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  1. #21
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    Default water water nowhere

    I have no idea how unusual it is to use liquid cooling in other power supplies. Water has some great and unusual properties, so I am sure that using it in some power supply settings might be in order. Heck, some folks are using it in the cooling solutions for their desk top computers.

    It was a failed attempt on my part to support the idea that sometimes a quantitative approach with TOTAL cooling needs is in order.

    We did find several other methods of cooling when the actual supply was opened, but none too unusual for the size being considered...or so others tell me.



  2. #22
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    Ya.. I was wondering why you had said that..
    I had a rectifier (400vdc @ 500amps) that I was using. This thing had an airplane propeller on the top of the box to draw cool air up from the bottom and over the transformers. The darn thing sounded like an airplane with a turbo prop. Wow was it loud... Never again..
    From now on, anything over 20KW gets water cooling as far as I am concerned. Much more efficient way to cool things, much quieter, less vibration, less dirt intake, bla, bla, bla...

    Murphy



  3. #23
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    Murphy is "spot on" with what he's saying however, if it were my project I'd firstly attempt to get the required product specs for the cooling side from the laser manufacturer (Chinese if I remember correctly). If that succeeds, we (on the forum) will quickly be able to tell you you whether the 600gph can be adapted to suit your application or not. Assuming other similar lasers run centrifigal pumps (i.e. for low pressure applications and they don't pulsate) then if your pump is too big (i.e. too much gph) then you simply bleed off the excess volume (= flow = gph) via a T junction with a tap. (i.e. you're simply dumping what flow (gph) you don't want back to return side). If you can't get the specs then find someone else with similar type of laser (i.e. CO2 x same wattage) and ask them for the necessary details that murphy was saying: (a) pump gph (b) system pressure (i.e. measured between pump and laser head) (c) inlet temp (temp before enter laser head) (d) outlet temp (after laser head but before cooling). Run it back by us and we'll soon adapt that for your situation. Lastly, Murphy said: "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.."
    This is particularly important, find out whether others have some kind of cooling system pre-warmer such as an electrical heating element somewhere in the cooling system to bring cooling water to minimum temperature before starting laser. Or instead of that they may require you to run laser on minimum setting for X time so that the cooling temp water reaches its minimum temp before normal operation can be used. That's probably what Murphy was saying when he said: "Are you required to "warm" up the lazer before using it?"
    Skippy



  4. #24
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    Default cooling stuff

    If it would be of value, we could provide a few things we have learned lately about cooling after using our laser and studying it with the other one.

    Being able to read the comments here and then firing up our laser to see how it correlates with a commercial system has brought home several things we did not consider initially. There are somethings we will implement no matter how much of the commercial system survives our adaptation. Cooling is more important than we initailly thought.

    If it is already among the common knowledge, we don't see the need to document our ignorance by further mistaking it for enlightenment!!

    keep sharing...some of us still learning!!



  5. #25
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    my laser requires 10,000 watts of cooling (pretty close to a carrier used for cooling a whole house). So I recently purchased a neslab chiller like the one shown.

    my $0.02

    owen

    Attached Thumbnails Attached Thumbnails water cooling-hx150aa-jpg  


  6. #26
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    Owen, I was really surprised to read that you had bought a chiller to cool your laser. Is this what other systems have? I don't have any laser experience at all so I don't know what is normal or not. It's just that when you said your machine needs 10,000 watts of cooling, I personally, wouldn't have interpreted that to mean you need a chiller. I don't have a list of heat disipation formulas/equations in front of me so I won't quote specific figures in my example BUT let's say that on your average 40W CO2 commercial/industrial laser, the cooled water (cooled by whatever means) reaches the head at 100 deg.F, leaves the head at 200 deg.F and the pump is operating at say 500gph. (I pulled these figures from the air as I don't have any idea what the ideal temperatures should be). From these figures we can easily work out that we have dissipated X watts/btu/calories of heat. I'm having trouble putting into words what I'm trying to say. If the ideal temperature of coolant reaching the head is not too close to (or below) the ambient temperature (eg. 100deg,F or above) then I would have thought a radiator would be the ideal means of cooling a laser. (In fact if 100deg.F was the ideal incoming temp and you used a chiller which delivered say 40deg.F coolant temp, damage would be sure to occur) If however, the ideal coolant temperature reaching the head is say 40deg.F then yes, it's clear that only a refrigeration device (chiller) will suffice because a radiator system will never drop the coolant temp below ambient temp. I think the important questions are: (A) what are other similar systems using (B) what is the ideal coolant temp as it reaches the head (tube?) (c) how many watts/btu/calories of heat do you need to dissipate. Armed with these three answers, a simple solution can be found to Paul's cooling requirements.
    Lastly Owen, let me state that I am in no way saying that you have done the wrong thing by buying a chiller. You have laser experience and I don't. It's just that I have an inquisitive mind and like to see not only the solution (in your case a chiller) but also the logic behind that solution.
    Skippy



  7. #27
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    Skippy,

    your post is a little choppy, but let me answer by saying the rating
    of cooling was what got from the manual. Its a laser that is
    specifically designed to operate continuously in an industrial setting
    so I view the spec as reliable. People have performed calculations but
    I didnt see the point, the Coherent people are pretty smart folks.

    The other thing I should mention is I got the rating wrong, in that it
    is 10,000 _btus_, and 2500 in watts. I just plain messed up the
    cooling units.

    I know some people just hook up their laser to their house water line,
    and run the hot water into the municipal system. This didnt seem
    practical at 90 gallons per hour, so went with a refriderated system. Your
    suggestion for a radiator was also considered, but I dropped that when
    I found that commonly-sized radiators had a rating of around 500 watts
    and not much more. Radiators with fans pointed at them work great, and
    they scale up well for really large cooling capacity. I my situation
    to get 2.5kW I could have made kind of a pump-house shed or something
    and put 4-6 radiators in there with fans. That didnt seemed
    practical. I have a reasonable amount of disposable income so I'm
    always happy to throw a check at a problem, so I just went ahead and
    got the chiller.

    If I were making a cooling system for a smaller wattage laser, I would
    probably go with a radiator and fan system. They might work just
    fine. The thing about glass tube lasers is that you can run them up to
    their rated temperature, and as long as some heat dissapation is
    happening, you wont break the laser, it will just stop working. So its
    not unreasonable to work by the seat of the pants. A person could just
    buy two large oil-cooling radiators from ebay, hook em up, and see how
    well it works. You'd just want to be prepared to scale-up by a couple
    more radiators if need be.

    owen

    Last edited by owhite; 04-01-2005 at 01:40 PM. Reason: typo


  8. #28
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    Can I jump in again????

    A radiator has only 500 watts of cooling??? I think you got that one wrong..

    I know the engine in my 4x4 truck puts out alot more than 500 watts of power or my gas milage would not be so bad....

    Also, your cooling capacity for a radiator is going to be rated by the Delta-T. (The difference between what is being cooled and the media being used to cool it.)

    If your lazer is pumping out 10KW of heat then your basicaly cooling about 7-1/2 Horsepower. (very easy to do)

    I work with heating and cooling industrial processes quite frequently.. If there is anything I can do to help, I would be happy to assist.

    Murphy



  9. #29
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    well what I know is that I was looking around on the web and I saw a listing for industrial radiators, and they had ratings no greater than 500 watt range. Your right, that was for a certain delta T. I think that the comparison to your truck may not be that apt, in that you have to keep the laser is happiest below a certain temp like 35c. That's very close to body temperature. Trucks operate at higher levels than that. But Its moot because there still is a good chance that a radiator could work just fine, you just may need a battery of them.

    The other point of clarification is, as I mentioned above, I actually dont need 10kW of cooling, its 10,000 BTUs which is 2.5kW. I got confused.

    Speaking of batteries, I think a very sensible solution would be to "store" cool. If you have two 55 gallons of water sitting at a nice cool temperature, you could run a laser for over an hour just by flowing that water through a laser tube.



  10. #30
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    What temperature is the water supposed to be comming out of the laser head??

    If your trying to use ambient room temperature to cool a 100 degF stream of water to 80 degrees F then your going to have a problem.. But if your water is supposed to be 150 deg and your trying to cool it to 130 with ambient air, you should have little difficulty doing it.

    It all depends on your Delta T.. Delta T is everything in heat exchangers..

    Murphy



  11. #31
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    Owen, sorry if my post was a little "choppy" as I was having trouble tying my points together. Hopefully you didn't take offence with my post as my only motive was to understand the logic behind your purchase (chiller) and to promote discussion about this interesting topic. I wasn't questioning Coherant's product or specs either. If it needs 10,000btu cooling then that's that. One of the points I was trying to make (but I didn't say it well) was that 10,000btu of cooling may be required to bring 110deg.C down to 60deg.C and at the same time it also needs 10,000btu of cooling to bring 70deg.C to 20deg.C (these figures aren't exact as I don't have cooling calcs/tables in front of me). Both examples require the same btu cooling capacity BUT you may find that with the first example a chiller won't handle being subjected to 110deg.C at the heat exchanger, and in the second example a radiator can not bring the coolant temp below ambient temp. Hopefully I said that a bit clearer.
    I wouldn't "run the hot water into the municipal system" either as it's ecologically irresponsible behaviour. "I have a reasonable amount of disposable income so I'm
    always happy to throw a check at a problem" I agree as there's not too many problems that money can't fix and secondly, I never cut corners when making something. Why do you suggest "oil-cooling radiators" instead of a normal truck/car radiator? I would be more inclined to horizontally (instead of the usual vertical) mount one or more truck radiators without fans. Vehicles only have fans to minimise the size of the cooling capacity (in this case a radiator) required. i.e. no fan just means a slightly bigger cooling capacity is required. That way your only energy requirement in the cooling system is the centrifugal pump which is not much. "If you have two 55 gallons of water sitting at a nice cool temperature, you could run a laser for over an hour just by flowing that water through a laser tube" That very statement demonstrates how little we are asking of the cooling system in this case. Hmmm! You could easily put that to work with a combination hot water system (switching between laser heat output and conventional electrical element) for your house. Sorry, getting off track! Your statement that "the laser is happiest below a certain temp like 35c" ties in with what I was saying. If in fact the ideal inlet coolant temp is 35deg.C (i.e. close to or below ambient temp) then a refrigerated cooling system is the way to go. If you had said that 70deg.C was the ideal inlet temp then a radiator would be the way to go. I said earlier that it was important to know the ideal inlet coolant temperature (i.e. what we're aiming for) and you are the first to throw a tangible figure (35C) into the ring. Well that's all I have to say. I've been following your progress with your machine in your log and have been enjoying it.
    Paul, you still there?
    Skippy

    Last edited by skippy; 04-01-2005 at 06:18 PM. Reason: addition


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