Water Cooling CXA 3070

Okay, so I've done some research on the efficiency of water cooling vs forced air cooling and it seems to me that water cooling is the way to go. I understand active air cooling is usually effective but my decision to go water is based on two things, I already have a few high gph pumps and other equipment used to create a nice water cooling loop, and I want to come as close to the max luminous flux possible with a 1400ma driver, which requires a Tc of as close to 25c as possible, at as low a cost as possible.
My plan is to mount my CXA3070 chips onto a one inch square aluminum tube with capped ends and intake/outtake barbs at either end. My feeling, backed by some research, is that with an increase in barb size I can increase water flow and boost cooling capabilities even though turbulence would be low in a tube. I understand that by using aluminum I limit my ability to use other more conductive metals such as copper in a radiator but this is mainly for proof of concept since I can't find anyone who actually tried it this way and copper tubing like that is prohibitively expensive at the moment if it can even be found.
I will be building a 5 foot length with 5 cobs running off a Meanwell 240h 1400a to test this out within the next week once I can get to the metal shop for some tubing. Any advice in the meantime would be greatly appreciated.
Thanks y'all!

I would not worry about copper. Alum works fine. Amazon delivers AL in many sizes and shapes. Harbor freight sells low-temp Al welding rods. Check out some water cooled posts here. some interesting designs.

Thanks for the heads up Jaybo, I went and got some brass brazing rods to try to join some 90 degree angle aluminum I had into a tube to test the concept but couldn't get enough heat with my propane torch. I assume low temp brazing rods have a different composition than the brass I got? Welding of any sort is new to me. If I can't braze anything with my current torch I might just plug the ends with rubber or something.

Condensation could be an issue with your stated goals. Other than that though shouldn't be a problem regardless of how you remove the heat from the system... less than 150watts...

Also there is no need for a proof of concept. It works. Myself and others on the board have used this method.

Thanks Shugglet, I couldn't find anyone with a journal of a finished project that used hollow bar instead of the Chinese milled cooling blocks. If I understand this correctly as long as my loop temp is above ambient I shouldn't have to worry about condensation right? Even if I manage a Tc of 25c that'd still be above my ambient currently running 500 watts of HPS.
You mentioned a max of 150 watts dissipation, with the plan I have if I did the math right out of the ~250W from the power supply I should have around 175W of heat to dissipate (using the assumption of 30% efficacy from Cree), that should still be fine right?

Propane will work. I have MAPP gas. It is hotter. You might need to pre-heat a large piece of AL on the outdoor grill. Otherwise it is a heat sink and cool off the joint to quick. Could also pack it with sand to hold the heat.
This is an end cap I made from stock AL flat stock and round tubing. The inlet/outlet is offset. In case of a leak. The water will stay in the tube and need to boil off first. You can use a tablesaw and chopsaw on AL. Just cover up. AL shards go everywhere. I used the tablesaw to make the lip that fits into the rectangle 2" x 3" x 4' long. I drilled a hole and put the tubing into it and welded it. If you have soldered wires you should be OK. Clean the parts. Even "pre-tinn" the parts first. Then put together and heat them up. 2- part AL epoxy (auto parts/engine block repair) will also work. This is low pressure. Just water flowing in loop. I sized my tubing to match an extra garden hose I had. That also makes it easy to attach to most water pumps. I have the pump in a large tuff tote filled with water. The return just dumps the water back into the bin.

Interesting build Jay, if I understand this correctly you're mounting your cob on the flat end on the left and the tubing is both your outlet and inlet? I feel like I might be missing something there.
The plan I have would look something like this shitty picture. In case you can't read my writing that's a plate of aluminum brazed onto the end to seal the tube on the left and a theoretical end cap brazed or epoxied on on the right. Which I know should exist but don't know if I can source. I would drill slightly undersized holes for a nylon intake barb at one end and outtake at the other end. Sand down the flat edges of the tube and mount the cobs directly to the tubing.

Side note I think either sand or MAPP or maybe more patience would work for me, in open air with an ambient temp of 70F I got the aluminum up to 400C which if I read the internets right means I was 200C short of the temp I needed after ~20 minutes of heat in one spot.

You need the Harbor Freight Al welding rods. They dont get that hot.
Use the 2 part epoxy if it is not working for you to weld. I used a rectangular tube 2x3x4' and had a cap on either end like the one in the pic. They fit on the ends of the rectangle tube.

Iv been running mine water cooled for 2 seasons now.
Bought cheap ebay blocks and made some plates to mount them to it if you wanted to copy my design.
http://rollitup.org/t/4-site-rdwc-with-res-water-cooled-457w-led-3-5x3-5-wip.925754/



Had a cad drawing for it that I got the local water cutters to cut out for me. Cost $1.50 each.

Hey majins, that's exactly what I was thinking at first. I have a total of 24 cobs I want to hang and didn't want to spend almost $250 for cooling blocks though. I made it to the metal shop yesterday and picked up my 5 foot lengths of tube. I plugged the ends with a hard plastic end cap and marine epoxy. Now I'm deciding how I want to mount my nylon barbs. I'm deciding between using grommets to create the seal and using a tap die set to thread the holes. I've used grommets on all my rdwc and been fine, but this makes me nervous.

Here are some pictures so far.

Thanks Jaybo, I couldn't find metal end caps premade so I went with plastic ones. Hopefully the marine epoxy will hold up.

So far I'm leaning towards something like this built with PVC and sealed to the tube with a grommet and some RTV sealant or silicone caulk. Any thoughts?

I do not use CoBs but I bought a couple of them to try with my system.
Each CoB is driven with a Mean Well HDD-1500 LED Driver. powered with a Mean Well HEP-185-48.
This was a crude test. If I were to go with CoBs I'd use a 1.50" x 0.125" C110 copper Rectangular Bar cut into 4" lengths.
Solder the 4" copper bar to a 1/2" copper water pipe. Use 1/2" ID tubing to connect copper pipes to a "water tower".

• 1" x .062 x 12" $2.77
• 1.25" x 0.125" x 12" $7.42
• 1.50" x 0.125" x 12" $9.89
• 10' Copper Pipe $11.76

I did not want a single point of failure so I use multiple 1 Watt 60 GPH 12V to pump from a "reservoir" to an elevated "water tank".


Top and bottom views





I have since making this one eliminated the 2" PVC "Riser" and the Water Tank was not necessary.
The water moves through the piping as quickly as it is pumped in.
The heatsinks do not take much water flow. 48 GPH was sufficient. I still use two 60GPH pumps.
I can run the pump tubing through the "pillar".
The Water Tank Tee is blocked at the bottom with a PVC 3" to 2" reducer. The OD of the 3" reducer is about the same as the 4" ID.
The 2" end of the reducer faces upwards with a 2" PVC pipe stub. This serves as an overflow and rises above the upper water level.
The reservoir hold 3+ Gallons. The forward stub keeps it from falling forward when placed up against a wall and increases the reservoir capacity.
It will fit in a 2.5 x 2.0 tent.

DrMisunderstood, that looks like an awesome setup, I probably should've gone for copper but I thought it would be significantly more expensive. My 1'' square aluminum tube with .125'' walls was almost $50 for the 20' I got.
Did you have any issues with leakage around the mounting screws in your cobs? I was thinking about using thermal paste and something like the custom piece majins has but with another plate on the other side of the tube instead of on the heatsink. I was also considering using some kind of electrical thermal wrap to hold the cobs in place.
How many gallons are you using total in the tower and your reservoir and how many watts of heat were you dissipating? Also what's the Tc of your COB in this setup? My goal is to get the largest barb I can fit into my bars to maximize flow. Are you using a radiator for cooling of your reservoir?

@QuinndianaJones I avoided 90 degree bends and came out straight from the ends then attached garden hose. It is flexible. I think you can use plastic caps. It is low pressure not much more than water flow. It is:
pump in a large container of water -> garden hose thru AL block-> garden hose-> return to container & pump. You can get thermal epoxy which transfers heat (Amazon). No screws needed. Same stuff used to glue heatsinks on computer parts.

Don't use thermal epoxy. I did that on my first build and made removing cobs a nightmare. 10-15mins with hair dryer and razor blade to get them off my old heat sinks.

I considered epoxy but don't want to deal with removal like majins said. I also think getting those pressure springs and two machined plates would distribute constant even pressure which I've read is beneficial. A couple dollars more than the epoxy for sure, but I can reuse these if I switch to copper pipe to boost my thermal conductivity and avoid any issues aluminum might present, and they're easily removable if I want to mix my spectrum and put in other cobs or have to replace one.