thermodynamic+properties

thermodynamic+properties - Properties of Steam First major...

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1 First major problem for thermo students Properties of Steam
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2 Steam Properties • Liquids: They are those fluids that do not have a definite shape, but occupy a definite volume at a given temperature and pressure. • Gases: These fluids that do not have a definite shape and expand themselves to fill the container at a given pressure and temperature. (same as vapor) • Fluids: A fluid generally has a shape determined by its container. Fluids include liquids, gases, and vapors or mixtures of these. A fluid cannot sustain shear stresses at rest.
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3 State and Phase A phase is homogenous, physically distinct, and mechanically separable part of a system. Each phase is separated from other phases by a physical boundary. – Thus ice, water and water vapor are three phases. Any number of gases mixing in all proportions constitutes one phase.
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4 State and Phase • State is the condition (being) of a thermodynamic system or a substance at a particular point in time, • It is described by an ensemble of thermodynamics properties like temperature, pressure, internal energy, enthalpy or entropy. • Consider: Absolute and Relative Pressure Absolute and Relative Temperature Density or Specific Volume of a Liquid
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5 Steam Properties Water is a simple compressible substance – Two reversible work modes (compression and heat) – Fixing any two independent variables fixes all other states States determined by experiment Modeled by: » Graphs » Models » Tables
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6 Boiling thought experiment – start with liquid under constant pressure – heat from below – measure temperature and position of lid Liq uid , g a s or mixture Heated from below Wall can slide, but no fluid escapes Weight creates c onsta nt p ressure
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7 Results of thought experiment
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13 Mixtures of Liquids and Vapors – As the mass changes from liquid to vapor, some of the mass is in each state. – We choose to use an average value for properties such as enthalpy and specific volume. – States under the vapor dome DO NOT EXIST They are averages consider a average value of a dice 1+2+3+4+5+6=21; average value = 3.5!
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14 Quality Note – a small amount of vapor takes up a lot of space What is the volume percentage occupied by vapor in a 1% quality mixture at room temperature? – Assume 1 kg of vapor and 99 kg of liquid – Specific volume liquid = 0.0010 m3/kg – Specific volume vapor = 57.8 m3/kg – Total volume = 57.8 + .1 = 57.9 – Volume percentage =99.8%
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15 Other definitions Latent heat of vaporization – Latent versus sensible heat Vaporization line or Vapor Dome Critical point, critical temperature, critical pressure The critical point of water is 647 K (374 °C or 705 °F) and 22.064 MPa (3206 PSIA or 218 atm) (Rankines are gotten by adding 459.67)
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16 Other Than Tables – Stmunpk is a nice steam property package available for download from the web.
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This note was uploaded on 09/13/2011 for the course MECH 462 taught by Professor Mul during the Spring '11 term at Rutgers.

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thermodynamic+properties - Properties of Steam First major...

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