Le19 - ME 200: Thermodynamics I Lecture 19: Heat Exchangers...

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ME 200: Thermodynamics I Lecture 19: Heat Exchangers and Throttling Devices Reading: Sections 4.9, 4.10; SP19, 4.74, 4.77, 4.92 10/8/2010 1 ME200 Therm I Lecture 19, Prof. Mongia Professor Hukam Mongia Office Hours: MWF 9:30 to 10:30 AM in ME 83 Other times email for appointment; Phone: 765-494-5640 Course Website: https://engineering.purdue.edu/ME200/ Course Secretaries: Diana Akers (ME 84) and Marilyn Morrison (ME 100) Grader: Abhro Pal , abhro.pal@gmail.com
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10/8/2010 ME200 Therm I Lecture 19, Prof. Mongia 2 Tube-Within-a-Tube Heat Exchangers Counter-flow Parallel Flow Reasonable assumptions made to simplify energy balance equation: 1. Steady-state operation; 2. Negligible stray heat transfer loss, pressure losses, changes in KE & PE; 3. No work in/out. 0 i i e e ie m h m h See derivation on next slide.
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10/8/2010 ME200 Therm I Lecture 19, Prof. Mongia 3 22 1 2 1 2 1 2 3 4 3 4 3 4 1 [( ) ( ) ( )] 2 1 [( ) ( ) ( )] 2 cv cv hot cold dE Q W m h h V V g z z dt m h h V V g z z Specific to the problem and with the assumptions made: 1 2 3 4 ( ) ( ) 0 hot cold m h h m h h Which generalizes to: 0 i i e e ie m h m h 1 st Law of Thermodynamics for a control volume:
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10/8/2010 ME200 Therm I Lecture 19, Prof. Mongia 4 1 2 4 3 43 12 0: ( ) ( ) cv hot Cold hot cold eff UsefulequationswhenW Q m h h m h h TT whichsometimesmaybedefined as hh , tan ' : p hot phot cold pcold Alternatively withcons tc swe get anotheruseful relation mc m c T T
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5 22 1 2 1 2 1 2 3 4 3 4 3 4 1 2 3 4 1 2 4 3 1 [( ) ( ) ( )] 2 1 [( ) ( ) ( )] 2 ( ) ( ) 0 0 0: ( ) ( ) cv cv hot cold hot cold i i e e ie cv hot Cold hot cold eff dE Q W m h h V V g z z dt m h h V V g z z m h h m h h m h m h UsefulequationswhenW Q m h h m h h 43 12 , tan ' : p hot phot cold pcold TT whichsometimesmaybedefined as hh Alternatively withcons tc sweget anotheruseful relation mc m c T T Skip over
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10/8/2010 ME200 Therm I Lecture 19, Prof. Mongia 6 Cross-Flow Heat Exchangers The same set of equations are applicable 0 i i e e ie m h m h If heat transfer to surroundings is not negligible, then: 0 CV i i e e Q m h m h
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This note was uploaded on 01/13/2011 for the course ME 200 taught by Professor Gal during the Fall '08 term at Purdue University-West Lafayette.

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Le19 - ME 200: Thermodynamics I Lecture 19: Heat Exchangers...

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