Lecture_6___centrifugal_separation

Lecture_6___centrifugal_separation - Centrifugal Separation...

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1 Centrifugal Separation Carmen I. Moraru Cornell University Centrifugal separation applications It is the method most widely used for separating: – Fluids with different densities – Solids from liquids – Solids from gases Applications in the Dairy Industry: – Clarification (removal of solid impurities) – Separation of fat/cream from whole milk or whey – Bactofugation (removal of bacteria) – Separation of curd from whey – Butter oil purification (separation of anhydrous milk fat from serum)
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2 Invention of centrifugal separators 1877: The concept was first described in the German trade journal “Milch-Zeitung” 1888: Patent for conical discs granted to Freiherr von Bechtolsheim 1890: First separators built by Gustaf de Laval, co-owner of the Swedish company AB Separator Evolution How they looked in the past: How they look today: Alfa A1 Separator (1882) Modern Westfalia cream separator
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3 In the gravitational field: In a centrifugal field: Separation principles g 18 ) ( d v : law s Stoke' l p 2 g η ρ ρ = g, v g 2 l p 2 c 2 r 18 ) ( d v 60 n 2 , r a ω η ρ ρ = π = ω ω = Symbols: v = particle velocity, m/s ρ = density, kg/m 3 η = viscosity, cP ω = angular velocity, rad/s n = angular velocity, rpm r = radial position of particle, m g = gravitational acceleration, m/s 2 a = centrifugal acceleration, m/s 2 For a fat globule of d=3 μ m = 3 x 10 –6 m : ( ρ p ρ l ) = (980 – 1,028) = – 48 kg/m 3 η = 1.42 cP = 1.42 x 10 –3 kg/(m•s) g = 9.81m/s 2 v g = 10 –6 m/s = 0.6 mm/h At a radial position r = 0.2 m in a centrifuge rotating at n = 5 400 rpm: ω = 564.49 rad/s v g = 1.08 mm/s = 3,896 mm/h How will the particle velocity change if: - Its radius triples? - The liquid viscosity increases by 50%? - The liquid density is higher than the particle density? - The rpm doubles? 2 l p 2 c r 18 ) ( d v ω η ρ ρ =
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4 How do particles separate? In order to be separated, particles must settle on the upper plate before B‘. The limit particle = a particle of such a size that if it starts from the least favorable position (A) it will only just reach the upper disk at B'. – All particles larger than the limit particle will be separated. – Particles smaller than the limit particle will be separated if they enter the channel between A and B. The smaller the particle, the closer to B it must enter in order to be separated. r 1 r 2 Milk with impurities Clarified milk Solid impurities A A’ B B’ Inside centrifugal separators: A series of conical discs form inclined separation channels Questions: Which is the advantage/effect of multiple channels?
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This note was uploaded on 05/02/2009 for the course FDSC 4250 taught by Professor Moraru during the Spring '09 term at Cornell University (Engineering School).

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Lecture_6___centrifugal_separation - Centrifugal Separation...

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