Thermodynamic State Calculator: Ideal Gas
Welcome to the Smart Thermodynamic
Table: Ideal Gas page, part of the 'Utility Applets' library of TEST,
The Expert System for Thermodynamics. TEST is a network of HTML pages with
embedded Java Applets that helps users solve thermodynamic problems and
perform parametric studies visually without any programming.
An Ideal gas can be simply defined as a gas (or
liquid) that obeys the ideal gas equation p=rho.R.T. All gases under low
pressure (compared to the critical pressure) and/or high temperature (about
250K or more) can usually be treated as ideal gases. Gases covered by the
Ideal Gas Calculator include: Air, Nitrogen(N2), Oxygen(O2), Hidrogen (H2),
Carbon-di-Oxide(CO2), Carbon-monoxide (CO), Argon(Ar), Neon(Ne), Helium(He),
Methane(CH4), Ethane(C2H6), Ethylene (C2H4), Propane(C3H8), Butane (C4H10)
The Smart Thermodynamic Table is more than a visual
thermodynamic state calculator for Ideal gases. In this ideal gas table
a state is visually presented (see the examples below) as a collection
of variables (such as p, T, v, h, s etc.). A gas is chosen from a selection
of gases and known variables are entered in any order and in any units
(the applet checks for redundancy of inputs, converts units internally,
provides balloon help and generates suitable warnings when appropriate)
and a click on the 'Calculate' button evaluates the states partially or
fully if sufficient information is known. The calculated states are auto-saved
and can be plotted on a 'p-V', 'T-s' or other thermodynamic diagrams by
choosing a plot-type from the diagram selector.
While evaluating a state related to another (say,
isentropic states), algebraic expressions involving state variables can
be used. For instance, to evaluate State-2, isentropic to State-1, one
can enter s2 as '=s1'. Once a series of states are evaluated, updating
all calculations for a change in any input variable is a snap. Simply change
the value and click on the 'Super-Calculate' button. The smart table takes
care of the rest making it an exciting visual design tool for the 'What-If'
people. A more comprehensive introduction can be found in the Introduction/Tutorial
page (linked at top) and is highly recommended for all users.
The examples below contain images of the ideal
gas table in action. Once you get a rough idea about how the smart table
works, you can start using the real thing by following these instructions.
There are two ways of doing anything,
the quick way and the right way.
If you are in a hurry, do the following: (a) Browse
the examples below (takes only a minute), and (b) Launch the customized
Java applet (called a daemon) by clicking the appropriate link at the top
of this page. If you have a modern browser (Netscape 4.5 or better, Microsoft
IE 4.0 or better), the daemon will appear in about 10-50 seconds (1 second
if you are running from a locally installed TEST) and you can start exploring.
To fully exploit TEST follow thest steps: (a)
Start the Introduction/Turorial for the Expert System by clicking the link
at the top of this page. (b) Explore a few daemons as explained in the
tutorial. (c) Browse a few topics of your choice from the Slide Show. (d)
Once you understand the algorithm TEST applies for locating the right daemon
for a given problem, you can use the TEST-Map to quickly launch a desired
daemon. Of course, all these may take better part of an hour - but, trust
me, you will not regret it.
The air in an automobile tire with a volume of
18 ft3 is at 90oF and 25 psig. Determine the amount
of air to be added to bring the pressure up to 30 psig. Assume the atmospheric
pressure to be 14.7 psia and the temperature and volume to remain constant.
To bring up the appropriate daemon (applet) navigate
to TEST Home Page, Test, Daemons, States, and Ideal Gas in sequence (or
directly using the 'Smart Ideal Gas Applet' link at the top).
The daemon page will be displayed on the upper
frame and a help page will appear on the lower frame of the browser window.
As the daemon gets loaded, you may see its shadow for about 5-15 seconds.
Trouble Shooting: If
the daemon (as pictured below) does not show up even after a minute, may
be your browser is unable to run Java applications. I know of three reasons
for this. (i) Your browser has not been updated since the Jurassic age,
(ii) Java is turned off, (iii) Security is set to 'high' (in case of Internet
Explorer). Because TEST takes advantage of JDK 1.2 (the latest Java revision),
you will need Internet Explorer 4.0 or Netscape 4.5 (not 4.05) to run TEST
effectively. If you do not want to update your browser, you can still use
TEST-2.01, a relatively primitive version. Instructions for how to rectify
these problems and links to download the latest version of the browsers
(Navigator or Explorer) can be found in the Troubleshooting/FAQ file on
the TEST Home Page.
If the daemon looks 'broken' (happens occasionally with Explorer 4.0) close
(not exit) and open the browser to refresh the display.
|Fig. 1. Image of the Smart Table (Ideal Gas
Daemon) producing solution to Example 1.
Choose the working fluid (air is the default gas),
air, from the fluid selector. Enter the values of the known variables,
volume of the tire, temperature and pressure (note the use of equation),
and click the 'Calculate' button to obtain the complete state. All the
properties have a suffix '0' as the state is identified as 'State-0'. Note
that mass is only one of the unknown variables calculated by the daemon
to give a complete picture of the state. The Ideal gas table offers many
other smart features like this, some of which are highlighted in the slide
show (link at the top margin) and some are left for the users to explore.
|Fig. 2. Image of the Smart Table (Ideal Gas
Daemon) completing solution to Example 1.
Choose 'State-1' from the state selector, enter
the new pressure, temperature and volume, and 'Calculate' the new mass.
How would the answer in Ex. 1 change if the temperature
is 30oF instead?
Example 1 has been solved, simply change the temperature in 'State-0',
click the 'Calculate' button to register the change and 'Super-Calculate'
button to update all calculations. The simplicity of performing a parametric
study is the real strength of the Smart Ideal Gas Table.
|Fig. 2. Image of the Smart Thermodynamic
Table (Ideal Gas Daemon) producing solution to Example 2.
These examples are only meant to give the reader
the flavor of a daemon (applet). Many more examples of solved problems,
grouped into fifteen different chapters, can be found under TEST Home Page>
TEST> Problems page. Before you start using this particular applet, it
is strongly recommended that you take a look at the 'Slide Show' to get
a feel for the breadth of thermodynamic topics TEST covers. Besides more
examples and a visual tour, you will also find a visual manual for the
daemons explaining different buttons and widgets found in the daemons.
You will see how a wide range of thermodynamic problems can be visually
solved and parametrically studied without the need for a single line of