Hilsch Tubes Revisited

Because refrigeration is free? Really? :)

(...)

OK, I'll give you that one.

(...)

My suggestion is just something to try for a few dollars.

If it works for the duration of the project, Bob is not out much money. If it does not work, refrigeration is not going to work either.

One experiment is worth years of theorizing. :)

--Winston

One could refrigerate a jug of water for a few days then use it as a heat sink for the copper tube. That'd be inefficient but it might be cheaper because it would eliminate the trip to the store for bags of ice.

I like it.

--Winston

Who needs a store? I make my own ice in a little stand-up freezer. In the summer, when I'm fishing, I make about 10 to 20 pounds of it every couple of days.

It's a lot cheaper than running a compressor at the low efficiencies of a Hilsch tube...or buying ice.

Like this?

So, locate a square 10 gallon bucket, submerge coil, fill with water and place it in the freezer. Figure out a pump to keep the drip leg dry and Bob's your Uncle.

--Winston

Yeah, I took all the shelves out of the freezer in my shop fridge and put a great big tub under the little ice maker in there. It holds 30-40 pounds of ice if I remember to turn the tub around so the other side fills. In the summer when I am fishing a lot that is never a problem. LOL.

I would consider using the freezer part of the fridge to pre-cool a coil of air, but its on the other side of the shop. I actually considered putting my CNC computers inside a little apartment fridge in the shop. Maybe now is the time to get a second shop fridge. LOL.

Yeah. Mine's a little bigger -- around 4 ft^3 -- but that one should do it. BTW, mine has run without a hitch for 32 years. Sears.

Probably. (Remind me to tell you about the piece of research equipment, using semiconductor Peltier chips, that I built for Japan's MITI back in the '80s. Bridgeport, South Bend lathe, and ancient Walker Turner drill press, and the thing went to Japan's research agency for OTEC. )

I'd be wary of doing it that way. The coil would develop a blanket of water around it and the conductivity from the ice would be problematic.

If it's enough chilling, great. Otherwise, I'd break the ice into chunks and toss them in the bucket.

I am sure it would be more efficent than a Peltier device, but I was thinking more about the space required.

=20 Dan

Hey Ed.

You were going to tell me about the time you created a Peltier-based test jig destined for Japan's Ministry of International Trade and Industry to be used in Ocean Thermal Energy Conversion research back in the 80's.

You used a Bridgy, a SB lathe and an ancient Walker Turner drill press. Is that right?

:)

--Winston

Oh, yeah, I remember that...

Okay, a long tail...

I left AM to pursue a juicy contract with MITI (Japan's Ministry of International Trade and Industry), to produce reports on new materials applications. One of their big energy projects was OTEC (Ocean-Thermal Energy Conversion). I wrote a paper on corrosion-resistant materials for that project and then, in discussions with them, they expressed an interest in the new semiconductor thermoelectric cells, as possible candidates for electricity generation from low-temperature-differential, high-volume seawater. They actually use the Seebeck effect, but Peltier and Seebeck are like yin and yang.

Anyway, they said they wanted some of the new cells from a company in Trenton, NJ, to test and evaluate. I drove down and bought a few dozen for them. When I delivered them they said they wanted to get started quickly because they had contracted with a company in Japan to build a refrigerator-size test module and it would take a couple of months to get it, and then another month to run tests.

I had a design in my head for a four-cell test unit that I could make in one weekend. They said it wasn't enough cells. So I explained that you could change cells in it in less than five minutes, and they could easily test 20 cells in a day. They they could run some statistics, figure the variance and standard deviations from a few day's worth of testing, and have the results they wanted. So they threw some money at me and said go ahead.

It was really simple. I took two 6-inch squares of 5/8" aluminum tooling plate (2024 -- it was all I had) and cut a serpentine groove in one side of each plate with a 1/2" end mill (mill -- I had to use a friend's Bridgeport). Then I turned some custom barb fittings from brass (turn). I drilled holes to clamp the two plates together, leaving room for the Seebeck cells, and then drilled and tapped holes for the barb fittings (drill). There were two barb fittings on each plate, at opposite ends of the serpentine groove. Through one plate you ran cold water. Through the other, warm water.

I placed four cells between the plates, smeared them with conductive silicone grease, and clamped them together. Then I hooked aquarium hose to the barb fittings. One pair of leads from each cell projected out of the space between the plates. Ta-dah. About five hours of work, IIRC.

You could measure the volume of water and the in-and-out temperatures from each plate, and the electrical output of each cell. You can see the implications -- a simple way to measure energy in/energy out at different absolute temperatures and temperature differentials (there was lots of insulation on the whole thing, in use) and to test the output variance among cells. Very, very simple.

That's the story. They loved it. And they decided not to invest in OTEC.

Oh, I forgot the Plexiglass covers. The grooves were on the outside of the sandwich, and I covered them with 1/8" Plexi. That way you could see if a bubble was trapped in there that would screw up the output readings from one cell.

I guess your clamping pattern assured that every cell had an equal share of hot and cold sink coupling.

That apparently is really difficult to do. One of our own disassembled a shorted PWM control for an RC application and found that say 30% of his SMT MOSFETs barely made contact with the heat sink. (You could really see the problem by inspecting the 'sil pad' that was wedged between the heatsink and devices. Some FETS made quite a deep impression and some were not apparent at all.)

Sounds like Science, too. One could bolt on thermocouples for instance.

Ouch! That's like deciding not to buy a car because all you could test were Yugos. :)

I love the TE concept but despair over their inefficiency.

I suspect that Stirling motors would work the best in this application, no? ('Sounds like a great purpose for 'flare gas' at last.)

Very nifty!

That'd be a way to create a solar heat collector, too. I expect the plexi would have to be replaced with another aluminum sheet, though.

--Winston

It was an even pattern, and any difference would be apparent at the plates' edges, but it also counted on the grease. In any case, it worked. We moved one set of cells all around on the plates and the results were pretty consistent.

I attached 1N914 diodes for my own initial tests. They're very linear for temperature when back-biased within a certain voltage range -- MUCH better than thermistors. But the leads have to be short. Amplify the results with a 714 op amp and drive a small meter. +/- 1 deg. F over quite a long range.

That was in 1981, remember. d8-)

Their primary tests were with steam turbines using ammonia for a working fluid.

I don't remember the values. I have a couple of them that I scrounged from an old camping cooler. It killed the battery in my van one night and I took it apart for revenge.

They'd likely be the most efficient energy coverter at those temperatures. But you're dealing with very small temp. differentials. It would take a *lot* of Stirlings to generate useful power.

(...)

You didn't have variation in solder thickness, as our friend did in his PWM MOSFETs, so that removed a significant variable. Very cool, and warm.

(...)

'Sounds like you had to 'level shift' and scale but you didn't have to 'linearize'. -2 mV per degree? Or is that the 'forward' and not 'reverse' tempco?

(Gasp!) Though I am sure it was perfectly safe.

That fridge *needed* disassemblin'.

In OTEC, Stirling 'ballast' would be a Good Thing, (at last).

--Winston

These chips had flat-finished ceramic wafers on both sides.

I really don't remember. I had used the same system years earlier for a temperature-tire gauge for SCCA races. Those little things respond in less than 2 seconds.

They were out at sea. The OTEC plants generally are old ships anchored in warm water, over fairly deep waters that are much cooler at the depths. I haven't heard anything about them for 20 years. The whole thing probably was a dud.

Speaking of Stirlings, have you heard anything about that multiple-Stirling solar array that PG&E was building a couple of years ago? I would have thought something would be reported about it by now.

(...)

Uh oh....

--Winston

'Wish they'd turn off that JLG lift. Those things are *noisy*.

:)

--Winston

These sound a *lot* better!

(I wonder how they made them sound like strings and horns?)

--Winston

Hmmm. That doesn't sound good.

Oh, well, we're going to have all the oil we could possibly want, after the Republicans win the White House. And gas will be $2.50 a gallon! Free, if you show your Tea Party ID card!

They'll probably drill in my back yard. I wonder who owns the mineral rights? d8-)

(...)

Situation: All Fracked Up.

--Winston