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What is the relation between superficial velocity and average fluid velocity in a packed bed?

What is the relation between superficial velocity and average fluid velocity in a packed bed? Correct Answer ϑ=φu

The correct relation between the superficial velocity and the average velocity is given as ϑ=φu, whereϑ is the porosity of the bed. The average fluid velocity is the cumulative mean of the velocity of fluid through the voids which is difficult to measure.

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Bed bugs are parasitic insects in the genus Cimex that feed exclusively on blood. Cimex lectularius, the common bed bug, is the best known as it prefers to feed on human blood. The name bed bug derives from the preferred habitat of Cimex lectularius: warm houses and especially near or inside beds or other sleep areas. Bed bugs are mainly active at night, but are not exclusively nocturnal. They usually feed on their hosts without being noticed. A number of adverse health effects may results from bed bug bites, including skin rashes, psychological effects, and allergic symptoms. Bed bugs are not known to transmit any pathogens as disease vectors. Certain signs and symptoms suggest the presence of bed bugs; finding the adult insects confirms the diagnosis. Assuming the information in the given paragraph is true, choose the correct statement.
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If water is to be used as the fluidising medium, in actual operation, the above bed has a height = 1 m. What is the porosity of the fluidised bed?
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