1lesson 11IV. First Law of ThermodynamicsA. Introduction to Open Systems1. 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).ControlvolumeCVMassentering(inlet)Massleaving(exit)QWlesson 11IV. First Law of Thermodynamics3. ExampleWe 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.⎟⎟⎟⎠⎞⎜⎜⎜⎝⎛−⎟⎟⎟⎠⎞⎜⎜⎜⎝⎛=⎟⎟⎟⎠⎞⎜⎜⎜⎝⎛lakeleaveswaterwhichatratelakeenterswaterwhichatratelakeinwaterofmassofchangeofrate⎟⎟⎟⎠⎞⎜⎜⎜⎝⎛−⎟⎟⎟⎠⎞⎜⎜⎜⎝⎛=⎟⎟⎟⎠⎞⎜⎜⎜⎝⎛FebruaryduringlakeleaveswhichwaterofamountFebruaryduringlakeenterswhichwaterofamountFebruaryduringlakeinwaterofmassinchangeWe obtain Form (2) by integrating Form (1). We use both forms for mass, energy, and entropy.(1)(2)
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