2300_les11 - IV First Law of Thermodynamics A Introduction...

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1 lesson 11 IV. First Law of Thermodynamics A. Introduction to Open Systems 1. Analysis of flow processes begins with the selection of an open system. 2. An open system is a region of space called a control volume (CV). Control volume CV Mass entering (inlet) Mass leaving (exit) Q W lesson 11 IV. First Law of Thermodynamics 3. Example We can write a balance equation for the conservation of any extensive property of the open system. As an example, consider the mass of water in the Great Salt Lake. We might be interested in (1) the instantaneous rate of change of mass or (2) the change that occurs over a period of time. = lake leaves water which at rate lake enters water which at rate lake in water of mass of change of rate = February during lake leaves which water of amount February during lake enters which water of amount February during lake in water of mass in change We obtain Form (2) by integrating Form (1). We use both forms for mass, energy, and entropy. (1) (2)
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