[labnetwork] Heated gas lines

[Paolini, Steven]

Matthiew,
    I highly advise against the practice of heating gas lines to keep low vapor pressure gases in gaseous form providing that you are feeding a vacuum system. Heating the gas lines and cylinder are an old school method of dealing with these materials but almost always results in condensation at some "cooler" region in the gas circuit. I believe the best approach is to specify sub-atmospheric regulators and regulate these materials to the lowest possible pressure that will keep up with the maximum flow rates of your equipment.
The concept is simple: lower the pressure and you lower the boiling point. I had "inherited" equipment when I was in industry that was plagued with MFC floods and liquid pooling as a result of a weak link in the heating chain when I decided to swap methods and lower the pressure. The problems were cured right away and it didn't matter how close the source was to the equipment.
On DCS for LPCVD, the delivery pressure of 2 PSI was sufficient to satisfy the systems gas flow rate and on BCL3, 5" Hg to 0PSI was enough. At my current facility, I practice the same method with slightly different pressures as a result of different demands. The use of sub-atmospheric (tied diaphragm) regulators allows precise control at these pressures where a standard pressure regulator performs sort of "jumpy".  I can be more specific if you wish but I need to scoot out of Boston in a couple of minutes before being trapped by tens of thousands of fireworks fans!

Steve Paolini
Equipment Dood
Harvard Center for Nanoscale Systems
spaolini at cns.fas.harvard.edu


-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Matthieu Nannini
Sent: Thursday, July 03, 2014 2:22 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Heated gas lines

Dear colleagues,

We are undergoing an analysis of our gas network and I would like to get the best practices out there.

For gases that need to be heated in order to avoid condensation, is it best to have the cabinet as close as possible to the tool ? Or, if one wants to consolidates all gases in the same area, could we have them far away ? if yes, how do you address the condensation issue.

Thanks

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Matthieu Nannini
McGill Nanotools Microfab

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