shs -> Identify the prepositional phrases in the following sentences. Write them on a separate piece of paper shs -> Smart Phone Class Security and Safety shs -> Bordon Luciano shs -> 1 Week before Scheduled Contact shs -> Informative Research Essay Assignment shs -> 10th Daily “Fix It” Sentences shs -> The story of Perseus as told by Diodorus Download 11.38 Mb. Share with your friends:
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(2-2)