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Hello,

Has anyone done any experiments to see how case humidifiers work in real world conditions? I'm not asking which are better than others, but what happens especially with a "fully charged" humidifier when the case gets overheated through solar radiation, such as being kept in the sun while waiting in line on a sidewalk on a summer day.

Cheers and thanks!

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Hi Dimitri;

I think the biggest problem would occur when the case cools again. All that extra water which evaporated while the case was hot (which would be desirable to keep the humidity at an adequate level)  would still be trapped inside, causing the relative humidity to go way up as the case cooled.

For example, if the humidity inside the case was 40% at 100 degrees F, it would be 100% after the case returned to 70 degrees.

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I think you would need to test the specific case, because they vary quite a bit in air leakage and water  vapor permeability. The calculation I gave above was based on zero moisture exchange between the inside and outside of the case, with the humidity change calculated on the temperature change alone, with the grams of moisture per cubic meter of air remaining the same.

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GeorgeH   
5 hours ago, Dimitri Musafia said:

such as being kept in the sun while waiting in line on a sidewalk on a summer day.

Or a warm room in the winter and then walking outside into sub-freezing temperatures.

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48 minutes ago, GeorgeH said:

Or a warm room in the winter and then walking outside into sub-freezing temperatures.

I've done plenty of those tests already, with wood laminate, carbon fiber, styrofoam, sandwich composite, and fiberglass-shell cases. I've got quite an inventory of cases actually. It's interesting to compare their performance against their advertised qualities, in terms of thermal insulation (i.e. slowing the change from warm to cold when you take the case outside in a cold night).

However I am currently interested only relatively about the performance of such cases with humidifiers because sub-freezing air absorbs little moisture compared to warmer air, making much less difference to measure. The colder the air is, the less the humidifier will work. That said, it is true that in winter time one starts often with very dry conditions due to home heating.

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La Folia   

In the absence of absorbing material or liquid water, the RH will go up when the case is cooled.  The actual behavior in a case is complicated and somewhat unpredictable, since different parts of the case (including humidifier) cool or heat at different rates.  It also depends on ambient RH and temperature.  Mr. Musafia has shown that case materials can release humidity into the case.  The reverse is also true.  It must also be able to absorb humidity.  In the case of cooling, I would usually expect the reverse of what Mr. Musafia found for heating:  i.e., a reduction in RH.  A humifier containing liquid water can also absorb moistureIt just depends on temperature of the humidifier, size of holes, etc.

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La Folia   

My ideal would be a sealed case with no absorbing materials and no extraneous space (i.e., no air). Under these conditions, wood would neither absorb nor release moisture.  Of course there is a large air space in any case, and in the violin itself, but my sense of it is that this is relatively unimportant.  Absorbing materials and a and humidifier would complicate the considerations, but may be unavoidable or desirable under certain conditions.

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In my area, the humidifiers wouldn't be used in the summer. I would guess that except for fiberglass and ABS cases, most would be pretty leaky when it comes to moisture retention. Good in the fact that condensation might go away fairly quickly, bad in the fact that you need to keep refilling the humidifier.

 

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59 minutes ago, La Folia said:

Mr. Musafia has shown that case materials can release humidity into the case. 

Actually I have only submitted an observation with my own theory (the "Pressure Cooker Effect") to explain it, rightly or wrongly. I do not believe that, especially during my tests of cases lacking any hygroscopic lining whatsoever (for example the carbon fiber shell, synthetic velour lined Gewa Idea 1.8, to name names) that case materials necessarily release humidity they cannot even absorb.

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29 minutes ago, La Folia said:

My ideal would be a sealed case with no absorbing materials and no extraneous space (i.e., no air). Under these conditions, wood would neither absorb nor release moisture.  Of course there is a large air space in any case, and in the violin itself, but my sense of it is that this is relatively unimportant.  Absorbing materials and a and humidifier would complicate the considerations, but may be unavoidable or desirable under certain conditions.

The dimensions of the air mass is indeed critical, as is the hygroscopic property of the lining. I believe the lining should be hygroscopic: to absorb moisture when there is too much of it, and to release it when there isn't enough. Otherwise, your violin will do that - and you may not be happy with the result.

But to which "wood" are you referring?

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La Folia   
26 minutes ago, Dimitri Musafia said:

Actually I have only submitted an observation with my own theory (the "Pressure Cooker Effect") to explain it, rightly or wrongly. I do not believe that, especially during my tests of cases lacking any hygroscopic lining whatsoever (for example the carbon fiber shell, synthetic velour lined Gewa Idea 1.8, to name names) that case materials necessarily release humidity they cannot even absorb.

Something in the case (or the wood in the case) released water when it was heated.  I don't think there is any other possible interpretation.  That was also GeorgeH's conclusion.  Please, let's not argue that again.

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15 hours ago, La Folia said:

In the absence of absorbing material or liquid water, the RH will go up when the case is cooled. 

No, it doesn't, it actually goes down.

Here's a graph from my experiments, in which three different cases were taken from a warm (68°F) environment and taken outside where it was 38°F, then brought back inside after 30 minutes.

TestCustodiaFreddoUmidita.jpg

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2 minutes ago, La Folia said:

Something in the case released water when it was heated.  I don't think there is any other possible interpretation.  That was also GeorgeH's conclusion.  Please, let's not argue that again.

Your or George's not acceptance of my theory does not invalidate it, sorry :-)

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La Folia   
22 minutes ago, Dimitri Musafia said:

The dimensions of the air mass is indeed critical, as is the hygroscopic property of the lining. I believe the lining should be hygroscopic: to absorb moisture when there is too much of it, and to release it when there isn't enough. Otherwise, your violin will do that - and you may not be happy with the result.

But to which "wood" are you referring?

Well, you could try to buffer the relative humidity with hygroscopic materials (or water in the humifier).  That can compensate for case leakage, but it does add kinetic complications of nonequilibrium temperature gradients.

I meant the wood of the violin, but to be sure, the wood in the case is probably part of the consideration too.

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1 minute ago, La Folia said:

I meant the wood of the violin, but to be sure, the wood in the case is probably part of the consideration too.

I perform my case testing without the violin and, as stated, with wood laminate, carbon fiber, styrofoam, sandwich composite, and fiberglass-shell cases. The results are the same.

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La Folia   
2 minutes ago, Dimitri Musafia said:

Your or George's not acceptance of my theory does not invalidate it, sorry :-)

If you heat air in a closed system, the RH goes down; if you cool it, the RH goes up.  If the RH does not behave like that, the system is not closed.  If you don't accept that, then I can't help you.

Sorry.  I'm doing this on my own time.

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1 minute ago, La Folia said:

If you heat air in a closed system, the RH goes down; if you cool it, the RH goes up.  If the RH does not behave like that, the system is not closed.  If you don't accept that, then I can't help you.

Sorry.  I'm doing this on my own time.

It's my time too. I guess I've been reading my probe information backwards for over ten years... thanks for waking me up. :-)

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La Folia   
1 minute ago, Dimitri Musafia said:

I perform my case testing without the violin and, as stated, with wood laminate, carbon fiber, styrofoam, sandwich composite, and fiberglass-shell cases. The results are the same.

Well, you asked which wood I was referring to.  I said that in a closed system with no air, the wood (in the violin) would not lose or gain moisture.  If there is no wood in the case, then it isn't a consideration, is it?

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GeorgeH   
11 minutes ago, Dimitri Musafia said:

Your or George's not acceptance of my theory does not invalidate it, sorry :-)

Your "pressure cooker" theory is invalid because you have not shown the test case(s) become pressurized and hold pressure, and your data is easily explained without positing pressure. Sorry. 

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36 minutes ago, GeorgeH said:

Your "pressure cooker" theory is invalid because you have not shown the test case(s) become pressurized and hold pressure, and your data is easily explained without positing pressure. Sorry. 

"Sorry"?

I'm sorry that I cannot accept "invalidations" by anonymous, know-it-all keyboard tigers who think they can freely criticize research already published in respected journals, but won't reveal their names, effective qualifications or credentials (assuming they exist).

In my next overheating tests I'll include a barometric sensor and if it reveals pressure then you guys can all go and eat your hats, OK?

See you next summer. Cheers!

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18 hours ago, Dimitri Musafia said:

No, it doesn't, it actually goes down.

Here's a graph from my experiments, in which three different cases were taken from a warm (68°F) environment and taken outside where it was 38°F, then brought back inside after 30 minutes.

TestCustodiaFreddoUmidita.jpg

I suspect an error in the calibration or programming of the measuring device. My tests showed the opposite, as would theory.

If these cases were completely sealed, so the internal pressure varied with temperature, that might change things, but I haven't gone as far as figuring that out, since most cases aren't sealed well enough to maintain a significant pressure difference between the interior and exterior.

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La Folia   

David, Musafia's cooling results are just the opposite of the heating experiments, and perfectly reasonable if something if outer layers of wood or insulation were absorbing and desorbing moisture.

But it's really interesting that your results show the opposite.  Experimental error was mentioned in passing, but all bets are off if the data are wrong.

Maybe we should have paid more attention to that.  I'm not sure a relative humidity meter (of unspecified design) would necessarily give correct results under transient temperature conditions.  Needless to say, it's essential to read the directions and ensure that the instruments are working correctly.  :)  It would help to test the equipment in a completely dry, closed metal (not iron) or glass vessel.

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6 hours ago, David Burgess said:

I suspect an error in the calibration or programming of the measuring device. My tests showed the opposite, as would theory.

If these cases were completely sealed, so the internal pressure varied with temperature, that might change things, but I haven't gone as far as figuring that out, since most cases aren't sealed well enough to maintain a significant pressure difference between the interior and exterior.

Thanks for weighing in on this, David.

I don't explain it either, and have simply reported it. In this event, the measuring devices were three separate units so I would rule out machine error. And I have to say that I did three separate tests and got the initial drop-off all three times (total = 9), although to varying degrees.

In the graph above,  the cases were A) a normal production wood laminate model (Case no. 2); the same but with thermal insulation (Case no. 1), and C) a Chinese copy of case no. 2, with the same design but a heavier mass (Case no. 3).

I'm sure you've noticed that they don't start from the same point of RH and that's my mistake. However I was measuring temperature and not humidity changes, trying to see how mass or additional thermal insulation changed these results and since my probes pick up also RH I gathered the info for possible future use anyway. 

Since I now have a large collection of different cases made of different materials (more or less hygroscopic, greater or lesser sealing characteristics) I plan to do a more focused testing period with these cases with the warm-cold-warm cycle and record the results. Since I prefer to do my testing under real-world conditions, I'll have to wait for this coming January when we'll have the coldest nights.

My overall impression is that the internal microclimate variations of violin cases does not follow simple air mass theory in a linear path, owing to dynamics generated by the characteristics of the object itself. Reason for which I am interested in learning more about it, through actual observation.

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Something else just came to mind. Temperature and air-moisture sensors don't always respond to change at the same rate, and an electronic relative humidity calculation requires both inputs, so a period without change may be required for the inputs to stabilize and furnish an accurate reading.

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