Notes_13_Control_Volume_Conservation_of_Energy

Notes_13_Control_Volume_Conservation_of_Energy - Meeting...

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1 Meeting 12--Sections 5-2—5-3
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What we covered last week Conservation of mass for a control volume 2
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Topics for Today Flow energy Energy carried into a control volume by mass The First Law for a control volume 3
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Example A 4-ft high, 3-ft diameter cylindrical water tank whose top is open to the atmosphere is initially filled with water. The discharge plug near the bottom of the tank is pulled out, and a water jet whose diameter is 0.75 in streams out. The average velocity of the jet is approximated as V=(2*g*h)^0.5, where h is the height of the water in the tank measured from the center of the hole and g is the gravitational acceleration. Determine how long it takes for the water level in the tank to drop 3 ft from the bottom. 4
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Teamplay A 100,000 gallon pool is being filled by a fire hose with a flow rate of 100 gal/hr. Beginning from the conservation of mass equation, applying assumptions, and solving the ODE, determine how long (in hours) it will take to fill the pool? 5
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6 Remember the difference between closed and open systems
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7 Flow work For open systems, obviously work must be done to move the fluid into and out of the control volume. It is a form of boundary work. “piston” of fluid having m, P, V. A is crossectional area of pipe. L Flow
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8 Flow work The force on the fluid element F=PA But AL is V, so W=PV or F and P have been assumed uniform over the surface A. = = = = PAL FL ds F Fds W Pv m V P w m W = = =
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Energy of fluid in closed system Remember from Chapter 2. Energy of a simple, compressible system is
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This note was uploaded on 10/04/2011 for the course MEEN 315 taught by Professor Ramussen during the Summer '07 term at Texas A&M.

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Notes_13_Control_Volume_Conservation_of_Energy - Meeting...

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