This is a very common question,that we must hear several times each day.
The answer to the question depends on a number of factors, the size of the bubbles, the number of bubbles & the location of the bubbles.
Pockets of localised air in the cooling loop of the laser tube will lead to a reduction in heat transfer, the larger the pocket of air the lower the efficiency of the loop to cool the specific area.
The laser tube is sensitive to temperatures greater than 25’c with long term irreparable damage being possible. air pockets located in the cooling cavities of the tubes optics, both reflective final mirror and columinating lens can lead to superheating of the optical components. This can cause misalignment due to thermal expansion, this could appear as a temporary side effect whist the laser is excited, or permanently if an expansion has been great enough to disturb the adhesive used to join the components.
Small air bubbles caused by pump cavitation or due to air ingress in the cooling loop are not a huge problem, but overall they are not desirable and should be removed from the system at the earliest opportunity. Not only do they reduce the loops cooling efficiency but also pose the risk of combining into a larger pocket of air.
What causes air bubbles to form in the laser tube?
- Air entering the cooling system via leaking connectors
- Pump cavitation
- Air not being removed during initial setup
How can we prevent bubbles from forming?
The cooling system should be a self bleeding closed system
- Ensure all hoses are air tight to prevent air ingress
- Use the same diameter hoses throughout the system
- Do not use restrictive connectors or joints to extend hoses
- Ensure the water return hose is under the water level of the reservoir to prevent splashing, and oxygenating the cooling medium.
- Make sure no hoses are kinked or have tight radius bends.
How can air bubbles be removed from the system?
Once you have followed the steps above to ensure your system is a closed self bleeding loop you should only have to bleed the system once.
- To remove large air bubbles you can either wait for the bubbles to disperse naturally, sometimes this will not work with large bubbles in the optical cooling chamber. Or you can tilt the laser tube or machine to help the bubbles exit the tube.
- Rotating the laser tube so the water exit is the topmost point of the cooling loop, this will prevent air bubbles from being able to form around the reflective mirror cavity.
- Pinching the water cooling tubing to create a pressure differential. Upon release the bubbles should surge towards the exit.
- Using a high flow pump is a must, aquarium style pumps with insufficient flow rates sometimes will not have the pressure required to move stubborn pockets of air.
- Reducing the surface tension of the cooling water is a last resort as it adds impurities to the cooling loop, but it is highly effective for removing smaller micro bubbles. Surface tension can be reduced by adding one or two drops of chemical safe dish soap. The concentration of the soap is very low, and can be reduced by dilution with fresh distilled water at a later point.
So to recap you must first ensure the system is a closed loop, follow the steps to remove air and then maintain. Check before operation for leaks, check the tube for air bubbles and most importantly, MAKE SURE THE PUMPS ARE OPERATIONAL.