2Properties-3-23-2012

1、1Property DataGreg NellisProfessor of Mechanical EngineeringUniversity of Wisconsin, M608-265-66262PropertieslEES provides thermodynamic and transport properties for a large number of engineering fluids Convenient, high accuracy functions These are not tables but rather fu

2、ndamental equations of state similar to REFPROP Flexible relative to the input parameters used to fix the state Eliminates the tedious process of interpolating from tables Enables design studies and optimization 3Unit SystemlBefore we use the functions we need to set the unit system These are the un

3、its that EES expects for the inputs that fix the state and the units that EES will use when it returns propertieslThere are two ways to set the unit system: Unit System dialog $UnitSystem directive (preferable for readability and portability) Mixed unit system is not allowedlOver-rides the unit syst

4、em set in the Preferences dialog4Function Information DialoglProperty functions are conveniently accessed using the Function Information dialogCompressible fluidsIncompressibleExternal property routines5Fluid PropertieslReal fluids Model can represent phase change Can exist as liquid, liquid-vapor,

5、and vapor stateslIdeal gases Ideal gas models built into EES Include transport propertieslAirH2O Mixture of air and water vapor for psychrometrylNASA Ideal gas models obtained from the NASA database Do not include transport propertieslBrines Incompressible mixtures (e.g., ethylene glycol-water)6Real

6、 Fluid PropertieslReal fluids can exist in sub-cooled, two-phase, & super-heated stateslAll properties are related according to the phase rule The state of a single phase pure fluid is fixed by two intensive propertieslCalling protocol for a property function:X = FunctionName(Fluid, Property1=Va

7、lue1, Property2=Value2)Name of the property function being called; corresponds to the property that is returned (e.g., Enthalpy, Volume)Name of the fluid being considered (e.g., Water, Ammonia)First intensive property indicator used to fix state (e.g., T, P, v)Value of first intensive property (in u

8、nits consistent with unit system)Second intensive property indicator used to fix stateValue of second intensive property7ExamplelThe code below returns the specific volume of R134a at 350 K and 250,000 Pa lEES will check that the units of the inputs are consistent with the units set by the $UnitSyst

9、em directive lEES will provide the output in units that are consistent with the $UnitSystem directivelUnit checking will provide a warning if any of these conditions are not met8List of Property Functions9List of Property FunctionslMore information can be found be found in Klein, S.A. and G.F. Nelli

10、s, Thermodynamics, Cambridge University Press, (2011).10List of Real FluidsSource of properties can be obtained by selecting Fluid InfoAll others are FEOS11Property IndicatorslEES is flexible with regards to the properties used to fix the state12Two-Phase StatelIt is not possible to fix a two-phase

11、state using temperature and pressureOften useful to specify fluid with a string variable13Function Informationcompressible fluidscategories of fluidsavailable propertiesavailable fluidsExample box can be used to construct a function callsource of correlation & range of applicability14Property Pl

12、otslProperty plots (e.g., T-s, h-s, etc.) are useful for representing cycles graphically helpful for visualization and understanding helpful for identifying appropriate range for guess valueslEES can generate a variety of property plots automatically using the property correlations that are internal

13、ly programmed state points stored in arrays can be overlaid onto these plots15Property Plot Dialog16Example*lIsenthalpic expansion of carbon dioxide:T1= 45CP1= 9 MPaP2= 5 MPa(1)(2)use arrays so that:1. state information is organized2. states can be overlaid onto a property plot17Create Property Diag

14、ram*lCreate T-s diagram for carbon dioxide include relevant pressures-2250-2000-1750-1500-1250-1000-750-500200220240260280300320340360380400s J/kg-KT K 9.00E6 Pa 5.00E6 Pa CarbonDioxide18Overlay States*state points are in the arrays tablestate points will move as the solution changesindicate numbers

15、 by the states19Overlay States*-2250-2000-1750-1500-1250-1000-750-500200220240260280300320340360380400s J/kg-KT K 9.00E6 Pa 5.00E6 Pa CarbonDioxide12state point moves as P2 changes20Ideal Gas SubstanceslSubstances that are modeled using the ideal gas lawlTypically, ideal gas substances are indicated

16、 by their chemical formula E.g., CO2 (ideal gas) vs CarbonDioxide (real fluid) One exception is air, Air (ideal gas) vs Air_ha (real fluid)lProperty functions for ideal work the same as real fluidslHowever, enthalpy, internal energy, and specific heat capacities are only functions of temperature for

17、 an ideal gas21Ideal Gas Substances Internal to EES22NASA Ideal Gas DatabaselThe NASA Ideal Gas Database consists of 1262 additional ideal gases Transport properties are not available for these fluids McBride, B.J., Zehe, M.J., and Gordon, S NASA Glenn Coefficients for Calculating Thermodynamic Prop

18、erties of Individual Species, NASA/TP-2002-211556, Sept. (2002):23The Ideal Gas Reference StatelThe reference state for specific enthalpy for all ideal gases in EES is based on stable elements having zero specific enthalpy at 25C The absolute value of specific enthalpy includes the enthalpy of forma

19、tion associated with chemical bonds EES reports the standardized specific enthalpy The specific enthalpy values can be used directly in problems involving chemical reactionsThis is the enthalpy of formation of carbon dioxide24The Ideal Gas Reference StateThere is no need to look up these enthalpy of

20、 formation valuesS.A. Klein and G.F. Nellis, Thermodynamics, Cambridge University Press, (2011)25Psychrometric PropertieslPsychrometric is the study of mixtures of air and water vapor at conditions near atmospheric pressure and temperaturelThe fluid AirH2O refers to an air-water vapor mixture modele

21、d as an ideal gas mixturelPsychrometric property functions require an additional property to fix the state An intensive property that specifies the concentration of water vapor Humidity ratio (W) or relative humidity (R):26Psychrometric Property FunctionsShaded properties are only available for the

22、fluid AirH2O27Psychrometric Property Indicators28Example*Determine the relative humidity of the air-water vapor mixture leavingsteam insteam outT2= 75Fsteam coil111moist air1atm45 F1 0100 cfmPT.V29lEnter inputs:lCompute psychrometric properties at state 1:lState 2 is specified by humidity ratio (w2

23、= w1), temperature and pressurePsychrometric Example*note - Psychrometric properties are defined on a per mass of dry air basis30Psychrometric Chart*lSelecting Property Plot for AirH2O will generate a Psychrometric Chart2732782832882932983033083130.0000.0050.0100.0150.0200.0250.0300.0350.0400.0450.050T KHumidity RatioPressure = 101300.0 Pa 285 K 290 K 295 K 300 K 305 K 310 K 0.2 0.4 0.6 0.8 0.8 0.825 0.85 m3/kg 0.875 0.9 0.925 AirH2O31Psychrometric Chart*lStates can be ove