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2300_les06

# 2300_les06 - II Energy and the First Law of Thermodynamics...

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1 lesson 6 II. Energy and the First Law of Thermodynamics A. Generic Statement of the First Law for a Closed System = system leaves energy rate system enters energy rate system within energy of change of rate Time System No mass enters or leaves. Heat Work out in system E E E = system in out dE E E dt = ± ± Rate form of energy balance: Integrated form of energy balance: E system + E surroundings = 0 Note: (4-12) (4-11) lesson 6 II. Energy and the First Law of Thermodynamics B. Specific Statement of First Law for a Closed System 1. Energy is conserved. 2. Energy can cross the boundary of a closed system by only two mechanisms: heat transfer and work transfer. 3. The change in energy of a closed system is equal to the net heat transferred to the system minus the net work performed by the system (4-17). 2 1 V ( ) 2 E mu m mgz kJ = + + ) kJ ( W Q E net , out net , in = 2 1 V 2 kJ e u gz kg = + + , , (kJ/kg) in net out net e q w = , , (kJ/kg) in net out net de q w δ δ = Energy per unit mass: in,net out ,net dE Q W (kJ ) δ δ = The differential form of (4-17): / and / w W m q Q m = = Total energy:

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