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lec 8 - Steady state assumptions and simplifications Time...

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Lec 8 Mass Balances, Energy Balances and Applications to Conversion Devices. Review of mass balance Conservation of energy for a control volume Energy balance can be expressed in terms of beginning and end states or in terms of flow rates
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Work for a control volume has two parts: Work due to the flow. ..… and everything else. 1-D Flow form of the control volume energy rate balance + + + - + + + + + = e e e e e e i i i i i i cv cv cv z g V v p u m z g V v p u m W Q dt dE 2 2 2 2 &
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Steady-state form for the mass and energy balances Steady state mass balance: = e e i i m m Steady state energy balance:
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Unformatted text preview: Steady state assumptions and simplifications Time averaged energy, mass flow rates, heat transfer rates, work rates, pressures, temperatures, etc are constant. cv Q & may be neglected when: cv W & is neglected when: KE and PE are dropped when: Application of Mass and Energy Balances to Devices Nozzles and Diffusers nozzle – cross sectional area of flow passage narrows in so that the flow velocity increases. diffuser – cross section area increases, the velocity decreases...
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