Pittsburgh Years

Almost Nothing

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here’s almost nothing in outer space; clusters of stars here and there, quite a bunch of planets apparently, mostly gaseous, a few eccentric comets, some leftovers (the odd meteorite), and then, possibly, “dark matter”, whatever that is (it’s being worked on).  But space itself, the immense playground of these “things”, is otherwise empty, null, nada.  In particular, there is no air, which is just the thing we people need most.  Well, usually it is, but occasionally it is not, it is something we don’t want and want to get rid of.  For this purpose, here on earth, surrounded by air, we have invented a thing called a vacuum chamber.

These chambers, emptied as much as possible of air, do not have a great many uses.  But the few uses they do have are important ones.  One of course is to simulate conditions in space.  A space suit, for example, can be put in a vacuum chamber here on earth to see if it leaks or, more generally, just to see if it works as well as it ought to.  Certain types of welding can best be done in a vacuum.  Some sorts of coatings can be applied best to materials within a vacuum.  Another use, and the one which will most interest us here, is drying, the dispersion of water.

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Broadway in Manhattan - 1890
In 1887, G. Westinghouse, Jr., of Pittsburg (the letter h had not yet been added to the city’s name), patented a gizmo which changes an electrical current from one voltage to another.  He called it an electrical converter; today we call them transformers.  Electricity, at high voltage, travels better: the wire doesn’t have to be as thick, and less of the electricity is lost from a long wire that must travel over many miles.  This might not sound extraordinarily important, but it is; because it’s the only practical way to get a current that has been generated at a power plant somewhere in the country out to cities, where most of it is used.  Try to imagine Los Angeles with a power plant every few blocks or so.  Worse, if you lived in the suburbs you would still be using kerosene to read with.  In fact, there probably would be no suburbs.  So it’s a big deal.

The trouble with transformers is that they get warm—hot, actually.  And they are made up of layer after layer of metal plates and coils, all packed closely together.  So to keep them from melting when they are turned on they must first be thoroughly dried and then filled with some sort of oil to act as a coolant.  The equipment can contain no water, nor even water vapor.  Otherwise, under heat,  it would turn into steam and cause no end of problems.  Vacuum chambers work very well for “extreme” drying because when the air gets pumped out, so does the water vapor.  It doesn’t get any drier than this here on earth.

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The electric superhighway
Certain transformers can be very large, not like the little ones you see on the wooden poles near your home.  Very large.  The reason they’re very large is that they have a very special use.  They step-up, or step-down the electrical voltage at each end of a high-voltage transmission line: up to go on the line and down when coming off the line.  The electrical grid, as it is called, is like a network of highways.  High voltage electric lines are the superhighways of the grid, and then, when they get to a place that needs power, they take some of it off the main line and step it down to a lower voltage, closer to that required by the equipment that is to be powered.  This, in effect, is an off-ramp.  The on-ramp is at the power plant itself.

Vacuum chambers are built in a variety of sizes, from rather small, for research work on small things, to large, to very large.  They are interesting for structural people to design because they’re quite unlike the design of a building or a bridge, the ordinary things that these designers plan-out all the time; new things are interesting.  A building and a bridge have essentially two types of loads: gravity loads, pushing down; and wind loads, pushing over.  A vacuum chamber is nothing like that.  Ordinarily they most resemble a vessel—not a ship, a pressure vessel.  And ordinarily they are shaped in just that way as well, with elliptical “heads”, for the simple reason that the loads on a pressure vessel, generally speaking, push outwards in all directions, thus the name “pressure” vessel.  A vacuum chamber is like that, except that all the loads are reversed—they push in.

A submarine is, in a sense, like a vacuum chamber too, the pressure of the water pushing in from all sides at once, and they are also shaped in such a way that the form itself helps to resist the pressure.  They are shaped like a cigar because this shape helps to resist forces that are pushing in on it from all sides (and of course submarines need to be streamlined as well to move easily through the water).

Since you walk around every day, and don’t feel any pressure (at least not from the air), you might reasonably ask: what’s the big deal about vacuum chambers?  It is this: the pressure inside your body is roughly the same as the pressure outside of your body, so you don’t feel much of anything at all, (unless you burp).  And where does this air pressure come from?  Air is not heavy; one can hardly feel it; if it weighs anything, it’s not as heavy as cotton.  But that is wrong; it is an illusion.

The extreme weight of air comes from the weight of the atmosphere that surrounds our earth.  On the one hand it’s difficult to conceive that air itself is heavy; it doesn’t seem like much of anything at all.  It’s mostly nitrogen and oxygen, not really heavy stuff.  But there is quite a lot of it out there.  It extends from the surface of the earth out nearly 75 miles, getting thinner and thinner the farther out one goes.  Yet, the gravity of our planet acts on it just the same, so the pressure adds up, and adds up, by the time you down to the surface of the earth.

The number ordinarily used for the weight of the atmosphere at sea level is 14.7 pounds per square inch.  That doesn’t sound like much, a bag of groceries, but multiply it times 144, the number of square inches in a square foot, and you get well over 2000lbs per square foot.  To a structural designer that’s a big number.  For comparison, consider that the last department store you walked through was probably designed for about 100lbs per square foot, and the place where you live is designed for perhaps 40lbs per square foot.

The other aspect of this heavy load that is interesting, because different than the ordinary structures that designers deal with, is that as the chamber is exhausted (not tired—the air removed) the pressure pushes in from all directions: down certainly, as do all gravity loads, but also up, and sideways, all at the same time, because air is essentially a fluid; in other words it’s trying to squash the thing you want to build as you might try to squash a raw egg from all angles.  But an egg, due to its shape, has a natural compressive resistance, similar in a way to that of an arch. This is why very deep water exploration is performed using bathyspheres

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A large vacuum chamber
Blaw-Knox designed and built not only petrochemical plants but occasionally other large components of production as well, each a unique design challenge.  A quite large vacuum chamber is pictured to the right.  Notice the size of the man at the bottom.  But this so-called large vacuum chamber was a miniature in comparison to what The General Electric Company needed.  They needed one to be used to dry out very large electrical transformers.  And it was to be rectangular—which didn’t help anything—and it was to be gigantic, much larger than the one pictured here.  It was to be large enough to accept a complete railroad car on which a single huge transformer was loaded, the railroad tracks extending into the chamber itself.

For some reason—it seems to me an illness—the engineer who was supposed to do this design work was not available and a deadline was approaching.  Since no one else was available at that particular time, I was given this unusual structural design project.  It was to be designed as a giant rectangular box made of steel plate and reinforced with a series of large, closely spaced, welded-steel beams that encircled entire box, like rubber bands.  It was a brute force approach.  At one end was a great, heavy, steel door on some sort of sliding mechanism.  Large enough for the railroad car and it’s transformer, it was made from 4 inch thick plate.  This vacuum chamber must have cost a fortune, but it taught me a great deal concerning structures that were not everyday occurrences.