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| Reviewed: |
Nov 24, 2004 by Engineering Editorial Board |
| Overview: |
This online applet is designed to calculate the thermodynamics properties of
steam. The software is simple and effective and provides a valuable tool for
students and instructors in a thermodynamics or related course. It displays
values in both English and SI units, and one version of the calculator presents
thermodynamic charts showing the location of the state entered. Developed using
ASME steam properties, it produces results consistent with the ASME 6th Edition
Steam Tables. Its main weaknesses are (1)the use of the term "humidity" rather
than the usual "quality" to describe the vapor fraction in a two-phase misture,
and (2) omission of internal energy as one of the properties, and (3)display of
15 or more significant figures.
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| Learning Goals: |
The software provides property data to enable quick thermodynamic calculations
rather than focusing on the often cumbersome task of obtaining steam properties
from tables.
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| Target Student Population: |
College-level students enrolled in an engineering thermodynamics or related
course.
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| Prerequisite Knowledge or Skills: |
Students should be familiar with basic thermodynamic fundamentals and
conventional steam tables prior to using the software.
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| Type of Material: |
Online applet for computing the thermodynamic properties of steam.
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| Recommended Uses: |
Efficient acquisition of the thermodynamic properties of steam for problem
solving.
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| Technical Requirements: |
A browser capable of supporting JAVA applets.
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| Strengths: |
The calculator provides an effective means to quickly obtain the thermodynamic
properties of steam for users who have some familiarity with thermodynamics.
Its accuracy appears to be quite good over the full range of thermodynamic
states tested, with calculated values agreeing with those in published steam
tables to within 1%.
Users can avoid the often time consuming task of determining the thermodynamic
states of steam using published steam tables. The ability to calculate
properties in various units extends the utility of the software. The property
diagrams offer the added value of visualizing the thermodynamic state relative
to phase changes. The display of the possible range of values for a selected
input property is also a useful reminder of its limitations.
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| Concerns: |
A major concern is that the calculator displays a property called "Humidity",
which appears to be the complement of Quality. Since Quality is the term used in
most thermodynamic courses for describing the vapor mass fraction in a
two-phase mixture, the use of the term "Humidity" is confusing to the beginning
student. This is more than a matter of semantics, since a Humidity of 23%
corresponds to a Quality of 77%. Thus, errors arising from confusion are quite
possible when beginning students use the calculator.
It is interesting that an earlier version of the calculator, still available on
the same website, used Quality rather than Humidity for the vapor fraction.
A second concern is that internal energy is not calculated. Granted it can be
determined from the enthalpy, pressure, and volume, but a direct display of this
very important thermodynamic property seems appropriate.
The software assumes the user has some previous knowledge of thermodynamics.
For example,
a user must know that he/she needs to define two thermodynamic
properties in order to identify a particular state and run the calculator.
The state diagrams are somewhat small and would be more effective if displayed
in a more visually stimulating manner. The display of the units would be
cleaner if they were represented with appropriate notation (e.g.,exponent for
ft3, etc).
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Potential Effectiveness as a Teaching Tool |
Rating:   |
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| Strengths: |
This calculator should easily compliment a traditional course in thermodynamics.
Most instructors will recognize that this tool will not pedagogically replace
the use of traditional steam tables in an introductory thermodynamics course as
a part of the initial learning process. However, it can easily compliment
traditional methods as an alternative means of obtaining property data for users
familiar with thermodynamic fundamentals.
Instructors can use this tool in a first semester course to illustrate how the
properties of steam are computed. This tool would be an excellent substitute
for steam tables in an advanced or 2nd semester course in thermodynamics or
power generation.
By being able to determine thermodynamic properties in a rapid and convenient
manner using the online steam calculator, students can spend more time on
analyzing thermodynamic problems and less time using conventional steam tables.
Thus, tasks like optimization of a thermodynamic system or parametric studies
become far less burdensome for the student.
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| Concerns: |
The aforementioned use of Humidity instead of the more familiar Quality as a
measure of the vapor component in a two-phase mixture makes the calculator less
effective as a teaching tool. The term "humidity" normally refers to the water
vapor content in moist air rather than the vapor content in a two-phase mixture
of steam and water. Thus,
confusion is quite possible, especially for the
beginning student. Again, the omission of internal energy from the properties
makes this tool less useful for the beginning student.
The software does not address the methods employed to calculate the properties,
which would be a nice linkage to the course material. All calculated results
appear with 15 or more significant digits. Results such as these diminish the
emphasis on making realistic calculations. The software could benefit by
limiting the number of digits displayed to four or five, in line with steam
tables.
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Ease of Use for Both Students and Faculty |
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| Strengths: |
The calculator is both simple and intuitive to use. The software loads quickly
and is easily accessible from the link. Aside from its purpose, the simplicity
of the applet is perhaps its most appealing quality.
A user with a limited background in thermodynamics can easily begin making
calculations immediately after the applet has loaded by checking the boxes and
entering values for any two of the six available properties. The software
changes the color of the box to illuminate where the input is to be entered or
that the value is out of range. Once these values are entered, clicking a SUBMIT
button results in an immediate display of the full set of thermodynamic
properties. The user can select a variety of units for most of the properties.
If desired, the user can select a calculator version which displays a set of
small thermodynamic charts (T-s, h-s, etc.) showing the location of the
thermodynamic state being considered.
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| Concerns: |
Although a Help screen is available with screen shots showing the various
components of the calculator, the links on the screen shot appear to be
inactive. Thus,
the Help function is virtually useless.
Checking the boxes next to the properties used as input for the calculation was
not immediately clear. A simple instruction within the applet would have
helped.
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| Other Issues and Comments: |
Overall, this calculator is both useful and accurate. It makes students less
apprehensive to take on problems involving steam since finding the required
thermodynamic properties becomes a simple task. Its main drawbacks are its
omission of internal energy, its use of the unfamiliar property Humidity, and
its display of an inordinate number of significant figures.
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