Cooling Silent Pump For Water Cooling

Hey Everyone,

I have been a "viewer" of this site for a long time and I guess I finally need the community's help. I am currently working on a setup using high powered LEDs (about 180W) and need a way to cool them. The idealistic solution would be completely silent (no fans) and I thought of two possibilities: passive water cooling, or just plain passive heat sinks. The LED chipset is 12mm by 12mm which means that any CPU heat sink will fit (mounting is not a problem). My big question is if there is some sort of SILENT water pump (I heard about a magnetic bearing pump I think?) that would be able to sufficiently cool this chip. If not, what type of CPU heat sink would you recommend that works best without a fan. Thanks a lot!

 

There are plenty of "quiet" pumps the Laing D5 is variable, but something like a Thermalright HR-01 was developed to run fanless along with the Sycthe Ninja. 180W is quite a bit of heat for a passive heatsink though. The Zalman Reservator 1 should handle the heat load better but it's more expensive just to cool an LED assembly down.

 

How many of these are there to make up 180W? And how are they laid out?
180W is a lot to get rid of, I think passive cooling might not be an option, unless you have massive heatsinks. You're surely looking at a good heatsink and fan, or perhaps even a watercooling loop.
The D5 is a pretty decent pump and you can get good flow for very little noise.

 

DDCs are also very quiet indeed. If you're after a completely passive solution I'd suggest knocking up something with a couple of heatpipes going to a very large extruded heatsink plate.

Is this a private or commercial project?

 

Thank you very much for all of your insight. By the questions you asked it seems I have not explained very well, so I guess I'll explain more (as some info is new to me). I am an engineering student and our design project is to create a stage light using high powered LEDs. The TOTAL power for the system is 180W, but we are using 3 LEDs to achieve this, so each LED is about 60W (which is far more reasonable for a passive heat sink). As of right now it seems the water cooling set up is far beyond our budget so ideally a completely passive set up will be used. After a few calculations regarding our chipset, we determined our resistive value for the heat sink needs to be at least 0.85 degrees C/W (my heat transfer is awful so this doesn't mean much to me). Does the scythe ninja or the thermalright sound like a viable solution now? Thanks again.

 

D5's are pretty silent but there are some even silenter (if that is a word)

 

DTek DB1 / DangerDen CPX1 (same thing) is the quietest 12v dc pump around at the moment... but is severely behind the DDC3.2 and D5 in the performance stakes... however, this translates to around 0.5 deg C difference with a single block'd loop and around 150w of heatload.

 

How long will the light have to be on for? If it's for stage use then potentially you could rely on thermal inertia to keep it cool for the periods of time it's on for.
Aluminium has a specific heat capacity of 900 J/kg.K, so a 1kg block will heat up by 12 degrees Centigrade per minute. That's probably a bit much as it only gives you 5 minutes of use before you have to let it cool down all the way. Water is a better bet with a specific heat capacity of 4200 J/kg.K - a 1 litre tank of water will heat up by 2.6 degrees centigrade per minute, giving you about 20 minutes before you run out of temperature headroom. All you really need for that is an aluminium tank heatsinked on to the back of the LEDs.

What is the maximum operating temperature of these LEDs?

 

If you're on a budget I'd say go for a near-silent HSF setup (from a PC) - something like an Arctic Cooling cooler is really cheap, but still works nicely.

 

60W is definitely more reasonable for air cooling. Im not sure you could run a heatsink on that completely passively, but you'd be fine with a fan. As Krikkit said, a decent, quiet HSF like an Arctic Cooling one would be pretty good. You'll have power running to the LEDs anyway so you should be able to power a fan as well without too much problem. I assume the LEDs are seperated so you have 3x60W to cool, rather than having to remove 1x180W all from one place. Air cooling of some kind is gonna be so much cheaper, easier, and less risky. Particularly if you're on a budget, I think it's your only option. Please let us know the max operating temperature though

EDIT: An Arctic Cooling Freezer 64 is 0.18C/W and is rated upto 130W. If I'm correct, it should run at about 10C above ambient with a 60W load; say 32C given normal room temp. This is probably with the fan at full speed. With any luck there'll be someone who knows more about this sort of thing to check this!

 

Hey guys sorry about the delay in response, but other aspects of the project took priority this past week. Unfortunately I am not very good with words so I have uploaded a picture at http://people.bu.edu/tstahl/Light Mount.png. There are three separate LEDs (all modeled in green but are actually: one red, one blue, on green) each mounted to an enclosure (the blue and yellow thing) that holds the lens (the red thing). This means that I would need 3 individual heat sinks or 3 individual water blocks (not sure how they would need to be looped or if they needed separate lines).

The red LED has a MAX operating temperature of 80 C and uses 38W of power. The blue LED uses 65W of power and has a max operating temperature of 120 C. The green LED uses 63W of power and also has a MAX operating temperature of 120 C.

As it being a stage light the time on will vary, but expect it to average a fairly long time (~ 1-2 hours) with of course much longer and much shorter run times (just like a processor).

As far as the fans go, yes there are some very quiet ones out there, but being a stage light I want to try to avoid fans if at all possible. I am willing to spend the extra money on a water cooling set up if it means have a quieter system (being a senior design project budget is a concern, but to meet the requirements money must be spent ).

This caught my attention. So you are saying to make an aluminum (even copper) water reservoir with fins and mount it to the LED like a heat sink. Is this how it works: the tank will transfer the heat to the water, thus heating it, which will be dissipated by the fins? So the drawback is that it can only stay on for a certain period of time before the water will boil. Interesting concept, perhaps we can expand on that.

Also, would using heat pipes to move the heat elsewhere be of any use? I know that the pipes need to be oriented in a certain way for the capillary action to work and, being a stage light, this thing will be moved around in all different orientations. If the heat pipe is mounted upright, then even if the angle changes by 15-20 degrees will it still work?

Again thank you for all of your help on this and sorry to be such a bother. I'll keep you posted with any new information.

 

OK, some assumptions here. All three lights will be on for a maximum of 3 hours, and the whole unit can't go above 80 deg C - so whatever you heat sink it to can't go above 70 deg C. Total system power draw for all three lights (i.e. combined into white light) is 166W.

1 Watt is of course 1 Joule per second, so over 3 hours the light will have 1.8 MegaJoules of heat to be removed. Thermal capacity of water is 4.2 kJ/kg.K, and you're operating at no more than 50 degrees above ambient. Thus, 8.5 litres of water will be sufficient to ensure good enough cooling (theatre lights are likely to be left off for long periods between use). I'm not totally sure, but I suspect that a total weight of 10kg is likely to be acceptable, particularly as this would be a totally silent cooling system.
Boiling off the water would be a bad idea - lights tend to be mounted quite high up, and taking them down to refill them regularly would not be popular. You would need to make a sealed tank for this reason.

Some data on the effect of gravity on heat pipes here: http://www.heat-pipes.co.uk/index.php?sectionid=7

Seperating out the three LEDs thermally may be a good idea. Doing this (and assuming 20 deg C ambient), the Red LED needs a thermal resistance of 1.8 deg C/Watt, while the Green and Blue need an efficiency of 1.5 deg C/Watt (i.e. marginally better cooling). Off the shelf passive heatsinks are more than capable of this - for example this one here - http://rswww.com/cgi-bin/bv/rswww/s...migmelkicefeceeldgkidhgj.0&cacheID=uknetscape
(if the link is dead, go to www.rswww.com and type in part number 507-5194 ). One of these for each LED will take up a space 120x300mm, and provide more than enough cooling. They're also light and cheap (under $40 for three).

In other words, off the shelf passive heatsinks provide more than enough cooling if the Red LED is kept seperate from the Green and Blue ones (which both consume more power and are happy to run hotter). This is much, much better than any more complicated idea - cheaper, much easier to build and far less to go wrong.

 

What kind of LED are you using? This is totally unrelated to the cooling, but I was under the impression that the most powerful you could buy was 5 watts, so I'd like to see what you've got.

If your LED is actually an array, consider spacing them out slightly more so you have more contact area for the heatsinks. Also, remember that most desktop processors on the market today are capable of producing between 60 and 130 watts, so if you can keep things separated into sections producing less than that, anything that would work for a modern CPU would work for your light.

 

PDF, thank you very much for all that input. I'm not sure if you saw the picture I posted, but I am confused as to what you mean by "kept separate". Each LED is positioned at a different point on the lens (keep in mind though that the lens is very small: its over length is only 70mm for reference), so did you mean a separate heat sink for each, or did you mean to make different compartments to keep the air temperature from mixing?

Also, I am not sure what values you used in your thermal resistance network (assuming that is what you used), but to help you and answer crazybob's question, the data sheet for the LEDs can be found here: http://www.luminus.com/content1092. Our initial calculation for the thermal resistance showed up at a more difficult to manage 0.90 degree C/W.

The only concern I have for the heat sinks is that they need to be mounted in a very small area (as you can see by the picture). Also since these LEDs are point sources of heat that do not take up the whole thermal contact area of the heat sink, will the heat sinks performance be reduced? Again thank you.

 

By kept seperate I meant thermally seperate. The problem you've got is that if you try and cool everything as a block then the whole block is limited to the maximum temperature of 80 deg C of the red LED. However, if you split the unit in two thermally (i.e. the blue and green LEDs don't heat up the bit with the red LED in it, and vice-versa) you can run it at two different temperatures - the red at 80 deg C and the blue/green at 120 deg C.

I think I'm starting to understand now. The three green bits in your drawing are individual PT120 devices, and the blue/brown/red bit is presumably some form of lensing arrangement. If so you'll almost certainly have to use some form of heatspreader (either a solid block of aluminium or - preferably - a set of heatpipes) to move the heat from chips to heatsink.

The heatsinks I linked to are designed for cooling electronic components, so the chances are the value of deg C/Watt quoted will be for a point heat source. Expand the contact area and performance should improve.

Based on what I know at the moment, I'd go for three passive heatsinks with a performance in the region of 1 deg C/Watt, attached to the LEDs by some fairly chunky heatpipes (say 8mm diameter or so - depends a bit on performance).

One final comment - the Tmax temperatures you have (80 and 120) are the maximum permitted sustained temperatures for a given lifetime (IIRC usually 10 years continuous use for electronic components, although you are likely to know this better than me). The maximum transient temperatures are 125 and 150 respectively. In a device which is only going to be used for a few hours a day, your required lifetime is correspondingly shorter so you may well be able to operate substantially hotter than Tmax...

 

DDC, 10W - you can always do a mod and make it 18W...
Or you can buy any pump and use fan controller to control the speed...

 

DDC or D5 - the one with speed control - all you need to do is to put some rubber pad or foam under and it will be silent.