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10 minutes ago, David Burgess said:

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.

I had noticed that already - the probes, no matter how accurate, have inertia to change, so I suspect they are recording things slightly late compared to actual conditions. That's why this is basically factored in: I always use multiple sensors of the same variety, calibrate them in advance, and then use a corrected values on my spreadsheets. If there is an inertia error, I believe it thus effects all readings the same way and so comparisons are still fully possible. (if one case hits 42°C after 60 minutes and the other hits 52°C in the same time elapse, it's reasonable to assume, including errors, that the second case is hotter inside)

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2 hours ago, Dimitri Musafia said:

 I always use multiple sensors of the same variety, calibrate them in advance, and then use a corrected values on my spreadsheets. If there is an inertia error, I believe it thus effects all readings the same way and so comparisons are still fully possible.

I haven't found inertia errors to be at all the same on various types of sensors, even from the same manufacturer, although they can sometimes be pretty close. My "Fluke" brand hygrometer turns out to be pretty accurate, within three minutes, if I use a fan to blow lots of air across it. Without the fan, it can take much longer.

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I would be interested in a comparison to an indoor system.  In an indoor environment we can certainly lower the temperature without raising the RH because the moisture is condensing off at the coils.  Is it possible the moisture is condensing off on the very outside skin, and if so, wouldn't a case with an outer skin and an inner skin be in order?  Couldn't this control the rising of the internal RH much the same as an air conditioning coil does indoors... sort of it's own dehumidifier?  I imagine a chemical reservoir could then be fashioned to hold the water until needed.

Isn't it possible that both Dimitri's observations can be valid without violating the laws of nature?

 

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10 hours ago, Jerry Pasewicz said:

Isn't it possible that both Dimitri's observations can be valid without violating the laws of nature?

 

I've been taking these observations with consistent results since 2005, using different equipment and most especially measuring the conditions inside vastly different kinds of cases. I believe it is prudent to state that what I have observed actually occurred - it's the "why" that I'm still working on, and that I'm happy discuss.  

That said, I'm sure that any measurement errors are within parameters insufficient to invalidate my observations. Not only did I read the instruction manual of my equipment, but the cases and the probes are always meticulously prepared before the tests to assure the most accurate results. I'm happy to give details if anyone is curious.  

Keep in mind that I performed these tests for 10 years *for my own use only* during my research to try to manufacture more protective cases, before deciding to render them public, so I have no hidden agenda, axe to grind, or whatever cliché one prefers to use.

Cheers!

>> EDIT:

Check out these graphs done by case making colleague Maurizio Riboni. Some of them reproduce exactly what I have described: RH increases with temperature increase (and some graphs don't). Could it be the glues we breathe..?  ;-) 

http://www.maurizioriboni.it/ENG/test.html

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12 hours ago, Jerry Pasewicz said:

  Is it possible the moisture is condensing off on the very outside skin, and if so, wouldn't a case with an outer skin and an inner skin be in order?  Couldn't this control the rising of the internal RH much the same as an air conditioning coil does indoors... sort of it's own dehumidifier?

Isn't it possible that both Dimitri's observations can be valid without violating the laws of nature?

 

Yes, the inside of the case shell falling below the dewpoint of the inside air, and condensing moisture, might explain that, temporarily. However, I'd also expect that when enough time has elapsed for the inside air to cool more uniformly, and come close to outside temperature, the RH would go right back up. The moisture condensing on the inside of the case shell relies on that air having been cooled enough that the RH has gone "over" 100%. Once all the air inside the case has reached that temperature, it should stabilize right around 100%.

A couple of caveats: This assumes a fairly air-tight and water-vaper-impermeable case, of non-hygroscopic material. Given enough time at the lower temperature, with a material like wood, some of the extra moisture on the inside would be absorbed by the wood, and eventually passed to the outside. Some of the extra moisture which has remained in the wood could also return to the inside of the case, when the case and interior air are heated again.

That description is a bit oversimplified, but I'll leave it at that for now.

Some of  the wooden-shell cases are quite water-vapor-permeable, and it can take an in-case humidifier with an unseemingly large evaporating area to change the interior humidity very much. Absorptive materials like that can also buffer changes, as others have already mentioned. I can also see how if the inner part of the wood has been moisture-saturated from condensation, the RH inside the case could rise upon a rise in temperature. The moistened wood could behave like a humidifier with a very large evaporating surface area.

 

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37 minutes ago, David Burgess said:

Yes, the inside of the case shell falling below the dewpoint of the inside air, and condensing moisture, might explain that, temporarily. However, I'd also expect that when enough time has elapsed for the inside air to cool more uniformly, and come close to outside temperature, the RH would go right back up. The moisture condensing on the inside of the case shell relies on that air having been cooled enough that the RH has gone "over" 100%. Once all the air inside the case has reached that temperature, it should stabilize right around 100%.

A couple of caveats: This assumes a fairly air-tight and water-vaper-impermeable case, of non-hygroscopic material. Given enough time at the lower temperature, with a material like wood, some of the extra moisture on the inside would be absorbed by the wood, and eventually passed to the outside. Some of the extra moisture which has remained in the wood could also return to the inside of the case, when the case and interior air are heated again.

That description is a bit oversimplified, but I'll leave it at that for now.

 

 

This seems to be what Dimitri's chart shows.  It would be definitive if the case was left outside longer and the data continued.

 

BFE627E0-77C0-4F82-BF84-072834627456-979-000002BCD6512E09.jpeg.609a3d42a3638cfd6828e5b35480eca0.jpeg

As an example, if the outer shell was carbon fiber, with a wooden inner shell and air holes to allow movement in and out of the inner shell, wouldn't that create the data Dimitri shows, even on a temporary basis?

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34 minutes ago, David Burgess said:

> Yes, the inside of the case shell falling below the dewpoint of the inside air, and condensing moisture, might explain that, temporarily. However, I'd also expect that when enough time has elapsed for the inside air to cool more uniformly, and come close to outside temperature, the RH would go right back up. The moisture condensing on the inside of the case shell relies on that air having been cooled enough that the RH has gone "over" 100%. Once all the air inside the case has reached that temperature, it should stabilize right around 100%.

...100% RH inside a case is something I've never encountered, or even come close to. But you've given me some ideas for my next tests.

> A couple of caveats: This assumes a fairly air-tight and water-vaper-impermeable case, of non-hygroscopic material.

... exactly, like many carbon-fiber or plastic sandwich cases. I'll be putting them to the test.

> Given enough time at the lower temperature, with a material like wood, some of the extra moisture on the inside would be absorbed by the wood, and eventually passed to the outside. Some of the extra moisture which has remained in the wood could also return to the inside of the case, when the case and interior air are heated again.

... that I don't think possible. Not only is wood laminate a number of plies with glue in between, but the inside of the cases has the lining glued in, often with non-water-soluble glues. These, together, would form quite a barrier against moisture passing from the interior of the case to the outside.

> Some of  the wooden-shell cases are quite water-vapor-permeable, and it can take an in-case humidifier with an unseemingly large evaporating area to change the interior humidity very much.

... from my specific experience, if you take a case with hygroscopic lining which is particularly "dried out", it takes several re-fillings of the humidifier to bring the RH to violin-tolerable levels (>40%). What happens is that the lining absorbs the moisture, which I believe to be a beneficial buffer-effect for the next dry moment.

> Absorptive materials like that can also buffer changes, as others have already mentioned. I can also see how if the inner part of the wood has been moisture-saturated from condensation, the RH inside the case could rise upon a rise in temperature. The moistened wood could behave like a humidifier with a very large evaporating surface area.

...IF there has been condensation.

 

 

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On 9/9/2017 at 10:34 AM, La Folia said:

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

 

On 9/9/2017 at 11:55 AM, 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

Under normal conditions the capacity for air to hold water increases as temperature increases.  Therefore the same amount of water in the air would have a lower RH, and the reverse is true.  Is it possible that the sensor was reading Humidity (amount of water in air) instead of relative humidity (amount of water in air relative to the capacity of the air to hold water)?  Another alternative, is that the ambient air outside had a much lower RH than the inside environment.  In this case the graph is simply showing how long it takes for the cases to equalize RH with the ambient air.

Dimitri, I really admire that you spend time and effort (not to mention money) to produce a better case.  Thanks for your efforts.

-Jim

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1 hour ago, Dimitri Musafia said:

...IF there has been condensation.

In one of the scenarios from your graph, with a starting interior temperature of 68 degrees and 46% RH, conditions would have reached the point of condensation (100% RH) when the inside temperature dropped to about 44 degrees. Entirely possible, since the case was placed outside at 38 degrees. Again, this assumes a fairly tight seal, and non-hygroscopic materials.

An online calculator: http://andrew.rsmas.miami.edu/bmcnoldy/Humidity.html

 

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1 hour ago, Jerry Pasewicz said:

BFE627E0-77C0-4F82-BF84-072834627456-979-000002BCD6512E09.jpeg.609a3d42a3638cfd6828e5b35480eca0.jpeg

As an example, if the outer shell was carbon fiber, with a wooden inner shell and air holes to allow movement in and out of the inner shell, wouldn't that create the data Dimitri shows, even on a temporary basis?

It might.

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59 minutes ago, Jim Bress said:

 

Under normal conditions the capacity for air to hold water increases as temperature increases. 

Absolutely. If I'm not mistaken one kg of air can hold:

Temperature                water vapor

 

              0°C                  3,9 grams

10                     7,9

20                   15,2

30                   28,1

40                   50,6

50                   89,5

Quote

Is it possible that the sensor was reading Humidity (amount of water in air) instead of relative humidity (amount of water in air relative to the capacity of the air to hold water)? 

...no.

Another alternative, is that the ambient air outside had a much lower RH than the inside environment.  In this case the graph is simply showing how long it takes for the cases to equalize RH with the ambient air.

... I'll answer this seperately.

Dimitri, I really admire that you spend time and effort (not to mention money) to produce a better case.  Thanks for your efforts.

... thank you!

 

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15 minutes ago, David Burgess said:

In one of the scenarios from your graph, with a starting interior temperature of 68 degrees and 46% RH, conditions would have reached the point of condensation (100% RH) when the inside temperature dropped to about 44 degrees. Entirely possible, since the case was placed outside at 38 degrees. Again, this assumes a fairly tight seal, and non-hygroscopic materials.

An online calculator: http://andrew.rsmas.miami.edu/bmcnoldy/Humidity.html

 

Right, so obviously there is some interference in the dynamics.

What do you think of Riboni's graphs? (I honestly have never seen anything remotely resembling his first one, top left)

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Here are some more recent graphs deriving from a sunlight-exposure test that I did on May 15 of this year, with two ultra-lightweight cases. I just now put the numbers into the spreadsheet to add this to the ongoing discussion.

Case no. 1 is a well-known ultra-light weight wood laminate model with external pocket. The declared weight by the manufacturer is 2.3 kg and this example weighs in at 2.29. The interior lining is not particularly hygroscopic, although the laminate shell potentially is. The case was built in 2016 and should be considered “dried out” from its production process at least.

Case no. 2 is a famous brand ultralight model with a sandwich construction (ABS + foam) also with external pocket, which according to the manufacturer possesses an astoundingly low thermal conductivity of only 0.025 W/MK. The declared weight of this model is 2.1 kg. although this example weighs in at 2.45. Neither the shell nor the lining could be described as hygroscopic.

Both cases were taken from an indoor location, subjected to direct solar radiation in 84°F heat for 45 minutes, and then brought back inside for another 45 to see how they cool off. In this test my usual probes were backed up by twin D’Addario Humiditrak units, which substantially confirmed the data of the probes (at least until one, past its operating temperature, died)

Here is what I interpret:

-          The Pressure Cooker Effect (or whatever we want to call it) strikes again: in the wood laminate case the RH went from 50% to 84% in only 20 minutes (not taking in account eventual probe inertia); the RH the leveled out and began to fall despite the continued increase of temperature for another 25 minutes. The synthetic sandwich shell case peaks even earlier (perhaps due to a more effective sealing?), but lower, at 77% and also leveled before starting to fall even while heating up.

 

-          The interior of the case with the sandwich construction heated up to 129.0°F after 45 minutes, the wood laminate case to only 112.6°F, showing considerably more thermal protection than the latter (despite the advertised superiority).

My initial conclusions, also in consideration of some of the comments that this thread has produced, are that the laminate case had more stored moisture somehow, likely in the inner wood layers.

Other thoughts?

TestWoodVsSandwich1.jpg

TestWoodVsSandwich1a.jpg

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2 hours ago, Dimitri Musafia said:

Right, so obviously there is some interference in the dynamics.

What do you think of Riboni's graphs? (I honestly have never seen anything remotely resembling his first one, top left)

It's similar to what I got on a cheap thermoplastic case shell, with no interior.

Once one gets into hygroscopic materials (and adhesives), there could be all kinds of things going on, including chemicals in which water content doesn't track well with relative humidity changes, like wood does. For instance, moistened table salt will absorb water vapor when the RH is over 75%, and release water vapor when the RH is lower than 75%. Propylene glycol can exhibit a similar behavior. Boveda makes packets for guitar cases (I don't think they are marketed for violin use any more) containing some kind of chemical stew which will absorb moisture over 49%, and release moisture at lower levels.

I'm sure you know this stuff already, I was just mentioning it for other readers who might not.

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GeorgeH   

In the context of these studies, it would be useful to understand the difference between "absorption" and "adsorption."

It is an incorrect and unreasonable assumption that the materials inside of a violin case do not contain significant amounts of adsorbed water. For example, plastics like nylon and polyester adsorb water vapor. They are not hygroscopic materials. The surfaces of glues are also likely to adsorb water.

And because adsorption is an equilibrium phenomena, adsorbed water is going to be released when the case is heated. 

All the graphs and data shown in these discussions where the RH increases when the case is heated can be explained by the release of adsorbed water by the materials inside the case.

Edited by GeorgeH
corrected "nylon and polyester absorb water vapor" to "nylon and polyester adsorb water vapor. "

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6 minutes ago, GeorgeH said:

In the context of these studies, it would be useful to understand the difference between "absorption" and "adsorption."

It is an incorrect and unreasonable assumption that the materials inside of a violin case do not contain significant adsorbed water. For example, plastics like nylon and polyester absorb water vapor. They are not hygroscopic materials. The surfaces of glues are also likely to adsorb water.

And because adsorption is an equilibrium phenomena, adsorbed water is going to be released when the case is heated. 

All the graphs and data shown in these discussions where the RH increases when the case is heated can be explained by the release of adsorbed water by the materials inside the case.

But wouldn't adsorbtion require a much higher RH value in order to take place, like 70% or 80%? These graphs show internal RH starting points as low as 43%, which is borderline dry - at this level wouldn't the moisture eventually adsorbed be released into the case interior even at room temperature?  

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GeorgeH   
15 minutes ago, Dimitri Musafia said:

But wouldn't adsorbtion require a much higher RH value in order to take place, like 70% or 80%? These graphs show internal RH starting points as low as 43%, which is borderline dry - at this level wouldn't the moisture adsorbed be released into the case interior even at room temperature?  

No, because adsorption is an equilibrium phenomena. The quantity of water adsorbed by a material depends on the temperature and humidity of the atmosphere, and the capability of the material to adsorb water. For example, if you put a perfectly dry piece of highly water-adsorbent material in a closed space with 43%, it would behave as a desiccant and lower the RH as it adsorbed the water vapor. Similarly, if you placed a water-saturated piece of highly water-adsorbent material in a dry atmosphere, it would release water vapor and cause the RH to go up until it reached equilibrium with the atmosphere and temperature.

 

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La Folia   
14 minutes ago, Dimitri Musafia said:

But wouldn't adsorbtion require a much higher RH value in order to take place, like 70% or 80%?

In a word, no.  They can adsorb water at relatively low RH.  It just depends on the material.

By the way, the last graph that you posted gives evidence that your humidity meter is reading correctly.  The ambient RH dropped as the ambient temperature rose.

The fact that the RH goes up with increased temperature is proof that something is desorbing water.  There is no other possibility.  All the evidence that you posted shows that something in the shell or the padding is desorbing and adsorbing water.

One other person suggested that there could also be condensation of water in the outer layers of the case in cold weather.  Although adsorption is taking place, condensation is also possible.

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54 minutes ago, GeorgeH said:

It is an incorrect and unreasonable assumption that the materials inside of a violin case do not contain significant amounts of adsorbed water. For example, plastics like nylon and polyester adsorb water vapor. They are not hygroscopic materials. The surfaces of glues are also likely to adsorb water.

 

I guess something like a "silk plush" fabric could have an awful lot of total surface area. Open cell foams too. Thanks guys, very enlightening. I had assumed that adsorption would be a rather insignificant player.

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55 minutes ago, David Burgess said:

I guess something like a "silk plush" fabric could have an awful lot of total surface area. Open cell foams too. Thanks guys, very enlightening. I had assumed that adsorption would be a rather insignificant player.

It would be interesting to see how much water vapor (expressed in grams) a given material can adsorb per square meter, and then cross this with the water vapor that a kg. of air can hold at a given temperature, and THEN see how much it can influence RH inside the case during overheating.

According to the table I copy-pasted above, just to maintain the same RH 50% between 20°C and 50°C (not too much different from the graphs I posted above) if I'm not mistaken the adsorbing phenomenon would have had to release 37g of water vapor per kg of air.

Is this possible?

To put this in persepective, I weigh each case completed in my atelier, in January as in July, when RH in the atelier is much different. The tolerance I have noted is +/-5% with no seasonal maximum.

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1 hour ago, Dimitri Musafia said:

It would be interesting to see how much water vapor (expressed in grams) a given material can adsorb per square meter, and then cross this with the water vapor that a kg. of air can hold at a given temperature, and THEN see how much it can influence RH inside the case during overheating.

 

I would be interested in that too. I I were chasing this down, I guess I'd start by weighing the material, after it had stabilized under a variety of RH conditions.

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On a slightly different note, since someone already brought up Occam, I'd like to add this personal anecdote.

My dad was a friend of Sir Karl Popper (the unimpressed of you can look him up). In one of their last conversations (Popper died in '94) they discussed problem solving. Popper explained how once you resolve a problem (call it P1), you immediately create a new one (P2). Resolving that one, a new one appears (P3).

My dad asked rhetorically: "well, if resolving problems creates unending problems, why even bother?" Popper: "Because it's interesting".

:-)

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15 minutes ago, David Burgess said:

I would too. I I were chasing this down, I guess I'd start by weighing the material, after it had stabilized under a variety of RH conditions.

Good idea. Tomorrow I'll take 1.5 square meters of silk plush (the average amount that goes into a violin case) and weigh it on my precision electronic scale (+/-2 g). The I'll put it away and weigh it periodically. I will hang it outdoors in the sun, and take it home with me and hang it in my bathroom when I take a shower, and whatever else I can think of.

I'll post the results here. Adsorbtion, you better watch out now...

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1 hour ago, Dimitri Musafia said:

On a slightly different note, since someone already brought up Occam, I'd like to add this personal anecdote.

My dad was a friend of Sir Karl Popper (the unimpressed of you can look him up). In one of their last conversations (Popper died in '94) they discussed problem solving. Popper explained how once you resolve a problem (call it P1), you immediately create a new one (P2). Resolving that one, a new one appears (P3).

My dad asked rhetorically: "well, if resolving problems creates unending problems, why even bother?" Popper: "Because it's interesting".

:-)

Assuredly!

However my Dad, when walking across the Princeton campus, once had a brief exchange with Einstein.  My Dad said, "Hi Mister Einstein", and Einstein, without ever looking up, gave something like an acknowledging grunt.

That's my claim to fame. :D

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2 minutes ago, David Burgess said:

Assuredly!

However my Dad, when walking across the Princeton campus, once had a brief exchange with Einstein.  My Dad said, "Hi Mister Einstein", and Einstein, without ever looking up, gave something like an acknowledging grunt.

That's my claim to fame. :D

Relativity, my dear David! :-)

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