[labnetwork] chiller water

[John Shott]

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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