Chap 6 - CHAPTER CHAPTER First Law Analysis for a Control Volume 6.1 Conservation of Mass Principle Example 6-1 Mass Conservation A hair dryer is

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HAPTER CHAPTER First Law Analysis for a Control Volume
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6.1 Conservation of Mass Principle
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Example 6-1 : Mass Conservation A hair dryer is basically a duct of constant diameter in which a resistance heater is placed in the air stream. Air is driven by a fan and is expanded and accelerated as it is heated by the heating element. he percent increase in the velocity of air as it flows The percent increase in the velocity of air as it flows through the drier is to be determined under a steady state. he density of air is given to be 1 20 kg/m 3 t the The density of air is given to be 1.20 kg/m at the inlet, and 1.05 kg/m 3 at the exit. ssumptions low through the dryer is steady process Assumptions Flow through the dryer is steady process. Properties The density of air is given to be 1.20 kg/m 3 at the inlet, and 1.05 kg/m 3 at the exit . V 2 V 1 ·
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Example 6-1 Continued V Analysis CV ie dm mm dt    0 for a steady state 0  V 2 V 1 e · 12 any location m 
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Example 6-1 Continued Analysis There is only one inlet and one exit, nd thus for a steady process and thus, for a steady process hen, 12 any location mm m   Then, V 2 V 1 1, 1 1 2, 2 2 , 1 , 2 3 21 , 1.20 kg/m 14 (or an increase of ) cc c c AA A A VV V 4% · 3 1.14 (or, an increase of 1.05 kg/m 14% V • Therefore, the air velocity increases 14% as it flows through the hair drier.
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low Work and the Flow Work and the nergy of a Flowing Energy of a Flowing iquid Liquid
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ork of a Flowing Fluid Work of a Flowing Fluid Focus on a segment of the flowing fluid in pink, force on the flowing fluid, F sec cc F PA A flow cross tion  flow W work added to the control volume when this segment is pushed inside ow W work added to the control volume L flow when this segment is pushed inside flow WF L c PA L PV V Total flow work or energy of fluid volume V In Joule F lo w W mm P v V v sp e c ific v o lu m e m pecific flow work in Joule/kg Work done by the pressure on the fluid segment stays with it, when the segment becomes part of the CV, this work (energy) is added to the CV. Specific flow work in Joule/kg
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Total energy .. .. hK E P E  E  Total specific energy of a flowing fluid Total specific energy of a stagnant fluid uP v ..
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This note was uploaded on 09/27/2011 for the course EML 3100 taught by Professor Sherif during the Fall '08 term at University of Florida.

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Chap 6 - CHAPTER CHAPTER First Law Analysis for a Control Volume 6.1 Conservation of Mass Principle Example 6-1 Mass Conservation A hair dryer is

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