Re: [APML]: Hypering thread ...

["Philip Perkins" <philip@astrocruise.com>]

Joe

Thanks so much for sharing this information and helping input some science
to this discussion.  It would seem that your experiment in the 50 degree
Celcius drying oven is analagous to the dessication process in a hypering
chamber - the main difference being the volume and atmospheric pressure  -
I assume that the oven was at normal atmospheric pressure?  Do you have any
view as to how much a vacuum of -27 in would accelarate the dessication
process?

The weight loss you recorded in the drying oven was astonishing - based on
these results would it be correct to assume that a lot of moisture / gases
must still be left in the film after the normal hyper process? (i.e. the
difference between your recorded 109mg per film and your calculated 5.09mg
per film based on my hypering procedure)

Agreed on the film odour you mention - it's quite a strong, distinct odour
(at least in the case of the PJM-2 that I normally work with).  If it's
relevant, there's a very strong whiff of it that comes from the hyper
chamber when the pressure is released at the end of the hyper process.


Very interested in your further results ...

Thanks  --Philip


> Philip observes a pressure increase of about 1.75 psi when he hypers 4
> rolls of film.  I have been exchanging email with him about how much water
> would have to be released to observe such a pressure increase.  He has
> encouraged me to share some of the information we have exchanged.  I have
> never hypered film, so my analysis is not based on experience.
> 
> The basic question is:  How much water would have to be released to
> observe a 1.75 psi increase in pressure?  The answer - not much.  Here
> are some assumptions that I made to reach this conclusion:
> 
>  Lumicon chamber volume = 310 cc (from online Lumicon catalog)
>  temperature = 50 deg C = 323 kelvin
>  4 rolls of film surface area = 2.5 sq ft = 2323 sq cm (Philip's number)
>  film thickness = 0.025 cm (this is a guess on my part)
>  film volume = 2323 * 0.025 = 58 cc
> 
> The film canisters also take up some volume, but I will neglect it.  So
> roughly, there is about 252 cc of air in the chamber.  I assume that the
> pressure increase comes from an addition of gas and not gas that is
> already present heating up.  The ideal gas law is:
> 
>  PV=nRT
>  where:
>  P = pressure
>  V = volume
>  n = numbers of moles of gas (multiply this by 18 to get grams of water)
>  R = gas constant
>  T = temp in kelvins
> 
> Let's assume you see a 1.75 psi increase in pressure.  From the ideal
> gas law this corresponds to:
> 
>  n = PV/(RT)
>    = (1.75/14.7 atm)*(252/1000 liters) / (0.082054 * 323)
>    = 0.0011319 moles of water per 4 rolls of film
>    = 0.0203747 grams of water per 4 rolls of film
>    = 20.3 milligrams of water per 4 rolls of film
>    = 5.09 milligrams of water per roll of film
> 
> This is not very much water.  These calculations assume that the off gas
> is all water vopor -- which is not the case.  For example - the fact
> that fresh film has a distinct odor to it means that gas molecules (other
> than water) must be escaping the film (and canister) at room temperature
> and pressure.
> 
> The emulsion side of film, non-emulsion side of film, and film
> canister will all adsorbed water from the atmosphere.  In fact, almost
> all surfaces will adsorb water and other gases from the atmosphere.
> Preheating, evacuation, and multiple flushes undoubtedly remove some water
> and other volatile gases prior to actual hypering.  The slow off gasing
> observed under high vacuum suggests that a diffusion process controls the
> release of some of the water vapor.  I can only guess that this slow
> release of water is due to slow diffusion of water within the
> emulsion of the film -- although I must admit that I know nothing
> about film.
> 
> So how much water and other volatile chemical compounds are present in
> fresh films?  I took a fresh roll of Kodak-X pan film and removed it from
> its canister.  I weighed it, placed it in a 50 degree Celcius drying oven
> for 2.5 hours, then reweighed it.  It lost 109 milligrams.  I returned the
> film to the oven and will reweigh on Monday.  I realize that my simple
> little experiment does not mimic the hypering process, but it does
> demonstrate that there is a lot of water and other volatile gases present
> in fresh film that is easily removed without resorting to a high vacuum.
> 
> Joe Pedit
> 
> -------------------------------------------------------------------------
> Joseph Allan Pedit
> Department of Environmental      joe_pedit@unc.edu
>    Sciences and Engineering      http://cmr.sph.unc.edu/~joe/CMRhome.html
> CB# 7400, 104 Rosenau Hall       voice : (919) 968-0647
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> 
> 

Philip Perkins  --  philip@astrocruise.com
51 27'N 1 36'W  --  Wiltshire, UK
43 54'N 5 32'E  --  Luberon, France
Astrocruise     --  http://www.astrocruise.com