EES (pronounced 'ease') is an acronym for Engineering Equation Solver. The basic function provided by EES is the numerical solution of a set of algebraic equations. EES can also be used to solve differential and integral equations, do optimization, provide uncertainty analyses and linear and non-linear regression, and generate publication-quality plots. Versions of EES have been developed for all Macintosh computers (including the PowerMac) and for PC/compatibles running all Windows operating systems. 

There are two major differences between EES and other equation-solving programs. First, EES allows equations to be entered in any order with unknown variables placed anywhere in the equations; EES automatically reorders the equations for efficient solution. Second, EES provides many built-in mathematical and thermophysical property functions useful for engineering calculations. For example, the steam tables are implemented such that any thermodynamic property can be obtained from a built-in function call in terms of any two other properties. Similar capability is provided for most refrigerants, ammonia, methane, carbon dioxide and other fluids. Air tables are built-in, as are psychrometric functions and JANAF data for many common gases. Transport properties are also provided for all substances. 

The library of mathematical and thermophysical property functions in EES is extensive, but it is not possible to anticipate every user's need. EES allows the user to enter his or her own functional relationships in three ways. First, a facility for entering and interpolating tabular data is provided so that tabular data can be directly used in the solution of the equation set. Second, the EES language supports user-written functions, procedures and modules.  Functions and procedures are similar to those in Pascal and FORTRAN in which assignment statements rather than equalities are employed. EES modules are callable EES sub-programs that use equalities. Functions, procedures and modules can be saved in library files which are automatically read in when EES is started. Third, compiled functions and procedures, written in a high-level language such as Pascal, C, or FORTRAN, can be dynamically-linked with EES. These three methods of adding functional relationships provide very powerful means of extending the capabilities of EES. 

The motivation for EES rose out of experience in teaching mechanical engineering thermodynamics and heat transfer. To learn the material in these courses, it is necessary for the student to work problems. However, much of the time and effort required to solve problems results from looking up property information and solving the appropriate equations. Once the student is familiar with the use of property tables, further use of the tables does not contribute to the student's grasp of the subject; nor does algebra. The time and effort required to do problems in the conventional manner may actually detract from learning the subject matter by forcing the student to be concerned with the order in which the equations should be solved (which really does not matter) and by making parametric studies too laborious. Interesting practical problems that may have implicit solutions, such as those involving both thermodynamic and heat transfer considerations, are often not assigned because of their mathematical complexity. EES allows the user to concentrate more on design by freeing him or her from mundane chores. 

EES is particularly useful for design problems in which the effects of one or more parameters need to be determined. The program provides this capability with its Parametric Table, which is similar to a spreadsheet. The user identifies the variables which are independent by entering their values in the table cells. EES will calculate the values of the dependent variables in the table. Plotting capability is provided to display the relationship between any two variables in the table. 

With EES, it is no more difficult to do design problems than it is to solve a problem for a fixed set of independent variables. EES offers the advantages of a simple set of intuitive commands which a novice can quickly learn to use for solving complex problems. The large data bank of thermodynamic and transport properties built into EES is helpful in solving problems in thermodynamics, fluid mechanics, and heat transfer. EES can be used for many engineering applications; it is ideally suited for instruction in mechanical engineering courses and for the practicing engineer faced with the need for solving practical problems. 

The 240-page EES manual is organized into seven chapters and four appendices. Chapter 2 provides specific information on the various functions and controls in each of the EES windows. Chapter 3 is a reference section that provides detailed information for each of the menu commands. Chapter 4 describes the built-in mathematical and thermophysical property functions and the use of the Lookup Table for entering tabular data. Chapter 5 provides instructions for writing EES functions and procedures and saving them in Library files. Chapter 6 describes how compiled functions and procedures written as Windows dynamic-link library (DLL) routines can be integrated with EES. Chapter 7 describes a number of advanced features in EES such as the use of array variables, the solution of simultaneous differential and algebraic equations, and property plots.