[Gray Wolf]

Originally Posted by WaterFarmFan

After a quick ponder of using 190 proof alcohol next to motor with open slots spinning at 3500 RPM, I decided that some basic precautions were in order. First, I secured the pump and raised it ~2" on a footer board to be more inline with the reservoir output. With a bit of spare aluminum sheeting and some foil tape, I made a covering that should prevent any accidental etoh from directly entering the motor.

I need to properly secure my hose fittings, but it is ready to test, and I will be straight to a torture test of 4-6 hours at -78C. If it is going to break/fail, I want it to happen sooner than later.

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How pump motor cooled? If it is a TEFC, the cooling air isn't in contact with the electrical.

[WaterFarmFan]

Hey GW. Not sure how it is technically cooled, but I can see lots of copper through wide slits along the back, and there is a fan at the very end to blow heat away from unit.

I did do some testing over the weekend, and it was not a success, but the pump did not fail (yet). The simple answer is that this pump is a bitch to prime. I had etoh with dry ice chilled down to -75C, but it simply would not prime. It would cycle 10-20ml every time that I turned pump on, but that its, and it would bubble after shut off indicating not being primed. The -75C temps did not seem to impact pump versus -50C.

My solution is to raise the reservoir around ~18 inches and really create some pressure that will force any trapped air to clear pump and thus prime. Need to be confident in my fittings to avoid leaking. Will pick up more dry ice and test tomorrow.

[Gray Wolf]

Originally Posted by WaterFarmFan

Hey GW. Not sure how it is technically cooled, but I can see lots of copper through wide slits along the back, and there is a fan at the very end to blow heat away from unit.

I did do some testing over the weekend, and it was not a success, but the pump did not fail (yet). The simple answer is that this pump is a bitch to prime. I had etoh with dry ice chilled down to -75C, but it simply would not prime. It would cycle 10-20ml every time that I turned pump on, but that its, and it would bubble after shut off indicating not being primed. The -75C temps did not seem to impact pump versus -50C.

My solution is to raise the reservoir around ~18 inches and really create some pressure that will force any trapped air to clear pump and thus prime. Need to be confident in my fittings to avoid leaking. Will pick up more dry ice and test tomorrow.

If you can see into the pump windings, it isn't a Totally Enclosed Fan Cooled (TEFC) motor. That is what the one pictured appeared to be. They have fins on the outside of the motor and fan is on the back end of the shaft, outside the motor, blowing air down the fins.

If you set your reservoir higher and your pump low, you can increase the head pressure on your flooded section pump.

[HashoftheTitans]

Originally Posted by WaterFarmFan

Hey GW. Not sure how it is technically cooled, but I can see lots of copper through wide slits along the back, and there is a fan at the very end to blow heat away from unit.

I did do some testing over the weekend, and it was not a success, but the pump did not fail (yet). The simple answer is that this pump is a bitch to prime. I had etoh with dry ice chilled down to -75C, but it simply would not prime. It would cycle 10-20ml every time that I turned pump on, but that its, and it would bubble after shut off indicating not being primed. The -75C temps did not seem to impact pump versus -50C.

My solution is to raise the reservoir around ~18 inches and really create some pressure that will force any trapped air to clear pump and thus prime. Need to be confident in my fittings to avoid leaking. Will pick up more dry ice and test tomorrow.

Good luck getting it to prime when the alcohol is carbonated. The CO2 bubbles will make it next to impossible to prime. I use a chugger pump to push ethanol through a coil submerged in dry ice and alcohol. It takes longer to get down to temperature but it keeps those pesky bubbles out of my coolant.

[WaterFarmFan]

Originally Posted by HashoftheTitans

Good luck getting it to prime when the alcohol is carbonated. The CO2 bubbles will make it next to impossible to prime. I use a chugger pump to push ethanol through a coil submerged in dry ice and alcohol. It takes longer to get down to temperature but it keeps those pesky bubbles out of my coolant.

Now that makes some sense about the co2 bubbles. Will try to see if additional head pressure can overcome it. Thanks.

[HashoftheTitans]

Originally Posted by WaterFarmFan

Now that makes some sense about the co2 bubbles. Will try to see if additional head pressure can overcome it. Thanks.

Put a lid on whatever vessel you are using to mix the dry ice and alcohol, and the CO2 will give you whatever pressure you need. However, that is only good for filling your column, not continuously recirculating, which you need to get down to temperature. Trust me on this one. All you need is a 1/2" x 50' coil, a chugger max pump, igloo drink cooler, and dry ice. This will get a 6" x 48" jacketed column down to -40 easily.

[WaterFarmFan]

Originally Posted by HashoftheTitans

Good luck getting it to prime when the alcohol is carbonated. The CO2 bubbles will make it next to impossible to prime. I use a chugger pump to push ethanol through a coil submerged in dry ice and alcohol. It takes longer to get down to temperature but it keeps those pesky bubbles out of my coolant.

+10 for HashoftheTitans on this comment! It is indeed the c02 bubbles that cause the issue with the chugger pumps, and not temps or viscosity. I raised my reservoir about 15 inches and it gravity primed instantly by flushing out the air. I had the pump running and as soon as I added the dry ice, it began sputtering. Raising the pump had a significant impact, as even with the co2 bubbles at ~-70C with 3 foot head, the pump put out a constant sputter (previously it would sputter at the very beginning and then stop).

My application is quite different then yours, in that I need a smaller amount coolant to be as cold as possible (for glass coiled condensers), instead of a large volume for bulk heat transfer. There are quite a few ways to accomplish my objective by tweaking the parts that I have. I could add a coil or another 2L reservoir that sits inside my existing 6L, which would be surrounded by dry ice/etoh but only pure etoh in 2L with no c02 bubbles.

[WaterFarmFan]

Originally Posted by HashoftheTitans

Put a lid on whatever vessel you are using to mix the dry ice and alcohol, and the CO2 will give you whatever pressure you need. However, that is only good for filling your column, not continuously recirculating, which you need to get down to temperature. Trust me on this one. All you need is a 1/2" x 50' coil, a chugger max pump, igloo drink cooler, and dry ice. This will get a 6" x 48" jacketed column down to -40 easily.

Your comments on pressure had me thinking. I could very easily just use some glassware that have - a heavy wall boiling flask with long stem dual 10mm take off adapter submerged in dry ice/etoh. Boiling flask would be full of pure etoh and the pump would pull from the bottom of the flask via the long stem. Take off adapter would be secured to flask with stainless clamp. Would this closed loop setup cause back pressure to help force the fluid to the pump? Would the pressure be too much for the glassware? Thanks for your input!

[WaterFarmFan]

I decided to do a bit of re-engineering. I ordered some parts, including fittings, bendable copper tubing and a stainless bain marie. I am going to shape my own coil to fit in my reservoir, and bain marie will sit in center of reservoir surrounded by dry ice and etoh. Coil will start at my top bulkhead and gravity feed down to bottom of bain marie. An output on the other side of bain marie will connect to my existing lower bulkhead and go straight to pump. Logic is that the coolant will pre-chill in coil and get as close to -78C as possible at the pump head. This setup will hold ~1L of pure etoh that will not come in contact with any dry ice. More soon...

[WaterFarmFan]

I have my coil shaped and all the new parts and fittings. Time to get her put together and tested.