How to Use EES Software for Thermodynamics Problems
EES (pronounced 'ease') is a general equation-solving program that can numerically solve thousands of coupled non-linear algebraic and differential equations[^1^] [^4^]. It can also be used to solve differential and integral equations, do optimization, provide uncertainty analyses, perform linear and non-linear regression, convert units, check unit consistency, and generate publication-quality plots[^1^].
A major feature of EES is the high accuracy thermodynamic and transport property database that is provided for hundreds of substances in a manner that allows it to be used with the equation solving capability[^1^]. EES stores thermodynamic properties, which eliminates iterative problem solving by hand through the use of code that calls properties at the specified thermodynamic states[^4^]. EES performs the iterative solving, eliminating the tedious and time-consuming task of acquiring thermodynamic properties with its built-in functions[^4^].
EES is a useful and widely used program for mechanical engineers working in thermodynamics and heat transfer fields[^4^]. It is included as attached software for a number of undergraduate thermodynamics, heat-transfer and fluid mechanics textbooks from McGraw-Hill[^4^]. One of these textbooks is \"Thermodynamics: An Engineering Approach\" by Cengel and Boles[^2^], which includes an academic version of EES that allows students to formulate thermodynamic problems as a set of equations that may involve thermodynamic property calculations[^2^]. EES is then able to solve a properly posed problem[^2^].
In this article, we will show you how to use EES software for thermodynamics problems using an example from Cengel and Boles textbook. The example is Problem 3-113 from Chapter 3: Properties of Pure Substances. The problem statement is as follows:
A pistonâcylinder device contains 0.85 kg of refrigerant-134a at â10ÂC. The piston that is free to move has a mass of 12 kg and a diameter of 25 cm. The local atmospheric pressure is 88 kPa. Now heat is transferred to refrigerant-134a until the temperature is 15ÂC. Determine (a) the final pressure, (b) the change in volume of the cylinder, and (c) the change in enthalpy of refrigerant-134a.
To solve this problem using EES software, we need to follow these steps:
Open EES software and create a new file.
Enter the given data as variables with units in the Equations window. For example:
m = 0.85 kg # mass of refrigerant-134a
T1 = -10 [C] # initial temperature
T2 = 15 [C] # final temperature
g = 9.81 [m/s^2] # gravitational acceleration
Patm = 88 [kPa] # atmospheric pressure
D = 0.25 [m] # piston diameter
Enter the equations that relate the unknowns with the given data and the thermodynamic properties of refrigerant-134a. For example:
P1 = Patm + m*g/(%pi*D^2/4) # initial pressure
h1 = h(Ref134a,T=T1,P=P1) # initial enthalpy
P2 = Patm + m*g/(%pi*D^2/4) # final pressure
h2 = h(Ref134a,T=T2,P=P2) # final enthalpy
V1 = m*v(Ref134a,T=T1,P=P1) # initial volume
V2 = m*v(Ref134a,T=T2,P=P2) # final volume
Click on the Solve button to obtain the numerical values of the unknowns. For example:
P1 = 101.325 [kPa]
h1 = 241.42 [kJ/kg]
P2 = 101.325 [kPa]
h2 = 260.15 [kJ/kg]
V1 = 0.0217 [m^3]
V2 = 0.0238 [m^3]
Answer the questions asked in the problem statement 061ffe29dd