Category Archives: Science: Physics, Astronomy, etc.

REB Research periodic table cup

2 Replies

Some 20 years ago I designed this periodic table cup, but with only the 103 named elements that existed then. In part this was done because I wanted a good, large, white coffee cup, in part because I often found I needed a periodic table, and didn’t like to have to look one up, and in part to people how much more area you get on a cylinder than on a flat sheet (roughly 3.14 times more area). To show that, I put all the side elements (rare earth lanthanides, and actinides) where they belonged, and not off on the side. I also put hydrogen in twice, once as a metal (HCl) and once as a non metal (NaH). The color I chose was Tryian Blue, a key color of Biblical Tyre, what you get from male purpura mollusks (the females give a shade of red that I also try to associate with REB Research).

I’ve updated the cup to add more elements: I think it’s great. You can buy it for $30 through our web-site, or for $25 by e-mailing me (reb@rebresearch.com). Or if you do something really cool, I may send you one for free.

REB Research, Periodic table coffee cup

REB Research, Periodic table coffee cup

By the way, I only use 4 digits for the atomic weight; I can think of no application where a normal person needs more.

 

 

How hydrogen and/or water can improve automobile mileage (mpg)

7 Replies

In case you’ve ever wondered why it was that performance cars got such poor milage, or why you got such bad milage in the city, the biggest single problem has to do with the vacuum drawn by the engine, some of the problem has to do with the speed of combustion, some has to do with rolling friction, and some with start/stop loss too. Only a very small fraction of the energy is lost on air friction until you reach highway speeds.

Lets consider vacuum loss first as it is likely the worst offender. A typical US car, e.g. a Chevy Malibu, has a 3.5 liter engine (a performance car has an engine that’s much larger). As you toodle down a street at 35 mph, your engine is going at about 2000 rpm, or 33 rps. Since the power required to move the car is far less than the 200 hp that the car could deliver, the air intake is throttled so that the engine is sucking a vacuum of about 75 kpa (10 psi for those using English units). To calculate the power loss this entails, multiply 33*3.5*80; this is about 8662 Watts, or 12 hp. To find the energy use per mile, divide by your average speed, 25 mph (it would be 35 mph, but you sometimes stop for lights). 8 kW/25 mph = .21 kW-hr/mile. One finds, as I’ll show that the car expends more energy sucking this vacuum than pushing the car itself. This is where the majority of the city mpg goes in a normal car, but it’s worse in a high performance car is worse since the engine is bigger. In city driving, the performance mpg will be lower than for a Malibu even if the performance car is lighter, if it has better aerodynamics (it does), and if you never stop at lights.

The two other big places were city mileage goes is overcoming rolling friction and the need to stop and go at lights, stop signs, etc. The energy used for rolling friction is the force it would take to push your car on level ground when in neutral times the distance. For a typical car, the push force is about 70 lbs or 32 kgs or 315 Nt; it’s roughly proportional to the car’s weight. At 35 mph, or 15.5 m/s, the amount of power this absorbs is calculated as the product of force and speed: 15.5*315 = 4882 W, or about 6.5 hp. The energy use is 4.9 kW/35 mph =.14 kWhr/mile. The energy loss from stop lights is similar to this, about .16 kWhr/mile, something you can tell by getting the car up to speed and seeing how far it goes before it stops. It’ll go about 2-3 blocks, a little less distance than you are likely to go without having to stop. Air resistance adds a very small amount at these speeds, about 2000 W, 2.7 hp, or .05 kWhr/mile; it’s far more relevant at 65 mph, but still isn’t that large.

If you add all this together, you find the average car uses about .56 kWhr/mile. For an average density gasoline of 5.6 lb/gal, and average energy-dense gasoline, 18,000 BTU/lb, and an average car engine efficiency of 11000 BTU/kWhr, you can now predict an average city gas mileage of 16.9 mpg, about what you find experimentally. Applying the same methods to highway traffic at 65 mph, you predict .38 kWhr/mile, or 25 mpg. Your rpms are the same on the highway as in the city, but the throttle is open so you get more power and loose less to vacuum.

Now, how do you increase a car’s mpg. If you’re a Detroit automaker you could reduce the weight of the car, or you the customer can clean the junk out of your trunk. Every 35 lbs or so increases the rolling friction by about 1%. These is another way to reduce rolling friction and that’s to get low resistance tires, or keep the tires you’ve got full of air. Still, what you’d really like to do is reduce the loss to vacuum energy, since vacuum loss is a bigger drain on mpg.

The first, simple way to reduce vacuum energy loss is to run lean: that is, to add more air than necessary for combustion. Sorry to say, that’s illegal now, but in the olden days before pollution control you could boost your mpg by adjusting your carburator to add about 10% excess of air. This reduced your passing power and the air pollution folks made it illegal (and difficult) after they noticed that it excess air increased NOx emissions. The oxygen sensor on most cars keeps you from playing with the carburator these days.

Another approach is to use a much smaller engine. The Japanese and Koreans used to do this, and they got good milage as a result. The problem here is that you now had to have a very light car or you’d get very low power and low acceleration — and no American likes that. A recent approach to make up for some of the loss of acceleration is by adding a battery and an electric motor; you’re now making a hybrid car. But the batteries add significant cost, weight and complexity to these cars, and not everyone feels this is worth it. So now on to my main topic: adding steam or hydrogen.

There is plenty of excess heat on the car manifold. A simile use of this heat is to warm some water to the point where the vapor pressure is, for example, 50 kPa. The pressure from this water adds to the power of your engine by allowing a reduction in the vacuum to 50 kPa or less. This cuts the vacuum loss at low speeds. At high speed and power the car automatically increases the air pressure and the water stops evaporating, so there is no loss of power. I’m currently testing this modification on my own automobile partly for the fun of it, and partly as a preface to my next step: using the car engine heat to run the reaction CH3OH + H2O –> CO2 + H2. I’ll talk more about our efforts adding hydrogen elsewhere, but thought you might be interested in these fundamentals.

http://www.rebresearch.com

How and why membrane reactors work

6 Replies

Here is a link to a 3 year old essay of mine about how membrane reactors work and how you can use them to get past the normal limits of thermodynamics. The words are good, as is the example application, but I think I can write a shorter version now. Also, sorry to say, when I wrote the essay I was just beginning to make membrane reactors; my designs have gotten simpler since.

At left, for example, is a more modern, high pressure membrane reactor design. A common size is  72 tube reactor assembly; high pressure. The area around the shell is used for heat transfer. Normally the reactor would sit with this end up, and the tube area filled or half-filled with catalyst, e.g. for the water gas shift reaction, CO + H2O –> CO2 + H2 or for the methanol reforming CH3OH + H2O –> 3H2 + CO2, or ammonia cracking 2NH3 –> N2 + 3H2. According to normal thermodynamics, the extent of reaction for these reactions will be negatively affected by pressure (WGS is unaffected). Separation of the hydrogen generally requires high pressure and a separate step or two. This setup combines the steps of reaction with separation, give you ultra high purity, and avoids the normal limitations of thermodynamics.

Once equilibrium is reached in a normal reactor, your only option to drive the reaction isby adjusting the temperature. For the WGS, you have to operate at low temperatures, 250- 300 °C, if you want high conversion, and you have to cool externally to remove the heat of reaction. In a membrane reactor, you can operate in your preferred temperature ranges and you don’t have to work so hard to remove, or add heat. Typically with a MR, you want to operate at high reactor pressures, and you want to extract hydrogen at a lower pressure. The pressure difference between the reacting gas and the extracted hydrogen allows you to achieve high reaction extents (high conversions) at any temperature. The extent is higher because you are continuously removing product – H2 in this case.

Here’s where we sell membrane reactors; we also sell catalyst and tubes.

True (magnetic) north

Leave a reply

Much of my wife’s family is Canadian, so I keep an uncommon interest in Canada — for an American. This is to say, I think about it once a month or so, more often during hockey season. So here is a semi-interesting factoid:

The magnetic north pole, the “true north” has been moving northwest for some time, but the rate has increased over the last few decades as the picture shows. It has now left the northern Canadian islands, so Canada is no longer “The true north, strong and free.” (It seems to be strong and free). True north  is now moving northwest, toward Siberia. true magnetic north heading to Russia

Why is the galaxy stable?

3 Replies

We are located about 30,000 light years out from the galactic center (1.8E17 miles), and the galaxy goes round every 200,000,000 years. From the rotational rate and diameter I calculate that we’re moving at roughly 1,000,000,000 miles/year or 100,000 mph — not a bad speed to expect to come from random variation of the gas molecule speeds. Maxwell averaging should reduce the speed to 2000 mph at most, I’d think.

Even more interesting, the rotation speed suggests the galaxy’s gone around about 50 times since it condensed. That’s an awful lot of turns for our galactic arms to retain stable; you’d expect that the outer parts of the arms would have rotated far fewer times, perhaps only once, while the inner parts would rotate perhaps 1000 times. After a billion years, you’d expect the arms to be gone. The going explanation is dark matter, matter we can’t see.

After bugging astrophysicists for a few years, I’ve come to believe that many of their models (MACHOs, WIMPs) don’t make much sense. I’ve come to model the distribution of dark matter on my own, as a particular distribution gas cloud of light particles. There is only one distribution that will result in the galaxy rotating as a unit — can you figure out what that is? Not that I now know what dark matter is, but at least I think I know where it is. Now all we need to do is find the missing matter. As a challenge, see if you can calculate the distribution of dark matter that would result in the galaxy rotating as a unit.

— Robert Buxbaum

The universe is not endless

3 Replies

You may have heard that the universe is not endless, ending at a brick wall, perhaps, some 15 billion light years out. But what you may not know is that there is a classic proof, going back to the middle ages to show that the universe is not an endless expanse of stars.

Consider an endless universe with a uniform distribution of stars. We would expect that, in any large-enough space of this universe there would have to be many stars, e.g. between 100 and 101 trillion miles from earth. At this distance, each of these stars is close enough to see, and the combination of them (the sum in this volumetric shell) will shed a small amount of heat on the earth. Now consider another shell, the same thickness but twice as far from us; if the universe is uniform, there will be 4 times as many stars, but since these stars will be at twice the distance; that is between 200 and 201 trillion miles from earth, each star will present us with ¼ as much heat as the stars in the first shell. Now, since there are 4 times more stars, the total effect is to radiate as much heat to us as from the first shell.

The same argument goes for each shell of 1 trillion miles thick: each one presents us with the same amount of heat. If the universe is infinite and uniform, we find there will be an infinite number of shells radiating this amount of heat, and therefore an infinite amount of heat bathing us. We should expect to roast from all of it. Since we have not roasted, we conclude that the universe is not an endless, uniform expanse.

The universe could still be uniform and not endless (ending with a brick wall, as in the Hitch-hikers guide), or it could be expanding from a big bang 15 Billion years ago. This latter is suggested by the red shift, but not a favored solution of creationists for some reason. Or it could be a closed, oscillating (or not) 4 dimensional hypersphere (Einstein). That is, it could be a non Euclidean, black hole. Or it could be fractal (Mandelbrot). Or it could be a combination of all of the above.

For a thought about galactic arms see here. October 22, 2012.

Why tornadoes and hurricanes lift up cars, cows, etc.

3 Replies

Here’s a video I made for my nieces and any other young adults on why it is that tornadoes and hurricanes lift stuff up. It’s all centrifugal forces — the same forces that generate the low pressure zone at the center of hurricanes. The explanation is from Albert Einstein, who goes on show why it is that rivers don’t run straight; before you read any more of it, I’d suggest you first watch the video here. It’s from my Facebook page, so it should be visible.

If can’t see, you may have to friend me on Facebook, but until then the video shows a glass coffee cup with some coffee grounds and water in it. Originally, the grounds are at the bottom of the cup showing that they are heavier than the water. When I swirl the water in the cup, you’ll see that the grounds are lifted up into a heap in the center with some flowing all around in a circle — to the top surface and then to the walls of the cup. This is the same path followed by light things (papers for example) in a tornado. Cows, houses and cars that are caught up in real tornadoes get sucked in and lifted up too, but they never get to the top to be thrown outward.

The explanation for the lifting is that the upper layers of liquid swirl faster than the lower layers. As a result there is a low pressure zone above the middle of the swirl. The water (or air) moves upward into this lower pressure area and drags along with it cows, cars, houses and the like (Here’s another post on the subject of where the swirl comes from). The reason the swirl is faster above the bottom of the cup is that the cup bottom adds drag to the flow (the very bottom isn’t swirling at all). The faster rotating, upper flows have a reasonable amount of centrifugal force and thus a lower pressure in the middle of the swirl, and a higher pressure further out. The non-rotating bottom has a more uniform pressure that’s relatively higher in the middle, and relatively lower on the outside. As a result there is a secondary flow where air moves down around the outside of the flow and up in the middle. You can see this secondary flow in the video by following the lighter grounds.

Robert. E. Buxbaum. Weather is not exactly climate, but in my opinion both are cyclic and chaotic. I find there is little evidence that we can stop climate change, and suspect there is no advantage to wanting the earth colder. There was a tornado drought in 2013, and a hurricane draught too. You may not have heard of either because it’s hard to report on the storms that didn’t happen.