Solar Oven Project
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Transcript of Solar Oven Project
University of Arizona Engineering 102B
Team Eight Solar Oven Report
November 4, 2015
Team Name: The Newspaper Thieves
Team Members: Adam Mcclintock
Yiming Wang Nathan Truong Kyle Schraven
Chris Miller
The Newspaper Thieves 1
Abstract:
Overall, the solar oven project was a successful experiment. After the first construction
and trial of our solar oven we decided that the initial design that we created would be
sufficient enough for our final project, with the exception of adding reflectors as we
could not reach our desired Tio without them. Our oven was extremely large when
compared to other group’s ovens meaning that our project was not as efficient as it
could have been in terms of cost effectiveness and weight. However, we were
successful after the final trial of reaching our desired temperature and having a
maximum temperature of 121.5 degrees Celsius. The temperature of the oven
fluctuated as the sun moved and fell behind clouds, the shadows of others blocked
sunlight, and as we constantly adjusted the angle to keep up with the setting sun
throughout our final test. Our solar oven was ultimately successful in the desired goal of
cooking the biscuit as it remained constantly hot enough to thoroughly cook it.
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Table of Contents:
Item: Page #
Introduction 3
Design Theory and Analytical Model 4-7
Design Requirements 8
Design Descriptions 9-10
Design Justification 11
Test Procedure 12
Test Results 13-14
Team Dynamics 15-16
Design Critique and Summary 17-18
References 19
Appendices 20-21
Solar Oven Performance Index 22
The Newspaper Thieves 3
Introduction:
The main motivation for this project came from how simple that the idea itself is. The
solar oven is relatively inexpensive as well making it easier to buy and/or produce.
These ovens can be used worldwide in many different areas and climates given that the
sun is shining, and learning how to appreciate another source of energy such as solar
will help us gain experience in the engineering field. The group had hoped to learn
about how working in a group will influence the way that one thinks about a project, and
we learned that by combining our ideas and views we can accomplish much more and
work our way around many more of the problems that we encounter. Something else
that we found is that it helps to learn more about how to analyze all of the variables that
can be changed in order to end with the best prediction model with the highest
temperature possible. The concepts hoped to be explored include learning how to test
the oven more than once as well as being able to change one of the variables to end
with an oven that can reach a higher maximum temperature and cook the given biscuit.
The ovens are appealing to the world because of its effectiveness and being
inexpensive to make or buy.
The Newspaper Thieves 4
Design Theory and Analytical Model:
The base design for the solar oven began with the math equations for Tio from the solar
oven comparisons document as well as the specifications for the design. Many of the
specifications dealt with variables like material type for the insulation(newspaper), the
oven itself (cardboard), size of the box(height, width and weight), and the design of the
solar oven itself (size of reflectors and window).
The design for the solar oven is in a term a box in a box. The design is visually seen
below where the smaller box, which holds what needs to be cooked, is suspended
above the floor of the outer box to allow room for us to insulate the chamber and
minimize the escape of heat from the cooking chamber. The bigger box is then filled
snugly with the insulation, in this case newspaper, so that it is not too heavy but also
properly does its job.
Figure 1: Top and Side Views of the Solar Oven
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As seen above from the top and side view angles, there is a small oven chamber
suspended above the floor of large box and in between the two borders is the insulation.
In the image shown below is another showing of the top side of the box showing what
happens to the heat around the box that is lost through convection.
Figure 2: Visual Diagram of Convection
Even though the heat loss itself was very small, it slowed the loss from conductivity
shown by the arrows coming off of the box’s chamber. The loss of heat from such a
small source was not included into the final solution because of the inability to account
for the small change.
The next step after defining the overall design and how to combat the heat loss is to
make a mathematical model of the oven using the following equation;
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This equation looks quite complicated but when you break it down into pieces it
becomes quite manageable. The following listing shows the breakdown of the equation.
Equation Terminology:
Tambient – ambient temperature (°C) r - reflectivity
n – # of layers of Mylar G - Gain
Θs - angle of the sun (°) Usb - Thermal Con of Side/Bottom
β - angle of the box to the
ground(°) Uw -Thermal Con of window
Io - solar power density Aw – window area (M2)
τ – transmissivity Asb – area,side bottom (M2)
a - absorption
Tio - Temperature in the oven
(C°)
The solar oven consisted of the cardboard exterior and the cardboard had an exterior
thickness of about 3mm. There were two layers of the 3mm thickness due to the inner
box being made of the same cardboard. Then the box was filled with insulation
(newspaper) which was about 10 cm in thickness. The window area, the area of the
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sides and bottom, and the volume of the chamber can easily be found by simple
formulas for area and volume. For the exterior of the box it was decided to use black
construction paper, as the color black is known to absorb the heat from the outside. The
darker body type helped in keeping the heat closer to the insulation warming up the
smaller box on the inside. The original design of the solar oven box went along with
these specifications although adjustments were made wherever needed. Mylar windows
were used to direct the heat to the designated area where the biscuit was. The gain was
added after the prediction models were made, so simply put the gain was put into the
equation and slightly affected the end result of the solar oven predicted temperature.
The Newspaper Thieves 8
Design Requirements:
There were a plethora of requirements and guidelines that were given to us when
first starting the solar oven project. First of all, the basic design had to have a cooking
chamber that had to be an enclosed cardboard box. This cooking chamber had several
requirements as well, such as the volume had to be 1000 cubic centimeters, the
chamber had to be an easily accessible box with dimensions larger than or equal to 5
cm. As well, the chamber needed a rack to support the biscuit and had to have
thermometer access that permitted it to be easily read. The outer box of the cooking
chamber had to have a flat top and could not be sloped. There were no requirements
that we had to use reflectors, but logically we had to or else we would not have reached
our target temperature, and thus the biscuit would not have cooked. With these
reflectors there was a requirement that they had to be flat and could not be parabolic.
This presented us with the problem of having to find what angles and sizes would work
best so as to reflect the most energy possible from the sunlight into the cooking
chamber.
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Design Description:
Our box solar oven is an enclosed cardboard box with aluminum foil reflectors.
First, according to the dimension we got, we cut the cardboard to make two boxes. A
small box with a transparent window is embedded in a big box. Between the small box
and the big box, we used wads of newspaper as an isolation to reduce energy loss. We
sealed every side of the big box and make sure it would keep the heat inside. Then we
covered the inside of the reflectors with aluminum foil, so that the reflectors can
concentrate sunlight onto the chamber. Once the light concentrates, it converts to heat
energy. To maximize the conversion, we also covered the entire cavity with black paper,
which can conduct and retain heat. Finally we fixed the reflectors on one side of the
window, so that we can open it and put the biscuit in.
Figure 3: Prototype Figure 4: Final Design
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Figure 5: SolidWorks Drawings of the Final Oven
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Design Justification:
The idea for the design of the solar oven was based off of the the solar oven
basics document and the past successful solar ovens. It was simply a box inside of a
smaller box with a lot of insulation in between. The idea of the reflectors came from the
solar oven comparisons sheet showing higher Tio than any of the other designs. It
would have been more preferable for the solar oven box to have been a bit smaller, to
have the heat confined to a smaller location. As well as having the entire box black
which was only accomplished for the outer ring of the box. It was not entirely black due
to a lack of resources and was only able to retrieve a different color of construction
paper. Again it would have been preferable to use a lighter form of getting black onto
the box, such as spray painting it, but a lack of resources once again. Overall the solar
oven design was based off of the popular designs of the past successful solar ovens as
well as on the solar oven basics guide.
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Test Procedure:
During the in class testing we tested our oven on the roof of the ECE building
without reflectors on to see how hot it would get on its own without the added help of
the reflectors. During the test the ambient temperature was roughly 35 degrees Celsius
and the temperature that our oven eventually reached was 49 degrees Celsius. Besides
not having reflectors, some of the critical features of the set up were that the oven was
directly aligned with the sun to maximize the amount of light and heat that our box
would be exposed to, and that our mylar did not have space between the two sheets
during the test run. The only items placed in our oven during the test run were the
thermometer to record temperature and the tray that would be used to hold our biscuit
during the Solar Oven Throwdown. Some of the Data that we recorded during the test
was how the structural integrity held up when the oven was left at the tilted angle
because it was a little heavy, and we recorded how the tray held up to the heat.
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Test Results:
Our test results were informative and helped us take into account more
confounding factors that will affect the oven’s temp and how well it functions. In each
test it took about fifty minutes for our oven to reach its maximum temperature and
stabilize at that temperature. During the first test our oven was without reflectors and the
mylar spacing was wrong. This explains the low temperatures that we achieved on the
first test. The second test however had many more confounding factors that attributed to
its abnormal graph behavior, even after the addition of reflectors, additional taping, and
adding the correct mylar spacing to our oven window. First of all was the fact that the
sun was in and out behind clouds for the middle part of the test. Second, the door that
we had designed to make putting in and taking out the biscuit from the oven had a small
air leak that let a lot of our hot air escape whenever it cracked open at the tilted angle
we had to keep our oven at to align with the sun. And the last confounding factor was
that we repeatedly had other students standing in between our oven and the sun. Some
ways that we could take these problems into consideration is by putting the oven up on
a pillar or table of some sort of table so that it will be out of the way of people’s shadows
and making sure to only use the oven on a sunny day so that the oven can cook at the
appropriate temperature. One other problem that we need to fix is that the duct tape that
made up our tray started to melt and contaminate the biscuit. this could be avoided by
using a material not made of plastic that also has a much higher melting point so we
don’t have to worry about contaminating the food that we are trying to make. Another fix
The Newspaper Thieves 14
that we could make is to redesign the opening oven door so that it is not so easily
moved up to displace the hot air that is needed to stay inside the oven.
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Team Dynamics:
● Adam: Helped with design and assembly, provided funds to buy the foil for
reflectors and duct tape to hold the oven together. Constantly texting group to get
together and work on what we need to get done. Kept pictures of initial designs.
Helped schedule group meetings.
● Kyle : Did majority of the actual construction of the solar oven when creating it
and aided in design. Picked up some of materials from the store when needed or
wanted. Most of hard labour trying to cut out cardboard oven designs with
scissors.
● Yiming: Used the new tape to fix every side of the oven again. Took notes of the
temperature every ten minutes during the first test. Took pictures of the oven
during testing. Looking at the finer details of the oven. Finding the smaller flaws
that others overlooked.
● Nathan: Supported members in their roles. Completed and finalized the solar
oven comparisons sheet. Main lead when it came to the equations. Constantly
pitching ideas. Helped schedule meetings and book the rooms needed. Created
the Solidworks model and drawings of the solar oven.
● Chris: Picked up most of the materials for the oven and housed the project.
Calculated the measurements for the reflectors. Contributed in the design and
building of the oven. Carried the oven to and from needed places. Helped book
rooms when we had a meeting scheduled
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● Whole team: Worked well together once we started actually working on a project,
but we need to work more on building planning and organization for the future.
Works fast and efficiently to get work done and solve problems. Brings together a
good variety of people with diverse views and opinions that help us as a group as
opposed to having five people who think the same way.
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Design Critique and Summary:
In hindsight, many features of the design of the project would have been better
off with more time spent increasing the efficiency of the box dimensions, tape, lid and
angle of the box. The dimensions of the box were made so that they met the required
1000 cm3 area but not much time was given to maximize the efficiency of the
dimensions of the box so that the maximum amount of heat was directed towards the
heating chamber. By making the box focus the energy to the heating chamber, the oven
would be more efficient in receiving more heat with no added materials to the price
index. The duct tape used to seal the heat into the box should have been given more
thought. The amount of duct tape used should have been minimized while making sure
to not let any chance of heat escaping the box. A better quality duct tape would have
improved the tape to not release the heat of the box. By decreasing the amount of heat
escaped through the tape, the temperature of the heating chamber would have been
higher with the same amount of materials used. The lid that allowed easy access to the
heating chamber should have been more efficient. The only thing that held the lid down
was the weight of the reflectors. By securing the lid down with tape or anything to
prevent heat escaping from the chamber would have made the oven reach higher
temperatures. The angle of the box was not measured out to be a perfect 90 degree
angle with the sun. Instead of using backpacks to tilt the box, a measured piece of
cardboard should have been attached to the box at the calculated angle so that more
sunlight would have been absorbed by the oven. A recommendation for a team
designing the box would be to list the features of the design and one by one go through
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the list deciding on the most efficient use of the features to add to the final design. As
far as team dynamics, the process would have gone much more smoothly if there was
better organization and leadership. A more organized way of handling the project would
have allowed for a smarter and better way of completing the oven. This is more efficient
use of human resources. Relating to this, there should have been a team leader and
specific roles for each member of the group so that each member had a more focused
job making better use of everyone's time promoting the idea of synergy.
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References:
● D2L
○ Solar oven basics
○ Solar oven excel guide
○ Solar oven predictions model
○ Lecture slides 5-7 on solar oven information
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Appendices:
Prediction Model:
● PI: Duct tape and aluminum foil: about $10
● Discussion notes:
○ What we needed to fix
■ Mylar spacing
■ Adding reflectors
■ It was too heavy
■ It was too bulky
■ It wasn’t as cost efficient as it should have been
○ What we did well
■ Sturdy structure
■ Good window size
■ It was well insulated
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● The design phase(not many pictures taken)
● Other documents regarding the solar oven project
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Solar Performance Index:
Team Name:The Newspaper Thieves
Solar Oven Cost Breakdown:
1)Materials
Material Amount used Cost Basis Material cost
Duct Taped ½ roll $2.99 per roll $1.50
Aluminum Foil 1/25 roll $4.99 per roll $0.20
Cardboard 1 ½ sheets $3.99 per sheet $3.00
Construction paper 15 sheets 2 cents per sheet $0.30
Scotch Tape ½ roll $0.99 per roll $0.50
Total material cost: $5.50
2)Transportation cost
Weight of oven 9.8 lbs
x $.20 /lb= $1.96
3)Labour cost: $5.00 per team (fixed)
4)Total oven cost: $12.46
5)Performance Index:
T(ambient)=30 Degrees Celsius
T(actual)=121.7 Degrees Celsius
Cost based PI=_______
SOTD PI=_______