Lecture_2 - ME 2322 Engineering Thermodynamics I Lecture...

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ME 2322 Engineering Thermodynamics I Lecture 02, 01/18/11 Prof. Zhaoming He
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Chapter 1 Introduction and Basic concepts • Concepts – Dimension and units – System and surroundings – Closed system (control mass) and open system (control volume) – Properties and state – State equilibrium and postulate – Process and cycle • Review concepts of temperature and Pressure • Introduce a systematic problem-solving technique.
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Dimensions and Units • Dimension: physical properties or characteristics of a system - Primary Dimensions: mass m , length L , time t , and temperature T, electric current I, luminous intensity Candela, amount of matter , mole - Secondary Dimensions: expressed in terms of the primary dimensions, velocity v , energy E (or work) , force F, and volume V… • Units: magnitudes assigned to dimensions (foot or meter) • Two Unit Systems: English and SI or International System English SI Conversion Factors mass: pound mass, lbm kilogram, kg 1 lbm = 0.45359 kg length: foot, ft meter, m 1 ft = 0.3048 m force: pound force, lbf newton, N 1 lbf = 4.4482 N work / energy: British Thermal Unit, Btu joule, J 1 Btu = 1055.06 J power: Btu/h watt, W 3.41214 Btu/h = 1 W
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Unit Conversion 1 lbm=0.454 kg Make it fraction Which is numerator/denominator depends upon conversion Example : What is kg weight for a person weight 200 lbm? – Arrange denominator so that you can cancel it (lbm) What is lbm weight for a person weight 100kg? lbm kg kg lbm 1 454 . 0 , 454 . 0 1 kg lbm kg lbm 8 . 90 1 454 . 0 200 = × lbm kg lbm kg 220 454 . 0 1 100 = ×
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• Thermodynamic System: quantity of matter or region in space chosen for study (within boundary) • Surrounding: matter outside the system • Closed System (no mass exchange): fixed quantity of mass –system boundary may be moving, - energy may cross the system boundary into the control mass but mass can not. • Open System (with mass exchange): arbitrarily selected region or control volume in space - energy and mass may cross the control surface . •Control surfaces may be fixed, moving, real or imaginary boundaries
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Lecture_2 - ME 2322 Engineering Thermodynamics I Lecture...

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