A. Quick Navigation

Task Bar: Located at the bottom of the home page (see Fig. 1), is the orange colored task bar. It is a control panel that links different TEST modules. The Tutorial, Slides, Problems, and VT have their own control panels, which links to the TEST home page through the link.

Map: Shown in Fig. 2 is an image map, called the TEST map, which provides direct link to important TEST pages. If you are an experienced user of TEST, you can bypass the step-by-step simplification process, discussed later, and jump to the desired daemon page using the Map, linked from the task bar.

The organization of the map is not arbitrary, but based on the standard approach of simplifying thermodynamic systems.

System Animation and Gov. Equations: The governing balance equations for mass, energy and entropy, and an animation describing the system (see Figs. 5) can be found below (scroll down the daemons.systems page) the simplification table. As more and more assumptions are used to chart a course through the TEST pages, the animation and governing equations adjust and finally reach their simplest form in the daemon page. Observe this by going back and forth among the daemons.systems, daemons.systems.open, and daemons.systems.open.process pages.

The Daemon Page: The leaf pages (pages at the end of a simplification trail) of the TEST-tree is where the daemons are embedded. The goal of a successful navigation is to locate the right daemon for the job. While an experienced user can use the Map to jump right into the right daemon, students of thermodynamics may benefit by going through a systematic search for the appropriate daemon page for a given problem. This is discussed next in the daemon locator.

C.1 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.

C.3 Unsteady Systems 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 begin-state (b-state) to a finish-state (f-state) executing what is 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.

Examples of open processes include charging and discharging. If you are in this branch, simply select an appropriate material model for the working fluid to launch an appropriate open process daemon.

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

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).

C.5 Closed Generic Processes - Uniform vs. Non-Uniform 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). 

Non-uniform systems have at least two identifiable uniform sub-systems. If the sub-systems are allowed to mix (for instance, a valve connecting two different gases in two tanks is opened), the system is called  non-uniform mixing system. The finish state is defined by a single f-state if mixing is allowed to go to completion. A variation of this daemon is the semi-mixing, non-uniform daemon which allows partial mixing, resulting in a composite finish state represented by fA and fB states. If the subsystems do not mix at all (a hot block of copper dropped into a bucket of  water), a  non-uniform, non-mixing system results. Once you classify a problem down to this level, you are ready to select the material model and launch the corresponding mixing , semi-mixing, or non-mixing daemons.
 

C.6 Open, Steady, Generic Systems - Single-Flow vs. Multi-Flow 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. 

In Multi-flow systems, there must be multiple openings or ports at the system boundary resulting in more than one flow in and out of the system. If the flows remain separated as in a heat exchanger, such a system is called the multi-flow non-mixing device. On the other hand, if the flows are allowed to mix or separate, as in a mixing chamber or separation chamber, the system is called a multi-flow mixing device.

D. Selecting a Material Model Having classified the system, all that remains to be done is to classify the working substance, the last step before launching a daemon. TEST divides all working substances into four broad categories. 

(i) Solids and liquids are lumped into a single group because they are both characterized by constant specific heat and density. The model is called the SL model. 

(ii) Gases are sub-divided into three categories:   Perfect gas or PG-Model is the simplest gas model with constant specific heats.  Ideal gas or IG-Model, treats specific heats to be temperature dependent. The IG model, therefore, is more accurate than the PG model, especially if there is significant temperature change in a problem.   Real gas or RG Model is a generalized model based on the compressibility charts (Lee Kessler simple fluid model or Nelson Ober compressibility chart). It is used mostly for gases under extreme pressure or very low temperature, at which the PC model (to be introduced shortly) lacks data.  It should be kept in mind that the generality of the real gas model is achieved at the expense of accuracy.

(iii) Gas Mixtures are sub-divided into binary mixtures of perfect (PG/PG), ideal (IG/IG), and real gases (RG/RG), or a general mixture of ideal gases (n-IG, n-PG). Moist Air , a mixture of dry air and water vapor, is also treated as a gas mixture. Dry air, a fixed  mixture of oxygen and nitrogen, is usually treated as a pure gas rather than a  gas mixture. In addition a general mixture of any number of components can be created for perfect and ideal gases.

Finally the (iv) Phase-Change or PC Model, which is based on saturated and super-heated tables, is the most accurate of all models.