Thermal Radiation

[spikeorrn]

We're just starting a project.
We are trying to be more "green" in 2009 so we wanted to be able to construct something practical- that we would use again. We like camping and cooking (and eating) so had an idea to construct a "reflector oven" and experiment with radiant energy. We would use our electric heater (which is in use in our attic anyway) as the heat source.
But what to investigate? Effect of distance from the heat source on the temperature in our oven? Maybe putting different barriers between the source and the oven? Design of the oven- then we'd have to make a few different one's?

Suggestions much appreciated.

Thanks,
Pat and Mike

[ChrisG]

Hi Pat and Mike,
It sounds like you main decision is whether to pursue design issues about how to make an effective oven, or basic science issues about how thermal radiation is reflected. For the basic science questions, I would recommend reading about interchange of energy (e.g. see http://en.wikipedia.org/wiki/Thermal_ra ... _of_energy). For design problems, you could add or remove components (what would happen if you combine a reflection oven with a "one-way mirror"?) or vary almost any aspect of the design.

In the end, you should choosing to study an aspect of the problem that you find interesting and a little puzzling. I include "puzzling" because it is usually not as fun or impressive to design an experiment with a foregone conclusion.

Good luck!

Chris

[spikeorrn]

Thanks Chris.

We have been reading about thermal radiation/heat transfer and saw that there were different formulas. They are difficult for us to understand.

We also saw an article on reflector oven cooking. The scoutmaster wrote, "The amount of energy captured by the oven depends a lot on the temperature of the fire, and on the oven’s distance from the fire. If the temperature of the fire is doubled, the amount of energy captured by the oven with increase by a factor of sixteen! So you will want a good, hot fire with lots of flames. Also, if the distance between the fire and the oven is cut in half, the amount of energy captured by the oven will increase by a factor of four. So you can adjust the temperature of your oven by changing its distance from the fire."

We were thinking of trying to test these statements but don't know how to put our variables into the formulas we researched.

But the idea of the one way mirror is interesting. We could investigate these questions: If we put the mirror between the oven and the heat source, with the reflective side facing the oven, would the energy pass thru the non-reflective side of the mirror to the oven? Would the reflective surface of the mirror increase the temp/effectiveness inside the oven (capturing heat that's lost through the open side)? We are concerned that we would need to find material fro the one-way mirror that would be able to withstand high heat. Maybe engineers have already designed these and they are in use in other applications? We're looking....

[spikeorrn]

Ahh... just thought of something. Should we look at solar energy systems to find this?

[Craig_Bridge]

But the idea of the one way mirror is interesting. We could investigate these questions: If we put the mirror between the oven and the heat source, with the reflective side facing the oven, would the energy pass thru the non-reflective side of the mirror to the oven? Would the reflective surface of the mirror increase the temp/effectiveness inside the oven (capturing heat that's lost through the open side)? We are concerned that we would need to find material fro the one-way mirror that would be able to withstand high heat.

To my knowledge, there isn't a "one way mirror" for heat. A piece of aluminum foil will reflect a significant portion of the radient heat but it will absorb a portion and some small part will be re-radiated. But this only consideres radient heat. Unless this is in a vaccum, air flow or convection will also occur. Any air tight surface will act as a convection surface and there will be thermal conductivity between the front and back surfaces of any material.

We have been reading about thermal radiation/heat transfer and saw that there were different formulas. They are difficult for us to understand.

I'm not sure which formulas you are referring to, but there are at least three basic different ways heat transfers occur, radiation, convection, and conduction. Each of these different heat transfer mechanisms have different behaviors and require different mathmatical models to describe.