[labnetwork] chiller water

Sat Oct 15 13:17:35 EDT 2011

John:

I don't think there is much more to be said on this subject ... well done ...

Dennis S. Grimard, Ph.D
LNF Managing Director
1246D EECS Building
University of Michigan
Ann Arbor, MI 48109-2122
(734) 936-1413 Office
(734) 368-7172 Cell
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http://www.lnf.umich.edu<http://www.mnf.umich.edu/>

From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of John Shott
Sent: Saturday, October 15, 2011 11:57 AM
To: labnetwork at mtl.mit.edu
Cc: jgood at utdallas.edu; bradshaw1234 at gmail.com
Subject: Re: [labnetwork] chiller water

Keith:

While I'm confident that others will contribute some important insights and recommendations to this discussion, let me take an initial stab at discussing some of the issues and approaches that we have tried.  Note: I don't consider myself an expert in this area, but have certainly had to deal with a lot of problems in these areas over the years .... both in tools with local chillers and heat exchangers and in tools connected to the building-wide process cooling water system.

We've likely had more problems over the years with the building-wide system and have tended to go to local chillers and/or heat exchangers when we either encounter a corrosion problem or have a resistivity requirement that cannot be met by the building-wide system.  That said, however, we also have periodically seen problems on our tools with local chillers and/or heat exchangers.

Note:  Just for reference, our building wide system is treated with Nalco TRAC107 at a 2000 ppm concentration, a pH of 7.5 to 8.0 but it ends up with a pretty low resistivity of about only 2000 ohm-cm (500 microSiemens/cm) by a closed-loop control system.  We recently had a problem due to a failed pH probe that resulted in water with a pH of 6-6.5 .... which begins to be bad news for aluminum and mild steel.  So, even a "professionally managed", closed-loop control system can have problems and is an ongoing struggle.

Back to your local chiller ....

1.  I think that it's always good to understand the metals in the system .... including parts of the chiller as well as the materials in your machine through which the water flows .... to understand how much of a galvanic reaction problem you are likely to have.  While we can't always control these things, systems that have mixtures of aluminum, yellow metals, and mild steel tend to be more problematic.  A lot of tool manufacturers seem to include quite a range of metals in contact with the water.

2. Can you measure the pH of the water in your recirculating tank?  If it has gradually drifted away from 7-ish .... particularly if it gets below 6.5 or so ... that may help to explain more recent problems.  If pH is either or low or high I'd try to fully exchange the distilled water.

3. Do you have a resistivity requirement .... for example, if this chiller is cooling RF supplies, then you need pretty high resistivity water.

What are some other options?

1. Analyzing the chemical content of the stuff that you are capturing in your filters is often useful to try to determine what is the primary corrosion material .... or whether you may be seeing organic material due to algae growth.  I believe that the little systems with open tanks are more prone to algae problems than truly closed loop systems because of ongoing oxygen entrapment in the water.

2. Adding a little deionizing cartrigde, resistivity monitor, and solenoid so that water can periodically be passed through the deionizing cartridge.  I believe that a lot of people will tell you that something in the range of 0.5 - 1.0 Mohm-cm is about optimum.  High enough resistivity to reduce galvanic corrosion, but not so high that the DI water corrodes everything in sight.  Note: if you go this route, you generally have a second solenoid controlled loop with the deionizing cartridge in it in parallel with the main flow loop.  That is because you can't typically get 2-3 GPM through a deionizing cartridge so you have a bypass flow channel that routes a little bit of the flow through the deionizer when you need to increase the resistivity.  Plus, you are only shooting for 0.5 - 1.0 MOhm-cm and don't want to be routing too much of the flow through a deionizing cartridge. I haven't priced this in a while, but I think that you can get a cartridge housing, a resistivity controller, and a resistivity probe for on the order of $1k.

3. There are additives that claim to be able to be added to these recirculators to inhibit corrosion with minimum monitoring or precise control.  For example, there is some stuff called Optishield (and Optishield II and Optishield Plus ....) that you mix in at about a 10% concentration with your distilled water.  That is supposed to be good for a year and then you empty the lines and refill with a fresh mix.  I have no personal experience with this stuff .... but maybe someone else has and cares to comment.

4. We have used 50/50 mixes of DI water an ethylene glycol in a number of tools .... particularly if they are going to be cooling to temperatures near freezing.  This mix, by itself, doesn't really include much in the way of corrosion protection .... and, as I understand it, if it is run to too long, can break down into a variety of acids that will once again create problems.

Note: when we've had systems that have gotten significant build up, we have used a variety of radiator flush type products ... with a fair amount of trepidation .... to try to clear some of the "stuff" out of a system.  I'm not particularly proud to admit this ... but desperate times call for desperate measures and a machine with a plugged (or nearly so) cooling channel is a desperate situation if you can't easily disassemble and/or replace cooling channels.

I fear that my conclusion is that we've tried a lot of things over the years and still don't have a particularly good approach that has resolved these issues on a permanent basis.  Maybe some or our more enlightened colleagues will provide a more comprehensive approach.

Good luck,

John

On 10/14/2011 6:31 PM, Keith Bradshaw wrote:
We have used distilled water in our chillers recirculating tanks.
Recently we have suddenly seen the inline filters clogged with corrosion.  We have seen more problems in the last 5 months than we had in the previous 6 years.

Any advice on this?
Should we be using an additive?

cordially,

Keith Bradshaw
Garland, Texas

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