Author Archives: R.E. Buxbaum

About R.E. Buxbaum

Robert Buxbaum is a life-long engineer, a product of New York's Brooklyn Technical High School, New York's Cooper Union to Science and Art, and Princeton University where he got a PhD in Chemical Engineering. From 1981 to 1991 he was a professor of Chemical Engineering at Michigan State, and now runs an engineering shop in Oak Park, outside of Detroit, Michigan. REB Research manufactures and sells hydrogen generation and purification equipment. He's married with 3 wonderful children who, he's told, would prefer to not be mentioned except by way of complete, unadulterated compliments. As of 2016, he's running to be the drain commissioner/ water resources commissioner of Oakland county.

This is not the most important election, 1860 was

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Every year we hear the same claim: that this the most important election of America’s history. This year is among the more contentious than most, but the issues dividing the candidates are few. Both, for example, claim they will protect the border and spur the economy. In lieu of issues, there’s name calling. Trump claims Harris is as incompetent buffoon and Harris claims Trump is a fascist dictator. The rancor practically guarantees as they’ll be riots whoever wins but, as these things go, the election is less important, and divisive than ’64 and ’68, and in particular, the election of 1860.

Following the 1860 election, election seven states ceded from the union and we had a Civil War. Even the most bleak prediction for 2024-25 is for a more peaceful transfer of power. The election of 1860 had two major issues on the ballot; one was slavery or rather the expansion of slavery to the territories, and the other was implementation of the Morrill tariffs. These import taxes, proposed by Justin Morrill and passed but not yet implemented, would have raised the average agricultural duty from 15% to to 47%. Duties on durable goods wool rise to 65%, with the burden falling disproportionately on the southern states. Duties on durable goods. There was also a price schedule that would have prevented British shippers from minimizing the effect by falsely claiming a price far below market, something China currently does. In September 1860, Republican Leader Thaddeus Stevens told a New York City audience that “the Tariff would impoverish the southern and western states, but that was essential for advancing national greatness and the prosperity of industrial workers.”

Matching the two sides to the two major issues of the day, there were four major candidates for president in 1860. All of them won states. Lincoln carried the greatest number, 18, and won the most electoral votes, 180. He was for high tariffs and against the expansion of slavery. Second was John Breckinridge, the Southern Democrat, who carried 11 states and got 72 electoral votes. He was for the expansion of slavery and against the higher tariffs. Then there was Stephen Douglas, the Northern Democrat, who was for allowing the expansion of slavery, considering it a “states right,” and also for the higher tariffs. Douglas carried only one state, Missouri, with 12 electoral votes. Finally, there was John Bell, the Constitutional Union candidate, who carried three states, Virginia, Tennessee, and Kentucky, representing 39 electoral votes. He opposed the expansion of slavery and also the increased tariff, but he generally believed that compromise was always possible. This was the worst vote split in US history. The worst split I’ve seen was 1968, when three candidates carried states.

Had either Bell or Douglas won, I suspect that the Civil War could have been avoided, at least temporarily. Virginia, the most important of the slave states, had shown it was willing to accept an anti-slavery president so long as he did not impose high tariffs — tariffs that benefitted the northern industrial workers and manufacturers at the expense of southern consumers and agricultural producers. Lincoln’s victory precipitated the immediate secession of 3 states. Another 4 seceded after inauguration.

The south imagined they could walk away because that’s how they read the constitution before the 13th amendment. They imagined they could win a civil war because they imagined they had British military support. “Cotton was king,” they claimed. The UK prime minister, Lord Palmerston, had told secretary Adams, “We do not like slavery, but we want cotton, and we dislike very much your Morrill tariff.” As it was, the British stayed on the sidelines, in part because of diplomacy. Besides, the gunship Monitor showed that the North could sink most any British ship that entered US waters.

As for 2024, I expect there will be riots whoever wins, but nothing more. The parties are realigning significantly, as happened in 1964-68, and neither side much understands the appeal of the other. This seems like less of a wrenching election than in 1964 and 1968, though. In ’64-’68 US boys were dying in Vietnam in numbers, and black folks and their white friends were being lynched in the south. Nothing like that is happening today. Today’s riots have been fueled by nothing more than name-calling, fear, and the occasional assassination attempt. Mild, even compared to 1968.

Robert Buxbaum, November 4, 2024. Justin Morrill is mostly remembered today for the Land-grant college act of 1862. This created an agricultural -technical college in each state. I taught at Michigan State University, Michigan’s land grant university. I’m generally a fan of tariffs, both as an aid to the domestic economy and as a tool of foreign policy. I present these views here. I got these views from Peter Cooper.

Sailors, boaters, and motor sailing at the hull speed.

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I’ve gone sailing a few times this summer, and once again was struck by the great difference between sailing and boating, as well as by the mystery of the hull speed.

Sailors are distinct from boaters in that they power their boats by sails in the wind. Sailing turns out to be a fairly pleasant way to spend an afternoon. At least as I did it, it was social, pleasant, and not much work, but the speeds were depressingly slow. I went on two boats (neither were my own), each roughly 20 feet long, with winds running about 10-15 knots (about 13 mph). We travelled at about 3 knots, about 3.5 mph. That’s walking speed. At that speed it would take about 7 hours to cross Lake St. Clair (25 miles wide). To go across and back would take a full day.

Based on the length of the boats, they should have been able to go a lot faster, at about 5.8 knots (6 mph). This target speed is called the hull speed; it’s the speed where the wave caused by the bow provides a resonance at the back of the boat giving it a slight surfing action, see drawing.

This speed can be calculated from the relationship between wave speed and wavelength, so that Vhull = √gλ/2π where g is the gravitational constant and λ is the water line length of the boat. For Vhull in knots, it’s calculated as the square-root of the length in feet, multiplied by 1.34. For a 20 foot boat, then,

Hull speed, 20′ = 1.34 √20 = 1.34 x 4.5 = 6.03 knots.

While power boats routinely go much faster than this, as do racing skulls and Americas cup sailboats, most normal sailboats are designed for this speed. One advantage is that it leads to a relatively comfortable ride. There is just enough ballast and sail so that the boat runs out of wind at this speed while tipping no more than 15°. Sailors claim there is a big increase in drag at this speed, but a look at the drag profile of some ocean kayaks (12 to 18 feet, see below) shows only a very slight increase around this magical speed. More important is weight; the lowest drag in the figure below is found for the shortest kyack that is also the lightest. I suspect that the sailboats I was on could have gone at 6 knots or faster, even with our current wind, if we’d unrolled the spinnaker, and used a ‘screecher’ (a very large jib), and hung over the edge to keep the boat upright. But the owner chose to travel in relative comfort, and the result is that we had a pleasant afternoon going nowhere.

Data from Vaclav Stejskal of “oneoceankyacks.com”

And this brings me to my problem with power boating. Th boats are about the same length as the sailboats I was in, and the weight is similar too. You travel a lot faster, 20 to 25 knots, and you get somewhere, but the boats smell, and provide a jarring ride, and I felt they burn gas too fast for my comfort. The boats exceed hull speed and hydroplane, somewhat. That is, they ride up one wave, fly a bit, and crash down the other side, sending annoying wakes to the sailboaters. We crossed lake St. Clair and rode a way down the Detroit river. This was nice, but it left me thinking there was room for power -assisted sailing at an intermediate speed, power sailing.

Both sailboats I was on had outboard motors, 3 hp, as it happened, and both moved nicely at 1 hp into and out of the harbor, even without the sail up. Some simple calculations suggest that, with I could power a 15 to 20 foot sailboat or canoe at a decent speed – hull speed – by use of a small sail and an electric motor drawing less than 1 hp, ~400 W, powered by one or two car batteries.

Consider the drag for the largest, heaviest kayak in the chart a move, the Cape Ann Double, going at 6.5 knots. At 6 knots, the resistance is seen to be 15 lbs. To calculate the power demand, convert this speed to 10 fps and multiply by the force:

Power for 6 knot cruising = 10 fps x 15 lbs = 150 ft lbs/s = 202 W or 0.27 hp.

Outboard motors are not 100% efficient, so let’s assume that you need to draw more like 250 W at the motor, and you will need to add power by a sail. How big a battery is needed for the 250 W? I’ll aim for powering a 4 hour trip, and find the battery size by multiplying the 250 W by 4 hours: that’s 1250 Hrs, or 1.25 kWh. A regular, lithium car battery is all that’s needed. In terms of the sail, I’m inclined to get really invovative, and use a Flettner sail, as discussed here.

It seems to me that adding this would be a really fun way to sail. I’d expect to be able to go somewhere, without the smell, or the cost, or being jarred to badly. Now, all I need is a good outboard motor, and a willing companion to try this with.

Robert Buxbaum, Sept. 9, 2024

China’s space station and the ISS, a comparison

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It gets so little notice from the news agencies that many will be surprised to find that China has a space station. It’s known alternately as the Tiangong Space Station or the CSS, Chinese Space Station; it’s smaller than the International Space Station, ISS, but it’s not small. Here is a visual and data comparison, both from Wikipedia.

China’s space station is smaller than the ISS, but just about as capable. Cooperation leads to messiness (and peace?)

The ISS has far more solar panels, but the power input is similar because the CSS panels are of higher efficiency. As shown in the table below, the mass of the ISS is about 4.5 times that of CSS but the habitable volume is only 3 times greater than of CSS, and the claimed crew size is similar, of 3 to 6 compared to 7. The CSS is less messy, less noisy, with less mass, and more energy efficiency. Part of the efficiency comes from that the CSS uses ion propulsion thrusters to keep the station in orbit, while the ISS uses chemical rockets. The CSS thus seems better, on paper. To some extent that’s because it’s more modern.

Another reason that the ISS is more messy is that it’s a collaboration. A major part of its mission is to develop peaceful cooperation between the US, Europe and Russia. It’s been fairly successful at this, especially in the first two decades, and part of making sure parts from The US, Russia, Europe, Japan, and Canada all work together is that many different standards must be tolerated and connected. The ISS tolerates different space suits, different capsules, different connections, and different voltages. The result is researchers communicate, and work together on science, sending joint messages of peace to the folks on earth. Peace is an intended product.

By contrast, the Chinese space station is solely Chinese. There are no interconnection issues, but also no peace dividend. It has a partially military purpose too, including operation of killer satellites, and some degree of data mining. This was banned for ISS. So far the CSS has hosted Chinese astronauts. No Chinese astronauts have visited the ISS, either.

Long march 6A rocket set to supply the CSS. It is very similar to the Delta IV.

India was asked to join the ISS, but has declined, wishing to follow China’s path of space independence. The Indian Space Research Organization plans to launch a small space station on its own, Gaganyaan, in 2025, and after that, a larger version. That’s a shame, though it’s not clear how long cooperation will continue on the ISS, either. See the movie I.S.S. (2023) for how this might play out. Currently, there is a tradition of cooperation about ISS, and it’s held despite the War in Ukraine. The various nations manage to work together in space and on the ground, launching people and materials to the ISS, and working together reliability.

Although it isn’t a direct part of the space stations, I should mention the troubles of the Boeing Star-liner capsule that took two astronauts to the ISS compared to the apparently flawless record of the CSS. The fact is, I’m not bothered by failures, so long as we learn from them. I suspect Boeing will learn, and suspect that this and other flailing projects would be in worse shape without the ISS. Besides, the ISS has been a major catalyst in the development of SpaceX, a US success story that China seems intent on trying to copy. SpaceX was originally funded, at low level, to serve as a backup to Boeing, but managed to bypass them. They now provide cheaper, more reliable travel through use of reusable boosters. The program supplying CSS uses traditional, disposable rockets, the Long March 5 and 6 and 7. These resemble the Atlas V, Delta IV and Delta IV Heavy. They appear to be reliable, but I suspect they are costly too. China is currently developing a series of reusable rocket systems. The Long March 9, for example will have the same lift capacity as SapceX’s Starship, we’re told. Will the Indian program choose this rocket to lift their space station, or will they choose SpaceX, or something else? The advantages of a reusable product mostly show up when you get to reuse it, IMHO.

Robert Buxbaum, September 10, 2024.

We’re depressed, allergic, overweight, alone, and demented. What causes what?

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Among the wonders of the western world is how many people are allergic to nuts compared to a few decades ago, and to gluten, and to a host of other things that hardly anyone was allergic to 50 years ago. Perhaps it’s a change in perception, but it doesn’t seem that way.

When I was in public school in NY, back in the 1960s, there was a subsidized lunch program serving, every day, peanut butter sandwiches. Peanut butter is nearly totally fat. It was ladled each day, from a giant tub, provided by the USDA, and slathered on USDA bread along with jelly from some other vat. The smell filled the lunch area, and the fats and sugars filled our stomaches. No one seemed bothered by the nuts, and no one showed obvious signs of passing out. And despite the ill diet, we were less obeease than today. Even today, in poor countries, thy still serve massive peanut butter dishes, or bread covered in lard, and these countries show fewer allergy problems, and less obesity in general.

Perhaps it is the lack of exposure to peanuts in the US that caused the allergy (sounds almost plausible), and maybe it’s the dietetic food that causes obesity, and the glut of non-gluten that causes gluten allergies. These connections may be false, but If true, it would suggest we’re in for many more problems.

Moving to depression and dementia. We’re seeing more and more of both, and at earlier ages. In our era, virtually everyone over 80 shows signs of clinical dementia, often Alzheimer’s dementia, but the rates are rising, especially in those 55-70, and it seems most every adult is depressed. I don’t know why, though lots of people on the internet have speculative explanations. There are also cures, and perhaps some work. The research behind at least one of the best hopes for an Alzheimers cure was shown to be falsified, just made up. Not that funding was stopped quite, highlighting another problem that is becoming more common: people in trust positions no longer behave in a trustworthy way. Nor are they punished for lying. Strange to add that an anti-obesity drug, Metformin, seems to actually work at weight loss, and helps against Alzheimers dementia. Then again, from other research, it seems that obesity protects from dementia.

Some of the problem seems to be societal, a lack of friendship and companionship. I could imagine that isolation leads to dementia, depression, and weight gain. Another thought, pushed by RFK Jr., is that new drugs and vaccines are responsible for allergies and ADHD, along with changes in diet. It’s possible. At least some comes from early diagnosis, and a change in the definition of dementia. Perhaps that’s the reason for the significant difference state to state. Yesterday’s curmudgeon is redefined as depressed, and drugged (more in some states than others), and becomes isolated (again more in some communities). The disoriented, lonely patient is then given anti anxiety drugs and classified as a dementia patient. It happens in some cases, but there seems to be a rise in real dementia too: the sort of stumbling and blankness that reflects general brain deterioration. As for ADHD, I’m still not convinced this is a new real disease; it could be that’s how boys always behaved.

Would we be less depressed or demented or less autistic with different vaccinations, or different foods, or with more human interaction? Would people be less isolated if they were less depressed or autistic? RFK’s family now claims that RFK Jr is demented himself for even asking these questions. My guess, totally unsupported is that the rise in allergies, dementia, obesity, and depression are related somehow, but I’m not convinced that RFK Jr. has picked out the right connection. What causes what? Perhaps someone can use statistics, or biology experiments to help untangle this stuff. It seems horribly important to the majority of Americans.

Robert Buxbaum, Sept 10, 2024. There was a. bit of a joke in the last comments: my daughter got a degree in epidemiology, and is employed in part to answer just the sort of questions I’ve posed.

Cursive writing is art, and should be taught in school

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Few people learn cursive these days with any skill or speed. It’s a shame. This is a form of traditional art and communication. Handwriting is a slower way of writing, that leads to a different type of letter or essay. The sentences are, typically longer, and the words more expressive because the experience of writing and reading cursive is more expressive than with text. The emotional state and energy of the writer comes through the cursive writing, because the writing itself is a form of creative art, adding to the words.

Send a letter or a post card, and you’ve sent a work of art. You’ve communicated words, or course, but far more than with a text or email. First off, there is the picture on the card. You bought that card, or took the picture. Then there is the art of how many words you use. Each letter is directed to only one person, not to 100 as with a text. As a result, people will keep your letter or card far more than they will not keep a text an email. It is more from you, and more to them. You are likely to put more (or different) things in: experiences and feelings that don’t go into an email or text-letter. The size of your writing communicates and even your cross-outs are part of a cursive communication. With email or text, there are no natural cross outs, and you can send the same letter to 100 people, so you write more blandly, with an eye for eventual reuse for someone else. A cursive note is intended for only one person, the one recipient, and this affects both the words, and the form of the words.

Cursive also lends itself to adding a small sketch or doodle. This becomes part of a personal part of the art in a way that does not fit with normal text. It’s calligraphy and conceptional art, an important part of education, and a continuation of western culture. In normal texts, some people have come to add emojis or GIFs, but these are nowhere near as personal or expressive. The cursive letter or note is personal and spicy. It’s an important art form, at least a valid an art form as any that could be taught in school, and it should be.

Robert E. Buxbaum, Sept 1, 2024. I’m running for school board, and like the idea of teaching basic knowledge as a foundation of creativity. One of these basics, I think, is cursive writing.

Fewer serial killers, more mass shootings, blame unfriendliness not lax gun laws

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It’s hard to notice the lack of something, but there’s been a sharp drop-off in the the number of serial killers. Nearly gone are folks like John Wayne Gacy (the clown killer), Jeffrey Dahmer (severed heads, cannibalism, necrophilia), Gary Ridgway, “The Green River Killer” (71 prostitutes killed). Mostly, they were sexual sadists, men who’d have sex with strangers (able or female) and then kill them. In 1987, there were 198 active in the US and many more inactive; by 2018 it was down to 12. And these few are less-prolific, and less-colorful, like Anthony Robinson, “the shopping cart killer”, who killed 4-6 in DC, transporting the bodies in shopping carts.

It’s not clear why there are so few these days. Perhaps it’s the prevalence of surveillance cameras, or improvements in DNA and other pic technology. But these explanations don’t explain why there were so few before 1960. There were some mass murderers, “Jack the Ripper,” “the Boston Strangler” but few before 1960.

Police like to credit the drop off to their detective skills, but there are still plenty of violent crimes that go unsolved, about half the murders in Detroit for example, or most of the rapes in Europe. I suspect that serial killing spiked up in the 60s because of a spike in friendliness, and spiked down in the 2000s because it ended. Before the hippy era, people were cautious of gangsters, rapists, homosexuals, and spies under the bed. But that changed in the 60s. Folks thought it was cool to hitchhike, or pick up random guys. Now, we’re back to being cautious.

A personal story: I was visiting Toronto in the late 1980s and someone I didn’t know overheard that I was planning to drive back to Detroit that afternoon. He asked if I would not mind driving his teenaged daughters to Detroit to see their grandmother, and I said “yes.” At the border, the guards asked who these girls were, and I said I didn’t know. I hadn’t asked. The border guards let us through without passports after a call to the grandmother. I would not be as ready to offer a ride today, and the parents would not be as trusting, nor would the guards.

Serial killings are down since 1990, but mass shootings are up.

Despite much the stricter gun laws, there’s been a rise in crime and a steady growth in the number of murderers in our major cities. There’s also been a rise in synagogue attacks, and a rise in mass murders. These folks kill many in one day or as part of gang-drug activity. Stricter gun laws seem to have made things worse, not better. They do not stop the killers and they hamper the defenders. I took a look at synagogue attacks, and find a pistol would have helped.

On a societal level, I think it would help to have fewer illegal aliens, or aliens who enter with no positive record or skills. It would help to have psychological treatment and lockup for crazy folks and prisoners. Currently, we send violent crazy folks out on the streets until they do something true horrific. More consistent prison sentences are needed for criminals too. We’ now’ve come to use the courts for political theater: Biden’s son should not go to jail for years because he lied on a gun purchase, nor should Trump get for putting down a prostitute as “legal fees”. Nor is his half-billion dollar fine appropriate. Minor crime deserves minor punishment. As a result of our crazy courts, violent criminals are let go as with the MSU killings near me. He was a crazy violent black man, and there was no way, in the law to give him a short sentence, or counseling, or job training. When our incarcerated leave prison, they have anger, plus no jobs or skills. Don’t be surprised when these folks turn to violent crime.

Robert Buxbaum, June 23, 2024

Germany’s hydrogen trains and boats almost make sense

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Germany’s green transition is a disaster. Twenty years ago, Germany had 23 nuclear power plants that generated 30% of the country’s electricity cleanly, cheaply, and reliably. These plants have all been shut by the government as part of a commitment to clean energy. What could be cleaner? Germany has switched to a mix of wind and solar, plus a significant shift to coal power. Wind and solar use a lot of land compared to nuclear, and they break down leaving fields of debris. There is now a lack of electricity to power homes and industries, and what power there is, is unreliable, due to the many dark windless days in Germany.

The lack of reliable electricity is crippling German industry now that Russian gas has been cut off. In this environment, why would the Germans order special trains and boats that burn, hydrogen that’s made from electricity and natural gas? My understanding of the reason is that, Germany sometimes has too much wind power and nothing to do with it. They plan to store this excess by making hydrogen that they can use to power their trains and boats. The cost is high, and the efficiency is poor, but the electricity is free.

Hydrogen is not as compact a fuel as gasoline, nor is it as cheap as electricity, but it’s cleaner than gas, and in some ways it’s better than battery-stored electricity. While hydrogen takes a lot of storage space relative to gasoline, high pressure helps, and the storage is cheaper than with batteries. Also, hydrogen fuel is transferred faster than electric fuels. Trains and ships are chosen for hydrogen because they are good at carrying bulky items. The transition to hydrogen is relatively straightforward with trains, since many are already powered by electricity. Hydrogen fuel cells can make the electricity on board (in theory), while avoiding the need for expensive overhead wires. The idea sort-of makes sense.

Germany’s first hydrogen train. cancelled after 1 year of poor operating.

The first German train to use hydrogen powered them with fuel cells that generated electricity. It began service in October 2022, but the fuel cells proved unreliable. Service ended one year later, October 2023, replaced by polluting diesel (see here). The Hannover line plans to replace these with battery-powered trains over the next few years. There are also plans for a hydrogen-powered ferry, but it is not clear why the ferry should prove more reliable than the train, or cheaper.

San Francisco’s hydrogen-powered ferry, $30 million, 15 knots top speed, 75 passengers, no cars. Long delayed.

In the US, the Biden administration has paid, so far, $30 million for a hydrogen ferry in San Francisco. It’s two years behind schedule and over cost, taking only 75 passengers and no cars at 15 knots, 17mph. In the US, and likely in Germany, most of the hydrogen will be made from natural gas. A better solution, I think would be to power the ferris and trains by natural gas and to store the excess electricity in land-based batteries or as land-based hydrogen for land-based fuel cells.

Germany is committed to electric trains, though, and hydrogen provides a route to power these trains with excess electricity. German customers take the train, in part, because they like them, and in part because German politicians have banned short-hop planes on competing routes, and subsidized electric trains. Yet another option to balance times of excess solar and wind power would be to subsidize electric cars, or at least allow theirs owners to trade electricity: to buy electricity when it’s cheap and resell it to the grid when demand and prices are high.

Robert Buxbaum, June 8, 2024

How I size heat exchangers

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Heat exchange is a key part of most chemical process designs. Heat exchangers save money because they’re generally cheaper than heaters and the continuing cost of fuel or electricity to run the heaters. They also usually provide free, fast cooling for the product; often the product is made hot, and needs to be cooled. Hot products are usually undesirable. Free, fast cooling is good.

So how do you design a heat exchanger? A common design is to weld the right amount of tubes inside a shell, so it looks like the drawing below. The the hot fluid might be made to go through the tubes, and the cold in the shell, as shown, or the hot can flow through the shell. In either case, the flows are usually in the opposite direction so there is a hot end and a cold end as shown. In this essay, I’d like to discuss how I design our counter current heat exchangers beginning a common case (for us) where the two flows have the same thermal inertia, e.g. the same mass flow rates and the same heat capacities. That’s the situation with our hydrogen purifiers: impure hydrogen goes in cold, and is heated to 400°C for purification. Virtually all of this hot hydrogen exits the purifier in the “pure out” stream and needs to be cooled to room temperature or nearly.

Typical shell and tube heat exchanger design, Black Hills inc.

For our typical designs the hot flows in one direction, and an equal cold flow is opposite, I will show the temperature difference is constant all along the heat exchanger. As a first pass rule of thumb, I design so that this constant temperature difference is 30°C. That is ∆THX =~ 30°C at every point along the heat exchanger. More specifically, in our Mr Hydrogen® purifiers, the impure, feed hydrogen enters at 20°C typically, and is heated by the heat exchanger to 370°C. That is 30°C cooler than the final process temperature. The hydrogen must be heated this last 30°C with electricity. After purification, the hot, pure hydrogen, at 400°C, enters the heat exchanger leaving at 30°C above the input temperature, that is at 50°C. It’s hot, but not scalding. The last 30°C of cooling is done with air blown by a fan.

The power demand of the external heat source, the electric heater, is calculated as: Wheater = flow (mols/second)*heat capacity (J/°C – mol)* (∆Theater= ∆THX = 30°C).

The smaller the value of ∆THX, the less electric draw you need for steady state operation, but the more you have to pay for the heat exchanger. For small flows, I often use a higher value of ∆THX = 30°C, and for large flows smaller, but 30°C is a good place to start.

Now to size the heat exchanger. Because the flow rate of hot fluid (purified hydrogen) is virtually the same as for cold fluid (impure hydrogen), the heat capacity per mol of product coming out is the same as for mol of feed going in. Since enthalpy change equals heat capacity time temperature change, ∆H= Cp∆T, with effectiveCp the same for both fluids, and any rise in H in the cool fluid coming at the hot fluid, we can draw a temperature vs enthalpy diagram that will look like this:

The heat exchanger heats the feed from 20°C to 370°C. ∆T = 350°C. It also cools the product 350°C, that is from 400 to 50°C. In each case the enthalpy exchanged per mol of feed (or product is ∆H= Cp*∆T = 7*350 =2450 calories.

Since most heaters work in Watts, not calories, at some point it’s worthwhile to switch to Watts. 1 Cal = 4.174 J, 1 Cal/sec = 4.174 W. I tend to do calculations in mixed units (English and SI) because the heat capacity per mole of most things are simple numbers in English units. Cp (water) for example = 1 cal/g = 18 cal/mol. Cp (hydrogen) = 7 cal/mol. In SI units, the heat rate, WHX, is:

WHX = flow (mols/second)*heat capacity per mol (J/°C – mol)* ∆Tin-out (350°C).

The flow rate in mols per second is the flow rate in slpm divided by 22.4 x 60. Since the driving force for transfer is 30°C, the area of the heat exchanger is WHX times the resistance divided by ∆THX:

A = WHX * R / 30°C.

Here, R is the average resistance to heat transfer, m2*∆T/Watt. It equals the sum of all the resistances, essentially the sum of the resistance of the steel of the heat exchanger plus that of the two gas phases:

R= δm/km + h1+ h2

Here, δm is the thickness of the metal, km is the thermal conductivity of the metal, and h1 and h2 are the gas-phase heat transfer parameters in the feed and product flow respectively. You can often estimate these as δ1/k1 and δ2/k2 respectively, with k1 and k2 as the thermal conductivity of the feed and product, both hydrogen in my case. As for, δ, the effective gas-layer thickness, I generally estimate this as 1/3 the thickness of the flow channel, for example:

h1 = δ1/k1 = 1/3 D1/k1.

Because δ is smaller the smaller the diameter of the tubes, h is smaller too. Also small tubes tend to be cheaper than big ones, and more compact. I thus prefer to use small diameter tubes and small diameter gaps. in my heat exchangers, the tubes are often 1/4″ or bigger, but the gap sizes are targeted to 1/8″ or less. If the gap size gets too low, you get excessive pressure drops and non-uniform flow, so you have to check that the pressure drop isn’t too large. I tend to stick to normal tube sizes, and tweak the design a few times within those parameters, considering customer needs. Only after the numbers look good to my aesthetics, do I make the product. Aesthetics plays a role here: you have to have a sense of what a well-designed exchanger should look like.

The above calculations are fine for the simple case where ∆THX is constant. But what happens if it is not. Let’s say the feed is impure, so some hot product has to be vented, leaving les hot fluid in the heat exchanger than feed. I show this in the plot at right for the case of 14% impurities. Sine there is no phase change, the lines are still straight, but they are no longer parallel. Because more thermal mass enters than leaves, the hot gas is cooled completely, that is to 50°C, 30°C above room temperature, but the cool gas is heated at only 7/8 the rate that the hot gas is cooled. The hot gas gives off 2450 cal as before, but this is now only enough to heat the cold fluid by 2450/8 = 306.5°. The cool gas thus leave the heat exchanger at 20°C+ 306.8° = 326.5°C.

The simple way to size the heat exchanger now is to use an average value for ∆THX. In the diagram, ∆THX is seen to vary between 30°C at the entrance and and 97.5°C at the exit. As a conservative average, I’ll assume that ∆THX = 40°C, though 50 to 60°C might be more accurate. This results in a small heat exchanger design that’s 3/4 the size of before, and is still overdesigned by 25%. There is no great down-side to this overdesign. With over-design, the hot fluid leaves at a lower ∆THX, that is, at a temperature below 50°C. The cold fluid will be heated to a bit more than to the 326.5°C predicted, perhaps to 330°C. We save more energy, and waste a bit on materials cost. There is a “correct approach”, of course, and it involves the use of calculous. A = ∫dA = ∫R/∆THX dWHX using an analytic function for ∆THX as a function of WHX. Calculating this way takes lots of time for little benefit. My time is worth more than a few ounces of metal.

The only times that I do the correct analysis is with flame boilers, with major mismatches between the hot and cold flows, or when the government requires calculations. Otherwise, I make an H Vs T diagram and account for the fact that ∆T varies with H is by averaging. I doubt most people do any more than that. It’s not like ∆THX = 30°C is etched in stone somewhere, either, it’s a rule of thumb, nothing more. It’s there to make your life easier, not to be worshiped.

Robert Buxbaum June 3, 2024

Veteran owned business startup ideas

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Someone has to repair airplanes, why not you?

I started my own business, rebresearch. It puts food on my table, and provides satisfaction that I’m helping people. It seems to me that other folks, particularly veterans, could benefit from owning their own businesses. Veterans seem to possess more of the skills for successful business startup than found the general population, and I notice that veterans start businesses more than most folk do, too.

Some 50% of returning veterans from WWII started their own businesses, I’ve read, and some were very successful. Walmart, the world’s largest retail company, for example, was founded by WWII Army intelligence officer Sam Walton. Then there’s FedEx, founded by Fred Smith, a Marine Corps Veteran of Vietnam, two tours, where he earned two Purple Hearts, a Bronze Star, and Silver Star.

Both of the above are in supply/ logistics, but veterans also open real estate shops, coffee shops, construction… Their success rate is higher than non-veterans perhaps due to skills they may not appreciate: physical stamina, organization, discipline, and the ability to “get the job done.” Having a successful business requires that you either show up every day at 6:30, or 7:30 — and to have a trusted replacement ready if you can’t. Many folks in the population don’t seem to understand the need to show up. This Is not to say that starting a successful business is easy, even if you show up and know what you’re doing, but reliability and hard work go a long way. Besides, many veterans have specific skills that transfer directly. See below, some business ideas with links to veteran-started companies in each area.

Aerospace and Defense
Aerospace and Defense Contracting (85) Aerospace and Defense Consulting (81) Aerospace and Defense Parts Distributors (43)		Agriculture and Forestry
Farms (101) Land Surveying and Mapping (46) Animal Control Services (30)
Arts and Entertainment
Photography Services (311) Artists and Art Related(138) Production Studios (126)		Automotive
Auto Repair Services (214) Auto Glass and Windshield Replacement (110) Auto Windshield Repair (90)
Business Services
Consulting Services (403) Franchises (281)Information Technology (222)		Commercial Contracting
Commercial General Contractors (366) Commercial Renovation, Maintenance and Repair Services (291)Commercial Cleaning Services (252)
Construction
Construction Management Services (274) Plumbing Services (109) Custom Home Builders (101)		Education and Training
Firearms Training and Instruction (243) Leadership Training Programs (86) Martial Arts Training (83)
Employment Services
Staffing (163) Recruiting Firms (99) Human Resources Consulting (73)		Energy and Utilities
Solar Energy (92) Energy Consulting Services (73) Green Energy (63)
Engineering Services
Civil Engineering (85) Architectural Engineering Services (80) Land Surveying and Mapping Services(52)		Environmental Services
Environmental Consulting Services (73) Recycling Services(37) Environmental Engineering Services (35)
Financial Services
Financial Advisors (170) Tax Preparation Services(155) Bookkeeping Services (150)		Food and Drink
Restaurants and Dining (191) Catering (137) Commercial Sales and Delivery (114)
Government
Government Consulting (95) Government Contract Consulting (75) Government Procurement Services(38)		Health, Medical and Dental
Exercise and Rehabilitation Services (199) Wellness Programs (181) Medical Equipment and Parts (143)
Insurance Services
Insurance Agencies (174) Life Insurance (160) Auto Insurance (117)		Internet Services
Web Design (420) Search Engine Optimization (SEO) (220)Web Development (172)
Legal Services
Law Firms (261) Legal Notary Services (136) Process Server Services (94)		Lodging and Travel
Travel Services (86) Vacations and Getaways (56) Vacation Cruises (49)
Manufacturing
Wood Products Manufacturing (120) Machine Shops(115) Fabrication (108)		Marketing and Sales
Marketing Services (207) Advertising Services (120) Public Relations (PR) (43)
Nonprofit and Free Help
Veterans Service Offices (VSO) (699) Veterans Services (685) Chamber of Commerce (399)		Publishing and Printing
Printing Services (209) Graphic Design Services (113)Embroidery Services (95)
Real Estate Services
Home Inspection Companies (507) Real Estate Agents (Independent) (430) Real Estate Agencies (313)		Residential Services
Residential Construction, Repair and Improvements (919)Residential Cleaning Services (405) Residential Landscape Services (335)
Security and Safety
Security Services (234) Surveillance and Alarm Systems (205) Investigations (191)		Stores and Dealers
Clothing, Shoe Stores and Accessories (357) Online Stores(336) Food and Drink Stores (291)
Technology
Information Technology Services (521) Technology Support Services (173) Telecommunications (160)		Transportation Services
Transportation Logistics Services (214) Trucking and Transportation Companies (193) Trash and Junk Haulers(180)
veteran-owned business directory copied from https://www.veteranownedbusiness.com.

One advantage of stating a business over working for others is that you are guaranteed to get hired. And you can hire your wife, etc. Also, there’s a bigger up-side than working for others. There are tax benefits too — your car and computer can be bought with pre-tax dollars assuming you use them in the business. These are not insignificant benefits — usually your tax bracket is higher than your profit margin. You generally have to work more hours per day as an entrepreneur, but if you like the work and have the skills that might not be too bad.

Perhaps you learned cybersecurity

Veterans often have credentials and skills that are rare in the country at large, and this can set you up for a good job. A high security clearance, for example– it’s necessary for many jobs in security –or skills in airplane repair, fire-arms, martial arts, shipping, recruiting, food service, communications, security, commissary… If these areas appeal to you, you can get extra training, either while still in the military or outside, and the gov’t will often pay for it. If you’re already out, think of using your VA benefits to go to school. You’ll want to fill in gaps, too, like in accounting. Good luck.

Robert Buxbaum May 14, 2024

7% of new US vehicles were EVs in 2023. Expect slow growth in 2024.

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About 7% of new US car and truck sales in 2023 were electric, 1.2 million vehicles. Of these, about 55% were Teslas. These numbers make sense based on US manufacturing and driving habits, so I don’t expect fast sales growth in 2024.

Currently home owners are the only major group of private drivers that save on fuel cost from owning an EVs. Home owners pay relatively little for electricity, about 11¢ per kWh, and they can generally charge their EVs conveniently, at home, overnight. Charging is more expensive and inconvenient for apartment dwellers. As a result, in 2023, some 95% of US EV sales went to home owners. Over 2 to 3 years they could hope to recover in gasoline savings the $7000 more that their EVs cost compared to petrol-powered vehicles, but they still have to drive a fair amount. A full charge of 80kWh EV at home will cost about $8.80 at current rates. This will power about 250 miles at a cost of 3.5¢/mile = $8.80/250.

Home, level 2 Chargers will cost about $1500 including the electrician cost.

The cost of gasoline is about 16.5¢/mile = $3.80/gal/ 23mi/gal) suggesting that you save 13¢ per mile by owning an EV. In order to recover the extra $7000 cost of the car in two years, you’d have to drive 27,000 miles per year, or 74 miles per day. To recover the difference in three years, you must drive 50 miles per day or 18,000 miles per year. This is more than most people drive.

EVs also offer reduced maintenance, but customers can balance this against the inconvenience of long charge times and spotty availability of chargers. My sense is that the fraction of Americans who benefit and drive 50-75 miles per day is about 7%. This fraction will increase as EVs get cheaper, but families that can benefit already own an EV.

The average Tesla costs today about $3000 more than the equivalent petrol car, but that still makes it relatively expensive, and it seems that the price differential was intentionally set to match sales to Tesla’s production capacity. Tesla could make EVs cheaper than petrol cars and still make a profit on each, but if they did this, they would have too much demand. Other US auto makers are mostly lose money on EVs and are unmotivated to lower prices. Based on this, my sense is that it is unlikely that sales will be much higher in 2024 than the 1.2 million sold in 2023.

The Chinese have plenty of new EVs, and they are eager to export. Their car market is currently about 50% EV, with companies like BYD selling EVs for as little as $12,000. The Chinese government subsidizes production and powers their EVs with cheap electricity by burning coal. These cars do not seem very good, compared to Tesla, but at this price they would flood the market if allowed to compete. The US government has kept them out with tariffs and with complaints about slave labor. Trump has promised a yet higher tariff, 100% on Chinese cars, if elected. The intent is to preserve US jobs and manufacturing. This is one of those situations where tariffs are good, IMHO.

Toyota Prius, the most popular hybrid.

Hybrids are a third option, cheaper than EVs, high mpg than normal engines. Though they are sometimes touted as a transition to EVs, to me they’ seem to suit a completely different demographic: those who don’t own their own home and drive a lot. Toyota makes the most popular hybrids in the US. They cost about $4000 more than the equivalent petrol car, $30,000 for a Prius vs $26,000 for a Corolla. When using a Prius in the city, you’ll get about 50 mpg, spending 7.5¢ per mile ($3.80/gal / 50 mpg = 7.5¢). This implies a gas savings of about 9¢ per mile vs an ordinary Corolla. Based on this, you have to drive about 27,000 miles per year in the city to recover the cost difference in two years. That’s a lot, and your performance is typically worse with a hybrid: you have a heavier car with a small engine. Maintenance cost is also higher with a hybrid than with an EV: you still need oil changes, fluid changes, belts, etc. and the mpg advantage vanishes on the highway. A hard driving home owner is better off with an EV, IMHO, an apartment dweller with a hybrid. Hybrids also should make sense for taxis and local-haul trucks. I can imagine hybrid sales rising in 2024, perhaps as high as 15% of vehicle sales. What we’re all waiting for is more near-shore manufacturing (or mandates), and this is not likely in 2024.

Robert Buxbaum April 28, 2024