## Thermodynamic Properties Of R134aP2006072mcc The University of Alabama at Birmingham, 1530 3rd Ave.S., BEC 358B, Birmingham, AL, 35294-4461, smcclain@uab.edu While developed for a two-course sequence in undergraduate thermodynamics, the function sets are useful for many other engineering courses.In fact, this effort began in an ME 448/548 Internal Combustion Engines course [7,8]. Undergraduates in thermodynamics based courses often become frustrated using property tables and fail to comprehend either the material or the significance of the material. As the case with all thermodynamic property evaluation software, the intent was 1) to take some of the effort and distraction away from working problems requiring extensive interpolation in the tables and 2) to allow the students to analyze more complicated problems.Each computational analysis package has strengths and weaknesses when compared to the others. EES also has the thermodynamic functions discussed here (and functions for many other fluids). While EES is not a traditional structured programming language, the appearance of EES programs is similar to the appearance of C or FORTRAN programs, and some users find the unit conversion procedures awkward in EES. MathCAD was chosen for this project because of its mathematical re its ability to perform calculations with automatic of its wide use in the DepartmentUniversity of Alabama at Birmingham. EFERENCING THE The functions are contained in thrents the files and the information formation in the property worksheets does not have to be copied into the new worksheet. The function worksheet may be referenced by using the Insert, Re,00;&#x R00;ference command, and identifying the file required. When this is done correctly, a statement similar to appear in the worksheet. All functions generated in referenced file will then be available for use in the new worksheet. The following three sections describe the individual functions available for MathCAD. All of the functions generated are available to the educational public on the condition that if the functions are used for instruction, the instructor agrees to have his students complete a survey form at the end of the course. The function sets may be obtained by emailing the author at smcclain@uab.edu“MathCAD: Thermo Function Set Request” in your email. Table 1.Property Function Files File Information Contained SteamProps.mcd Thermodynamic properties of water Thermodynamic properties of R-134a Thermodynamic ideal gas properties of CO, CO, and dry air and equilibrium constaA consistent naming scheme was chosen for the functions evaluating properties of the phase change fluids
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The function calls for water and R-134a begin with the variable to be determined, followed by an underscore, followed by the independent property(s), followed by a fluid identifier (H2O or R134a), followed finally by the values of the independent property(s) in parenthesis. Figure 1 presents the format of function calls for the phase change substances. The functions require that all independent properties be entered with the appropriate absolute units. The functions were constructed to reflect and reinforce how property information is provided in traditional property tables. Functions are provided for the saturation pressure based on temperature and for the saturation temperature based on pressure. Saturated liquid and saturated vapor functions are provided for specific volume () based on either temperature or pressure. Functions for of saturated mixtures are also provided as functions of quality and either temperature or pressure. Functions that return quality are provided. Functions that return temperature or enthalpy as functions of pressure and entropy, often required in the analyses of Rankine and reprovided. Finally, a function that determines temperature based on pressure and enthalpy, often used when analyzing reversed-Rankine cycles, is provided. Table 2 presents a summary of the functions provided for the phase-change substances.The property functions for water were created using the IAPWS 97 formulation [9]. The IAPWS formulation presents fundamental property equations for five regions. The functions provided are for Regions 1 (compressed liquid below 623.15 K), Region 2 (superheated vapor), and Region 4 (saturated mixture below 623.15 K). Functions pressure very high tempcreated but may be added at a later time.Table 2. Functions for the Thermodynamic Properties of Water and R-134a (P) Returns the saturation temperature as a function of pressure (T) Returns the saturation pressure as a functions of temperature (T) Returns the property () for saturated liquid as a function of temperature (P) Returns the property () for saturated liquid as a function of pressure (T) Returns the property () for saturated vapor as a function of temperature (P) Returns the property () for saturated vapor as a function of pressure Returns the property () for a saturated mixture as a function of temperature and quality Returns the property () for a saturated mixture as a function of pressure and quality Returns the property () for either a compressed liquid or a superheated vapor as a function of temperature and pressure Returns the quality of a saturated mixture as a function of the temperature and the property (Returns the quality of a saturated mixture as a function of the temperature and the property ((P,s) Returns the temperature as a function of pressure and entropy (P,s) Returns the enthalpy as a function of pressure and entropy (P,h) Returns the temperature as a function of pressure and enthalpy The reader should note that all functions presented in this paper are for educational use only, and that the user assumes all responsibility for calculat |

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