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Keith:<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
Back to your local chiller ....<br>
<br>
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.<br>
<br>
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.<br>
<br>
3. Do you have a resistivity requirement .... for example, if this
chiller is cooling RF supplies, then you need pretty high
resistivity water.<br>
<br>
What are some other options?<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
Good luck,<br>
<br>
John<br>
<br>
<br>
On 10/14/2011 6:31 PM, Keith Bradshaw wrote:
<blockquote
cite="mid:CA+naYihGwbAMcVV0b_PJqVCDSQ_xCrZ=bkR+2cTrx=wDnNwiww@mail.gmail.com"
type="cite">
<div class="moz-text-html" lang="x-western">We have used distilled
water in our chillers recirculating tanks.<br>
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.<br>
<br>
Any advice on this?<br>
Should we be using an additive?<br>
<br>
<br>
cordially,<br>
<br>
Keith Bradshaw<br>
Garland, Texas<br>
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