hi,
i've got a problem with the statement that the dessicant 'pulls' moisture out of the component...something that nitrogen can't do because it is a gas that water isn't soluble in (see mcdry). somebody help me with that one.
as i see it, dessicant in the cabinet pulls moisture out of air in the cabinet. the moisture in the air in the cabinet gets there from the component that has moisture in it. the initial drying force is that of moisture in the component migrating to dry air which then gets transferred to the dessicant because of it's affinity to the dessicant (up to a point).
now, replacing the dessicant-air combo with a continuous flow of dessicated nitrogen should give you the same result.
it seems to me the argument in favor of the mcdry is that it's more convenient than dry nitrogen. with the cost of electricity sky rocketing (at least here in california) mcdry may not be less expensive (this is just a guess).
phil
-----Original Message-----
From: Joyce Koo [mailto:[log in to unmask]]
Sent: Friday, May 25, 2001 5:41 AM
To: [log in to unmask]
Subject: Re: [TN] Moisture Sensitive Components
Steve, thanks. I think I need a cabinets for the weekend jerky making
as supplement income...
jk
-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: May 24, 2001 8:10 PM
To: [log in to unmask]
Subject: Re: [TN] Moisture Sensitive Components
Hi Guy!
I'm like you, the physics make me feel a little lightheaded too. But, we
fairly recently bought some desiccant cabinets from McDry, and they keep
the
humidity down to 4% inside the cabinets...and that's here in Oklahoma,
we see
humidity levels at 80-90% quite often here. McDry's claim to fame is
that a
desiccant cabinet will actually pull moisture out of devices over a
period of
time...something that dry nitrogen cabinets can't do. You can check
their
charts out at:
http://www.seikausa.com/mcdry/page5.html
I actually think that you could make beef jerky inside these
cabinets...hehehe.
They are a little pricey, but when you consider the costs of inerting a
cabinet with nitrogen, and the added aspects of a desiccant type system,
I
think they're worth it.
With these cabinets all you do is plug them into a standard receptical,
and
forget about it. The desiccant is self regenerated by the system...
-Steve Gregory-
<< Anyone out there ever considered drying moisture sensitive devices by
lowering the pressure in a storage vessel?
It is difficult to achieve 40°C and less than 5%RH when ambient RH is
50-60
percent. So, someone called and asked how long he would need to keep
the
parts at a pressure equivalent of 80,000 ft above sea level,
temperature at
room ambient to dry out parts.
No one here had considered it before. The physics made me feel like I
was at
altitude.
Guy Ramsey
Senior Lab Technician / Instructor
E-Mail: [log in to unmask] <mailto:[log in to unmask]>
Ph: (610) 362-1200 x107
Fax: (610) 362-1290 >>
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