Homemade Copper Thermowell, "To Grease" or "Not to Grease"?

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joeymac
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Homemade Copper Thermowell, "To Grease" or "Not to Grease"?

Post by joeymac »

I've done some HD searches for greasing thermowells and found differing responses. I even saw a recommendation for glycerin :|

I put together a copper thermowell by soldering some 3/16" tubing to 1/4" tubing and capping the end with silver solder. I then used a piece of 5/16" Teflon FEP tubing to slide over part of the 1/4" copper tube. This is VERY tight leakproof fit and the temperature port on my copper column is a little 1/4" copper stub. So my thermowell slides right into the hole on the column and seals when you press the teflon tube up onto it. Easy.

I have an Omega K-type Thermocouple that slides into the thermowell all the way to the end. I plan to use some heat shrink or a dab of hot glue to keep it securely in place. What i don't know is should I put some sort of thermal grease in there first like Arctic Alumina (heatsink grease), or some other kind of grease that is safe for copper/solder/thermocouple? Or no grease at all? I'm hoping to minimize lag times if possible becaust I'm running an LM reflux column, so temperature responsiveness is very critical.

I actually got my inspiration from this thread a couple years ago:
http://w.homedistiller.org/forum/viewto ... =2&t=47618" onclick="window.open(this.href);return false;" rel="nofollow
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Last edited by joeymac on Tue Jan 24, 2017 8:57 am, edited 1 time in total.
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still_stirrin
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by still_stirrin »

Maybe an "instrumentation guy" will chime in here...but I think you're nuts!
ss


edited to add- If you want accuracy on your thermocouple, eliminate the thermowell all together. Stick the thermocouple junction IN the vapor path. And plug the 1/4" hole with flour paste.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by rad14701 »

Temperature change response will be mush faster if you can bypass the thermowell as still_stirrin suggested... But this would only be possible if you have a stainless steel probe which doesn't appear to be the case by checking the pictures... Perhaps you could get one with a probe for better reaction times...
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by joeymac »

still_stirrin wrote:Maybe an "instrumentation guy" will chime in here...but I think you're nuts!
ss


edited to add- If you want accuracy on your thermocouple, eliminate the thermowell all together. Stick the thermocouple junction IN the vapor path. And plug the 1/4" hole with flour paste.
The thermocouple is covered in PVC. I would think that's no bueno for being in contact with hot distillate. And even without the PVC insulation, isn't one of the metal wires in a k-type an alloy of aluminum or something?
"Woe to those who are heroes at drinking wine and champions at mixing drinks" - God (Isaiah 5:22)
So evidently, God wants us to drink our whiskeys single barrel and our Bourbons neat.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by joeymac »

rad14701 wrote:Temperature change response will be mush faster if you can bypass the thermowell as still_stirrin suggested... But this would only be possible if you have a stainless steel probe which doesn't appear to be the case by checking the pictures... Perhaps you could get one with a probe for better reaction times...
The stainless probes and thermometers are the same thing, no? Just a thin SS tube with the thermocouple wires inside the tube and some sort thermally conductive potting compound at the end that junction sits in.

In the past, I just used a stainless digital food thermometer in the past shoved through a cork bung. My line of thinking here is that perhaps the 3/16" copper tube will work just as well as the 1/8" stainless tube of thermowells because copper is way way more thermally conductive. And then I can have remote temp readout down near me instead of a thermometer 6ft up in the air on the column.
"Woe to those who are heroes at drinking wine and champions at mixing drinks" - God (Isaiah 5:22)
So evidently, God wants us to drink our whiskeys single barrel and our Bourbons neat.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by still_stirrin »

Yes, as Rad said...Joey, you need the "probe-style" TC.

This is the ones I use: http://www.omega.com/pptst/88000_Insert_surf.html" onclick="window.open(this.href);return false;" rel="nofollow. The 88306 model (I have 4 for my 4-channel digital thermometer). Not cheap...but you're the one who wants to run by temperature, right?

I rarely use mine anymore, because operation is so predictible. I can tell when I'm coming online by the touch. And I don't need to know the vapor temperature to make cuts...I use my senses for that. Purity....I have a Proof & Traille hydro for that.
ss
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by joeymac »

Oh I know about omega pricing ... :lol:
My temp readout is an old Omega DP116, the TC is an Omega K with 3m wires and my panel connector is even an Omega mini-k plug. I actually already HAD the omega thermocouple stuff so it was free to use. I was not thrilled about possibly buying new omega probes or a regular stainless thermometer with remote readout. So I built this because I already the copper and stuff.

But Like you mentioned, I guess I don't really need temperature readout that is all that responsive... being an engineer by trade I just like the technicality of things.

I think I'll could dig out my old digital thermometer and a cup of ice water to do a side by side responsiveness test of the omega thermocouple bare vs. in the new copper thermowell thermocouple along side a typical stainless digital thermometer. I'll post results.
"Woe to those who are heroes at drinking wine and champions at mixing drinks" - God (Isaiah 5:22)
So evidently, God wants us to drink our whiskeys single barrel and our Bourbons neat.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by Danespirit »

No to be a nay sayer...but the tip with the stainless steel one directly in the vapor path is excellent..!
You can get such a K-type probe on E-bay without ripping a hole in your pocket. You also get a compression fitting thrown at you for almost nothing.
I also used some of them for another project of mine, they seem ok even for a china product.
Now..the way I've put my thermometer in my VM still is like this:
Use a stainless steel compression fitting like the one in the picture below (a 6 mm one accepts the probe+tape). Give the probe a couple of wraps PTFE tape and tighten it carefully.
As there is no pressure in a still, this method creates a sufficient seal. Mine has held the probe for several years now, without leaking. :idea:
Compression fitting, stainless steel.
Compression fitting, stainless steel.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by skow69 »

FWIW I have read that mineral oil is a good thermally conductive medium to use in a thermowell, but I have no evidence. Maybe you could include that in your test. It's all just conjecture until you can quantify it.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by rad14701 »

Copper filled with either grease or mineral oil would be nowhere near as responsive as a thin walled SS probe... Just sayin... It's your still... Do as you please but I'd go with a SS probe if it were me...
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by shadylane »

I've stuck a thermometer in a thermowell, and also stuck the thermometer in direct contact with the vapor.
The thermowell was better at measuring the temp of the copper :oops:
Having the thermometer in the vapor, was better at measuring the temp of the vapor :lol:
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by joeymac »

Experiment Results:

I got a glass of icewater (exactly "0" degrees C) and a glass of hot water ("Ouch" degrees C). Then I got my Omega K thermocouple and my kitchen stainless probe digital thermometer... the kind you get for $10-$15 at any grocery store. I've used in the past in my column and it's very accurate. Reads 0 at freezing and around 99 at boiling (1000ft alt.).

I looked up a table for things I could use as a heat transfer medium inside of the copper thermowell and decided on... water. Check it out, water is over 4X more thermally conductive than mineral oil (also known as transformer oil). It's actually the highest rated thing on the list that's not dangerous. http://www.engineeringtoolbox.com/therm ... _1260.html" onclick="window.open(this.href);return false;" rel="nofollow

Method: The kitchen stainless thermometer was the control instrument. I held it in a glass of hot water about 65+ degrees C along with the competing thermocouple until they stabilized to the same temperature. Then at the same time I placed both into the ice bath and observed the race to zero degrees. I repeated a few times to verify the results.

1) Stainless Thermometer vs. Bare Thermocouple
The stainless thermometer was fast. It went from hot to less than 1 degree C in a matter of 10 seconds and took maybe another 10 to slowly trickle down to ZERO. So 20 seconds total for the stainless. The bare thermocouple was significantly faster. It took maybe 5 seconds to get under 0.5 degrees and another 5 seconds to get to zero. Well, I don't want to put a pvc/aluminum/chromel thermocouple in my product vapor path so this doesn't help much.

2) stainless thermometer vs homemade copepr thermowell (dry)
Again, the Stainless raced under 1 degree in about 10 seconds and took another 10 to register 0.0C but the dry thermowell lagged pretty notably. In about 10 seconds the copper thermowell was only at about 5 degrees when the stainless thermometer was at 1 degree. And the dry copper thermowell took probably another 25 seconds to stabilize only to about 0.2C degrees. As it turns out, the fact that I was holding the base of the thermowell must have been conducting heat down into it. To get it to reach 0.0C I had to submerge nearly the whole thermowell and not touch it. After that, the copper thermowell would consistently reach 0C in about 35sec in the ice water (as opposed to about 20sec for the stainless thermometer). Overall, it is about 1/2 as fast as the stainless probe.

4) stainless thermometer vs homemade copper thermowell (water filled)
This was interesting. The stainless probe thermometer got down to about 1-2 degrees C just a couple seconds quicker than the water filled copper thermowell, but the copper thermowell made it to 0.0C more quickly. It not oly caught up to the stainless thermometer but passed it in the race to 0.0C degrees. It didn't win by much, maybe only a second or so, but it's like it just kept motoring towards 0.0C while the stainless probe would slow way down for that last degree. This was repeatable several times and I did not expect this. Also, I was able to maintain hold of the base of the copper thermowell this time without adversely influencing the readings. I could be wrong but I attribute the copper thermowell's slightly slower drop from the high temperatures to the fact that the copper is thicker and heavier than the thin stainless probe tip although it almost does keep up with the stainless probe though because copper is just that much more thermally conductive. And because it is more thermally conductive than the thin stainless, it was able keep moving closer to 0.0C rapidly when the temperature differentials became very minor.

Conclusion:
The stainless probe thermometer is better than the dry copper thermowell. But I do think the dry copper thermowell with a thermocouple inside is still decently usable in a column still. If I get a temperature change indication 5-8 seconds after it happens instead of 2-3 seconds... that's not a big deal so long as it does show the changes. However I do think my copper thermowell with some sort of heat transfer compound inside will be at least as good as a stainless probe thermometer. It seemed to make those small 0.1C changes slightly more quickly in ice bath using only water to fill the thermowell. Perhaps it could be even better with proper heatsink compound inside.
Last edited by joeymac on Wed Jan 25, 2017 10:38 am, edited 1 time in total.
"Woe to those who are heroes at drinking wine and champions at mixing drinks" - God (Isaiah 5:22)
So evidently, God wants us to drink our whiskeys single barrel and our Bourbons neat.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by skow69 »

Excellent information. Thank you. Now I can save the mineral oil for my homemade transformers.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by skow69 »

Come to think about it, transformers is probably where the mineral oil got it's reputation. Since you can't fill a transformer with water, mineral oil probably represents a good balance of dielectric properties, thermal conductivity, and economy.
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Re: Homemade Copper Thermowell, "To Grease" or "Not to Greas

Post by shadylane »

@ joeymac
Thanks for sharing the results of your experiment :thumbup:
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