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Unformatted text preview: 2.25 ADVANCED FLUID MECHANICS Fall 2005 Final Exam FRIDAY, December 16, 2005, 1:30 – 4:30 P.M. OPEN EXAM WHEN TOLD AT 1:30 PM THERE ARE TWO PROBLEMS OF EQUAL WEIGHT Please answer each question in SEPARATE books This exam book consists of SIX (6) pages You may use ELEVEN (11) pages of handwritten notes as well as the single page handouts posted on MIT server plus any tables you feel are necessary 2. Flow Focusing in Microfluidics [40 points] There is a lot of interest at present in using microfluidic devices to produce very fine scale droplets which are also all monodisperse (i.e. the same size). To do this, two immiscible fluids ( i.e. the fluids don’t mix) are brought together via suitable inlet tubing and then special geometries are designed which focus the fluid motion down to very small scales. Typically two and the outer fluid ( μ i ! μ o fluids are used with different viscosities. In what follows we will always label the inner fluid ‘i’ ‘o ’. The inner fluid is usually more viscous than the outer one ). Two representative geometries are shown in the figures below. On the left is a planar flow- focusing geometry consisting of a converging channel (with opening angle α ) in which fluid i s pushed under pressure from left to right. On the right is an axisymmetric flow-focusing geometry in which the two fluids are sucked (via a negative gage pressure) into the cylindrical tube. In each case a long thin thread of the inner fluid is formed, which ultimately breaks up into monodisperse droplets. In this question we first consider some generic features of these problems from the point of view of dimensional analysis and then analyze these two geometries sequentially....
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This note was uploaded on 02/27/2012 for the course MECHANICAL 2.25 taught by Professor Garethmckinley during the Fall '05 term at MIT.
- Fall '05