SHPE Foundation Online SHPE Jr. Member Activities TeachEngineering Hands-on Activity: * Solar Ovens TeachEngineering Digital Library: teachengineering.org teachengineering.org Online SHPE Jr. Member Curriculum is funded with generous support from:

TeachEngineering Digital Library The TeachEngineering digital library provides over 1300 free engineering lessons and activities. Engineering lessons and activities connect real- world experiences with curricular content already taught in K-12 classrooms. TeachEngineering's comprehensive curricula are hands-on, inexpensive, and relevant to students' daily lives. SHPE Foundation Online SHPE Jr. Member Activities

Solar Ovens Learn about heat transfer, then design, build, and test a solar oven that can bake cookies! Engineering focus: o Full Engineering Design Process Follow all the steps of the engineering design process to build, test, and redesign a device, optimizing its performance. Learning objectives: o Explain the concept of radiation and give examples of ways that the sun's energy can be collected and stored for useful purposes. o Explain that certain materials do not conduct heat well and are therefore good for insulation. o Give examples of different materials that can be used for collecting and storing heat energy from the sun. o Plot and analyze temperature vs. time data. SHPE Foundation Online SHPE Jr. Member Activities Reference Activity on TeachEngineering

Suggested time: minutes (plus time for baking!) Materials o cardboard boxes (at least 2), where one box fits inside the other o 1 piece of Plexiglas (1/4-3/8 inch thickness) that will need to be cut to fit specific dimensions of each oven (or the oven can be designed to fit the piece of Plexiglas appropriately). Alternatively, plastic oven bag may also be used for this top layer and is easier to work with. It does not provide as much insulation against heat loss by conduction. o scotch tape o black duct tape o 1 Granite Ware pan or regular black metallic cooking pan sized to fit inside your oven. o foam insulation (find at any home improvement store), enough to insulate your oven box. Foam peanuts or newspaper are less expensive alternatives. o 3-4 feet of aluminum foil o utility knife or scissors; scissors must be strong enough to cut corrugated cardboard o (optional) glue o 3-4 pieces of black construction paper o ruler o food item to be cooked on metallic pan, pre-made cookie dough works best o thermometer SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens

SHPE Foundation Online SHPE Jr. Member Activities Engineering Connection (Real World Application): The design, construction and testing of solar ovens is an engineering project that combines materials science with mechanical engineering through harnessing heat transfer mechanisms. Solar ovens are in use worldwide, providing fuel-free and smoke-free cooking, baking and water decontamination especially helpful in remote and poor regions. Solar Ovens Solar tea kettle in Tibet Solar cooker used in a village in Ghana “Solar cake” in a solar oven (GSO: Global Sun Oven) made in developing countries and USA

SHPE Foundation Online SHPE Jr. Member Activities Engineering Design Process : In this activity, you will act as a real engineer by following the full engineering design process. The engineering design process is a series of steps that engineers use to guide them as they solve problems. The design process is cyclical, meaning that engineers repeat the steps as many times as needed, making improvements along the way. Solar Ovens

SHPE Foundation Online SHPE Jr. Member Activities Vocabulary Terms Definitions conduction Heat flow due to the contact of two objects or within a solid object. convection Heat flow due to fluid movement such as water. radiation Energy transferred through the movement of electromagnetic waves; heat transfer not requiring a medium. thermal conductivity The property of a material that determines how well it conducts/transmits heat. (Examples: Metal generally has a high thermal conductivity, plastic generally has a low thermal conductivity.) insulator/ insulation A material that does not conduct heat very well and has a low thermal conductivity. (Examples: A good jacket, fiberglass insulation, a sleeping bag, anything with air trapped in it.) emissivity A property of the surface of an object that determines how much electromagnetic energy is reflected and how much is absorbed by an object in the form of heat. Emissivity is very dependent on color. (Examples: Aluminum foil has a low emissivity because it reflects a majority of heat and a black surface has a high emissivity because it absorbs a lot of heat; a black shirt gets hotter than a white one in the sun.). solar radiation The amount of power received on the Earth's surface per unit area. (watts per square meter in the SI unit system) renewable resource A resource that is inexhaustible or replaceable by new growth; limitless supply. (Example: Solar energy.) nonrenewable resource A resource that is not replaceable after it has been used. (Examples: Fossil fuels such as oil or natural gas, iron ore.) Solar Ovens

SHPE Foundation Online SHPE Jr. Member Activities Introduction/Background: o How does heat move from one thing to another? There are three fundamental mechanisms of heat transfer: conduction, convection, and radiation. Conduction is heat flow due to the direct contact or two objects, or within an object. Convection is the heat flow due to fluid movement, such as the movement of air or water. Radiation is energy transferred through the movement of electromagnetic waves, and does not require a medium. o The design, construction and testing of solar ovens is an engineering project that combines materials science with mechanical engineering through harnessing heat transfer mechanisms. Solar Ovens

SHPE Foundation Online SHPE Jr. Member Activities Introduction/Background: Solar Ovens

SHPE Foundation Online SHPE Jr. Member Activities Procedure Overview Learn about ways that heat transfer occurs and discuss ways to limit heat transfer. Then, design an ‘oven’ that runs off the sun’s power, build it, and see if you can use it to bake a cookie! Solar Ovens Procedure o Using the suggested materials, take the freedom to choose your own designs. o Clearly read the design considerations on the following two slides prior to building your solar oven.

SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens Design Considerations o Design should ideally be independent of position of sun. For this purpose, make use of reflectors and consider designs that would not require you to continually reposition your solar oven. o Heat loss, heat gain and heat storage: The best insulation is a natural substance such as newspaper or Styrofoam. Another option is to use an inner cardboard box and leave a small empty space between the two boxes. It is also important to consider the color of the inside box. Lining the sides with reflective material such as aluminum foil will reflect solar radiation towards the food to be cooked. If the inside is painted, it is important that the paint be non-toxic. (Note: Do not use materials in the oven that are likely to melt at 200 to 250 °F. For example, a black garbage bag used to line the inside of the box will melt at high temperatures.)

SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens Design Considerations o The solar oven collects heat through the heat transfer mechanism of radiation. Reflect as much sunlight as possible towards the food that is being cooked. Make the pot or cooking container a dark color so that it absorbs as much solar radiation as possible. Make sure that the box is large enough to hold a dark, lightweight, shallow metallic cooking container. Graniteware, which can be found in any chef store, is a good material to use. o The solar oven combats heat transfer through conduction through the use of insulation to maintain its temperature. Heat is lost through conduction through the sides of the oven. Insulation slows this heat loss mechanism. o Convection is generally only a significant heat loss mechanism for a solar oven if it is in a particularly windy environment. Heat loss through convection can be reduced by shielding the solar oven from the wind.

SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens Procedure (continued) A detailed explanation of how to construct an example solar oven can be found at o Upon completion of constructing your solar oven, test the effectiveness of your oven on a sunny day by baking cookies in the oven to qualitatively determine how effective your oven is. o While cookies are baking, attach a thermometer to measure the temperature inside the oven at a location where you can read the temperature on the thermometer without having to open and remove the thermometer. o Measure and record the temperature every 10 minutes for 1 hour or for the length of time it takes to fully bake your cookies. Use your data to plot temperature vs. time on a graph. Take notes about any environmental changes, such as cloud cover, etc. o Eat your baked goods!

SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens Safety Issues o Be extremely careful when cutting cardboard boxes with scissors or utility knives. o Do not cut the Plexiglas yourself. Have someone at the home improvement store when the material is purchased cut it, or use fit your design to the shape of the Plexiglas or use an oven bag as an alternative material to replace the Plexiglas. o Remember to use oven mitts to remove cookies from the oven. o Be careful when opening your oven after it has been sitting in the sun as it may be very hot and may release steam, which can burn skin.

SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens Troubleshooting Tips o If the oven is not reaching the desired temperatures, make sure that all seals are tightly closed and air is not leaking out. Make sure any cracks in the box are glued or taped and well insulated and that the lid forms a tight seal with the box and where the glass meets the box. Adding foam around the rim where the lid meets the box can help improve this seal. o If all seals have been insulated and the box is still not reaching 185 °F, make sure that the box is facing toward the sun for at least 20 minutes every hour. This project should only be done during the spring or summer months. If the box still will not heat adequately, add more insulation by placing the box inside an even larger container and adding insulation. Finally, the box may simply be too large. Consider making the area that needs to be heated smaller by placing another box within the original space or allow more time for heating. o To make the reflectors, cover the flaps of the box with aluminum foil. o Get plenty of black duct tape, as it tends to run out. o Foam insulation tends to work better than newspaper. o The reflectors are hard to attach and may cause the oven to tip over. Stabilize your oven in case of mild breezes.

SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens Investigating Questions o Why is it important to understand heat transfer and storage? o What advantages does solar energy provide over other types of energy? o The Sun's corona has a temperature of millions of degrees. Why does it not incinerate us? o Why and for whom could solar ovens be important? o What are the similarities between the greenhouse effect and the solar ovens?

SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens Assessing Your Understanding! Presentations: o Present to a friend or family member about your solar oven. Describe how your oven works and why you made certain material/design choices, such as reflector types and insulation used. In addition, describe the three basic forms of heat transfer— conduction, convection and radiation – and the role each type of heat transfer plays in the baking a cookie in your solar oven. Questions: o How does the oven work and why did you choose those materials? o What parts of the solar cooker have high thermal conductivity? Low thermal conductivity? o How is radiation used? o Do reflector panels have high or low emissivity? Why? o How is convective cooling prevented? o Where are your insulators? What kind of insulation did you choose and why? Analyze your temperature versus time plots: o At what time did your oven get the hottest? o Was your oven temperature affected by clouds?

SHPE Foundation Online SHPE Jr. Member Activities Solar Ovens Activity Extensions o Visit a nearby solar house that uses solar hot water or passive solar heating. o Determine how well the oven performs in the winter. How important is the season? How important is the time of day? How important is the outside temperature? o Modify your design to determine the importance of individual aspects, such as the color of the box or how different insulators affect the temperature.

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