![]() The value or algebraic expression representing the value of the argument follows the equal sign. Arguments must be separated with commas (semi-colons for the EU format) and may be in any order, provided that the substance name is first. Additional information concerning the methods, reference states, and ranges of applicability for the thermophysical properties are provided in the online help for each substance.Īll arguments in thermophysical property functions, aside from the substance name, are identified by a single case-insensitive letter followed by an equal sign. AirH2O is the notation for air-water vapor mixtures, i.e., psychometrics. Exceptions to this rule occur for Air and AirH2O, both of which are modeled as ideal gases. In this case, it is possible to use the $Reference directive to shift the reference state so that the substances use the same reference states as the corresponding ideal gases. Whenever the substance name is spelled out (e.g., Steam (or Water), Nitrogen, R134a, CarbonDioxide, Methane, etc.) the substance is modeled as a real fluid with subcooled, saturated, and superheated phases. ![]() The entropy of these substances is based on the Third Law of Thermodynamics. The JANAF table reference for enthalpy is based on the elements having a specific molar enthalpy value of 0 at 298 K (537 R). Whenever a chemical symbol notation (e.g., N2, CO2, CH4) is used, the substance is modeled as an ideal gas and the enthalpy and entropy values are based on JANAF table references. It may appear that some substances in the built-in property data base, e.g., N2 and Nitrogen, CO2 and CarbonDioxide, H2O and Steam (or Water), are duplicated, but this is not true. numerical format and a semicolon for the European numerical format. EES also allows User-Supplied Property Data.Īrguments are separated with the list separator character, which is a comma for the U.S. The fluid may be any of the built-in fluids provided with EES, any of ideal gas fluids provided with the NASA ideal gas data base, or any of the fluids in the Brine fluids or Incompressible substances libraries. This argument is a string that may be provided as a string constant (enclosing quote marks are optional) or a string variable that contains the name of the fluid. ![]() The first argument of all built-in thermophysical property functions is the name of the substance. Not all of these functions are applicable to all substances. Since entropy is a state variable, just depending upon the beginning and end states, these expressions can be used for any two points that can be put on one of the standard graphs.All built-in thermophysical property functions are listed below in alphabetical order. Using the ideal gas lawīut since specific heats are related by C P = C V + R. This is a useful calculation form if the temperatures and volumes are known, but if you are working on a PV diagram it is preferable to have it expressed in those terms. ![]() Making use of the first law of thermodynamics and the nature of system work, this can be written With kT/2 of energy for each degree of freedom for each atom.įor processes with an ideal gas, the change in entropy can be calculated from the relationship This gives an expression for internal energy that is consistent with equipartition of energy. Then making use of the definition of temperature in terms of entropy: Expanding the entropy expression for V f and V i with log combination rules leads toįor determining other functions, it is useful to expand the entropy expression using the logarithm of products to separate the U and V dependence. One of the things which can be determined directly from this equation is the change in entropy during an isothermal expansion where N and U are constant (implying Q=W). The entropy S of a monoatomic ideal gas can be expressed in a famous equation called the Sackur-Tetrode equation. Entropy of an Ideal Gas Entropy of an Ideal Gas
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