Exam3_F10

Exam3_F10 - Name Last First CIRCLE YOUR DIVISION Div 1(9:30...

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Name:__________________________________ Last First CIRCLE YOUR DIVISION: Div. 1 (9:30 am) Div. 2 (11:30 am) Div. 3 (2:30 pm) Prof . Ruan . Naik Mr . Singh School of Mechanical Engineering Purdue University ME315 Heat and Mass Transfer Exam #3 Wednesday, November 17, 2010 Instructions: Write your name on each page Closed-book exam – a list of equations is given Please write legibly and show all work for your own benefit. Write on one side of the page only Keep all pages in order You are asked to write your answers to sub-problems in designated areas. Only the work in its designated area will be graded. Performance 1 30 2 35 3 35 Total 100
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Name:__________________________________ Last First Problem 1 [30 pts] Consider a well-insulated, concentric tube, counter-flow heat exchanger used to heat cold water. Saturated steam at a temperature of T sat condenses in the outer tube at mass rate of o m . Cold water enters the inner tube of diameter D and length L at a temperature of T i , with a mass flow rate i m , and an average heat transfer coefficient h i . The latent heat of vaporization of water is h fg and the average specific heat of water is c p . Assume that the inner tube has negligible thickness. Neglect any surface fouling effects. (a) Find an expression for the outlet temperature T o of water in the inner tube. (b) Sketch the temperature variation of the two fluids along the length of the heat exchanger and clearly label the temperatures. (c) Find an expression for the effectiveness ε of the heat exchanger only in terms of T sat , T i , and T o . Write an expression for NTU in terms of ε . (d) Express the average heat transfer coefficient for steam condensation h o only in terms of known quantities and/or those obtained in parts (a) and (c). Start your answer to part (a) here [6 pts]: Assuming heat lost by condensing steam to be equal to the heat gained by cold water, we can write:  of g i p o i mh mC T T   Outlet temperature of water: g oi ip TT mC  Start your answer to part (b) here [6 pts]: g i T sat T Steam Water T x
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Name:__________________________________ Last First Problem 1 – cont.
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Exam3_F10 - Name Last First CIRCLE YOUR DIVISION Div 1(9:30...

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