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  1. #1
    Join Date
    Mar 2003
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    6855

    water cooling

    OK I getting all the rest of the stuff I need for my laser, does anyone see a problem with using a 600 gal/hr pump? Is that too much pressure for a sealed co2 laser? Usually I see people using a 500 gal/hr pump.

  2. #2
    Join Date
    Jun 2003
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    1365
    Paul, the galons per hour does not relate directly to the pressure, or relate much to the pressure at all. I have a pump thatll put out 350gph with a max of 2psi(wont put out full 350), and another that will put out about 60gph at max of 40psi. so basicly it depends on the pump. What pump is it that your using? what are the components made up of?(aluminum, steel, copper etc.) It is always best to keep the materials in a water system the same so they dont corrode.

    I dont knwo what kind of backpressure those components have, so depending on that you could have your choice of many pumps.

    Jon

  3. #3
    Join Date
    Feb 2004
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    2337
    If in any doubt you can always put a T join in the hose between the pump and the laser. Put a tap on the T so that you can adjust the presure.
    But as Jon said, it really depends pressure of the pump and not on the flow rate.
    The resistance of the presure in the laser is also a consideration.
    Being outside the square !!!

  4. #4
    Join Date
    Mar 2003
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    6855
    Here are the sepcs on the one I bought Eheim 1260 Pump - Centrifugal pump # Pump Output: 635 gph # Delivery Head: 12`1"

  5. #5
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    Jun 2003
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    1365
    That eheim pump is one of the bigger ones I believe, It should be fine, just make sure to use hose clamps. Im sure the components are made to withstand more pressure than that.

    Jon

  6. #6
    Join Date
    Apr 2003
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    42

    International units for water flow

    While I had the covers off of the 40 watt Coherent surgical laser, we read the specs on the coolant pump.(laser units manufactured in Hull, England, with a Japanese coolant pump no less)

    The coolant appears to be water with typical ethylene glycol, (antifreeze),

    The coolant pump shows 3 numbers for flow, indicating three conditions....(lots of specs for medical equipment)
    "MAX FLOW 11/12/11" liters per minute (1 liter ball parks with 1 quart, so 3 gallons per minute, just approximate)and "HEAD 1.5/2.1/1.5 m" , taken to be "m" for meters.

    so, different output for the laser and different units, with unknown coolant (until I get documentation)

    but at least it is something to compare with for a commercial unit, once you break out the calculator.

  7. #7
    Join Date
    Nov 2004
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    446
    I'd like to break in here to ask a few questions...

    What is so special about this water cooler? If your passing water to cool a beam head, wouldnt you be more concerned with input temperature compared to output temperature?
    Further, would I be correct in assuming that calculating the required flow rate would be to take the rating of the power supply and design to cool that many KW?
    1 Liter of water up 1 deg = 1 BTU.. ??

    Am I on the right track here?

    Murphy

  8. #8
    Join Date
    Mar 2004
    Posts
    564
    Pressure is also subject to the size of the pipe area. use the following formula to guess-tamit your set-up. Pressure, flow, and area are all related in designing hydraulic systems.

    F
    ~~~
    P | A

    Where f= flow (GPM)
    p= pressure (PSI)
    a= area (SQ")of pipe diameter.

    this formula is wrong... I apologize, I've confused it with the formula for FORCE. susbstitue the "F" above as FORCE not flow.
    menomana

  9. #9
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    Mar 2003
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    6855
    The big problem to me is that 30k is DEADLY and you don't need a hose coming off and allowing water to come in cotact with that voltage. No clamps can't be used because of fitting on glass ends. So to much pressure may allow the hose to slip off. That may not even been a big problem. I'm just plaing ahead, as for cooling the water will flow through a radiator with a fan so I will be able to keep the temps down, HEAT is will kill a laser and less it's life.

  10. #10
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    Nov 2004
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    446
    What is the input connection size and the output connection size?

    How many KW is the power supply?

    Do you know the volume of the cooling area? Square inches? Gallons?

    Murphy

  11. #11
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    Mar 2003
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    6855
    Quote Originally Posted by murphy625
    What is the input connection size and the output connection size?

    How many KW is the power supply?

    Do you know the volume of the cooling area? Square inches? Gallons?

    Murphy
    18-30kv, the tube is 50 watts and 55" long and about 2" dia.

  12. #12
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    Nov 2004
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    446
    It doesnt matter how big the tube or the head is..
    About 99% of the energy put into a laser is given off as useless heat.. Your not rating your cooling size on the power of the head.. You need to rate it at the power of the power supply that feeds that high voltage to the head.

    Also, there is a place where the water enters the cooling jacket.. what size are the in and out ports??

    Murphy

  13. #13
    Join Date
    Jan 2005
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    1880
    Another thing to think about too is the flow rate thru the heat affected zone. Move the water too fast and the heat transfer goes to hell (pun intended). So too much pressure isn't the only thing that you have to worry about.

    Michael t.

  14. #14
    Join Date
    Nov 2004
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    446
    Paul,

    Let me clarify what I think you need to do.
    1st. You need to find out how much heat that has to be removed. Knowing that a laser dumps most of its energy into waste heat, lets assume you have to remove an equivelent amount of energy of the thing that powers that laser. (voltage is irrelevant here as you need to know how much power (KilloWatts/Hr) your powersupply is. So lets assume your supply is 480 volts at 25 amps. 480x25=12000 or 12KW.
    So we know know you have to remove a maximum of 12KW which works out to about 40,000 BTU's.
    It takes 1 BTU to change 1 pound of water by 1 degree F.
    You need to know what your inlet temperature is, and what you want your outlet temperature to be.
    A few calculations, and you should be able to find out how many pounds of water that head needs per hour to keep it cool.
    Once you know that, convert the pounds of water into gallons. Once you have gallons, you need to determine how much pressure it will take to push that much water threw your cooling head. A 1/4 inch connector is going to require a bunch more pressure than a 1 inch connector will to get the same volume of water.
    Doing the above should allow you to figure your lowest pressure required so as not to fry yourself in case of a busted line.

    Hope this has helped.
    Murphy

  15. #15
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    Mar 2003
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    Here is anther consideration"As most CO2 lasers have glass tubes, special pumps need to be used to keep the pressure and pulsation low which would break the tube"

  16. #16
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    Nov 2004
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    446
    The pressure I understand...

    What pulsation??
    Maybe I am missing something. Im thinking of a properly sized, close-coupled horizontal centrifigul pump with a closed impeller. I would assume it to be either a polysomething or stainless pump. There should be no pulsation coming from it.


    How many Watts is your power supply to the head?

    Also, if the glass tube is in direct contact with the water, there may be thermal shock considerations. (like the cooling water may need to be pre-heated to a certain temperature before operation) Cold water and warm glass dont mix well..
    Are you required to "warm" up the lazer before using it? As the head warms up, the beam will actually moves around until things stabilize thermaly. I dont see this being a problem if your work piece is only a few centimeters away and your tolerances are large, but for long range calibrations or precise meausurements, our heads had to run for at least 10 to 15 minutes before it would stop walking on us.

    What about the power supply ? How is it cooled?

    Murphy

  17. #17
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    Aug 2004
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    2849
    Well you could add a pressure sensor that would open up a bypass valve...or you could just add an adjustable bypass valve and adjust it without power up the tube....

  18. #18
    Join Date
    Apr 2003
    Posts
    42

    water and numbers

    Murphy and others have brought up some good specifics as far as actual cooling needed and they have introduced the quantitative aspects of the cooling operation.

    Since many formulas show up in some laser tutorials we have been struggling through, I thought that it may be important to mention that CO2 sealed lasers are more efficient than others. SAM's mentioned 5% to 8 % efficient being normal for CO2 lasers and that other gas lasers are not as efficient. That means less heat is given off than if they were throwing 99% of the energy off as heat. (The flowing gas ones are supposed to go up to 20 % efficient, but few hobby folks will probably be messing with those.)

    At some point, the difference between 8% and 1% might change calculations enough to change some characteristic of a pump, or coolant design. I would not know for sure, yet.

    On the 40 watt sealed tube laser we have, the recirculated coolant IS channeled into the very heavy duty power supply as well. The input starts out as 110 volts AC. (The design and manufacture is British, so they were not thinking of JUST 110 volts to start out, as the laser does here in the US.)

    Can you imagine a leak in such a system??

    Just thought to share how one commercial product deals with the heat problem and the possible value of dealing with actual numbers in design.

    Number crunching might be better than glass crunching...

    Marc

  19. #19
    Join Date
    Apr 2003
    Posts
    42

    Red face Ignorance strikes again...

    I can get away with flaming myself, right?

    We were not getting any leads as to pin outs or schematics, so we hauled the laser into a lot more light, and pulled panels off...

    We found that the large hose going INTO the power supply was not only mixed in with the coolant hoses, but was actually a RF lead coming OUT of the power supply...
    give aways were the "gaskets" made from the shielding left when the core of shielded wire is pulled out....there were lids on boxes with lids inside the massive power supply....and lots of RF shielding. MUST BE A BIG CLUE AS TO JUST WHAT KIND OF STIMULATION IS USED, HUH?

    I apologize for the mistake that coolant was pumped INTO the power supply.
    It is amazing what happens when one turns on the light.

    just which smiley icon is the sheepish face ??
    Marc and boyz

  20. #20
    Join Date
    Nov 2004
    Posts
    446
    Quote Originally Posted by Marc Soren
    I apologize for the mistake that coolant was pumped INTO the power supply.
    It is amazing what happens when one turns on the light.


    Marc and boyz
    Are you suggesting that you have never seen a power supply with coolant going into it?

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