Simple Cold Trap for PEM Cell Deuterium

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Mark Rowley
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Simple Cold Trap for PEM Cell Deuterium

Post by Mark Rowley » Sun Apr 05, 2020 5:15 am

After mixed results with Drierite, I decided to move forward with the cold trap as an alternative approach. After today’s test, I am very pleased with the results. The cold trap improved my neutron output by close to 50%. Using the same power input that normally generates 4000cpm on the CHM11, the cold trap D2 pushed it close to 8000cpm. The neutron output also reflected a corresponding increase with indium activation and BTI bubs.

The cold trap is fairly basic. Just a coil of 1/8” copper tubing within a copper end cap.
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To use, it was just a matter of filling it with 90% grade isopropyl and feeding it with small chunks of dry ice.
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Once the alcohol achieved a gel-like consistency, the temperature had reached its lowest with dry ice.
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At this point it’s just a matter of lightly purging the line with D2 and off ya go. No issues with clogging during the two runs conducted this evening.

For those with access to liquid nitrogen, I’d expect this arrangement to work even better.

Mark Rowley

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Richard Hull
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Re: Simple Cold Trap for PEM Cell Deuterium

Post by Richard Hull » Sun Apr 05, 2020 5:28 am

This reminds me of the fabulous diffusion cloud chamber built in the Scientific American in the late 50's found in the "Amateur Scientist" section, always in the back of the magazine. It was constructed of copper and brass, the very large bottom tank was filled with the alcohol and dry ice mix. I built that chamber in high school. It worked great!

Nice little cold trap! Water will not make it through that little add-on. Just make sure to keep the dry ice replenished when in use and to disconnect it from the system quickly when not in use. Heating it up a bit on a stove or with a torch should get the water vapor trapped in it out for the next use.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Rich Feldman
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Re: Simple Cold Trap for PEM Cell Deuterium

Post by Rich Feldman » Sun Apr 05, 2020 7:05 am

Wow!
Is the neutron yield up 50% or a factor of two?
You mentioned same power input.
Have you ruled out changes in the plasma pressure?

Have you tried measuring the water content of gas coming from PEM cell?
I bet electronic humidity sensors would work.
Or make a dew-point checker. How 'bout a small test tube or similar-size metal vessel, serving as a cold finger. Around it is a slightly larger test tube or ordinary glass tube, with the gas under test flowing through the space in between. Inner cylinder is filled with a freezing bath (or thermoelectrically chilled). The amount of coldness to make water condense depends, I think, only on the partial pressure of water in the gas (see vapor pressure). Would it be more polite to do the experiment myself (or at least build the apparatus) instead of proposing it for someone else? Cabin fever is kicking in.

Couple years ago I made a pipe freezer that could be dragged under the house, to form temporary ice plugs as an aid to finding a perplexing leak in ancient galvanized plumbing. Dry ice and denatured alcohol worked fine. Freeze spray is storable, unlike dry ice, but expensive and inefficient and un-green and much more toxic in close quarters. One successful outdoor test used liquid propane, collected in a thermos from a BBQ-style tank.
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Mark Rowley
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Re: Simple Cold Trap for PEM Cell Deuterium

Post by Mark Rowley » Sun Apr 05, 2020 8:10 pm

Hi Rich
At the same operating parameters I’d normally get ~4000cpm on the neutron detector. With the cold trap it’s around 8000. D2 flow rate and pressure were as close to the same as I could manage it.

Good question about the level of moisture. I believe Bob said he saw condensation in his PEM cell lines but I’ve never seen it on mine. Regardless, moisture is present and to a level to make a significant difference. With that being said, un-treated PEM cell D2 is still very good for making neutrons.

I’m somewhat in a race against the clock regarding the lifetime of my bubble detectors. So far they have been extremely useful In a myriad of experiments as well as calibrating my CHM neutron detectors. However, they were bought primarily for the pinch tube and I’d like to get some decent numbers from it before they become useless. Building a diagnostic for the moisture content would be counterproductive at the moment. But its totally a worthwhile endeavor.

Mark Rowley

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