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The importance of water chillers

Precise laser output power measurement

The importance of water chillers

One of the most, if not the most important factors in ensuring stable power output is the temperature of CO2 laser tube. Often overlooked and misunderstood is the water cooling loop. In this post we hope to clear up any misconceptions and myths in regards to water cooling and the do’s & don’ts of laser cooling.

Chillers

A closed water cooling system, usually consists an internal radiator, fans and most often an internal water circulation pump. Water chillers come in two forms, ensure when purchasing you buy the chiller most suitable for your application.

Refrigerated

A refrigerated chiller removes heat from a liquid using a refrigerant via vapor-compression the refrigerant is then circulated though  a heat exchanger. The primary benefit of a refrigerated chiller is the ability to maintain a temperature below ambient. E.g if you live in a client with ambient temperatures above 18’C in order to maintain a temperature less than ambient will require a refrigerated chiller.
Secondary benefit is temperature stability, regardless of workload your laser tube will maintain a stable temperature.

None refrigerated

A none refrigerated chiller uses a water to air heat exchange, similar to the radiator you would find in your home. Ambient air is used to remove heat from the exchanger. Due to heat being removed from the cooling fluid using only moving ambient air, this type of chiller cannot cool below your ambient temperature. If you live in a very cold climate this might work, but i would never personally recommend someone purchase a none refrigerated chiller.

Bacterial growth

Bacterial growth in a close water system is a big problem! It can cause numerous issues and reduce the systems ability to cool and flow water around the co2 laser tube.

  • System blockages – build ups of bacterial & microbial slime can cause blockages in the pipework, complex bends and control valves.
  • accelerated corrosion – corrosion is caused by formation of organic acids, hydrogen sulphide, ammonia etc. within the closed system.
  • reduced efficiency – microbial build up on the heat exchanges surface will severely reduce its effectiveness of transferring waste heat.

How to check for bacterial growth?

  • Smell – strong pungent smell, stagnant water.
  • Clarity – cloudy water is a clear sign of bacterial growth
  • Color – If your cooling medium is changing brown or green its a sign of bacterial growth.

How to prevent bacterial growth?

  • Replace tubing from clear to black, light is required for algae to grown, but bacterial does not need light to grow.
  • Replace tubing for Tygon Micorbore tubing, this tube is infused with silver and other things to kill microbial growth.
  • Add a black light water purifier, it is scientifically proven that black light kills bacterial growth.
  • Do not add long term additives that are corrosive such as bleach, chlorine etc. It is OK during regular maintenance / cleaning to flush a system with a safe dilution of certain chemicals but long term use will cause corrosion.

What is the optimum temperature?

15’C -20’C anything between this range is safe, as temperature rises laser power begins to drop. Also long term damaged caused by prolonged used outside of this range can be caused.

What is dew point?

When air touches a surface which is colder than the air itself it will begin to condense on the surface forming water droplets. Another factor that will change the dew point is humidity.
As a rule on hotter days run your chiller closer to the recommended 20’C to try and limit the formation of dew on your laser tube.

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