×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Dessicant Sizing

Dessicant Sizing

Dessicant Sizing

(OP)
Folks-
Given a sealed electronics enclosure, if one knows the outside air temperature, pressure, and humidity profiles, is there a way to analytically predict how much moisture will condensate within?  The seal is a conventional linear O-ring in an O-ring gland of traditional design.  Also given are the inside surface area and volume.  I dug out my old thermo textbook but it contained no problems remotely close to this one!  Everywhere else I've looked, including a Google search turned up nothing.  TIA for your help!

Tunalover

RE: Dessicant Sizing

Oddly, I'm working on a similar problem.  However, your question seems to be different than the ones I would ask.

> What temperature range do you want to have non-condensation?

> This establishes the dewpoint, which dictates the amount of water allowable at room temp

> Which determines the RH at RT

> Which determines the steady-state desiccant demand

> What is your max temp and how much leakage, both outflow and inflow

> Which determines the amount of potential moisture introduced into the structure

> Which determines the amount of moisture to be removed at any given time

TTFN



RE: Dessicant Sizing

(OP)
IRStuff-
I'm trying to determine the amount of dessicant to use in the enclosure and how long it will last until requiring recharge.  I know the time history of outside RH, temperature, and altitude.  I just need to know how much condensate will form inside the enclosure.  Do you know of any papers on the subject where someone actually comes up with NUMBERS?

Tunalover

RE: Dessicant Sizing

I'm kind've with IRStuff on this one.  A simple Psych chart will tell you everything you need about the air-water vapor mixture properties.  It will even assist with modeling the process.  However, you still need to estimate/measure the factors that he points out.

Condensation occurs when heated air, containing a higher moisture level, is cooled beyond the dewpoint temperature of the air-water vapor mixture.  Now, that may seem like stating the obvious, but the rest is up to you.

Out of IRStuff's list, I would count airflow into and out of the enclosure, and heat transfer through the enclosure's surface as most important - and totally dictated by your specific situation, your estimates, and your measurements.

RE: Dessicant Sizing

How sealed is sealed?

If you can safely assume that there is no air exchange with the outside then the problem is relatively straight-forward.

If there is air exchange things get more complicated.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources