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Microwave x 2

Posted: 12 Jun 2018, 18:07
by yogi
At times I use the microwave oven to cook frozen vegetables. The popular ones come in what they call "steamer" packages. Nuke them and steam is created inside the package which in turns cooks the frozen veggies. The amount of time to expose them to microwaves depends on the power of your oven. Been doing that for years, but today I decided to have two vegetables. I did them one at a time for the full amount of time, but I was wondering if I could do them both together. Does putting twice as many veggies in the oven affect the time it takes to steam them properly? It would not in a conventional oven, but microwaves are different. What's the formula here?

Re: Microwave x 2

Posted: 13 Jun 2018, 11:50
by Kellemora
Yes, the volume of what is in the microwave determines how long it needs to cook.
It's actually faster to do one item at a time, because it's not a 50/50 deal here.
A scenario - If it takes 1 minute to bring 1 cup of water to a full boil (not the first chemical release boil).
Logically, it would take 2 minutes to bring 2 cups of water to a full boil, but it takes 2 minutes 20 seconds.
Three cups of water takes about 3 minutes 45 seconds.
Although, using water is not the best way to test due to the impurities in water causing false boiling points.

Remember the original advertising for microwaves? They said items cook from the inside out.
If that were true, then the plug-in thermometers to tell you when they are done would not work. The inside would be done and the outside still raw, hi hi.

The only true formula is trial and error due to the differences in all microwaves.
I've seen microwaves rated at 950 watts cook faster than ones advertised as 1,200 watts.
Items cook in a 1 cu ft microwave faster than in a 1.5 or 2 cu ft microwave too.

One thing I do not like the flavor of when cooked in a microwave is Bacon. It changes the flavor considerably.

Re: Microwave x 2

Posted: 13 Jun 2018, 13:05
by yogi
Theory does not always match practice. I understand that. But, there is something going on in the microwave that I do not understand fully. If I put a 100 grams of potatoes into a 1000 watt microwave oven, it will take 4 minutes to increase the internal temperature to 200F. Why does it take more than twice the time to bring two 100 gram potatoes to the same temperature?

The theory is that the radiated energy from the magnetron is constant. Admittedly not all 1000 watts of its energy is absorbed by the potato mass, but the amount needed to elevate the temperature to 200F is fixed - you know, so many watt-minutes per degree. I don't understand where the loss (requiring more time) is when two potatoes are nuked. Why isn't the 1000 watts of energy absorbed equally by equal masses?

Thinking about it now, I can speculate that the microwaves (energy) being reflected probably increase and the efficiency decreases when two masses are in the oven. The increase in surface area of the taters is where the losses must originate. The same amount of energy is still needed, but less energy reaches the potato core when there are more reflections.

Re: Microwave x 2

Posted: 14 Jun 2018, 10:32
by Kellemora
I understand it, but don't know if I can explain it very well.

It's not exactly like a radio wave where all receivers can pick up the signal.

The Photons bounce around, lose energy, and get absorbed by the item you are cooking.
How about if I try it this way.
Take 100 ping pong balls and drop them in a concrete box. Assume they can keep bouncing around until they land in a cup.
If you place 1 cup in the box, all of the ping pong balls will eventually end up in the cup.
But if you place 2 cups in the box, each cup will only catch 1/2 of the ping pong balls.
If you place 3 cups in the box, each cup will only catch 1/3 of the ping pong balls.
Now, if one cup can hold all 100 ping pong balls, when it is filled it is done.
With two cups, you have to add another 100 ping pong balls to fill both cups.
Three cups takes another 100 ping pong balls.

Microwaves are more like light waves, perhaps this is why they are called Photons.
If you shine a light at a wall, it illuminates the whole wall.
But if you stand a tall box up in front of the wall, some of the light hits the box instead of the wall.
Add two boxes and less light hits the wall.
Now, if that wall was a solar cell, and you blocked part of the light hitting it, it would put out less current.
Although a microwave is putting out continuously, just like a light, part of it's power is absorbed by the item.

Another example: On DSL, if you add a second computer, the data transfer cuts in half.

Re: Microwave x 2

Posted: 14 Jun 2018, 13:56
by yogi
So ... what you are saying is that the entire 1KW of microwaves does not excite each individual blob of mass in the oven. Each item in the oven gets it's proportional share of the source.

Never heard of microwaves being called photons. However, the electrons in the mass being heated jump energy levels when struck by a microwave of the proper wavelength (frequency). This increase in energy level is what causes the heat. It also explains why it is said things are heated from the inside instead of by an external heat source. I have read where it has been observed that when the electrons drop back to their natural energy ring, a photon is emitted in the process. Thus light is emitted by food being microwaved. Some claim they can see it, but most of that light is beyond human senses.

Re: Microwave x 2

Posted: 15 Jun 2018, 11:29
by Kellemora
Electromagnetic radiation when up in the light emitting ranges (above our vision range of course) is called photons.
Below light emitting ranges they are called radio waves.
I have no idea what they call the range that is in the light wave region but used to carry radio signals.

I do know a microwave oven is not exactly like a lawn sprinkler, but similar in that the microwaves spray out all over the place. However, the microwaves bounce around in the oven and probably lose half their power at each bounce so run out of steam so to speak.
Once the water from a garden sprinkler hits the ground or blade of grass, etc. It has finished its travel. It doesn't reflect back up into the air again. Well, perhaps it splashes a tad, but you know what I mean.
If you consider a photon as only light, it would either be absorbed by something or reflected back if the surface is reflective. I think this is more how a microwave works. The photons bounce around inside as they fade away, and only some of them hit the object to be heated.
Of course, using that logic, then all items in the microwave should be heated at the same pace, except for the fact once a photon hits something it can be absorbed into, aka used, it is not reflected back out to bounce around to something else.

Now I could be all wet behind the ears, but that is how I see a microwave working.
Based a little bit on a microwave transmitter we had at one of our radio clubs.
Took a lot of power, and a horn with reflector, to concentrate and send the signal a short distance.

Re: Microwave x 2

Posted: 15 Jun 2018, 13:18
by yogi
The reason posted this topic is largely due to the fact that I didn't want to research it on my own. I'm past that point now. :mrgreen: I didn't apply for a government grant, but, as they say, "Google is your friend."

First of all the term "photon" is generic.
The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force
Thus, you are correct to say microwaves are photons. But that's like saying a forest is trees. Regardless, I never heard of microwaves being called photons, not even in the cell phone industry for which I worked.

Microwaves (at a frequency of 2450MHz) are generated by a magnetron buried inside the oven's innards. A wave guide points them to the business end of the oven - presumably somewhere near the bottom center of the cubed cooking chamber. As we already know, microwaves travel in more or less a straight line as they leave a wave guide or a parabolic dish. Like light waves, microwaves reflect off dense surfaces and are subject to the standing wave phenomena. That is what creates hot spots inside the oven.
Microwaves do most of their work on the water in food,. Water molecules constitute what are known as 'dipoles, A dipole is sort of like a bar magnet, with a positive pole and a negative pole. The oven's electromagnetic field oscillates as it passes through the water molecules in the food, changing the polarity of the field and causing the dipole/water molecules to flip themselves in order to be aligned with the new polarity. Heat is created by the resulting friction of the water molecules reversing direction millions of times a second.
So ... the quantum energy of the microwave photons get absorbed by the water molecules in the food. This absorption is what generates the heat. Because there are inevitable hot spots, due to standing waves, it's a good idea to use that built in turntable to distribute the heat energy evenly.

Getting back to the original question, all the above makes sense. There are only so many photon packets of energy to go around. Thus, twice the mass should take twice as long to cook and absorb the photon energy. However, as you point out, it takes longer than that. My guess is that extra time is due to the rotation of the food on that turntable which changes the standing wave pattern. There must be some losses as a consequence.

Re: Microwave x 2

Posted: 16 Jun 2018, 16:02
by Kellemora
There ya go Yogi, now you know more than I do about the little box that Nukes our food, hi hi.

Re: Microwave x 2

Posted: 16 Jun 2018, 16:53
by yogi
I never knew water had dipoles. Next time you need an antenna ...

Re: Microwave x 2

Posted: 17 Jun 2018, 11:07
by Kellemora
Water is one of the most interesting of all things to study.
It has properties unlike anything else I know of.
It is possible to get water too pure though, such as triple distilled, or deionized.
You wouldn't want to drink pure water, it would suck the electrolytes out of your body.
Without the extra minerals in water, it would have no readable pH level.
The funny thing about that is, logically that would mean it was a perfect pH 7.00000, but that's not the case.
It simply has no pH at all.
Gotta have those Anions and Cations to be palatable and safe to drink, hi hi.

Re: Microwave x 2

Posted: 17 Jun 2018, 13:57
by yogi
Apparently pure water doesn't have dipoles (if I understand this right). It's the stuff dissolved in the H2O that does it:
Deionized water (DI water, DIW or de-ionized water), often synonymous with demineralized water / DM water, is water that has had almost all of its mineral ions removed, such as cations like sodium, calcium, iron, and copper, and anions such as chloride and sulfate.
Way back during the last century, those days when I had a paying job, deionized water was used all the time. I never had to use it, but it was part and parcel of some process or another. I think it had something to do with the crystal manufacturing, but I'm not certain anymore.

Re: Microwave x 2

Posted: 17 Jun 2018, 17:21
by pilvikki
ah, thank you (very) much!

i will now feed this to the kids, they might as well learn something while loafing about for the summer! :mrgreen: :mrgreen: