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J. Peter Bercz, PhD
USEPA/EMSL/EMRD
Cincinnati, OH 45268
(513) 569 7480
------------------- COOLSUM.ASC follows --------------------
There were 28 INTERNET responses to my recent request for
evaluating various modes of water cooling lasers. It appears that
this issue hit a raw nerve with some cytometrist-correspondents. As
some of you cytometry cyber-networkers have requested, a summary
evaluation of the topic is provided in the following: (Individual
names and affiliations are deleted to protect the innocent.)
1. Nine responders (1/3-rd of sample) positively recount no
problems whatsoever with straight, filtered tap water cooling.
Average duration of "No problem cooling" appears to be about 8 yrs.
2. Three reports give account of suspended and dissolved
solids ( grunge)-associated problems, corroded water wheel, mud
build up in cooling jacket, calcium deposits around plasma tube
needing vinegar treatment and 5 micrometer filter replacement
schedule as often as weekly or even daily.
3. Two reports came from northern US installations about
excessive cold causing moisture condensation, thermal expansion and
contraction problems, and sometimes the need for blending in warm
water. About as many users however claim no problem with winter
cold water.
4. Two reports from metropolitan areas wrote about nagging
pressure drops in tap water causing laser downtime.
5. Three responses take exception to cooling lasers with any
effluent production whatever (tap or tap-cooled heat exchanger).
They refer to local and state regulations for conserving water
resources. These people recommend chillers, even though they
acknowledge anti-social nature of these, e.g. problems with
oversize footprint of chillers, bulk, noise and excess local heat
production. There seems to be an uncertainty as to how far chiller
units can be located from the laser, there exists two installations
with >200 ft.
6. Two correspondents for flow cytometry tend shunning water
cooled units altogether in favor of a 50 mW He-Cd laser (in spite
of the noise problem).
7. Friends from DOWN UNDER (Australia, New Zealand) and from
southern US have only positive experiences with the tap water-only
mode. They report no damage to lasers, no grunge problems and
certainly no water shortage (Specially not in New Zealand).
8. Four responders say: Chillers are BIG, NOISY, PRODUCE
TREMENDOUS HEAT, DRIVE WORKERS OUT OF THEIR WITS.
9. One response finds a chiller (size not specified)
insufficient for 5 Watt UV work, requiring tap water cooling.
10. NESLAB's chillers are usable and NESLAB's engineers are
helpful according to 2 responders, however NESLAB chillers are
unreliable, noisy, hot and too big according to 3 responders.
11. A SpectraPhysics Closed Loop Heat exchanger connected to
the building's central cooler tower is an excellent technical
solution according to one correspondent.
12. Laserpure heat exchanger are small, quiet and efficient
according to two experiences.
As for my local solution to laser cooling:
For the Coherent Enterprise (on the confocal), we elected to
install a closed loop recirculating (deionized water based) system
with coolant coil-to-air heat exchanger.
Our Innova on the EPICS Elite remains connected to the tap
temporarily. However this will be switched to a different cooling
system as soon as facility engineering study is complete.
Conclusion: Clearly on the first decision level, local regulations
for water conservation. Thereafter costs and convenience drives the
selection for laser cooling. There is sizable variation in
opinions and experiences, still the absence of problems with tap-
water cooling (from diverse geographical parts of the US and
abroad) suggests that this issue may not be as trouble-prone as
originally suspected.
Still the fact remains that it is incumbent to all new
installation planners to do a detailed study of:
a. Local water usage regulations and sewerage charges.
b. Local water quality in terms of suspended and dissolved solids.
c. Differential seasonal ambient water temperatures and pressures.
d. Generic building specifications and capabilities for tying into
existing heat exchanger facilities.
existing heat exchanger facilities.
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