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A MathCAD Function Set for Solving Thermodynamics Problems

Abstract

A set of MathCAD functions was constructed to evaluate the thermodynamic properties of steam, R-134a, air, and twelve ideal gases. The functions were constructed to ease the need for time-consuming interpolation using tabularized thermodynamic data while reinforcing the functional representation of traditional thermodynamic property tables. A consistent scheme was adopted for naming the functions. Three examples are provided to demonstrate the use of the functions in an undergraduate applied thermodynamics course. The examples include the design of a reversed-Rankine refrigeration cycle, the analysis of a turbojet Brayton cycle, and the selection of a reheat pressure that maximizes the efficiency of a Rankine-reheat power cycle provided fixed boiler and condenser pressures. The examples are presented in their entirety in appendices to demonstrate the report-quality worksheets possible using MathCAD. While the examples provided focus on the use of the functions in an undergraduate applied thermodynamics course, the functions have also been used in an internal combustion engines course and in a turbomachinery course. Survey results from three courses and several student comments are discussed.

Introduction

Learning with a combination of a textbook and a software package is a contemporary engineering-thermodynamics pedagogy. Many software tools are available for evaluating thermodynamic properties of engineering fluids. Many of these software tools are proprietary packages sold by textbook publishers, such as “Interactive Thermodynamics: IT” [1]. In fact, finding a thermodynamics text that does not come with a software package is difficult. Some textbooks are now built around using a software or web-based internet package [2]. While many educational software packages are available for evaluating thermodynamic properties, evidence that shows that practicing engineers continue to use these thermodynamic-property software packages after entering the workforce is not readily available.

MathCAD, MatLab, and Engineering Equation Solver (EES) are all powerful computational and analytical packages [3,4,5]. Many schools teach and require the use of a computational tool such as MathCAD, MatLab, or EES [6]. From informal conversations with engineers who learned to use one of these computational tools, many of them continue to use these tools after graduation. Developing extensions or toolkits for software that the students will use after graduation seems more appropriate than developing complete software packages that will only be used by students in an educational environment. Because of the need for thermodynamic property functions for the widely used computational tools, functions were generated to evaluate the thermodynamic properties of water, R-134a, air, and twelve species of the CHON system in MathCAD. Equilibrium functions for eight independent reactions involving species of the CHON system are also included. The function set created provides the minimum number of thermodynamic functions required to teach a two-course sequence in undergraduate engineering thermodynamics.

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McClain, S. (2006, June), A Mathcad Function Set For Solving Thermodynamics Problems Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--25