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| a. Closed Steady Systems:
In Navigation section, we
have discussed in details the questions that need to be answered to completely
classify a problem. As you read the problem description you define
the system at hand (somewhat subjectively) by drawing an imaginary boundary
around the object of interest. If there is no mass transfer across
the boundary, the system is closed . For a steady system, the snapshot of the system taken with the state camera (discussed
in the States page) remains frozen in time even though the system
may exchange heat and work with its surroundings. Problems involving such systems
are called Closed and Steady .
At first thought, closed steady systems appear to be quite trivial - for instance, a book resting on a desk is closed and steady as long as it is undisturbed. But all closed steady systems are not so trivial since heat and external work transfer is allowed. A light bulb, a gear box, an electrical adaptor, are all examples of closed system that can operate at steady state. There are another important class of devices that can be classified as closed steady systems. In the case of a heat engine, a conceptual closed system operating on a continuous basis produces work at the expense of heat, with the heat transfer taking place between the system and two thermal reservoirs at two different temperatures. Refrigerator or heat pump constitute similar practical examples of closed steady systems. As long as the internal details of a heat engine or a refrigeration (or heat pump) cycle are unimportant, the overall analysis can be based on the closed and steady assumptions. In general, heat engines, refrigerators, or heat pumps are implemented either by connecting a series of steady-state devices back to back to form a loop, or having a piston-cylinder device execute a series of processes (involving heat and work transfer only) forming a cycle. While it is easy to understand that a closed loop of steady devices will form a closed steady system, one may question how a system executing a sequence of unsteady processes can constitute a steady cycle, especially when the system steps through a series of drastically different states within a single cycle. The answer lies in averaging the cycle over a time of interest that is much larger than the cycle period. If the exposure time of the state camera is large enough, the picture of the system will assume an average constant state validating the steady state assumption. These daemons appear under the branch Daemons. Systems. Closed. SteadyState on the TEST-Map. When the internal details of the Cycles are important,
more specialized branches such as the Daemons.
Systems. Open. SteadyState. Specific. Cycles or the Daemons.
Systems. Closed. Process. Specific. Cycles page should be visited. |
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b. The Analysis Panel: The analysis panel for a closed and steady system
daemon is simple.
Unlike most other system daemons, the state panel is absent here. In the analysis panel, you select the type of cycles, enter the known variables and Calculate the rest. As with any other daemon, moving the pointer slowly over a variables brings up its definition and its relation to other variables in the message panel at the bottom margin of the daemon. |
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c. Parametric Studies: Once a cycle problem is set up, it is relatively simple
to evaluate the effect of changing one or more variables on the problem.
Because of the simple nature of the relationship among the cycle variables, the daemon does not support use of algebraic expressions and does not generate TEST-codes. You will find a number of examples in the Examples page, VisualTour and the Problems pages. |