Le16 - ME 200: Thermodynamics I Lecture 16: Control Volume...

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ME 200: Thermodynamics I Lecture 16: Control Volume Analysis: Energy conservation Reading: Sections 4.4, 4.5; SP16, 4.24, 4.25 10/1/2010 1 ME200 Therm I Lecture 16, 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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First Law of Thermodynamics for Closed Systems First Law of Thermodynamics Closed Systems : General Form Q W U KE PE ,: Neglect KE PE Q W U : Per unit mass q w e : Differential form q w de E 2 -E 1 =Q-W
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9/29/09 3 Energy/Mass Balance Equations for Open Systems (Control volumes) Steady-state? For single inlet and single outlet? Specific energy balance equation?
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10/1/2010 ME200 Therm I Lecture 16, Prof. Mongia 4 Conservation of Energy Control Volume Analysis for an Open System Consider a closed system that contains a fixed quantity of mass m. At time t , the mass in the closed system is distributed between the control volume and an inlet to the control volume: CV CS Inlet Exit CV CV mt Et i m i CV m m m t For the closed system that contains the total mass m: 2 1 2 CV i i i i E t E t V m u g z
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5 We have assumed that the velocity and flow properties are uniform at the inlet. Now at some time t + t , the quantity of mass m i in the inlet will have just moved completely into the control volume. At that time, a quantity of mass m e will have moved out of the control volume, as shown in the following diagram: CV CS Inlet Exit CV CV m t t E t t e m
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10/1/2010 ME200 Therm I Lecture 16, Prof. Mongia 6 The quantity of mass in the closed system is unchanged at time t + t, CV e m m t t m but the energy for the closed system may have changed: 2 2 2 e CV e e e V E t t E t t m u g z Now for the closed system of fixed mass we can apply the first law to determine the change in energy: 3 E t t E t Q W
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10/1/2010 ME200 Therm I Lecture 16, Prof. Mongia 7 Subtracting Eqn. (1) from Eqn. (2) and using Eqn. (3) to eliminate the
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Le16 - ME 200: Thermodynamics I Lecture 16: Control Volume...

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