Heat/radiation types

[menaceh2k]

I actually have a real question that i need answered but i figured i should make it science-sy to be relevant to the forum.

my cousins dorm only has a microwave, with no kitchen. I remembered what that was like, so i let him cook in my apt whenever he wants.

I do however remembered a long time ago there was this infomercial for these microwave bags that would cook the food like it was in an oven, it supposedly evenly distributed the heat. I also remembered that on of my old dormates microwaving a pizza that was in a box with some kind of metalic-like thing on the inside that cooked the pizza like it was in an oven. im sure it was not metal maybe some kind of silverish paint.

So my question are:

1. are there contraptions out there that can make a microwave oven distribute the heat like an oven.

2. is it even possible to convert the microwave radiations to pure thermal radiation. essentially turning your microwave into a toaster oven.

3. if these things exist how do they work. and do they sell them outside of package foods.

4. should we have a question and answer section, or will people not use it.

 

[warryer]

There are three types of heat transfer: conduction, convection and radiation.

Conduction is the energy transfer from the more energetic to the less energetic.

Convection is the energy transported due to a moving fluid.

Radiation is emitted energy.

*from my heat transfer book

In vacuums the only way to transfer heat/energy is by radiation. Conduction and convection both require some type of medium. The way I think about radiation is on the moon, the surface lit up by the sun is very hot but just a few feet away down in the shadow of a crated it is extremely cold.

The radiation itself doesn't have temperature it's just energy. Temperature is a measure of how much energy an object has in it.

I am no expert on this stuff but I can explain the basic idea.

1. are there contraptions out there that can make a microwave oven distribute the heat like an oven.

I suppose you could do this if you had some kind of liner that goes inside your microwave that can "catch" the energy waves. This would cause the liner to heat up and convect the energy into the air inside the microwave. It would be made out of some kind of metal.

2. is it even possible to convert the microwave radiations to pure thermal radiation. essentially turning your microwave into a toaster oven.

You would have to replace your microwave emitter with a thermal one.

I don't know that you can change frequency of energy without first converting the original wave into a different form of energy then back into a wave.

It seems to me that you are asking if it's possible to directly convert the frequency of a wave. This is something I would love to know more about myself.

3. if these things exist how do they work. and do they sell them outside of package foods.

They already use this principle. I've never looked to see if they are sold to consumers.

I believe the way these things work is to become excited by microwaves and as a result heat up. Think about those sleeves you get with hot pockets or a popcorn bag. You will see this dull gray stuff on the inside- this stuff is made of metal and captures the microwave energy.

In tv dinners it's different. It's the water molecules which absorb the radiation and heat up.

4. should we have a question and answer section, or will people not use it.

There's always google and wiki - searching is half the fun anyways.

 

[Cogwulf]

The problem is that a normal oven cooks food using hot air. The design of microwave ovens is to heat up the food but leave the surrounding air cold, they are not designed to contain hot air.
To make a microwave oven cook more like a normal oven, you would need to start with a semi-airtight box. And then you would need to make something to heat up the air in the box and keep the food from being directly heated.
Popcorn bags and hot pocket type things probably work partly using this principle.

As for microwaveable foods that have a grey or silver sheet in the packaging, I'm fairly sure that these are just to reflect the microwaves back into the food to cook it more evenly.

 

[Melllvar]

Even if they aren't making them yet it shouldn't be that complicated to have such a device. Make a container for the food consisting of at least two layers, the outer layer being a thermal insulator that allows for transmission of microwaves, with the inner layer being for absorption of microwaves.

Waves go in, are absorbed by the "inner layer" (heating it up), and heat tends to stay trapped in the container with the food instead of radiating outwards (hence the outer thermally insulating layer).

 

[Cogwulf]

It's a hell of a lot of effort to go to when you consider that microwaves are supposed to be about convenience. There'd also be the problem of regulating the heat the things would be cooked at.

It'd be easier to get a small desktop oven, or perhaps a halogen oven.

 

[gcomeau]

It seems to me that you are asking if it's possible to directly convert the frequency of a wave. This is something I would love to know more about myself.

Yes, you can convert the frequency of a wave. Certain lasers use frequency doubling and tripling mechanisms to achieve different desired illumination wavelengths. It requires very precisely engineered materials, isn't terribly efficient, and I doubt anyone has ever tried to create one designed to step microwaves down into the infrared since it would be fairly pointless. If you wanted to cook your food thermally instead of with microwave excitation we already have much easier and more efficient ways of doing that.

Waves go in, are absorbed by the "inner layer" (heating it up), and heat tends to stay trapped in the container with the food instead of radiating outwards (hence the outer thermally insulating layer).

...and then the container bursts into flames because you've described an ideal way to cause it to superheat.