Watercooling, different coolants

What to cool a laser machine with has been and probably will be a split opinion for many users.
When asked in forums and discussion groups the replies are many and spread across a lot of different mixes and products.

With this article i will explain the different mixes, what they do and how they fit our machines, and why some may not fit.
In the end, it´s up to you as the owner to decide what mixture you want to use, read this article to decide and see what properties the different mixtures have and what the goal is with your machine.

Biocides

Preventing growth of bacteria, algea and other microorganisms. You do not want algae in your laser tube, it prevents heat transfer and may kill your tube.
I have seen usage of small amounts of bleach or chlorine in the coolant, it acts like a biocide too but in wrong amounts it will make the coolant very low pH and the mixture is corrosive for metal parts in the loop.
Biocides made for hot tubs or pools shouldn’t be used either.
There is readily products for this so i would suggest using a real biocide. Check out PC water cooling stores.

Surfactants

Or wetting agents is a premix, like Water Wetter, Purple Ice, HydrX and Hy-Per Lube with many more names depending where in the world you are.
Wetting agents lowers the natural surface tension of water. The effect causing water beads to form.
This helps water transfer, prevents bubbles from forming, lowers the viscosity and acts as a corrosion agent for metal parts in the loop.
Dish soap is one type of surfactant, but it also contains alot of other additives, like perfume and similar, read the bottle before using.
In auto stores you can find additives for your wiper fluid, DO NOT use this in your coolant, most of them are flammable and is dangerous to add to a 16000 volt system, just don´t do it to be safe!

Conductivity

Our laser tubes have ~16000 volts flowing trough the tube, the water inside the machine will get charged if it contains any particles carrying this charge.
Distilled water has almost no particles at all and do not get static charges. When you add anything to the water, you amp up the static charges also.
Why is this bad for a laser tube?
First off, having a couple of thousand volts in our coolant tank is dangerous, it hurts pretty bad if you happen to touch it.
Second, if alot of the energy in the tube goes away to charge the water, less energy is carried to the other end of the tube, thus lowering the power of your laser tube.
Third, static charges helps mineral build ups in your tube. With time these may create hot spots and a temperature difference in the tube, cracking it.
Remember, without any minerals/particles in the tube, you cannot have a static charge.
The static charge may also interfere with the beam, making it deviate from the path and hit the edges of the end mirror and you get a split beam inside your machine.

Cleaning and maintenance

Basic rules for your cooling tank
– Keep it out of sunlight
– Keep the return hose below water surface
– Have a lid on the tank, leave a small gap around the hose for pressure differences.

When changing the water in your tank, use 50-50 mix with Listerine+distilled water, or vinegear to flush your loop for a hour.
Then refill with your favorite mix of coolant.

Using tap-water for shorter runs

It works to use tap water for shorter runs. Use with caution, fill your tank with tap water, use the machine and empty the tank right after use. Add a mixture of vinegear+water or listerine+water and run the pump for 30-60mins.
I would not suggest keeping tap water in the tank longer than 3-4 days.
Depending on your tap water quality, it may go bad over night, or you´ll be fine for two weeks. Just as a precaution i never recommend tap water at all, even though i use it myself sometimes.

Different coolant mixtures, and their properties
Tap water
  • Good thermal properties
  • Microorganisms will flourish
  • Very high conductivity
  • Risk with mineral deposits creating hot spots, depending on water quality.
  • No corrosion inhibitants
Distilled water
  • Good thermal properties
  • With time, microorganisms may flourish
  • No corrosion inhibitants
Distilled water + RV antifreeze
  • Fair thermal properties
  • Corrosion resistance
  • Good protection against algea and other growth
  • False sense of security using a pre-mix.
  • Higher viscosity, less thermal pickup
  • Higher conductivity (about 400x more than distilled)
Distilled water + surfactants + biocides
  • Excellent thermal properties
  • Corrosion resistance
  • Not conductive, less than 2μS/cm (tap water: 1000-2000μS/cm)
  • Good protection against algea and other growth
Distilled water + surfactants
  • Excellent thermal properties
  • Corrosion resistance
  • With time, microorganisms may flourish
RO/DI-water
  • Good thermal properties, similar/identical to Distilled water
  • Will re-ionize very quick and go back to regular water.
  • With time, microorganisms may flourish
The “I have done it, you are wrong”-tale

Of course there is users who have cooled their laser with tap water, RV-antifreeze, camel urine or whatever, just because it works for them isn´t a rule to say it works for everyone :)
How fast a laser cooled with camel urine will fail depends on so much more than the coolant, as power usage, how often and how long it´s used, room temperatures, lasing temps of the water and so on.
The facts are there, you be the judge of how you want to cool your machine, i can only suggest what to do, or not to do.

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HP Persson

Digging up the strange ideas and convert them into useful tools and addons for the lasers.
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