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ME200 - Lecture 13

# ME200 - Lecture 13 - IdealGasModel ME200 ThermodynamicsI...

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9/25/2010 1 Compressibility Chart and Factors Ideal Gas Model ME 200 Thermodynamics I L 13 Purdue University , Dr. Tim Pourpoint – [email protected] Lecture 13 September 24 th , 2010 Last Week • Specific heat at constant volume (Cv) and specific heat at constant pressure (Cp) Cp > Cv Cp/Cv = k • Incompressible substance i.e. no change in specific volume for solids and liquids • Approximations for compressed liquid property evaluation ME 200 2 • Only one specific heat for solids and liquids • Calculation of internal energy and enthalpy changes for solids and liquids

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9/25/2010 2 • Equation of State • Ideal Gas Model Today • Compressibility Factor ME 200 3 • What is an Equation of State (EOS)? – A relationship between pressure, temperature and specific volume (or density) of a given pure substance (may involve other Equation of State properties). Usually in form p = f(T,v). U sually valid only under a limited range of conditions of pressure and temperature. • Why do we need equations of state? ME 200 4
9/25/2010 3 • Why do we need equations of state? Equation of State Property tables provide very accurate information; but need to be d ith f t t measured with some reference state. Most are calculated from sophisticated equations of state. Use of simple relations such as ideal gas EOS and van der Waals EOS desirable for qualitative physical understanding of fluid behavior ME 200 5 understanding of fluid behavior. Incorporation in numerical codes for calculation of thermodynamic properties, system performance. Ref.: Simulation of High Pressure Metal Hydride Systems, Smith, K.C., Zheng, Y., Fisher, T.S., Mudawar, I., Pourpoint, T.L., 19 th National & 8 th ISHMT ASME Heat & Mass Transfer Conference, 2008, JNTU Hyderabad, India, Paper No: US 53 Ideal gas is an imaginary substance that has certain characteristics: No molecular volume : Ideal Gas molecules are simply points is space No molecular forces : molecules are on average very far apart from each other Is this possible? Not really. However, we can get very close to such behavior at very low density ME 200 6 All substances will become ideal gases at sufficiently low pressure and high temperatures

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9/25/2010 4 Based on experimental data, ideal gases obey Pv = RT P, v, T = pressure, specific volume, Ideal Gas Equation of State (IGEOS) temperature R = specific gas constant = R u /M R u
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ME200 - Lecture 13 - IdealGasModel ME200 ThermodynamicsI...

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