Step 1: List the requirements (constraints)
Step 2: List the outputs of the model
Step 3: Sketch the system and write out the equations
Step 4: Model the system in Excel
Step 5: Solve graphically for T io and U w
Step 6: Change the design variables in the Excel spreadsheet to help solve for the desired outputs
Requirements Outputs
Sketch &
Equations
Excel Model
Solve for T io
U w
& Adjust design variables

Chamber volume = 1,800 cm 3
Chamber dimensions > 5 cm each
Chamber window is square (W = L)
Chamber has convenient access (food item can be conveniently inserted and removed)
Chamber has a rack to support the food item from the walls and bottom
Chamber has thermometer access with readout face outside of the oven

Stand of some kind – backpacks, books, rocks
OK
Reflector(s):
M/L < 3
Zero to four panels
Minimum final oven temperature = 100 degrees C
No focusing lenses or parabolic reflectors

Why no parabolic lenses/reflectors?
Sources: http://solarcooking.wikia.com/wiki/Matt_West http://www.lvrj.com/news/vdara-visitor---death-ray--scorched-hair-
103777559.html

Predict temperature from equilibrium condition
Show temperature effect from chamber dimensions
Give reflector design angle
Show improvement, if any, from double glazing
Calculate PI from T ambient
, T io
, and Cost
Show temperature effects from layers of insulation
Show temperature effects on misalignment with the sun
(how sensitive is this to angle errors?)
Show effect of reflector length, M, on the gain, G

Notes:
You will not create the final list the first time you work on it.
As you get into the design you will think of other things and make changes.
However, it saves time and cuts down on the number of iterations by making a list.

Step 3: Sketch the system and write out the equations
Design Variables:
U w
: heat transfer coefficient for window
A w
: the area of the window
τ : optical transmission coefficient of window a : absorption coefficient of the cavity walls
β : angle of the window wrt the ground
U sb
: heat transfer coefficient for sides & bottom of cooking chamber
A sb
: area of sides & bottom of cooking chamber

Step 3: Sketch the system and write out the equations
I o
: Incident solar power density (pp. 31)
τ : optical transmission coefficient of window (pp.
8 and 31); this could change if you use a different window material. a : absorption coefficient of the cavity walls (pp.
8 and 31) - this could change if you use a different color.

Step 3: Sketch the system and write out the equations
At Equilibrium (Highest Temperature): Power in
= Power out
T = T io
- T ambient
Power out
= U sb
A sb
T
Power in
= I o
A w t n a G
Power out
= U w
A w
T
Important!
I o
A w t n a G = U w
A w
T + U sb
A sb
T
T = T io
– T ambient
=
I o
U w
A w
A w t n a G
+ U sb
A sb

Step 3: Sketch the system and write out the equations
T io

T ambient


U sb
I o

A w
A sb

G

 
U w n

 a
A w

• We need to increase T io
• Only 3 ways to do that…
1. Increase T ambient, which is possible if you are close friends with sun.
2. Increase the numerator of the equation.
3. Decrease the denominator of the equation.

Step 4: Model the system in Excel
Note: This spreadsheet example for graphical illustration purposes only.

Step 5: Solve U w
/ Temperature Variability Graphically
Note: This spreadsheet example for graphical illustration purposes only.

Step 6: Experiment with Excel Model to find T io
• See Excel Spreadsheet Prediction Homework
Instructions for further information (pp. 30-33, Solar
Oven Document)
• Ultimately, try to find the combination of design variables that predicts the highest internal oven temperature
• From these design variable settings, build your oven!
• When your oven is actually tested, compare actual T io vs. predicted T io
§ Last semester’s top team: 1 degree difference!

Some design variables are specified for you in the
Solar Oven documents
Other design variables are your choice
Use the tools given to you in the Team homework and
Team Excel Predictions Spreadsheet to calculate optimal values for your oven
Don’t forget to factor in material costs, though

Ultimate goal: Maximize Performance Index (PI)
See Solar Oven Document, pp. 34 – 37
PI = (Temperature inside oven – Temperature outside oven)/Total costs of building oven
Two ways to increase PI:
Increase temperature difference
Decrease costs
Another goal: predicted T io
≈ actual T io

As explained on page 11, U w is a function of T io
You are given 3 different ways to solve for this, I suggest that you do it graphically.
You plot 2 lines:
One line: Using the given values for U w and T io from
Table 1
Second line: Using your T io
(based on all of your design variables) and the given U w values.
Where they intersect is your oven’s predicted internal temperature at equilibrium.

Deliverables via D2L:
Solar Oven Comparisons Team Homework due Dec 12
UPDATED(pg. 29, Solar Oven Document)
Solar Oven Excel Prediction Model HW due Dec 16. (pp.
30-33, Solar Oven Document)
Team Presentation PPT, due TBD
Final Team Report, due TBD

Actual Oven Demos
First oven, Mar. 8 (Tuesday)
Final oven, Apr. 1 (Friday main lecture time)
Prizes?
Oral & PPT presentations in class, Mar. 22 &
Mar. 24
Based on initial oven test, other oven dissection, and your spreadsheet analysis

Friday: we will examine the Gain, G, from the addition of reflectors
Read pp. 13 – 20 in Solar Oven Document for Friday
This example has
4 reflectors

Solar Oven Team Comparisons HW due Dec 12
Solar Oven Team Prediction Model due Dec 16
Read pp. 13 – 20 in Solar Oven Doc. For Friday
Remainder of class: