Monthly Archives: May 2017

A clever, sorption-based, hydrogen compressor

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Hydrogen-powered fuel cells provide weight and cost advantages over batteries, important e.g. for drones and extended range vehicles, but they require highly compressed hydrogen and it’s often a challenge compressing the hydrogen. A large-scale solution I like is pneumatic compression, e.g. this compressor. One would combine it with a membrane reactor hydrogen generator, to fill tanks for fuel cells. The problem is that this pump is somewhat complex, and would likely add air impurities to the hydrogen. I’d now like to describe a different, very clever hydrogen pump, one that suited to smaller outputs, but adds no impurities and and provides very high pressure. It operates by metallic hydride sorption at low temperature, followed by desorption at high temperature.

Hydride sorption -desorption pressures vs temperature.

Hydride sorption -desorption pressures vs temperature, from Dhinesh et al.

The metal hydriding reaction is M + nH2 <–> MH2n. Where M is a metal or metallic alloy and MH2n is the hydride. While most metals will undergo this reaction at some appropriate temperature and pressure, the materials of practical interest are exothermic hydrides that is hydrides that give off heat on hydriding. They also must undergo a nearly stoichiometric absorption or desorption reaction at reasonable temperatures and pressures. The plot at right presents the plateau pressure for hydrogen absorption/ desorption in several, exothermic metal hydrides. The most attractive of these are shown in the red box near the center. These sorb or desorb between 1 and 10 atmospheres and 25 and 100 °C.

In this plot, the slope of the sorption line is proportional to the heat of sorption. The most attractive materials for this pump are the ones in the box (or near) with a high slope to the line implying a high heat of sorption. A high heat of sorption means you can get very high compression without too much of a temperature swing.

To me, NaAlH4 appears to be the best of the materials. Though I have not built a pump yet with this material, I’d like to. It certainly serves as a good example for how the pump might work. The basic reaction is:

NaAl + 2H2 <–> NaAlH4

suggesting that each mol of NaAl material (50g) will absorb 2 mols of hydrogen (44.8 std liters). The sorption line for this reaction crosses the 1 atm horizontal line at about 30°C. This suggests that sorption will occur at 1 am and normal room temperature: 20-25°C. Assume the pump contains 100 g of NaAl (2.0 mols). Under ideal conditions, these 100g will 4 mols of hydrogen gas, about 90 liters. If this material in now heated to 226°C, it will desorb the hydrogen (more like 80%, 72 liters) at a pressure in excess of 100 atm, or 1500 psi. The pressure line extends beyond the graph, but the sense is that one could pressure in the neighborhood of 5000 psi or more: enough to use filling the high pressure tank of a hydrogen-based, fuel cell car.

The problem with this pump for larger volume H2 users is time. It will take 2-3 hours to cycle the sober, that is, to absorb hydrogen at low pressure, to heat the material to 226°C, to desorb the H2 and cycle back to low temperature. At a pump rate of 72 liters in 2-3 hours, this will not be an effective pump for a fuel-cell car. The output, 72 liters is only enough to generate 0.12kWh, perhaps enough for the tank of a fuel cell drone, or for augmenting the mpg of gasoline automobiles. If one is interested in these materials, my company, REB Research will be happy to manufacture some in research quantities (the prices blow are for materials cost, only I will charge significantly more for the manufactured product, and more yet if you want a heater/cooler system).

Properties of Metal Hydride materials; Dhanesh Chandra,* Wen-Ming Chien and Anjali Talekar, Material Matters, Volume 6 Article 2

Properties of Metal Hydride materials; Dhanesh Chandra,* Wen-Ming Chien and Anjali Talekar, Material Matters, Volume 6 Article 2

One could increase the output of a pump by using more sorbent, perhaps 10 kg distributed over 100 cells. With this much sorbent, you’ll pump 100 times faster, enough to take the output of a fairly large hydrogen generator, like this one from REB. I’m not sure you get economies of scale, though. With a mechanical pump, or the pneumatical pump,  you get an economy of scale: typically it costs 3 times as much for each 10 times increase in output. For the hydride pump, a ten times increase might cost 7-8 times as much. For this reason, the sorption pump lends itself to low volume applications. At high volume, you’re going to want a mechanical pump, perhaps with a getter to remove small amounts of air impurities.

Materials with sorption lines near the middle of the graph above are suited for long-term hydrogen storage. Uranium hydride is popular in the nuclear industry, though I have also provided Pd-coated niobium for this purpose. Materials whose graph appear at the far, lower left, titanium TiH2, can be used for permanent hydrogen removal (gettering). I have sold Pd-niobium screws for this application, and will be happy to provide other shapes and other materials, e.g. for reversible vacuum pumping from a fusion reactor.

Robert Buxbaum, May 26, 2017 (updated Apr. 4, 2022). 

Future airplane catapults may not be electric

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President Trump got into Hot Water with the Navy this week for his suggestion that they should go “back to god-damn steam” for their airplane catapults as a cure for cost over-runs and delays with the Navy’s aircraft carriers. The Navy had chosen to go to a more modern catapult called EMALS (electromagnetic, aircraft launch system) based on a traveling coil and electromagnetic pulses. This EMAL system has cost $5 Billion in cost over-runs, has added 3 years to the program, and still doesn’t work well. In response to the president’s suggestion (explosion), the Navy did what the rest of Washington has done: blame Trump’s ignorance, e.g. here, in the Navy Times. Still, for what it’s worth, I think Trump’s idea has merit, especially if I can modify it a bit to suggest high pressure air (pneumatics) instead of high pressure steam.


Tests of the navy EMALS, notice that some launches go further than others; the problem is electronics, supposedly.

If you want to launch a 50,000 lb jet fighter at 5 g acceleration, you need to apply 250,000 lbs of force uniformly throughout the launch. For pneumatics, all that takes is 250 psi steam or air, and a 1000 square inch piston, about 3 feet in diameter. This is a very modest pressure and a quite modest size piston. A 50,000 lb object accelerated this way, will reach launch speed (130 mph) in 1.2 seconds. It’s very hard to get such fast or uniform acceleration with an electromagnetic coil since the motion of the coil always produces a back voltage. The electromagnetic pulses can be adjusted to counter this, but it’s not all that easy, as the Navy tests show. You have to know the speed and position of the airplane precisely to get it right, and have to adjust the firing of the pushing coils accordingly. There is no guarantee of smooth acceleration like you get with a piston, and the EMALS control circuit will always be vulnerable to electromagnetic and cyber attack. As things stand, the control system is thought to be the problem.

A piston is invulnerable to EM and cyber attack since, if worse comes to worse, the valves can be operated manually, as was done with steam-catapults throughout WWII. And pistons are very robust — far more robust than solenoid coils — because they are far less complex. As much force as you put on the plane, has to be put on the coil or piston. Thus, for 5 g acceleration, the coil or piston has to experience 250,000 lbs of horizontal force. That’s 3 million Newtons for those who like SI units (here’s a joke about SI units). A solid piston will have no problem withstanding 250,000 lbs for years. Piston steamships from the 50s are still in operation. Coils are far more delicate, and the life-span is likely to be short, at least for current designs. 

The reason I suggest compressed air, pneumatics, instead of steam is that air is not as hot and corrosive as steam. Also an air compressor can be located close to the flight deck, connected to the power center by electric wires. Steam requires long runs of steam pipes, a more difficult proposition. As a possible design, one could use a multi-stage, inter-cooled air compressor connected to a ballast tank, perhaps 5 feet in diameter x 100 feet long to guarantee uniform pressure. The ballast tank would provide the uniform pressure while allowing the use of a relatively small compressor, drawing less power than the EMALS. Those who’ve had freshman physics will be able to show that 5 g acceleration will get the plane to 130 mph in only 125 feet of runway. This is far less runway than the EMALS requires. For lighter planes or greater efficiency, one could shut off the input air before 120 feet and allow the remainder of the air to expand for 200 feet of the piston.

The same pistons could be used for capturing an airplane. It could start at 250 psi, dead-ended to the cylinder top. The captured airplane would push air back into the ballast tank, or the valve could be closed allowing pressure to build. Operated that way, the cylinder could stop the plane in 60 feet. You can’t do that with an EMAL. I should also mention that the efficiency of the piston catapult can be near 100%, but the efficiency of the EMALS will be near zero at the beginning of acceleration. Low efficiency at low speed is a problem found in all electromagnetic actuators: lots of electromagnetic power is needed to get things moving, but the output work,  ∫F dx, is near zero at low velocity. With EM, efficiency is high at only at one speed determined by the size of the moving coil; with pistons it’s high at all speeds. I suggest the Navy keep their EMALS, but only as a secondary system, perhaps used to launch drones until they get sea experience and demonstrate a real advantage over pneumatics.

Robert Buxbaum, May 19, 2017. The USS Princeton was the fanciest ship in the US fleet, with super high-tech cannons. When they mis-fired, it killed most of the cabinet of President Tyler. Slow and steady wins the arms race.

Nestle pays 1/4,000 what you pay for water

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When you turn on your tap or water your lawn, you are billed about 1.5¢ for every gallon of water you use. In south-east Michigan, this is water that comes from the Detroit river, chlorinated to remove bacteria, e.g. from sewage, and delivered to you by pipe. When Nestle’s Absopure division buys water, it pays about 1/4000 as much — $200/ year for 218 gallons per minute, and they get their water from a purer source, a pure glacial aquifer that has no sewage and needs no chlorine. They get a far better deal than you do, in part because they provide the pipes, but it’s mostly because they have the financial clout to negotiate the deal. They sell the Michigan water at an average price around $1/gallon, netting roughly $100,000,000 per year (gross). This allows them to buy politicians — something you and I can not afford.

Absopure advertises that I t will match case-for-case water donations to Flint. Isn't that white of them.

Absopure advertises that I t will match case-for-case water donations to Flint. That’s awfully white of them.

We in Michigan are among the better customers for the Absopure water. We like the flavor, and that it’s local. Several charities purchase it for the folks of nearby Flint because their water is near undrinkable, and because the Absopure folks have been matching the charitable purchases bottle-for bottle. It’s a good deal for Nestle, even at 50¢/gallon, but not so-much for us, and I think we should renegotiate to do better. Nestle has asked to double their pumping rate, so this might be a good time to ask to increase our payback per gallon. So far, our state legislators have neither said yes or no to the proposal to pump more, but are “researching the matter.” I take this to mean they’re asking Nestle for campaign donations — the time-honored Tammany method. Here’s a Detroit Free Press article.

I strongly suspect we should use this opportunity to raise the price by a factor of 400 to 4000, to 0.15¢ to 1.5¢ per gallon, and I would like to require Absopure to supply a free 1 million gallons per year. We’d raise $300,000 to $3,000,000 per year and the folks of Flint would have clean water (some other cities need too). And Nestle’s Absopure would still make $200,000,000 off of Michigan’s, clean, glacial water.

Robert Buxbaum, May 15, 2017. I ran for water commissioner, 2016, and have occasionally blogged about water, E.g. fluoridation, hidden rivers, and how you would drain a swamp, literally.

Why did Hamilton wear his glasses at the duel?

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The musical play “Hamilton” ends with his duel with Burr. A song leading up to it, the world was wide enough tells the audience that Hamilton “wore his glasses” at the duel, and that he “methodically fiddled with the trigger.” It doesn’t say why, but tries to imply a sort of death-wish where Hamilton “threw away his shot” (fired into the air) because he didn’t want to kill his first friend, or because he thought of his son, who died near the spot. The theory is supported by popular myth, though the details of the events are, by necessity, muddy. All the witnesses testified that they looked away before the shooting started –customary in duels at the time.

There are some problems I find with this theory, and I’d like to present another: that Hamilton was so eager to kill Burr that he over-stacked the deck in his favor. The witnesses noted that Hamilton performed some provocative actions that seem out of character for someone who wants to commit suicide: “As they were taking their places, he (Hamilton) asked that the proceedings stop, adjusted his spectacles, and slowly, repeatedly, sighted along his pistol to test his aim”[1]. This seems like a taunt, if anything. As I reading the letters too, I find Hamilton taunting Burr to duel. He could have bowed out in many ways, as Washington always had, or been neutral. Why taunt? Why wear glasses and fiddle with the trigger? Why test your aim and then throw away your shot?

The choice of guns is important too, along with where the shot actually went. First the shot: While Hamilton’s second originally thought Hamilton had shot in the air, when the seconds went back the next day they found the shot in a cedar limb, “at an elevation of about twelve feet and a half, perpendicularly from the ground, between thirteen and fourteen feet from the mark on which General Hamilton stood, and about four feet wide of the direct line between him and Col. Burr, on the right side”.[2] The men stood 10 paces apart (16-18 feet), so apparently the shot hit about 6 feet above Burr’s head on a line reasonably towards him. That’s not quite shooting in the air.

The pair of Wogdon dueling pistols used in the Hamilton - Burr duel.

The Wogdon pistols used in the Hamilton – Burr duel. Currently the property of the JP Morgan Chase Manhattan Bank, in 1976 they were found to have a hidden hair trigger, something Hamilton knew, but Burr would not have known.

The choice of pistols is also suggestive. The pistols were the property of John Church, a brother-in-law to Hamilton, and a business partner of both men. Church had fought a duel with Burr some years before and, using Burr’s pistols, shot a button off Burr’s coat. Burr missed completely. Church then bought these new pistols in London — Wogdon pistols, with an extra-large bore and sights. Sights were not considered “sporting” for duels, and not ordinarily allowed. With sights on the pistols, one could not miss if one aimed. As for the bigger bore, this too was unusual. If you hit, you killed; most gentlemen preferred a less-deadly duel. Hamilton chose to use these pistols even though he owned two, “legal” pistols (smaller bore, no sight). As the challenged party, it was his right. Still, why not choose your own, if not to make use of the sight and the large-bore. And, according to his second, he seems to have practiced with the pistols beforehand [4].

Analysis of the guns, done in the late 1970s [3] turned up another illegal feature. While they appear to be normal dueling pistols, these guns have a hidden feature. If you move the trigger a fraction of an inch forward it sets a hidden, hair-trigger. It’s a hidden feature that Hamilton knew about [3] but Burr almost certainly did not. If Hamilton surreptitiously set the hair-trigger, it would give him a tremendous advantage. He would be able to shoot more quickly and more accurately, with a much lighter squeeze on the trigger. The sights ensured it would be a kill. Burr’s gun, unset, would have required the normal, heavy, 10-15 pound pull. His shot would have been slower and less accurate. As it was, it seems Burr fired second.

Ten paces is not very far apart. People missed because of the 10-20 lb pull and lack of sights made it hard to hit. Besides, many people who were hit survived.

Ten paces is not very far apart. People missed because of the 10-20 lb pull and the lack of sights made it hard to hit anyone. Besides, with a small bore, you didn’t kill.

There are a couple of problems with using hair-trigger pistols, though. They can go off prematurely, even if you know the trigger’s been set [4], and it’s worse if you are not quite sure you’ve set the trigger. The Wogdon guns intentionally made it hard to tell if you have set the trigger or not, and made it impossible to unset the trigger without firing. I suspect that Hamilton cleaned his glasses, fiddled with the trigger, and sighted his aim because he was unsure whether he’d set the hair-trigger. My theory is he came to the wrong conclusion. According to the seconds, Burr’s shot was almost simultaneous, but his apparently achieved a lucky/ un-lucky hit. Burr killed his rival, but also killed his own political career, the unhappy end to a beautiful animosity, discussed in the play, and discussed by me from a different angle. [5]

References:

1. Testimony at trial, Centinel of Freedom, November 24, 1807, cited in Winfield, 1874, p. 220.

2.  Nathanial Pendelton’s Amended testimony of Nathaniel Pendleton and William P. Ness’s Statement of July 11, 1804. Amended after the pair revisited the site and found the bullet.

3. “Pistols shed light on famed duel”, Merrill Lindsay, Smithsonian Magazine. 1976.

4. ibid. Hamilton told his second not to set the hair-trigger, and then seems to have set his own. Linsay’s theory is that Hamilton knew he’d set the trigger, but squeezed it too early.

5. Since the witnesses looked away, you might think of another explanation: that Burr fired first and Hamilton’s gun then went off in death throw, in the general direction of Burr. A couple of problems with this theory: for the gun to go off like that, Hamilton would have had to set the hair-trigger. The ordinary 10-15 lb trigger would require a determined squeeze. Also, for the bullet to hit the tree like that, Hamilton would have had to raise his gun past Burr, though not to the side or down as one might if he wished to throw away his shot. And Burr would have to have set the trigger himself to shoot so fast and so well. Randall’s book, “Alexander Hamilton, a life”, claims he did, p. 424, but looking at this video of the hair-trigger mechanism, I find the mechanism is too cleverly hidden for Burr to have noticed. It escaped detection for 170 years. Finally, for Burr to shoot to kill without provocation, would require that he murder in cold blood, and Burr shows no evidence of that. Besides, Burr would have had to worry that the witnesses might turn around and see his dastardly deed. As it was, even with Hamilton’s gun going off, Burr’s reputation was ruined. I reject this theory, and assert as others have: “Hamilton did fire his weapon intentionally, and he fired first.”

Robert E. Buxbaum, May 10, 2017. You may like these other songs from Hamilton, “your obedient servant,” and “the ten duel commandments.” And you may like this essay about Burr, Tammany Hall and the Manhattan bank.

summer science: a toad or turtle terrarium

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Here’s an easy summer science project, one I just made: a toad habitat. It’s similar to a turtle terrarium (I’ll show how to make that too). I’d made the turtle terrarium ten years ago for my 8-year-old daughter (here’s some advice I gave her on her 16th birthday).

For this project you’ll need: a large flower-pot, fish tank, or plastic clothes bin. You’ll need some dirt for the bottom, and a small plastic bin, jar, or Tupperware for toad (or turtle) transport. You’ll also need a smallish plastic dish or tub (~6″ by 1″ deep) to serve as a lake in the toad habitat. For the turtle version you don’t need the lake, but will need a rock or brick. And that’s all, besides your toad or turtle. The easy way to get your pet is to find one by a river. If that doesn’t work, go to a pet-store and get one that is native to your area of the country. Local fauna (fauna= animals) will be heartier and cheeper, and will allow you to keep your terrarium outside if you choose. Keeping my toad outside means he (or she) can catch bugs without me having to buy them all the time. It also seems more “natural” to study animals in their natural temperature cycles. I caught my toads three weeks ago, in mid April after the last frost — I plan to set one free in the fall –the other I gave away.

For my toad habitat, I used a large, old flower-pot that I had sitting outside my house. It is 21″ across at the top and 18″ tall. I put 6″ of dirt in it. six inches is deep enough for the toad to dig in, and it left 12″ of airspace — I don’t think the toad can jump a foot in the air to get out. I made sure the soil was muddy, and had worms. Toads seem to like mud and they eat worms. Toads drink water through their skin, and may not like chlorinated water. I also added some leaves and a small flower pot for shade, and put in some bits of fruit and some bugs, and planted a single plant. My hope was to develop a colony of ants and bugs for the toads to eat. I buried my plastic water bowl, my mini-lake, slightly below ground level with the top 1/2″ above. I then went off with my toad transport to catch a toad or three in the wetlands areas near me (I live in Oak Park, MI).

Some good toad hunting spots in Keego Harbor MI

Some good toad hunting spots in Keego Harbor MI

The first place I went was the banks of the Rouge river near Lawrence Tech. Sorry to say, the area showed no signs of toads, frogs, turtles, or even fish. There was an illegally connected drain, though — not good. I plan to bring the illegal grain up with the “Friends of the Rouge” (good group). I then went to an oak swamp on the Rouge. The area was beautiful and scenic, but there was no oxygen in the water and so no fish or toads; oxygen is important for the health of a river; without it, you’ve got  a swamp. I finally hit pay-dirt in Keego Harbor, MI, see map, a rural community 10 miles away from my home. In Keego harbor I found American toads aplenty: jumping all over, and big, hollow toad-mounds by the river. The locals were friendly too. Toad catching is a good conversation starter. I put two toads in my bin with some lake water and took them home to the terrarium, see movie.

My neighbor got the other toad and put him/her in a fish-tank terrarium in his bathroom. His terrarium has a screen on top with holes small enough to keep the toad and his food from escaping. He is feeding his toad meal worms, but I don’t have a movie. Apparently they like it.

I left my pot outside, as I mentioned, so my toad can catch insects that fly by, and spiders. My toad seems to like spiders. I also tried putting in wax-worms ($1 for 12). The good thing about wax worms is they move slowly, unlike crickets (crickets cost more and can jump out). My toad ate all 12 worms in 2 days. I have not put a lid on my pot yet. Perhaps that’s a mistake. My colony of bugs seems to be breeding fast enough to make up for escapees and eating, but perhaps that’s because the toad doesn’t eat many. A fellow at the pet store sold me ten small crickets for $3.00, but I don’t think the toad ate any before they escaped. See what your toad eats; it’s science. I think my toad is a female: it doesn’t vibrate or croak at night. Male toads vibrates and croak. Toads can be gender fluid, though; somethings two “female” toads will breed. Your job is to watch, enjoy, and perhaps learn something.

The main difference between this project, and the turtle terrarium I’d made is that the turtle terrarium was mostly water, with a brick, and this is mostly mud with a lake. I made the turtle terrarium in a laundry bin, a bigger environment, and flooded it except for the brick. I bought the turtles (a red-ears and a snapping) and fed it chicken bits and dandelion leaves. As with this terrarium, I kept the turtles outside through the spring, summer, and fall, but I brought the turtles in the winter. They lasted that way for about 8 years. Toads only live for 2-3 years, and mime may be a year or two old already. I won’t be too surprised if it croaks on my watch. For now, she seems safe and hoppy.

Robert Buxbaum, May 3, 2017. Here are some other science fair projects, chemical, and biological.