Description
IMPORTANT:
Unless otherwise stated, please turn in any pre-lab or group reports at the beginning of each lab session. There will be one lab report per group, where each group member will include a conclusion section of their own that will be submitted individually.
Objectives
-
Understand the thermodynamics of the Stirling cycle.
-
Describe the thermodynamics of a displacer-type Stirling engine.
-
Use thermodynamics to quantitatively analyze power cycles.
-
Write a technical report.
Experimental Background and Description
-
Out of the various sub-categories of
Stirling
en-
gines, the one chosen for
this
lab
is
a
gamma-type
engine (Figure 1).
This implies
that
the
power
pis-
ton
is housed in its own cylinder, but both the power
and
displacer pistons are connected to the same fly-
wheel.
The power
piston is connected to the dis-
placer
piston
by
the
same crankshaft, but their phases
are
offset.
In
the
engine
used
for
this
lab,
the
displacer
piston
is
made
out
of an insulating mate-
rial
(Styrofoam)
and
it
does
not seal the inside of
the
large
cylinder.
The
purpose
of
the displacer
pis-
ton
is to push the working fluid (air) from one ther-
mal
reservoir
to
the
other.
The
air
freely
flows
around the foam displacer to
travel from the hot to
cold side and vice versa.
This
displacement
of the
working
fluid
creates
a
forced
convective
heat
trans-
fer and thus creates pressure gradients across the main
displacement
piston
housing
which
are
used
to
drive
the
power
piston.
As Stirling engines are classi-
fied
as
an
external
combustion
engine
these
engines
are
ideal
for
situations
that
require a
very
efficient
non-internal combustion engine.
The ideal example
Figure 1: Gamma-type Stirling Engine
of
this situation
is
providing
power
to
spacecraft
sent
into
deep
space
where
solar cells
become
impracti-
cal.
Stirling engines have been used in many aerospace applications including providing electric power to spacecraft where solar power is not practical, and acting as a cooling system to prevent electric parts from overt-heating. A Stirling engine has the potential to produce the same amount of power as a traditional RTG, while using only one fourth the amount of plutonium (Pu-238). Though Stirling engines are extremely efficient and convenient, they are
prohibitively expensive to research and produce. Due to this cost, most Aerospace companies choose to use more conventional means to power their spacecraft.
Part of this lab is based on a CAD model of the gamma-type engine that you will be testing. Included in the pre-lab is a short exercise to confirm your ability to extract the necessary measurements and data from this CAD model. If you have not used SolidWorks much before, the introductory online tutorials provided for you last week should help. Refer back to those.
The lab report must be completed in the AIAA format. Please visit the AIAA homepage* for FAQ’s regarding this layout.
The following links may be useful in visualizing and understanding Stirling engines: http://auto.howstuffworks.com/stirling-engine.htm http://en.wikipedia.org/wiki/Stirling_engine http://www.animatedengines.com/ltdstirling.html http://www.ohio.edu/mechanical/stirling/engines/engines.html
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AIAA Author’s Toolkit; https://www.aiaa.org/techpresenterresources/ 2 of 7
Appendix A
Appendix B
Appendix C:
SolidWorks Flywheel Supporting Documentation
-
Copy the “Flywheel” part from the directory “courses Z:nAESnlab-documentsnASEN 3113nLab1 Stirling En-ginenSolidWorks model”. The file are also available on Canvas for those working remotely.
Open the “Flywheel” file, and begin by editing the sketch on “Boss-Extrude 1”. Display the drop down arrow for ”“Boss-Extrude 1”, highlight Sketch 1 and select sketch in the top left corner.
-
With the circumferential encoder hole on the bottom, remove the top two spokes entirely, but leave the spoke adjacent to the encoder hole intact. Remove all curves and construction lines near the center. Create a construc-tion circle in the middle with a 9mm radius. Draw two more lines for construction that are 45°off of the center line. To do this use the smart dimension tool by clicking on both lines to set the angle between them.
-
Using two three point arcs, create fillet between the vertical lines of the spoke and the construction circle that you just made. Constrain the fillets to be tangent to the vertical lines and the construction circle. Do this by selecting both the arc and the construction circle and select a tangent relation. Repeat for vertical lines of spoke. You may need to add another relation to intersect your fillets with your construction lines. Make sure (using dimensions, construction lines, or another technique) that the tangent points on the construction circle are symmetric about the spoke and take up 90°of the construction circle:
-
Revolve the spokes by using “Circular Pattern” feature found under Tools i Sketch Tools. Click on each line you would like to rotate.
-
Exit the sketch.
-
Create the Part Drawing: Click File: Make drawing from model. Add views consistent with Appendix B.
Hint: Uncheck “Only show standard formats” and use “A (ANSI) Landscape”.
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Annotate the part drawings with the necessary dimensions using Smart Dimension. Also indicate tolerances as shown on the drawing in Appendix B.
-
Save any necessary changes/files.
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University of Colorado at Boulder
