Pre Lab 1 - Stirling Lab

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

1

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












































    • AIAA Author’s Toolkit; https://www.aiaa.org/techpresenterresources/ 2 of 7



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Individual Pre-Lab



NOTE: You are not required to write a report for this part of the lab. Simply type your responses in the order they were asked. Each student will submit their own pre-lab.

    1. General Theory

        (a) What is the difference between alpha, beta, and gamma-type Stirling engines? Please be thorough but concise.

        (b) How does the gamma-type Stirling engine work? Describe how the four thermodynamic processes of an ideal Stirling cycle are carried out by the physical device. Hint: Open the Stirling engine assembly CAD model and analyze how the pistons move relative to each other.

        (c) In the Stirling engine used for this lab, how does the internal volume of the system change with time?

    2. The Stirling Cycle

        (a) Provide a sketch of an ideal Stirling cycle P-V diagram.

        (b) Using your above diagram and the real cycle P-V diagram provided (Appendix A), label each of the four processes in the Stirling thermodynamic cycle (For example, isothermal expansion is one of the four thermodynamic processes.). Don’t worry about units on your ideal cycle for this pre-lab. Identify why the real cycle does not look exactly like the ideal cycle.

        (c) Using the provided wireframe of the engine you will be testing in this lab (Appendix A), label all heat/work transfers and temperatures for an engine running in a room temperature environment with T = 10°C. No calculations need to be made for this step.

    3. CAD Model

Using the provided flywheel model from the SolidWorks assembly, change the number of spokes from three to four. Using this updated model create a one page drawing with a standard three-section view that includes the dimensions that would be required for manufacturing. Use the drawing show in Appendix B as a reference for necessary dimensions and layout. Appendix B is NOT a solution and you must add additional dimensions to receive full credit. There are many different techniques for developing this CAD model, but one method is outlined in Appendix C for reference.















Figure 2: Three Spoke Flywheel    Figure 3: Four Spoke Flywheel









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Appendix A

















































Figure 4: PV Plot One Rotation. Note: Pressure is plotted as a gague pressure












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Appendix B































































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Appendix C:
SolidWorks Flywheel Supporting Documentation


    1. 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.

    2. 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.

    3. 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:

































    4. Revolve the spokes by using “Circular Pattern” feature found under Tools i Sketch Tools. Click on each line you would like to rotate.

    5. Exit the sketch.

    6. 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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    7. Annotate the part drawings with the necessary dimensions using Smart Dimension. Also indicate tolerances as shown on the drawing in Appendix B.

    8. Save any necessary changes/files.





























































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