Boiling point of water heated via microwave

In summary, the author took 100 ml of distilled water and put a small, clean rock into it. He then heated the water repeatedly in a microwave oven on high for 45 seconds. After each heating, he checked the temperature of the water with a digital temperature probe. The highest reading he ever got was 93.5 degrees C. He gave up when the quantity of water became noticeably reduced (50%).
  • #36
Fun, and fascinating experiment.
Those first few seconds are critical!

The only thing it cost me, was about 1 hour, and one RTD.*
My RTDs are NOT microwave safe.

*along with the obligatory bits of duct tape, and sundry items, of course.

Images, data, and my recommendations on improvement of the experiment are available upon request.
 
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  • #37
OmCheeto said:
Fun, and fascinating experiment.
Those first few seconds are critical!

The only thing it cost me, was about 1 hour, and one RTD.*
My RTDs are NOT microwave safe.

*along with the obligatory bits of duct tape, and sundry items, of course.

Images, data, and my recommendations on improvement of the experiment are available upon request.
Go on then - give us all a look. (I am "requesting")
It would be about 54 years ago that i did it and I HAVE LOST MY EXERCISE BOOK ( the dog ate it, I think)
 
  • #38
sophiecentaur said:
Go on then - give us all a look. (I am "requesting")
It would be about 54 years ago that i did it and I HAVE LOST MY EXERCISE BOOK ( the dog ate it, I think)

Do you want all of the experiments?
The first one, told me that my setup was wrong, as trying to hold an RTD in a teeny tiny little 100 ml glass, in one position, is nearly impossible, whilst checking the time and temperature.

microwave.exp.rev.1.png


x axis: seconds
y axis: °C
 
  • #39
OmCheeto said:
Do you want all of the experiments?
Why not? I did it once and that was quite enough. :smile:
Are you deliberately holding us all in suspense? Where's the second, improved version - with the extrapolation to t=0? I am agog in anticipation.
 
  • #40
sophiecentaur said:
Why not? I did it once and that was quite enough. :smile:
Are you deliberately holding us all in suspense? Where's the second, improved version - with the extrapolation to t=0? I am agog in anticipation.

Wait...

sophiecentaur said:
It would be about 54 years ago that i did it and I HAVE LOST MY EXERCISE BOOK ( the dog ate it, I think)

Are you saying you had a microwave oven 54 years ago?
hmmm...

Phase II:

microwave.exp.rev.2.png

x axis: seconds
y axis: °C

freakishly linear, just by eyeballing it.

but:

microwave.exp.rev.3.png


There's something going on there, at that phase-changey end of the graph...
 
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  • #41
OmCheeto said:
Are you saying you had a microwave oven 54 years ago?
Why not? They had Radar in the 50's you know and the UK was full of hi tech.
But no. My expt was the cooling curve and finding the start temp.
Interesting results and I agree about the "phase changey" bit at the start. Local condensation could have kept the temperature up at the start of the curve. but it seems not to start at 100. Is your thermometer ok?
 
  • #42
sophiecentaur said:
Why not? They had Radar in the 50's you know and the UK was full of hi tech.
But no. My expt was the cooling curve and finding the start temp.
Interesting results and I agree about the "phase changey" bit at the start. Local condensation could have kept the temperature up at the start of the curve. but it seems not to start at 100.
As I stated, my RTDs are not microwave safe, so it took me several seconds to get the first measurement.
Is your thermometer ok?

Ok? I have about 20 of these thermometers. They were surplus medical grade RTD's I purchased about 30 years ago.
I calibrated them by immersing them in (stove top) boiling water, water at 100°F (fever thermometer), and near freezing water (ice cubes in a water bath).
I was in university at the time, and somehow knew how to figure out a curve fit.
Don't ask me to do that again.

Experiment #3 would have me building a much more "proper" bomb calorimeter. (bubble wrap!)

The difference between experiment #1, with no cover on the glass, and #2, with a double layer of cellophane over the top, was, to say the least, significant.

Temperature drops over the 1st 65 seconds:
Exp #1: 0.18°C/second
Exp #2: 0.04°C/second​

ps. I have high confidence in my 1990 calibration of the RTD's, as, I also just purchased an infrared thermometer recently, and, at 175°F, both read identically.
pps. For the uber-nerds:

microwave.exp.rev.4.nerds.png

x axis: seconds
y axis: °C
t-ambient: 16 °C
 
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  • #43
It wasn't boiling as much as it was Evaporating therefore you hit a Wet Bulb Temp where the liquid "sucked some of the heat out of itself to evaporate and therefore was below boiling point. Notice if you left the water in the bowl it wouldn't be there tomorrow.

Just an HVAC thought to share. Does it pass Muster?
 
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  • #44
Mike Bergen said:
It wasn't boiling as much as it was Evaporating therefore you hit a Wet Bulb Temp where the liquid "sucked some of the heat out of itself to evaporate and therefore was below boiling point. Notice if you left the water in the bowl it wouldn't be there tomorrow.

Just an HVAC thought to share. Does it pass Muster?

Sounds good to me.
I've been waiting for the OP to tell us more about his experimentation before I shared more thoughts and data.
Always good when two people do the same experiment with similar results.

hmmmm...
What the hell.
Here's a graph of the temperature rise on my second run.
Guess what my microwave oven is rated at.
(The only variable held constant, was the volume of water: 100 ml. And the oven of course. )

microwave.exp.rev.5.temp.vs.time.png

x axis: seconds
y axis: °C
mass of container: 0.04 kg
ps. Can a Mentor please scratch the word "bomb" from my earlier comment about calorimeters. hmmm... Never mind. I should know better by now. :redface:
 
  • #45
OmCheeto said:
ps. Can a Mentor please scratch the word "bomb" from my earlier comment about calorimeters. hmmm... Never mind. I should know better by now. :redface:
Too late. You have already been reported to the authorities :wink:
 
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  • #46
Mike Bergen said:
It wasn't boiling as much as it was Evaporating therefore you hit a Wet Bulb Temp where the liquid "sucked some of the heat out of itself to evaporate and therefore was below boiling point. Notice if you left the water in the bowl it wouldn't be there tomorrow.

Just an HVAC thought to share. Does it pass Muster?
I think it does. But a deeper point might be, do microwaves alter the vapor pressure in a non-thermal way?

I think what we all may be missing here is the non-thermal effects of microwaves on intermolecular hydrogen bonding.

Those affects of microwaves persist even after the microwave bombardment stops. See the link I posted.
 
  • #47
We'll know we're approaching the truth when the forums censor shuts us down, which I expect any time now.
 
  • #48
ScepticAmatuer said:
I think it does. But a deeper point might be, do microwaves alter the vapor pressure in a non-thermal way?
I doubt it. But I'll alter my experiment to verify my doubts.
BTW, what model thermometer are you using, and what is its response time?
(I'm conducting this experiment at the moment)
I think what we all may be missing here is the non-thermal effects of microwaves on intermolecular hydrogen bonding.

Those affects of microwaves persist even after the microwave bombardment stops. See the link I posted.
This one?: http://pubs.acs.org/doi/full/10.1021/la5019218

It says; ...the irradiation intensities used in this study are well above those in household devices...

How on Earth do you expect us to do this experiment if all we have are microwave ovens from the 50's and 70's?

ScepticAmatuer said:
We'll know we're approaching the truth when the forums censor shuts us down, which I expect any time now.

No!
I'm sure everyone will be fascinated by the response curve of my RTDs. :biggrin:
 
  • #49
OmCheeto said:
I doubt it. But I'll alter my experiment to verify my doubts.
BTW, what model thermometer are you using, and what is its response time?
(I'm conducting this experiment at the moment)

This one?: http://pubs.acs.org/doi/full/10.1021/la5019218

It says; ...the irradiation intensities used in this study are well above those in household devices...

How on Earth do you expect us to do this experiment if all we have are microwave ovens from the 50's and 70's?
No!
I'm sure everyone will be fascinated by the response curve of my RTDs. :biggrin:
I found a bunch of lug RTD's myself, but I'm becoming distracted. No idea the sparks that will fly when the microwaves hits those. And I am looking.forward to your response curve.

A.microwave oven is a very powerful emitter of microwaves. It should not be underestimated. Many factors besides intensity are at work.
 
  • #50
ScepticAmatuer said:
We'll know we're approaching the truth when the forums censor shuts us down, which I expect any time now.
What "truth"? Are you saying you think microwaves change the boiling point of water? What exactly do you think is going on that hasn't been adequately explained?
 
  • #51
russ_watters said:
What "truth"? Are you saying you think microwaves change the boiling point of water? What exactly do you think is going on that hasn't been adequately explained?
If microwaves can change a property as basic as surface tension, and that change persists even after the waves are shut off, then why not?

Or does that offend some scientific canon law or the other? So you appear the minute "censor" is mentioned?

In fact there is no general agreement about the mechanism of microwave action in accelerating (most) chemical reactions.

I look forward to the current canon law position on sonoluminescence and the electrohydraulic effect. More "bizarre" phenomenon not worthy of serious study, no doubt.

Why would anyone want to stifle debate on these topics? Hmmmm...
 
  • #52
ScepticAmatuer said:
I found a bunch of lug RTD's myself, but I'm becoming distracted. No idea the sparks that will fly when the microwaves hits those. And I am looking.forward to your response curve.
Fast!
98°C to 12°C in approximately 1 second.

A.microwave oven is a very powerful emitter of microwaves.
Well, I would hope so. How else am I to warm my coffee in the morning?
It should not be underestimated.
I've yet to estimate the power of my oven from my earlier graph.
I imagine that it's pretty close to nameplate.
Many factors besides intensity are at work.
Ummm...

ScepticAmatuer said:
If microwaves can change a property as basic as surface tension, and that change persists even after the waves are shut off, then why not?

Or does that offend some scientific canon law or the other? So you appear the minute "censor" is mentioned?

In fact there is no general agreement about the mechanism of microwave action in accelerating (most) chemical reactions.

I look forward to the current canon law position on sonoluminescence and the electrohydraulic effect. More "bizarre" phenomenon not worthy of serious study, no doubt.

Why would anyone want to stifle debate on these topics? Hmmmm...

The thread is still open.

Where is @Bandersnatch when you need him? :biggrin:

ps. Ok with me if you lock this thread. We seem to have deviated from experimentation into the whackadoodle universe.
pps. As always: Ok to delete, infract, and ban me. My thoughts are saved. :smile:
 
  • #53
OmCheeto said:
Fast!
98°C to 12°C in approximately 1 second.Well, I would hope so. How else am I to warm my coffee in the morning?

I've yet to estimate the power of my oven from my earlier graph.
I imagine that it's pretty close to nameplate.

Ummm...
The thread is still open.

Where is @Bandersnatch when you need him? :biggrin:

ps. Ok with me if you lock this thread. We seem to have deviated from experimentation into the whackadoodle universe.
pps. As always: Ok to delete, infract, and ban me. My thoughts are saved. :smile:
Ok. Thanks, man.
 
  • #54
ScepticAmatuer said:
Ok. Thanks, man.
You are quite welcome.
sophiecentaur said:
...
But no. My expt was the cooling curve and finding the start temp.
Interesting results and I agree about the "phase changey" bit at the start. Local condensation could have kept the temperature up at the start of the curve. but it seems not to start at 100. Is your thermometer ok?
I've been thinking about this some more, but have run into technical/safety concern issues.
I wanted to use a sealed container in the microwave, but am afraid if I heat it much above boiling, I might end up with a steam explosion, if I release the pressure too fast.
Also, the only device I have that is microwave-ably sealable would be a plastic coke bottle, and I'm not sure that would be safe.

Another idea is to seal the container after it comes out of the microwave, and draw a vacuum on the heated water until it boils again, and see how that affects the temperature drop. It would be quite the contraption though, as I'd have to monitor temperature and pressure inside the vessel. And without a vacuum pump, I don't know if I'd be able to get any meaningful data.

Today I attempted to double check the calibration of my RTD's using my new Infrared thermometer, but I couldn't get a stable reading. Perhaps tomorrow.
 
  • #55
Here's the link to the full pdf of that article on surface tension. Surface tension affects vapor pressure which in turn affects boiling point, as you no doubt are aware.

http://www.researchgate.net/profile/Harisinh_Parmar/publication/264640617_Influence_of_Microwaves_on_the_Water_Surface_Tension/links/547c15370cf293e2da2d7919.pdf

IIts bibliography contains a plethora of interesting papers on microwave effects on "hydrogen bonding (unfortunately named).

Interesting that several of the articles/ research papers I've read claim that microwaves actually raise the boiling point of water to as much as 105°. (Standard conditions.)

They attribute this to-called non-thermal effects. Apparently, boiling points are not as sacrosanct as one would be led to believe by some postings in this thread.

I thank you for the opportunity to learn from you and contribute information of possible value.
 
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  • #56
ScepticAmatuer said:
Interesting that several of the articles/ research papers I've read claim that microwaves actually raise the boiling point of water to as much as 105°. (Standard conditions.)

They attribute this to-called non-thermal effects. Apparently, boiling points are not as sacrosanct as one would be led to believe by some postings in this thread.
You will have to post proper references for this claim.
 
  • #57
I did a little snooping on the subject and found that a superheating temperature above 101 C have been documented. I could not find anything stating a specific temperature of 105 C that was documented. But the article did state that depending on the altitude that the temperature of pure water could continue to rise above 101 C. So a temp of 105 C doesn't seem implausible under perfect circumstances.
 
  • #58
DrClaude said:
You will have to post proper references for this claim.
I don't recall you posting any references at all.
 
  • #59
Thread closed for Moderation...
 
  • #60
ScepticAmatuer said:
I don't recall you posting any references at all.
You are the one claiming to have found some interesting information. So show your sources so we can learn! (And a link to "researchgate.net" is not a reliable source.)

Where were the papers published?
 
  • #61
Thread will remain closed until @ScepticAmatuer sends me a private message with acceptable sources (see the PF Rules under Info at the top of the page for the list of acceptable references).
 
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