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| Reviewed: |
Jun 21, 2005 by Engineering Editorial Board |
| Overview: |
This learning object discusses and provides animations of the basic processes
and components in a thermal electric power plant. It is comprised of two main
parts: 1)Rankine cycle descriptions and animations, and 2)a Rankine cycle
calculator.
Cycle descriptions and animations include the Carnot cycle, the basic Rankine
cycle, and advanced Rankine cycles with reheating and feedwater heating.
The Rankine cycle calculator allows the user to vary several operating
parameters and observe the effect on power output and cycle efficiency.It is
capable of simulating a Rankine cycle that includes a single reheat stage and a
single open feedwater heater. As the setpoints of various parameters are changed
by the user, performance parameters are recalculated. In addition, a T-s
diagram is continuously updated as parameters are changed.
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| Learning Goals: |
The major learning goals are:
To learn about the ideal Rankine cycle for power generation and about
modifications of the cycle for improved performance.
To learn how to analyze the performance of a Rankine cycle that may include a
single reheater and a single open feedwater heate by varying several operating
parameters.
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| Target Student Population: |
Undergraduates taking classes in thermodynamics or power generation.
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| Prerequisite Knowledge or Skills: |
Elementary thermodynamics with some knowledge of power cycles.
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| Type of Material: |
Learning object for visual demonstration of an engineering power cycle and java
applet for performing interactive calculations.
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| Recommended Uses: |
This module may be used as supplementary material for teaching vapor power
cycle principles. Students can also be assigned exercises that would involve use
of the simulation applet.
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| Technical Requirements: |
Browser with both JAVA and Shockwave support.
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| Strengths: |
The object presents a collection of thermodynamic cycles that are useful in
understanding modern electrical power generation. It starts with the Carnot
cycle and concludes with a Rankine cycle incorporting superheating, reheating,
and feedwater heating. By combining cycle schematics with thermodynamic
diagrams, a better understanding of each cycle variant is achieved.
This learning object can definitely be useful in explaing the fundamentals of
power cycles. It culminates with a "Rankine Calculator" that allows the user to
vary a number of pertinent parameters such as boiler, condenser and reheat
pressures, superheat and reheat temperatures, and turbine and efficiencies. Once
the parameters are entered, the simulator presents the cycle in a familiar
temperature-entropy (T-S)diagram and the various cycle performance parameters
such as efficiency and turbine net work.
Comparing the values provided by the Rankine Calculator with those determined
from steam tables, excellent agreement is observed.
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| Concerns: |
None
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Potential Effectiveness as a Teaching Tool |
Rating:    |
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| Strengths: |
The animations make this object well suited for classroom demonstration. By
including a plant schematic and a T-s diagram in the same animated graphic, the
user can clearly see how the various processes are represented on the
thermodynamic chart.
The online Rankine calculator is an excellent tool for demonstrating cycle
performance and for developing parametric studies as homework assignments. Since
it removes much of the tedium normally associated with steam cycle analyses,
students can focus more on the effects of each parameter (e.g., boiler pressure,
condensing temperature, etc.) on the overall cycle operformance.
The "Issues" section on each of the cycle simulations is a nice touch for it
shows the student the problems inherent in each typeof cycle and how further <
br/>cycle embellishments (e.g. reheat) can overcome these problems to some extent.
The learning object can be used to teach an applied thermodynamics course and
also used in a technical elective course that involves vapor power cycle
analyses. It can also be used as a reference source for a design purposes.
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| Concerns: |
A bit of confusion can arise in the superheat and reheat portions of the Rankine
Calculator. At first glance, it would appear that the actual boiler leaving
temperatures are to be entered, but in fact the amount of superheat occurring in
the boiler is what is expected.
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Ease of Use for Both Students and Faculty |
Rating:  |
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| Strengths: |
This learning object is very easy and inviting to use. The cycle animations are
excellent and the material is presented in ways familiar to engineering students
and faculty alike. The slider bars on the Rankine calculator offer a
convenient way to change input parameters quickly, and the nearly instantaneous
response provides excellent feedback.
It has been used successfully with Internet Explorer 6, Netscape Navigator 7.1
and Firefox 1.0 browsers. In all cases, the appropriate JAVA and Shockware
plug-ins were installed.
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| Concerns: |
The aforementioned possibility for confusion in the superheat/reheat section of
the Rankine Calculator detracts a bit from its potential effectiveness as a
teaching and learning tool. While not a serious problem since it can be easily
explained, it does detract from the ease of use. Perhaps it would be better to
simply have the user enter the actual temperatures rather than the amount of
superheat.
It would be nice if on the "Cycle" home page, the user could immediately go to
the particular cycle of interest instead of having to go through each of the
cycles in a series fashion. Also,
there is no way to get to the next cycle
unless the "Issues" are explored for each cycle.
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| Other Issues and Comments: |
Users should be informed that review progression to the other modifications to
the cycles listed on the cycles page can only be accessed when the "issues"
button is selected after the review of a cycle.
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| Comments from Author: |
I thank the reviewers for their helpful comments and would like to comment on a
couple of issues which they raise.
One detail that the reviewers correctly points out is that the Rankine
calculator applet requires "degrees of superheat" to be specified at the turbine
inlet (rather than the temperature directly). This has certainly been a common
source of confusion as my own students use the applet to complete their
assignments. As a result I have often considered changing it. However, the
classic balance between ease of use and making students think is at play here.
I WANT my students to know what "degrees of superheat" means. (Perhaps causing
misery and frustration for the user is a poor teaching technique!!)
A second issue addressed by the reviewers is that users must progress through
the various cycles rather than being able to jump directly to the more
complicated cycles. In fact they have to view the "Issues" information for each
cycle before they progress. I did this intentionally to encourage the students
to build their understanding of the most complex cycle in a step-by-step
fashion. My preference would be to have all cycles available after a particular
student has gone through the whole story once - but I haven't had time to do
this.
Another issue (related to the two above) that was not identified by the
reviewers is the desirability of having the Rankine Cycle Calculator
also output thermodynamic properties at each state point. At present,
it only reveals the work and heat transfers for each component. My
thinking, again, was to restrict the amount of information provided to
the students. I do, after all, insist that they be able to perform all
of the calculations by hand. This allows me to configure assignments
that require the students to use the applet for "design type" questions,
yet requires them to do hand calculations for questions about more
detailed information such as state variables at various points in the
cycle.
If anyone has any thoughts on these issues, or other comments on the
site, please feel free to email me at jim.bugg@usask.ca.
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