Super "chilled" ethanol Cooling system for NUBM44. Pic Heavy

Me too - there should be a significant shift in wavelength, and perhaps you can run a room temp and cooled unit side by side. Once you go below 635 nm or so you should be seeing a difference in color, not just intensity.

Even if you cannot collimate the submerged unit, you would be able to see it with the naked eye.

I'd really suggest going for submersion though, not the spiral cooling design you used before. If you do not have a dewar you can actually use a styrofoam feezer box with walls an inch thick or so. This insulated just fine, but you'd have to point the laser upwards to get the light out.

Before going all in with an expensive diode i'd suggest testing stuff with a cheap 10 mW 635 nm diode. You sould get a visible wavelength shift from that, and if the setup breaks it financial loss is very limited.

I did a test tonight to check the conductivity of the ethanol. It's very conductive under a load. This might pose a problem for submersion.

I agree. A DVDs demolition 650mn would be a good start though if I was going to pursue submersion.

Hmm, I have access to a special type of heat transfer liquid called Therminol # ???
Haven't acquired it yet but I can get a requisition this week. The down side is the oil is yellowish and somewhat opaque but it is guaranteed non conductive.
This project will continue after the new year.

Under a 4.1 volt load. (I should have ran a control but this is the only ethanol I have at the house, no distilled water either)


Is it possible the CO2 baths deposited carbon into the Ethanol?
I already know it drastically changed its pH from 7.33 to 5.5.
Something to think about.

How is that very electrically conductive? You're measuring against an open circuit multimeter that has an imput impedance of at leat 1 megaohm, probably 10 megaohms.

If you want to test it, you should put some wires in the ethanol, run 5 volt over them and measure how much current passes through the liquid.

This should not be very much at all. I doubt it would be over a mA in the pictured setup, which is negible compared to the diode current. And is it even -dry- ethanol, or the 96%-ish technical grade, the remainder of which is water? Not that water is that conductive itself, but when CO2 dissolves in it it becomes quite a bit more conductive compared to pure.

I don't think that electrical conductivity of ethanol with CO2 sould be a problem here, but you could add some molecular sieve beads to keep water away if you need too.

Benm said:

If you want to test it, you should put some wires in the ethanol, run 5 volt over them and measure how much current passes through the liquid.

This should not be very much at all. I doubt it would be over a mA in the pictured setup, which is negible compared to the diode current. And is it even -dry- ethanol, or the 96%-ish technical grade, the remainder of which is water? Not that water is that conductive itself, but when CO2 dissolves in it it becomes quite a bit more conductive compared to pure.

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I can check the conductivity how you described.
My thought process was that if neither electrodes were touching and I was getting a reading on the meter the liquid must be conductive.

Or go straight to a cheap diode test.

Many fluids are conductive to a certain degree, especially ones with -OH and/or -COOH groups. But don't over-estimate that conductivity by any means, pure water is actually hardly conductive at all, it just becomes more conductive if minerals are dissolved in it, or it absorbs CO2 from the air making it acidic.

It's all very relative though: Say you had a laser diode that runs at 500 mA, 5 volts, effectively 10 ohms. If the added resistance of the fluid trough all the wires, cases and such is 1k ohm, only 1% would be lost in that.

The best way to measure it would be to submerge the entire thing without a diode present in the fluid and just measure the current. Cold liquid ethanol will probably not be a very good electrical conductor: it's dissociation constant is high, and it's very viscous at low temperatures as well. I doubt it'd conduct more than 0.1% compared to such a laser diode even with quite some exposed wiring.

I like your ethanol build. It has a serious steam punk look. I would carry that further. You might add a thick, soda lime type glass enclosure. This would help to prevent frost build up as well. An interesting property of a hermetically sealed enclosure is that whatever water vapor remains will preferentially condense on the copper tubing leaving the slightly warmer diode and window clean.

I've done a lot of work with super cooled diodes including carrying some down to LN2 temps. The GaN diodes (blue) shift about 1nm/20 degrees C. The GaAs based lasers (red) shift about 0.25nm/degree C. In addition, the efficiency of the red diodes increases about 1%/degree of cooling.

LN2 is really easy to work with. It leaves no residue, is not flammable, costs around $2/liter and it gets REALLY cold.

TECs are nice if you want moderate cooling and your laser will sit for long periods, unattended, but it requires serious waste heat removal which means more power, fans and of course the waste heat will begin working against your goal.

Thanks, CDBeam

The problem with LN2 is mostly availability - not so much cost, as it is indeed inexpensive, but a lack of places you can buy it.

The only way i can get it is to ask friends at the university. They have big dewar tanks with plenty of it and get it delivered weekly or so. A couple of liters won't be missed on such volumes.

The same problem applies to dry ice in the netherlands, but i understand that in some countries it is available from some big stores - probably intended to keep your purchase of frozen foodstuffs cold during transport over larger distances.

Update: I have a meter & thermocoupling to measure this with since I have been able to come home for the holidays.
Here's another idea I had; drilling a small hold maybe 3-4mm deep into the cylinder head close to the diode to function as a sample port for the probe. A dab of Arctic silver 5 should help with conduction.
I have access to LN2 and liquid Argon but no dewer for transportation. I can't even borrow one
Hermetically sealing the unit would prove difficult but is an interesting idea. How would you go about this Planters?
Thanks for the input guy!
Thought this project is not on the back burner I am pretty involved with the Sold State Tesla coil. One at a time or I will be spread too thin.

The dewers are amazingly inexpensive on eBay. If the unit is less than 35L and you're willing to take something ugly (often from a farmer for freezing bull sperm:shhh:, seriously), you can probably find one for $100. Plan to pick it up. Main Oxy fills mine for $2/L.

Sealing it would be very easy if that's all you wanted to do. I would pick up some clear PVC pipe and press fit pipe fittings to the ends with one end cap equipped with a small central hole and covered with an optical window for the laser. The air tightness does not have to be absolute, just pretty good, will drastically reduce condensation. But, to continue with the aesthetics...that's much harder. If you found find a heavy glass tube to replace the PVC pipe and used copper end caps RTV'ed to the glass this would be better.

Don't worry too much about dewars for short term storage and transportation really.

For small amounts, you can easily rely on thermos bottles. Not the new metal ones, but the old fashioned, fragile type. Their construction is virtually identical to a proper dewar, with a double glas flash with vaccuum in between, and usually reflective coating to reduce losses by radiation as well.

Obviously their volume is often limited to something like one liter, but if you need more just get a couple of them, these things cost next to nothing and do a very good job.

One thing to be careful for is transporting them in your car, which goes for both proper dewars and thermos bottles used as such. Nitrogen is constantly evaporating and could impair you as a driver without much notice.

Put the ventillation to max and/or drive with 2 windows open when transporting it. I used to drive between buildings on campus and nearby with those in the car - technically not allowed but sometimes you have to make due.

Just sitting there clamped between the rear seats and and front seat there is no problem, but if you got into a collision and the contents spilled it would be best to have windows open as a precaution. A few liters of LN2 spilling inside a car will drive out all oxygen pretty quickly.

planters said:

The dewers are amazingly inexpensive on eBay. If the unit is less than 35L and you're willing to take something ugly (often from a farmer for freezing bull sperm:shhh:, seriously), you can probably find one for $100. Plan to pick it up. Main Oxy fills mine for $2/L.
The air tightness does not have to be absolute, just pretty good, will drastically reduce condensation. But, to continue with the aesthetics...that's much harder. If you found find a heavy glass tube to replace the PVC pipe and used copper end caps RTV'ed to the glass this would be better.

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Though I prefer MaineOxy over Airgas any day I doubt they would fill a thermos. I tried talking them into filling some med gas cylinders with industrial grade oxygen and they wouldn't budge.
I might peruse eBay for cheap "farmer" dewers and they might fill those. Uncharted territory for me.
Aesthetics is something I'm going for here. A clear sheet rolled around the host might help.
This winter when the air temp is sub zero that might reduce frosting.

Benm said:

For small amounts, you can easily rely on thermos bottles. Not the new metal ones, but the old fashioned, fragile type. Their construction is virtually identical to a proper dewar, with a double glas flash with vaccuum in between, and usually reflective coating to reduce losses by radiation as well.
Nitrogen is constantly evaporating and could impair you as a driver without much notice.

Put the ventillation to max and/or drive with 2 windows open when transporting it. I used to drive between buildings on campus and nearby with those in the car - technically not allowed but sometimes you have to make due.

Just sitting there clamped between the rear seats and and front seat there is no problem, but if you got into a collision and the contents spilled it would be best to have windows open as a precaution. A few liters of LN2 spilling inside a car will drive out all oxygen pretty quickly.

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Great advice Ben, how long do you think one liter would last before it boils completely off? Given the ambiant air temp is 5 degrees Celsius we have that going for us but the efficiency of the thermos would come into play here as well.
If it's <1 hour it would be a tough time crunch.
Venting could be as simple as loosening the cap if the expanding gas didn't compress the cap to the threads; maybe drilling a hole in the top of the thermos would be best.

I might peruse eBay for cheap "farmer" dewers and they might fill those. Uncharted territory for me.

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They asked no questions, I told them no lies. They probably assume that if you are laser cooling, you must be smart enough to use the LN.

My 35L dewer lasts about 2 months if I only use a little. And you're right, its MaineOxy.

I wonder if mineral oil would be good for cooling. Mineral oil isn't electrically conductive and is in fact used to cool computer components in a submerged unit except for the hard drive as its mechanical.

The only thing which may be a problem is that it's a oil so it could screw stuff up. Also, if its contaminated it could be bad.

Just my thought which I wanted to put out there

For cooling to dry ice temps a multi-stage TEC with good heat sinking will get you about 1/2 way there (-38C). Beyond that I would go to solid conductors like thick, short bars of Al or copper from a dry icy holder (Styrofoam box) directly to the diode mount. Beyond that I would use LN2. It's really easy to work with.

I have used a 2 qt Thermos bottle to bring LN2 home. It is the glass
vacuum style. I drilled an 1/8" hole in the cap to prevent over
pressure. You can make LOX using LN2 !!! Be careful with it.
HMike

Down with Umbrella said:

Great advice Ben, how long do you think one liter would last before it boils completely off? Given the ambiant air temp is 5 degrees Celsius we have that going for us but the efficiency of the thermos would come into play here as well.
If it's <1 hour it would be a tough time crunch.
Venting could be as simple as loosening the cap if the expanding gas didn't compress the cap to the threads; maybe drilling a hole in the top of the thermos would be best.

Click to expand...

It doens't evaporate that fast really. If you get a good quality thermos with some insulating styrofoam on the cap it will take several hours to completely evaporate. I'm sure there are differences between these bottles, but if you fill a litre one up in the morning there certainly is some left in the evening.

If you have a 2 litre one i'm quite sure there would still be LN2 left after 24 hours at room temperature.

One thing that is important is to keep it steady. If you have it in a car driving around it will slodge around and cool down the top part of the vessel giving much greater losses. Creating a little vent to prevent overpressure is a good idea. It doesn't need to be large, just a pin-prick will do fine.

As for liquid oxygen forming: that can be a problem indeed. An open dewar can condense some right out of the air, and when the nitrogen boils off you're left with a small amount liquid oxygen. Normally this isn't much of a problem, but if you started the day with a liter in an exposed vessel, the last couple of ml's that evaporate can be rich in oxygen and potentially dangerous - don't use those last drops.