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.

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

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.

Here are the sepcs on the one I bought Eheim 1260 Pump - Centrifugal pump # Pump Output: 635 gph # Delivery Head: 12`1"

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

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.

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

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.

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.

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

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.

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

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.

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

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"

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

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....

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

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

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?

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.

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

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

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!!

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

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

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

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

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.

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

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