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Lecture_08262007_Compatibility_Mode_ - ENGR 301 ENGR 301...

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Unformatted text preview: ENGR 301 ENGR 301 Thermodynamics 8/26/2009 Madison 201 MWF 12:00 – 12:50 PM ENGR 301 Thermodynamics The field dealing with forms of energy in systems and their transfer between fi th systems. Energy is conserved, but it can be transformed from one form to another. Energy has a quality that determines 1. the direction of its transport and transfer the direction of its transport and transfer 2. the transformation from one form to another. ENGR 301 FORMS of ENERGY • Microscopic (internal reference) Internal energy (U) • Macroscopic (external reference) Mechanical Kinetic energy (KE) energy (KE) Potential energy (PE) …. Electrical ….. Total energy E = U301 KE + PE + ….. + ENGR ENGR 301 ENGR 301 A system can be • Open (mass can enter and leave) • Closed (energy can enter or leave; (energy can enter or leave; mass can not) • Isolated (neither mass nor energy can enter or leave) can enter or leave) Mass Energy ENGR 301 Open system = Control Volume Control Volume ENGR 301 Property: Any characteristic of a system P, V, T, ….. Intensive properties: do not depend on mass P, T, density Extensive properties: depend on mass properties: depend on mass Total mass, volume, total energy Specific property: property / mass specific volume = v = V/m specific energy = e = E/m State: defined by a set of properties of system If any property changes, the system acquires a new state. Equilibrium: state in balance i.e. no tendency to change Thermal equilibrium Mechanical equilibrium Phase equilibrium Chemical equilibrium ENGR 301 You have been asked to do a metabolism (energy) analysis of a person. How would you define the system for this purpose? What type of a system is this? system is this? You are trying to understand how a reciprocating air compressor (a piston cylinder device) works. What system would you chose? What type of system is this? Is the number of moles of a substance contained in a system an intensive property or an extensive property? Explain your answer. ENGR 301 HOW MANY PROPERTIES ARE NEEDED TO DEFINE THE STATE OF A SYSTEM? State Postulate: The state of a simple compressible system is completely defined by two independent intensive properties. Simple compressible system – A system in absence of any electrical, magnetic, gravitational motion and surface tension effects gravitational, motion, and surface tension effects. Independent properties: properties that can be changed independently of each other. ENGR 301 ENGR 301 ENGR 301 Rules: • An equation must have same units on both sides of equality sign. • Multiplication and/or division of variables results in new variables with derived and/or division of variables results in new variables with derived units. • Only variables with similar units can be added or subtracted. • The result of addition, subtraction, multiplication, or division of variables cannot increase number of significant units. ENGR 301 1-10 ENGR 301 1-10 Weight at elevation Z = mass x gravitational acceleration WZ = m g = m (a – b Z) Weight at sea level = W0 = m a Z = 0 at sea level Change in weight = W0 – WZ = m b Z Percent change in weight = 100 (b/a) Z = 1 Z = 0.01 (a/b) = 29539 m ENGR 301 What happens when a system undergoes change from state 1 to state 2? ENGR 301 ENGR 301 ENGR 301 ENGR 301 Steady flow ENGR 301 Under steady flow conditions, mass and energy contents of a control volume remain constant. ENGR 301 Zeroth law of thermodynamics: If two bodies (A and B) are individually in thermal equilibrium with a third body (C), then the two bodies are in equilibrium with each other. ENGR 301 ENGR 301 ...
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