A. Select a Problem
Open a new browser window - we will call it the Problems window to distinguish it from the current (tutorial) window. To select the particular problem we are about to solve, open the Problems>Chapter-3 (Evaluation of States and Properties) page, by first clicking the Problems link on the task bar (see Fig. A.1) and then on Chapter-3. Browse the chapter until you find the problem statement (note that the problem number may change as additional problems are inserted in the future) shown in Fig. A.2 below.

Note that the problem description has various links associated with it. For instance, clicking the schematic (Anim. 3-4-3) brings up a technical animation about the thermodynamics behind the problem description. You can resize the split screens by dragging the divider up or down, or get rid of the animation by clicking the close button, , displayed on the right end of the divider. Similarly, all the other links (Manual Solution, TEST Solution, Table C-1, etc.) display different documents on the bottom window. We will discuss these links later.

B. Simplify the Problem
TEST offers scores of daemons, thermodynamic calculators for problem solving. Knowing what daemon to launch to solve a particular problem requires a thorough knowledge of how thermodynamic systems are simplified during an analysis. Open the daemon map by clicking the Map link on the task bar in the Problems window. Because the problem at hand involves evaluation of state properties, the choice of daemon is relatively straightforward. Assuming the system to be uniform in the beginning and at the end (so that only two unique states are necessary to describe the beginning and end of the process), follow the path Daemons>States>Systems to reach (see Fig. B.1) and click the desired group of daemons. Alternatively, you can start with the Daemons link on the task bar and navigate your way by reading the choices offered by a daemon selection table.

State daemons come in two groups, one for evaluating states of uniform systems and another for uniform flows. As you click the Uniform System link, you arrive at the Daemons>States>System page (see Fig. B.2 below), which offers a list of material models suitable for different groups of working substances. Hydrogen gas can be handled by different gas models with varying degrees of accuracy. In this problem we select the IG (ideal gas) model as stated in the problem description.

Selecting the material model launches the daemon as shown in Fig. B.3 below. It may take a minute or so for the daemon to load for the first time. The access speed, however, will increase progressively as you access more and more daemons (this is because modern browsers cache recently accessed files).

C. Evaluate the Principal States
The layout of the daemon will be covered in more details in the Daemons section of the tutorial. A brief review is given below.

The daemon is enclosed within the rectangular box under its hierarchical address. The first line, called the title panel, displays the pathname as well as the version number - v8.0be28 in Fig. B.3 - of the daemon. In the next line, called the global control panel, you select a unit system (mixed, SI, or English) for the entire problem, mixed unit being the default choice. Try selecting English system and watch how the units adjust. Now select the SI and then the Mixed button again. The Super buttons next to the unit buttons are for global calculations and can be ignored at this point.

Below the global control panel is the tab panel, allowing you to switch between the state panel and the I/O (input/output) panel. Click each tab and watch the display area below the tabs change accordingly. Now click on the state tab to return to the state panel.

The state panel has its own control panel with two buttons (Calculate and Initialize) and three choices (state choice, plot choice, and a working fluid selector). Eighteen properties constitute the extended system state in this daemon - of those, two (red symbol) are invariant material property, eight (blue symbols) are thermodynamic properties comprising the core thermodynamic state, six (green symbols) are extrinsic properties (they depend on observer's velocity and location), and three (black symbols) are extensive properties (they depend on system geometry). As you move the pointer over any property, you will find a short explanation on the message panel located right below the state schematic.

Let us now evaluate the initial or beginning state, state-1, of the gas. Select H2 from the working fluid selector (see Fig. C.1) and observe how the material properties, molar mass (MM1) and gas constant (R1) adjust immediately to the new selection.

Thermodynamic properties (blue symbols) constitute the thermodynamic state, the core state representing thermodynamic equilibrium. According to a fundamental principal of thermodynamics - called the state postulate - a thermodynamic state can be completely evaluated from just two independent properties, pressure and temperature for instance.

To enter a property, you must first activate it by clicking the checkbox next to the symbol. The text field turns yellow and the cursor is automatically positioned ready for you to type in a value. If you change your mind, simply de-select the property by clicking the checkbox again. Now let us enter the known temperature T1, by clicking the checkbox, typing in the number 20 in the yellow text field, and then selecting deg-C as the unit from the units associated with T1 (see Fig. C.2). You have to press the Enter key for the value to be read, which is indicated by the change in background color from yellow to green (Fig. C.2).

A second blue property is necessary to evaluate the state. Try to enter any arbitrary value for properties u1, h1, or c_p1. You will find that the daemon does not allow you to activate those properties and alerts you (on the message panel) to the fact that u1, h1, and c_p1 are functions of T1 (for the IG model), and, therefore, not independent. We could enter p1 or v1, but they are not given. Vel1 and z1, initialized to zero, are not much help since they do not give us any clue to a second thermodynamic property.

Note that m1 and Vol1 are given. As you enter these properties, a second thermodynamic property - the specific volume v1 (=Vol1/m1) - is calculated by the daemon; consequently, the entire state - well, almost the entire state, since specific exergies phi1 and psi1 cannot be found unless state-0, called a dead state, is calculated first - is now evaluated as shown in Fig. C.3 below.

Knowing that mass and volume remain unchanged, state-2, the final state, can be calculated from T2, m2, and Vol2 (see Fig. C.3). Note how the expressions '=Vol1' and '=m1' are used instead of the numerical values of the properties.

Now that the anchor states of the process have been found, the I/O panel can be used as a scientific calculator to find the differences in desired properties. For that, switch to the I/O panel by clicking the I/O tab, and evaluate expressions such as '=p2-p1', '=m1*(e2-e1)', etc., as shown in Fig. C.4. The answers can be seen to match the posted answers under the problem statement.

Often, it is a sound practice to plot the states on a thermodynamic plot such as the p-v or T-s diagram. Once the states are evaluated, simply select a suitable diagram, say, the p-v diagram, from the plot menu, and the diagram appears in a floating window (see Fig. C.5.). Note that you can visually verify that v remains constant during the heating process. You can also do various constant property lines through selected or all calculated states.

D. What-if Studies
Go back to the States panel, select CO2 from the working fluid selector, and click the Super-Calculate button. Both the states are recomputed for CO2 from the given (checked) input, and a detailed output is generated on the I/O panel as shown in Fig. D.1. You can copy and paste the output into your favorite word processor and then print it (note that Java applets are not allowed to access local resources such as printer or hard disk as a security precaution). The desired results, differences in properties, can be calculated as before on the I/O panel.

It is not only the working substance that can be changed in a what-if scenario. Any input to the problem can be altered - for instance, the initial temperature, volume, or mass - and its effect on the solution can be similarly evaluated.

E. TEST-Codes There are complex problems in thermodynamics that require evaluation of tens of states in a single analysis. Because Java applets are not allowed to write into your disk, saving a partial or complete solution poses a problem. This is where TEST-codes, generated in the I/O panel as part of the detailed output (generated by Super-Calculate operation), can be useful.

In the state panel, select H2 as the working fluid again. Super-Calculate to produce the detailed output. Scroll up to find the TEST-codes as shown in Fig. E.1. The syntax used in the TEST-codes are quite simple (as in C, C++, or Java). Comment statements can be seen to begin with the pound sign (#). All state computed are listed inside the States block, enclosed within curly braces. Each state is followed by a state number and the working fluid used (State-1: H2; for instance). All the given properties are then listed along with their respective units and separated by semicolons. The codes are quite readable, and they essentially describe the known variables of the problem in a succinct manner.

What makes TEST-codes so useful is their ability to regenerate the solution without having to enter all the known variables manually one by one. For that, all you need to do is to launch the daemon (its path is given as a comment statement at the start of the TEST-codes), copy and past the codes on the I/O panel, click the Load button, and then the Super-Calculate button.

Although, TEST-codes are model specific, they can be shared among similar models such as the IG and PG model. The PG (perfect gas) model is a simplified IG model with the additional assumption of constant specific heats. Suppose we are to evaluate how the answers to problem 3-4-3 would change if the PG model was used. For that all we need is to launch the PG system state daemon, load the TEST-Codes, and Super-Calculate.

The Daemons section of the Tutorial contains hands-on examples on many other state and system daemons. Before you explore those solutions, we recommend that you go thorough My Second TEST Solution that illustrates the analysis panels of system daemons.