Senior Environmental Science Majors Nick Hurn and Kevin Burks are creating a small parabolic mirror cooker to demonstrate the wide uses of alternation energy in Humboldt County. It is part of an Spring 2013 ENGR305 class at Cal Poly Humboldt and will be featured on permanent display at Jefferson Community Center in Arcata, California. Parabolic cookers are designed to harness the sun's energy and transfer it directly into the process of cooking raw material. It will serve as a functioning solar cooker for lunches and activities for the students and staff as well as an example of a creative use of alternate energy for the community to enjoy.
Introduction[edit | edit source]
When we first took on this project, we had three different design opportunities to consider and we were overwhelmed to say the least. But luckily for us, we had help from Bart Orlando, a local expert on solar cookers. The first design we considered was using a recycled radar dish as a frame, the second was a portable parabolic cooker with a collapsible frame, and the third was using a recycled papasan chair as a frame. We were looking at using a recycled chair or radar dish because of there inherent parabolic shape already.
Once we decided that our most feasible design would be the Papasan Chair, we had to next decide what kind of reflective surface to cover the chair with. We had to choose between a Mylar coating, stainless steel faucets, or polished aluminum faucets. Our project criteria focuses on durability and efficiency, so we decided to use polished aluminum sheets because they are highly reflective yet durable enough to mend and not rip or tear.
Once our.025" polished aluminum sheet came in we had to decide our faucet designs, the sliver like triangles that would cover the outside of the chair to reflect the sunlight to the focal point. We decided to make our faucets 8" on the thick end and a 2" truncated end on the other side where we can drill through and align all facets with a bolt.
Once we completed the reflective chair aspect of the project, we started on the tripod/grill rack design. We thought about mounting a rack system directly onto the chair, but the constant adjustment for proper sun angle deterred us. Instead, we settled on a tripod system made out of three 1" thick bamboo rods held together with tightened recycled bicycle tubes at the top. From the top of the tripod, we hung a 2ft section of chain with three other 2ft sections of chain hanging off of that chain. Those three pieces of chain we connected to our grill racking making a flat, maneuverable cooking surface to put a assortment of pans on. With some adjustments and tests, we were able to calibrate our solar cooker to burn paper, boil water, and educate the community about the importance of sustainable cooking practices.
Problem statement[edit | edit source]
The object of this project is to create a parabolic mirror cooker that is a successful example of the ways to capture and use the sun's energy in a sustainable manner. We plan to do this in two steps by first testing the most efficient and effective way of building the cooker, then implementing the most environmentally friendly construction techniques to achieve the creation of it.
Project Evaluation Criteria[edit | edit source]
The following Criteria will be used to assess the success of this project. After deliberation with the client, we determined the following criteria to be critical for the success of our project. The 1-10 scale signifies the importance of each listed criteria.
|The cooker must reach an optimal temperature (TBD) within a certain time (approx. 2 hours)
|Ease of Use and Safety
|Design must be straightforward and child-friendly
|The cooker must effectively demonstrate the power of alternative solar heating
|Placement and Storage
|Cooker must fit into a designated storage area (approx 4 ft. square) and fit through specified double doors
|Must be big enough to effectively cook food in relatively short period of time while still maintaining mobility
|The cooker must be able to be moved by 1-2 people (i.e. wheels, handles, lightweight)
|Must function for multiple years around children and withstand UV rays
|Must stay within the means of our budget
|Successfully captures kids imaginations and inspires them to seek further education in appropriate technology
Literature Review[edit | edit source]
The Shape[edit | edit source]
Parabolas and Paraboloids are always something fun to learn about. They have a unique shape that gives them properties that are pretty interesting. They have the power to focus radio, light, and even sound waves into one focal point using reflection. The unique shape of the curve gives the paraboloid this unique characteristic. In order to find the focal point for the paraboliod, one must use the equation y = p * x^2, where p is the constant, y is the depth of the paraboloid, and x is the max circumference of the paraboloid. With this equation, were were able to find our focal point which was about 4.5" inches above the center of our paraboloid.
The History[edit | edit source]
Parabolic Solar cookers are devices designed to capture the suns direct heat using a parabolic shaped reflective surface. They work by reflecting the suns rays into one central focal point creating temperatures exceeding 500 F used to heat, cook, and pasteurize food or water. Parabolic Solar cookers date back many centuries to civilizations all around the world. From the Greeks, to the Aztecs, to The Ancient Chinese and Romans, they all had a version. And since the sun is the only source of fuel needed to create heat for use, they are practical to create and inexpensive to operate and maintain, making them a perfect educational tool for sustainable cooking.
Construction[edit | edit source]
Measure and trace facets on aluminum sheets
Cut out all facets using the Beverly Shear. This process is time consuming as the shear only cuts several inches per slice.
Drill attachment holes in top corners of all facets. These should be about 1/4 inch in diameter to allow for zip-ties to easily slide through. Drill a half inch hole at the small end of the facet to allow for the anchoring bolt.
Place facets on chair and insert anchoring bolt
Slowly fan out facets, being careful not to scratch aluminum. Note: pink protective plastic is left on until all facets are securely in place.
Insert zip-ties in each corner and attach to outer bamboo rim of Papasan chair frame
Remove plastic and inspect for any blemishes
Assemble tripod. Bundle up the 3 bamboo poles and place bike inner tubes around one end. Keep doubling the tubes over on themselves until tight. This will allow the poles to expand into a tripod and easily retract down into bundle form.
Suspend chain from top of tripod and attach white metal grate with mini carabiners. This grate will hold numerous different cooking surfaces.
Cook, boil, and burn!
Maintenance Instructions[edit | edit source]
We build our solar cooker with maintenance in mind, our motto was simple construction means simple maintenance. There are very few moving parts on this project making the maintenance a breeze. There main concern for maintenance is proper storage and cleaning. Prior to every use, the polished aluminium faucets must be polished. And without proper storage, the cooker could fall apart in a few years. The main components of the cooker are the zip ties, the chain, and the bamboo rods. All very inexpensive and easy to replace. We have an extra aluminum faucet as well in case of damage to one of the original faucets, and extra zip ties to donate as well.
Proposed Time Line[edit | edit source]
These are the tentative dates for the completion of each goal.
|Acquire all necessary materials
Cost[edit | edit source]
Here is the proposed sortable budget for the Jefferson Community Center Parabolic Cooker
|2' Length of Stainless Steel Chain
|Pot for cooking demonstration w/ Lid
|Bicycle Inner tube
|Old bike tires in garage
|White metal grate
|Bamboo Poles 1" x 8'
|Mad River Garden Supply
|Sheet of reflective Aluminum - 5' x 8'
|AluMet Metal Supply (ordered online)
Conclusion[edit | edit source]
Testing results[edit | edit source]
Directly after construction of the cooker, several tests were administered to determine the effectiveness of the parabola.
The first test was simply placing a small bundle of paper in what we assumed was the focal point to see if it would ignite. It smoked and charred for approximately 30 seconds but never ignited. Next, we put 1 pint of water in a pot which was suspended form the bamboo tripod. After approximately 20 mins, some bubble were visible but no boiling was recorded.
To better aim the dish at the sun, we employed the "pencil shadow" technique. This entails screwing a pencil into the securing nut at the center of the cooker. With the pencil sticking up perpendicular to the dish, we placed a piece of paper with a hole in the middle around the nut so a shadow from the pencil was easily visible. This allowed us to adjust the cooker until no shadow was visible, meaning it was pointed directly at the sun.
Once the panels had been thoroughly cleaned and the dish aimed directly at the sun, we ran the same two test again. A soda can sized bundle of brown paper was placed in the focal point of the cooker and within 20 seconds it was on fire. This means that the temperature at the focal point was at least 451 degrees F. Second, we placed 1 pint of water in the same pot and found that it took 10-15 minutes to boil.
Further testing will include an infrared temperature gun to accurately measure the focal point temperature. Different cooking mediums, such as skillets, pans, and dutch ovens, will also be tried to determine which cooks food/water most efficiently.
Discussion[edit | edit source]
After final testing we can safely assume that the cooker is capable of producing temperatures well in excess of 450 degrees F. The focal point of the cooker is approximately the size of a softball, thus cooking with a small to medium pan or pot is most efficient. The most important part of the cooking surface is that the bottom be black. Lighter, reflective surfaces do not absorb as much heat, thus food will not cook nearly as efficiently. This project was very enjoyable to work on and we look forward to inspiring and educating others.
Lessons learned[edit | edit source]
- ALWAYS watch for stray rays of light, they can and will start a fire, the more concave the dish, the less the concern.
- ALWAYS wear UV protective eye wear when working with sun light and reflective materials.
- Try to find a pot with a black bottom, greatly increases cooking temp for pan. If not, Black Tempera paint applied to the bottom of the pan will help greatly
- ALWAYS store with something covering it or upside down, stray sun can find them
- Constant adjustment is necessary as the sun tracks across the sky
- Wind can cause chain to sway and rob cooking surface of heat
- Make sure parental supervision is given if in the presence of kids
- Perfect conditions are hard to find
- Works best when sun directly over head(full sun)
Next steps[edit | edit source]
Developed mainly as an inspirational tool, the parabolic cooker will be used in demonstrations and educational events.
To reach the widest audience possible, we plan to display the cooker during several of Arcata's Farmer's Market events on the Arcata plaza. These demonstrations will show the cooker in action as it cooks food and boils water. Pamphlets or informational signage will be prepared to further the public's knowledge on cooking with solar energy. Additionally, warning signs will be prepared to ensure onlookers are protected from the bright reflections that can escape the parabola.
Jefferson Community Center
After several plaza demonstrations, the Jefferson Community Center in Eureka, California has agreed to permanently house the parabolic cooker. They plan to use the cooker in demos and for community events held at the center. The cooker will serve mainly as an inspirational tool for the center's youth, sparking an interest in sustainable and renewable energy in future environmental scientists.
During the building process we noted several areas for improvement in future projects. Instead of using the bamboo papasan chair as a frame, the aluminum facets could be connected using a small rope or cord. This cord would weave through the holes drilled at the top corners of each facet and when pulled tight would force the middles of the facets to bow out, creating a stand alone parabolic dish. This model has numerous implications, as it would be portable, lightweight, and smaller, making it perfect for travel.
Team[edit | edit source]
- Kevin Burks-Fourth Year Environmental Science Major with an Emphasis on Energy and Climate and a Minor in Geospatial Sciences at Cal Poly Humboldt
- Nick Hurn-Fourth Year Environmental Science Major with an Emphasis on Energy and Climate at [[Cal Poly Humboldt
See also[edit | edit source]
- Projects with Bart
- Compound parabolic concentrators
- Compound parabolic reflectors for solar cookers
- Parabolic solar cookers