Boiling point of water heated via microwave

[ScepticAmatuer]

In order to calibrate a thermometer for the 100^o C point you have to put in in boiling water.
Not in water that was boiling some time ago.
So the idea with the microwave was not good to start with, if this is your goal.
Unless you put the thermometer in the microwave so it measures the temperature while water is boiling. But this won't be a good idea for most thermometers.
The temperature goes down quite quickly once the water stops receiving heat.

I believe this may be partially responsible for the effect. It probably takes me about 5 seconds to get the jar out and get the probe in the sample. Then probably 3 maybe 4 seconds for the thermometer reading to stabilize.

Would you expect the cooling rate to be linear? In other words, by subsequent measurements during the cool down period, could I extrapolate how far it dropped during the 7 seconds?

 

[nasu]

No, it is not linear.
But why would you do this in the microwave, if the purpose is to calibrate your thermometer?

 

[ScepticAmatuer]

No, it is not linear.
But why would you do this in the microwave, if the purpose is to calibrate your thermometer?

The thermometer is calibrated now. I did it the first time because I thought it would be quicker.

 

[sophiecentaur]

could I extrapolate how far it dropped during the 7 seconds?

If you plot the temperature against time, you would expect an exponential curve. If you plot log(temperature) against time (t=0 would be the time you stopped the heating and removed the container), from the earliest you manage to grab a reading, you would expect to get a straight line. If you extrapolate backwards to the time you removed the container, your straight line would go through the temperature it started with. As with all heat measurements, there are possible errors and it would only help to reduce them. Actually, if you do a linear plot of temperature against time and you find that you can draw a fairly good straight line through the first few points, extrapolating back to t=0 could probably be good enough. Why not use both methods and see which one takes you closer to 100°C?
If this is all done with digital sensors, a decent spreadsheet could take in all the data and do all the hard work for you. And if you are not familiar with the simple coding that you can do with Excel, now could be a good time to get stuck in. Excel is pretty wonderful and has been for nearly thirty years of my experience.

 

[ScepticAmatuer]

If you plot the temperature against time, you would expect an exponential curve. If you plot log(temperature) against time (t=0 would be the time you stopped the heating and removed the container), from the earliest you manage to grab a reading, you would expect to get a straight line. If you extrapolate backwards to the time you removed the container, your straight line would go through the temperature it started with. As with all heat measurements, there are possible errors and it would only help to reduce them. Actually, if you do a linear plot of temperature against time and you find that you can draw a fairly good straight line through the first few points, extrapolating back to t=0 could probably be good enough. Why not use both methods and see which one takes you closer to 100°C?
If this is all done with digital sensors, a decent spreadsheet could take in all the data and do all the hard work for you. And if you are not familiar with the simple coding that you can do with Excel, now could be a good time to get stuck in. Excel is pretty wonderful and has been for nearly thirty years of my experience.

That was a lot of work to write that post. Thanks for that. I know some Excel. I'll try it both ways. and post the results.

 

[OmCheeto]

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.

 

[sophiecentaur]

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)

 

[OmCheeto]

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.

x axis: seconds
y axis: °C

 

[sophiecentaur]

Do you want all of the experiments?

Why not? I did it once and that was quite enough.
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.

 

[OmCheeto]

Why not? I did it once and that was quite enough.
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...

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:

x axis: seconds
y axis: °C

freakishly linear, just by eyeballing it.

but:

There's something going on there, at that phase-changey end of the graph...

 

[sophiecentaur]

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?

 

[OmCheeto]

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:

x axis: seconds
y axis: °C
t-ambient: 16 °C

 

[Mike Bergen]

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?

 

[OmCheeto]

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. )

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.

 

[DrClaude]

ps. Can a Mentor please scratch the word "bomb" from my earlier comment about calorimeters. hmmm... Never mind. I should know better by now.

Too late. You have already been reported to the authorities

 

[ScepticAmatuer]

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.

 

[ScepticAmatuer]

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

 

[OmCheeto]

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?

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.

 

[ScepticAmatuer]

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.

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.

 

[russ_watters]

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?

 

[ScepticAmatuer]

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...

 

[OmCheeto]

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...

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?

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.

 

[ScepticAmatuer]

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?

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.

Ok. Thanks, man.

 

[OmCheeto]

Ok. Thanks, man.

You are quite welcome.

...
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.

 

[ScepticAmatuer]

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.

 

[DrClaude]

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.

 

[gjonesy]

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.

 

[ScepticAmatuer]

You will have to post proper references for this claim.

I don't recall you posting any references at all.

 

[berkeman]

Thread closed for Moderation...

 

[Doc Al]

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?