RelativeResourceManager-2

RelativeResourceManager-2 - Concept Question(s for...

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Concept Question(s) for filtration – series A
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2 Concept Question 1 filtration time volume of filtrate A 0 0 B C D The figure below pertains to dead-end (conventional) filtration, relating filtrate volume to time under conditions of constant applied pressure. Pick the letter for the line that describes the filtration of pure water by the filter.
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3 Answer to CQ 1 For filtration of pure (particle-free) water, the filter volume vs time is a straight line, reflecting a forever constant filtration flowrate (slope of line). What is the capacity** of the filter for such a stream? **Filter capacity is the maximum volume of filtrate it can process before its flowrate decays to zero. Answer: Infinite capacity. Ans = A
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Concept Question 2 The figure below pertains to dead-end (conventional) filtration, relating filtrate volume to time under conditions of constant applied pressure. Pick the letter for the curve that describes the filtration of a stream containing particles where a cake forms and the cake resistance grows in proportion to the volume filtered. 4 filtration time volume of filtrate A 0 0 B C D
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5 Answer to CQ 2 For filtration of a particle-containing stream, where the resistance from the growing filter cake is proportional to cake depth (and cake depth is proportional to volume filtered), you can recast Harrison p 106 formulas to reveal that the volume filtered increases with the square root of time: V = const * t 1/2 What is the capacity of the filter for such a stream? This model predicts infinite capacity , although the filtrate flowrate will continue to get slower and slower. Curve C has a finite capacity. Curve D is illogical, as it predicts the total filtrate volume starts to go back down as time continues. Ans = B
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6 Concept Question 3 Darcy’s Law predicts how the flowrate through a porous medium depends on the pressure drop, ΔP, fluid viscosity, μ, and other factors. It describes the flow through a filter cake in dead end filtration (and also the flow through a packed column of chromatography resin). According to Darcy’s Law, flowrate is proportional to… A ( red ): ( ΔP/ μ) 2 B ( yellow ): ΔP/ μ C ( green ): ( ΔP) 0.5 / μ D ( blue ): ( ΔP) 2 / μ
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7 Answer to CQ 3 Darcy’s Law applies to low Re “creeping flow” in a porous bed. This is laminar flow. As for laminar flow in a pipe, the flowrate is proportional to the pressure drop. Answer C, (ΔP) 0.5 / μ , is more characteristic of high Re turbulent flow in a channel. (For such flow, the pressure drop roughly increases with the square of the flowrate.) Ans = B ( yellow ): ΔP/ μ
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8 SUPPLEMENTAL INFO– How flowrate through a filter cake depends on particle size. The Kozeny-Carman equation gives an approximate picture, predicting how flowrate through a cake of particles, all of one size and geometry, depends on the particle diameter , D p , and the cake porosity, ε.
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This note was uploaded on 08/10/2011 for the course CHEN 4820 at Colorado.

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RelativeResourceManager-2 - Concept Question(s for...

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