HW6 - CHEN 4820 Fall 2010 Homework 6 DUE: Monday, October...

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CHEN 4820 Fall 2010 Homework 6 DUE: Monday, October 11 th – Beginning of Class DIRECTIONS: 1. Please start each problem on a new, full sheet of paper. 2. To obtain partial credit, all work must be shown in a clear, logical manner. (1) Centrifuging and Sedimentation. [10 points] A certain flocculant is added to a suspension of cells 4μm in diameter. These cells have a density of 1.08 g/cm 3 and are suspended in liquid with a density of 1.00 g/cm 3 and viscosity of 1.0 cp. This flocculant causes about half of the cells to form fairly solid aggregates, all of which are 90μm in diameter and have a density midway between that of the liquid and the cells. A 50 cm high vessel is filled with the suspension. The aggregates take 7.7 hours to settle to within 1 cm of the bottom of the vessel. You want to reduce the total sedimentation time by a factor of 10 by using a centrifuge with 20 cm high containers. The center of rotation is 3 cm from the tops of the containers. Assume a swinging-bucket centrifuge. a. At what speed should the centrifuge be operated to sediment the aggregates to within 1cm of the bottom of the container in the given time? b. Assuming the same speed, how long would it take to sediment all the single cells to within 1cm of the bottom of the container? (3) Determination of S for a New Pilot Scale Centrifuge. [5 points] Harrison Problem 5.6 (4) Tubular Bowl Centrifugation of E. coli [15 points] A tubular bowl centrifuge is applied to concentrate a suspension of E coli prior to cell disruption. The bowl of this unit has an inside radius of 12.7 cm (i.e. the radial position of the air-liquid interface), and outside radius of 25 cm, and a length of 73.0 cm. The speed of the bowl is
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This note was uploaded on 08/10/2011 for the course CHEN 4820 at Colorado.

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HW6 - CHEN 4820 Fall 2010 Homework 6 DUE: Monday, October...

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