These calculators can be used to solve even the most complicated thermodynamic problem in a visual spreadsheet. The flow of calculations closely follows how we would solve a problem manually. Moreover, calculated states can be visualized on various thermodynamic diagrams, a solution report can be generated, and the solution can be shared with other users through generated TEST-codes. Additionally, since all variables are visually exposed, any combination of input parameters can be changed and any conceivable what-if scenario can be explored by clicking a single (Super-Calculate) button.

1. Property evaluation for a given substance: From the TEST-Map (see The Map section below) select the System State Daemons page. Pick an approriate material model to launch the daemon. Enter known properties (click the checkbox to go into input mode) and click the Calculate button to find the complete state.
2. Improve interpolation skill: Find a property manually using the Tables link from the TEST task bar. Many a times a manual evaluation of a property requires interpolation, an important engineering skill. Experiened engineers generally avoid messy linear interpolation by simply making educated guess for an interpolated value. This important skill can be honed by using the state daemon to verify your guesstimates.
3. Property classification and dependency: Properties are color coded in each daemon - red for material properties (depends on the working substance), blue for thermodynamic properties (that determines equilibrium), green for extrinsic properties (depends on velocity and/or elevation), and black for extensive properties (depends on the extent of the system). If you try to enter too many properties, the daemon will catch your mistake and produce appropriate error message. A very important part of understanding equilibrium is to figure out how many indpendent properties are required. The daemons can be helpful in reinforcing that insight.
4. Thermodynamic plots: Each daemon offers a large selection of thermodynamic plots (T-s, p-h, T-v, etc). You can locate the calculated states on the thermodynamic diagram and draw constant-property lines for further insight.
5. Comparing material models: Superheated steam can be analyzed with various models: pc model which uses superheated tables, IG model that treates steam as an ideal gas with variable specific heats, PG model that treates it as a perfect gas with constant specific heat, or the RG model that uses the compressibility chart. TEST-codes generated by one model can be used in another to quickly reproduce an analysis to see how the results compare numerically. Such exercise can highlight the strength and weaknesses of different models.
6. Verify manual solution: Selecting the right daemon for a problem walks one through the series of assumptions necessary to simplify the governing equations. Once the daemon is launched approximations such as whether the kinetic energy can be neglected must be made. A systematic solution procedure much like a manual solution is required to solve a problem using the daemon. That is what makes a daemon a great validation tool while learning how to solve a problem manually. Comparing material models: Superheated steam can be analyzed with various models: PC model which uses superheated tables, IG model that treates steam as an ideal gas with variable specific heats, PG model that treates it as a perfect gas with constant specific heat, or the RG model that uses the compressibility chart. TEST-codes generated by one model can be used in another to quickly reproduce an analysis to see how the results compare numerically. Such exercise can highlight the strength and weaknesses of different models.
7. What-if studies: One of the rewards of a TEST solution is its ability to create various what-if scenarios from a base case. Once a solution is obtained, it is stored as Case-0 by default. Suppose you want to change the working fluid or an input property and update the solution. Simply select a new case, say Case-1. The original case is automatically copied as the new case. Now you can change the working fluid or any other input property (or properties) and update the solution by clicking Super-Calculate button. It is that simple. You can calculate as many cases as you want and retrieve an old case by simply selecting it from the menu.
8. Breadth: A quick look at the TEST-Map would tell you the diverse range of daemons offered by TEST. Topics covered by the daemons include state evaluation, analysis of generic steady and unsteady systems, exergy analysis, IC engines, gas turgines and vapor power plant, refrigeration, mixture analysis, psychrometrics, combustion, chemical equilibrium, and gas dynamics.
9. Depth: Most daemons are programmed to go much beyond what is required to obtain a solution. The psychrometric daemon for example can handle any total pressure (not just standard atmospheric pressure) or many different moist gases (not just moist air). The chemical equilibrium daemon uses database from NASA as well as NIST and can perform sophisticated equilibrium calculations. The RG daemons allow switching between Lee-Kesler and Nelson-Obert charts. The gas dynamics daemon allows analysis of oblique shock waves as well as Prandtl-Meyer expansion waves. The combustion daemon allows analysis of combustion of premixed as well as non-premixed mixtures of fuel and oxidizer.

The daemons in TEST are organized into three branches:

1. Basic Tools: The Basic daemons branch offers rudimentary tools such as unit converter, scientific calculator, and traditional charts and tables.

2. States & Properties: The state daemons are for finding properties of thermodynamic working substances (e.g. H20 from steam to moist air). They are divided into two groups (1) system-state daemons for finding states of a substance occupying a fixed volume, and (2) flow-state daemons for finding states at different cross-sections of a flow.

3. System Analysis: Selecting a system daemon is not trivial. It depends on how the system can be simplified with assumption appropriate for a given problem. The system daemons are divided into various categories and their classification is discussed in more detail in the Selecting a Daemon section below.

Open vs. Closed System Daemons: A system that allows mass transfer across its boundary (tubes and pipes carrying flow in and/or out of the system) is called an open system. A closed system, on the other hand does not allow any mass transfer. The transport terms of the governing equations, therefore, drops out for a closed system. Visit the Daemons.Systems.Closed and Daemons.Systems.Open page, and compare the governing equations.

Steady vs. Unsteady Daemons: A system, open or closed, is steady when its global state - a snapshot taken with an imaginary state-camera, which records all the state variables (pressure, temperature, velocity etc.) at each location of the system at a given instant - does not change with time. While the state of a fluid lump flowing through a steam turbine continuously changes from the inlet to the exit, the picture of the turbine, with hot zones near the inlet and relatively cooler zones near the exit, exhibits no change over time as long as the system operates at steady state. The global extensive properties such as the total mass, energy, or entropy of the system, obtained by summing up the corresponding local properties over the entire system, therefore, do not change with time. Thus, dm/dt, dE/dt, and dS/dt=0, and the governing differential balance equations simplify to algebraic equations. Compare the governing equations in the Daemons.Closed.Steady page with those in the Daemons.Closed.Unsteady page.

Open steady systems, on the other hand, are abundant in applied thermodynamics and further classification is necessary to locate the right open, steady daemon.

In most thermodynamic problems involving unsteady systems, we are generally interested in what happens over a finite period of time rather than an instant. During the period of interest, the system - open or closed - goes from a beginning-state (b-state) to a final-state (f-state) executing what is thermodynamically called a process. The governing equations are integrated between the two limits (b-state to f-state), producing process equations that are algebraic in nature. If instantaneous changes in the system is of interest, the system is called transient.

There are no dedicated daemons for transient problems in TEST since such problems are generally uncommon. Also, the transient term can be indirectly calculated by evaluating all other terms using the state daemons.

Examples of closed processes in thermodynamics are plenty and, like open steady systems, require further classification.

Because most thermodynamic problems belong to either closed-process or open-steady categories, an artificial division is created between the general-purpose systems and specialized systems involving one of the topics listed below.

Specific topics on closed processes include: (i) air-standard cycles such as the Otto cycle, Diesel cycle, Ericson cycle etc., which execute a sequence of processes (strokes) on a closed mass of gas (Chapter 7); (ii) HVAC (Chapter 12); (ii) Combustion (Chapter 13).

Specific topics on open-steady systems include: (i) Gas power cycles such as Brayton cycle (Chapter 8); (ii) Vapor power cycles such as Rankine cycle (Chapter 9); (iii) vapor and gas refrigeration cycles (Chapter 10); (iv) Psychrometry and HVAC (Chapter 12); (v) Combustion (Chapter 13); (vi) Chemical Equilibrium (Chapter 14), and (v) Gas dynamics (Chapter 15).

Generic problems involving closed processes and open-steady systems are generally covered in the first half of most thermodynamics textbooks (chapters 1-6 in the textbook by Bhattacharjee) while specific system problems are covered in the rest of the textbooks. Let us first look at the generic systems

A system is called uniform if a single state can represent its global state at any given time. Note that a uniform system must be made up of a pure substance (same chemical composition at all locations).

If an open system has a single inlet and a single exit, it is called a single-flow device. Most open-steady problems fall into this category.