2300_les04 - II Energy and the First Law of Thermodynamics...

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1 Lesson 4, Geof Silcox, Chemical Engineering, University of Utah II. Energy and the First Law of Thermodynamics A. Energy Transfer by Work . Energy is Conserved. 1. Energy can cross the boundary of a closed system by only two mechanisms: heat transfer and work transfer . 2. 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. , , sys in net out net E Q W = Closed system Net work out, W out,net = W out - W in Net heat in, Q in,net = Q in - Q out (2-34); (4-17) total system surroundings E E E 0 = + = system surroundings E E = − Lesson 4, Geof Silcox, Chemical Engineering, University of Utah II. Energy and the First Law of Thermodynamics B. Mechanical work and power 1. Introduction a. Work done by force F on a body displaced distance s is b. Power supplied to body moving with velocity V: ) kW ( F W V = ± ) kJ ( Fs W = ) kJ ( ds F W 2 1 = (2-22) Constant force Variable force F s 2 1 W = area under curve s 2 s 1
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