Solar Oven Project

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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

Transcript of Solar Oven Project

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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

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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

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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.

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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.

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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

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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=_______