Vacuum leak detector question

Perhaps you could share this paper you allude to

In terms of the other stuff:

-your ground breaking equation that proves everything you say is nothing more than a measure of internal energy.

- of course Boyle's Law does not apply once the housing is sealed, it refers to change of pressure with volume. Once sealed, the volume remains the same.

- if dew point doesn't apply because of changing pressure, then the dew point wouldn't apply in the atmosphere, pressure changes there all the time.

Any, I can't be bothered any more. You win.

It is in the Wikipedia link isochroic process. First principle of thermodynamics. The variation of pressure in the atmosphere are so slow to be considered not happening. The housing with an active device inside heating up is not the same. A process that is similar is somewhat similar is heating a gas in a sealed container the difference is that the device heating our container is inside the housing though. Anyway as you correctly said you loose and it's time to go into that quiet corner

Just finalized a little experiment to confirm to you lot of experts what really happens in a housing so that you can read it through in your own time.

I set my housing at 21.3C 61% humidity and 997 pascal pressure the dew point for this is 13.16C

I put inside a container with water at 12C. According to your theory of relative humidity this should have increased as the air inside the housing was dropping in temperature.

But it did not. The housing did not fog after a good half hour and when I opened it there were no signs of any condensation. The camera that had been off reported a temperature of 15C in the battery compartment.

Afterwards I did the same but set the camera to record video for 30 minutes, at the end of the 30 minutes the camera internal temperature was 26C and the camera port started fogging so the housing is not getting drier (probably because the moisture content has not changed!) and it is indeed starting to fog inside.

Another thing to consider is the different behavior of aluminum housing to plastic housing and in general of metal versus glass or plastic. Metal conducts heat so in whatever conditions you are there is a much better chance that the systems is leaning towards some equilibrium. Plastic does not so when it gets really hot inside the heat has nowhere to go hence plastic housings fog most.

What matters to fogging is the temperature gradient between the inside of the housing, mostly driven by the camera, and the water not the absolute diving conditions (housing could fog in cold and warm water). This relates to the phenomena happening at the various interfaces between the mediums that are not strictly insulated and the moisture inside the housing which is what condenses as the particles kinetic energy makes them move more hit the walls and change status and condense when faced with a colder material (surface condensation).

So what is important is a moisture free environment and as little temperature gradient as possible. No matter what when the inside of the housing is really hot either because left in the sun or because the camera is really hot condensation can occur so desiccant is required.

The thermodynamic process is explained here

http://en.wikipedia.org/wiki/Isochoric_process

And the explanation of the thermal energy here

http://en.wikipedia.org/wiki/Thermal_energy

Condensation here

http://en.wikipedia.org/wiki/Condensation

Dew point is just an explanation of a process and not the cause of it. In order to understand what really happens you need to look at thermodynamics.

Prepping the camera in an warmer or cooler room has little impact as the housing will be immersed in a heat sink with infinite thermal capacity what matters is the moisture so a dehumidifier more than an air conditioning unit is what is required.

Vacuum does reduce the number of particles inside the housing and helps to some extent but as the pressure difference is rather low it has a very mild effect and should not replace desiccant packets.

It is always good to learn things better!

Congratulations, you've proved that water requires heat before it will evaporate.

You could get a Nobel prize for that.

As for your other comment, you misunderstand me, it's your tenacity fir being wrong that has beaten me.

Back to the quiet corner please i see you need more reading . If you have a personal issue with reading mine this is another piece for you

http://www.wetpixel.com/articles/housing-fog-condensation-fix

http://wetpixel.com/forums/index.php?showtopic=17361

What you and your buddy seems to fail to understand is that you are not compressing a gas. The analogy is correct in the old wetpixel post you are heating a container on one end and condensation forms on the other colder end

The condensation by compression at ambient temperature of a gas reported earlier does not apply here as conditions are different. The theory is fine but the situation is different

Have fun

It's a good thing we got a separate mirrorless forum for such engaging topics.

Sent from my iPad using Tapatalk

It's a good thing we got a separate mirrorless forum for such engaging topics.

 

 

Sent from my iPad using Tapatalk

In my defense, it started out as a discussion about The Nauti vacuum system on a mirrorless housing, but it has kind of taken on a life of its own

Sorry about that Draq! I will try to clearly answer the 2 questions posted in this thread using what little expertise I have in the area as a hyperbaric physician. I will not get drawn into a pettifoggery once again.

Your question if the negative pressure generated by the Nauticam system will make it less likely to flood -the answer is yes, because the o-ring is sucked into the mating surfaces of the housing, preventing blow-by.

watboy, your question if an additional benefit of a vacuum system would be that it would eliminate condensation issues , the answer is no. It will greatly decrease them though. If you close your housing at 30°C and 75% relative humidity, condensation will form when the housing wall reaches 25°C. Under the same conditions, If you pump the housing down negative 10 inches Hg, condensation will form when the housing wall reaches 18°C. Starting conditions will certainly modify the results, but not the manner in which you can calculate the benefit. The explanation is below.

Condensation forms at the dew point which is when relative humidity (RH)= 100%

RH= partial pressure of water vapor (PW) / vapor pressure of water (VP) at a given temp.

Vapor pressure of water at a given temp. (VP) is independent of pressure

When you decrease the pressure by 10 inches Hg, you are decreasing the pressure inside the housing by 30%

Following Dalton's law, decreasing the housing pressure by 30% will decrease the partial pressure of water (PW) by 30% once the temperature equilibrates. Therefore, relative humidity will decrease by 30%

So starting at 30°C and 1atm and a RH of 75%, pumping the housing down to .7atm will yield a RH of 67.5% once the housing equilibrates with the 30°C ambient temp.

Using the dew point curve we know that at 30°C and 75% RH the dew point = 25°C

Using the dew point curve we know that at 30°C and 67.5% RH the dew point = 18°C

So after vacuum there will be a 7°C degree difference in how cold you have to get the housing wall before condensate will form.

I will be happy to answer any questions not originating from Interceptor.

Are you still going in with this non sense? This is not an isothermal compression of a gas as per your experiment. Go and read my post and the older ones on wetpixel. The condensation will diminish if you suck vacuum only because there is less matter to condensate. Humidity doesn't change inside the housing. If that is so hard for you try to look up at why you have condensation on windows on a cold day maybe that's easier to understand. Have been attacked by two supposed experts with non sense that I could not understand and guess what? It was non sense so please stop plaguing this post with additional misinformation and try to make sense of the real process happening inside the housing.

And to give some example figures pumping out 200mbar reduces the matter of 20% so you have 20% less condensation as the same conditions.

For what concerns the benefit of the vacuum you need to consider that a sealing surface is actually small just a few mm. So if you have an oring of 2mm for example over a dome of 4" you need around 1.2 kg force to pull that out. But if you hit it laterally with much less than that it would drop because of of momentum.

A larger 8" dome will need much less force to drop. Those values at the surface. Also consider that if your camera has heated up the pressure has increased and most likely the effect will be reduced.

Conclusion there are some benefits of vacuum but your housing preparation practices in terms of carefully putting the parts together and using desiccant do not change because of it.

End of story

Sorry about that Draq! I will try to clearly answer the 2 questions posted in this thread using what little expertise I have in the area as a hyperbaric physician. I will not get drawn into a pettifoggery once again.

 

Your question if the negative pressure generated by the Nauticam system will make it less likely to flood -the answer is yes, because the o-ring is sucked into the mating surfaces of the housing, preventing blow-by.

 

watboy, your question if an additional benefit of a vacuum system would be that it would eliminate condensation issues , the answer is no. It will greatly decrease them though. If you close your housing at 30°C and 75% relative humidity, condensation will form when the housing wall reaches 25°C. Under the same conditions, If you pump the housing down negative 10 inches Hg, condensation will form when the housing wall reaches 18°C. Starting conditions will certainly modify the results, but not the manner in which you can calculate the benefit. The explanation is below.

 

Condensation forms at the dew point which is when relative humidity (RH)= 100%

 

RH= partial pressure of water vapor (PW) / vapor pressure of water (VP) at a given temp.

 

Vapor pressure of water at a given temp. (VP) is independent of pressure

 

When you decrease the pressure by 10 inches Hg, you are decreasing the pressure inside the housing by 30%

 

Following Dalton's law, decreasing the housing pressure by 30% will decrease the partial pressure of water (PW) by 30% once the temperature equilibrates. Therefore, relative humidity will decrease by 30%

 

So starting at 30°C and 1atm and a RH of 75%, pumping the housing down to .7atm will yield a RH of 67.5% once the housing equilibrates with the 30°C ambient temp.

 

Using the dew point curve we know that at 30°C and 75% RH the dew point = 25°C

Using the dew point curve we know that at 30°C and 67.5% RH the dew point = 18°C

 

So after vacuum there will be a 7°C degree difference in how cold you have to get the housing wall before condensate will form.

 

I will be happy to answer any questions not originating from Interceptor.

Little exercise for you Stuart to make you understand, you are allowed out of the quiet corner for this.

Find a pressure cooker and leave it empty, seal it. Now put the gas on in a cold room and let it stay there for a while (not too long as this could be dangerous)

Now if you look on the glass top there will be condensation from the inside.

The non sense in the previous posts is that what is changing is the temperature because inside the housing there is a heat generator so you can't make any assumptions on how many degrees you gain. You only now that will be X% less you are not able to predict anything more

Today I followed diverdoug experiment and immersed an housing under the dew point in water and let it there for over half hour. It did not fog and this is because the temperature was not constant so humidity never increased. On the contrary the inside of the housing getting hot, that if kept at constant pressure would reduce humidity, but the pressure is not constant the volume is, resulted in condensation. Which occurs because of the interfaces not because of compression of the gas in itself.

This is some relevance to the dew point but is an entirely different thermodynamic process

Sorry about that Draq!

 

No worries, I am fine. I am still inclined to think the vacuum offers some added seal at the surface but there clearly is a difference of opinion on that. It doesn't change anything for me either way, so I am perfectly content watching you more science-oriented types duke it out. Nothing much to watch on television lately anyway.

I will make a final attempt. Let's assume that the process is governed by relative humidity as suggested.

Moisture content is unchanged absolute humidity does not move, dew point that is by definition the absolute humidity does not change

(example 2 here http://books.google.co.uk/books?id=Eq1OqmBjSvYC&pg=PA1&lpg=PA1&dq=relative+humidity+in+sealed+container&source=bl&ots=oivk44m59G&sig=kFqeASCuaUucgbWSyiGaq9EAu5Q&hl=en&sa=X&ei=ZXg8U8ebL-6g7AbQqoGIAQ&ved=0CD8Q6AEwAg#v=onepage&q=relative%20humidity%20in%20sealed%20container&f=false)

Is this was what was governing the process condensation would happen as temperature goes down as result of increase of relative humidity and as temperature goes up relative humidity goes down and the air is drier.

So why does a housing fog as the camera is getting used (even in warm water) despite the fact that the relative humidity should drop?

Why did my camera fog when the internal housing temperature was 25C?

Because the model of the gas getting heated is not actually a representation of the physical process happening in the housing. The condensation happens at the interfaces between the materials in virtue of temperature gradients and the fact that the vapor is more volatile (and in theory the air inside is drier) makes things worst.

The only case where the theory of mr doug would hold is if your housing was only full of air. Instead inside there is a heat generator (the camera) with its own personality!!! LOL

The very simple post dated 2009 in wetpixel had already the handle on it, and yet there was a guy at the end saying why is fogging if it is hot, relative humidity should drop and air is drier? As above you don't dive with a housing full of air, you dive with a camera

To the op there is a an advantage of holding ports together with vacuum but in comparison to the strength of the nauticam lock system is nothing, and if you use a camera for one hour and it gets hot the pressure will be same as the atmosphere and your port would drop at the surface...

Good night

I know Draq, it is killing me that the '"Walking Dead" is over for the season!

Games of thrones is starting I am going to send a few dragons out on a mission

Maybe tomorrow I go diving at the lake with an empty housing so that I can wash it inside with a bit of steam as opposed to keep the camera in as that may keep it to dry

You could in theory, drop the pressure until the dew point is below the water temperature, eliminating condensation. Not yet including the the heating effect from the camera. To geek out in another direction, does anyone know the piston and port diameter of the hand pump? We could assume what the human pull strength is, and estimate how strong a vacuum one could pump. One could flip the chart around to see, how low you have to drop the pressure to completely eliminate the chance of condensation for a given water temperature. In your scenario, if the water temp was 22c, there would be no possibility of condensation no?

 

 

watboy, your question if an additional benefit of a vacuum system would be that it would eliminate condensation issues , the answer is no. It will greatly decrease them though. If you close your housing at 30°C and 75% relative humidity, condensation will form when the housing wall reaches 25°C. Under the same conditions, If you pump the housing down negative 10 inches Hg, condensation will form when the housing wall reaches 18°C. Starting conditions will certainly modify the results, but not the manner in which you can calculate the benefit. The explanation is below.

 

I have devised a little formula to avoid false alarms (nothing to do with this subject) as the indicator changes colour when you reach -200mbar if you divide this by the number of strokes you know how much vacuum each stroke creates (it is approximate) however the whole point is that you don't create anything more than needed otherwise you defeat the object if in water leak alarm. The nauticam system is set at 200mbar delta and you should not pump more vacuum or if your housing leaks when you dive the warning will be delayed

After around 100 posts about this condensation debate is probably time to call it a day.

The nauticam housing for the EM5 is made of aluminum, the ports are either glass or acrylic.

Aluminum conduces heat much more than glass or acrylic so in general terms if any condensation occurs it will be on the walls of the housing and not on the port or the LCD.

I picked up my housing and noticed there was a fingerprint inside the port so my housing did not fog in any circumstance with camera cold or hot yesterday.

So the choice of materials pretty much solves all issues as long as you prepare the housing at temperature colder or anyway as near as possible to the water you will be diving into. In cold water diving this may be a challenge and preparing the housing on the dive site (as long as it is not raining) could be better than doing it in a heated environment even if this is dryer. Either way a desiccant packet will suck the moisture that forms on the walls of the housing.

It was useful to have a better understanding of the process and condensation will occur if you have a plastic housing as the housing is more insulating than the port. So if something had to happen there your photos will be screwed. But who has a plastic housing anyway?

For what concerns the additional sucking of the port, bearing in mind nauticam locking system can hold probably 5+ kg before cracking the seal when the lock is closed, if you look at the port on the housing to have around 67mm and a mating surface of 2mm you are looking at additional 800 grams of force needed to pull it out - the weight of the port itself say that this is 400-500 grams you have additional 300 grams insurance in case you did not lock the port.

Aluminum conduces heat much more than glass or acrylic so in general terms if any condensation occurs it will be on the walls of the housing and not on the port or the LCD.

 

Obviously the many people who experienced condensation on their glass port in an aluminium housing were just seeing scotch mist.

Edited: Admin