The story of Einstein’s refrigerator [Mad Physics]

We are likely to consider Albert Einstein has a highfalutin theoretical physics guru, but the physicist also worked on far more everyday tasks…like developing an energy-efficient refrigerator. Allow Jennifer Ouellette from Cocktail Party Physics to provide an explanation for.

Ah, innovation! What would we do without this driver of latest technology and new consumer markets? Science is the breeding ground for said technological creativity, and even those scientists who focus primarily on curiosity-driven basic research – which includes theoretical physics – often find their curiosity piqued by the challenge of finding a method to a real-world problem. 

Take, for instance, Albert Einstein, best known to most people for devising the area’s most famed equation: E=mc2.  But his contributions to physics extend over an impressively broad range of topics, including Brownian motion, the photoelectric effect, special and general relativity, and stimulated emission, which brought about the advance of the laser. Less favourite, even among physicists, is his work with Leo Szilard to develop an energy efficient absorption refrigerator without moving parts.

Szilard was born in Budapest, Hungary in 1898, the son of a civil engineer. In 1916, he enrolled as an engineering student at Budapest Technical University, but his education was interrupted the subsequent year, when he joined the Austro-Hungarian Army. After the war, he attended the Institute of Technology in Berlin – not so much by choice, as due to ” racial quotas” (he fled Berlin in 1933 to escape Nazi persecution) – where he met Albert Einstein and Max Planck. Szilard earned his doctorate in physics in 1922, and he and Einstein became close friends.

His dissertation was in thermodynamics, and in 1929 he published a seminal paper, ” On the Lessening of Entropy in a Thermodynamic System by Interference of an Intelligent Being” – element of an ongoing attempt by physicists to raised understand the ” Maxwell’s Demon” thought experiment first proposed by James Clerk Maxwell. It contained a description of ” Szilard’s engine,” a hypothetical heat engine that violates the second law of thermodynamics by continuously turning the heat energy of its environment into work.

This was the example the Spousal Unit featured in a blog post prior to the Thanksgiving holiday, about a new Maxwell’s-Demon-type experiment conducted by Shoichi Toyabe and collaborators in Japan, that appeared recently in Nature. Alas, as with many things inside the nuanced field of thermodynamics, the end result was misinterpreted in different press accounts as converting information into energy. Per the Spousal Unit: ” That’s not quite right – it’s more like using information to extract energy from a heat bath.” And he cited Szilard’s Engine let’s say the adaptation:

Consider two pistons with an analogous number of gas particles inside, with an identical total energy. But the end container is in a low-entropy state with the whole gas on one side of the piston; the bottom container is in a high-entropy state with the gas equally opened up.You spot the variation – from the tip configuration we will extract useful work by simply allowing the piston to expand. Inside the process, the full energy of the gas goes down (it cools off). But inside the bottom piston, nothing’s going to happen. There’s just as much energy inside there, but we will’t get it out because it’s in a high-entropy state.

In 1929, Leó Szilárd used an analogous setup to ascertain a great result: the connection between energy and data. The connection isn’t that ” information carries energy” ; if I let you know some information about gas particles in a box, that doesn’t change their total energy. But it surely does assist you to extract that energy. Effectively, learning additional information lowers the entropy of the gas. That’s a loosey-goosey statement, [we adore that the Spousal Unit says stuff like " loosey-goosey" ] because there is a couple of strategy to define ” entropy” ; but one reasonable definition is that the entropy is a measure of the data you don’t have about a system. (Within the piston above, we know more concerning the gas within the low-entropy setup, since we’ve a wiser idea of where it’s localized.)

Anyway, the point is, that early dissertation work of Leo’s proved useful when it came time to design a new form of refrigerator. Szilard had a knack for invention, applying for patents for an x-ray sensitive cell and improvements to mercury vapor lamps while still a young scientist. He also filed patents for an electron microscope, in addition as the linear accelerator and the cyclotron, all of which have helped revolutionize physics research. Szilard’s most necessary contribution to 20th century physics was the neutron chain reaction, first conceived in 1933. In 1955, he and Enrico Fermi received a joint patent on the first nuclear reactor, which america Patent Office compared in significant to the patents issued for the telegraph and telephone within the 19th century.

Einstein wasn’t a stranger to the patent process, either, having worked as a patent clerk in Berlin as a young man. He later received a patent with a German engineer named Rudolf Goldschmidt in 1934 for a working prototype of a hearing aid. A singer of Einstein’s acquaintance who suffered hearing loss provided the foundation for the invention.

The impetus for the two men’s collaboration on a refrigerator occurred in 1926, when newspapers reported the tragic death of a whole family in Berlin, because of toxic gas fumes that leaked inside the house while they slept, the outcome of a broken refrigerator seal. Such leaks were occurring with alarming frequency as more people replaced traditional ice boxes with modern mechanical refrigerators which trusted poisonous gases like methyl chloride, ammonia and sulfur dioxide as refrigerants. Einstein was deeply plagued by the tragedy, and told Szilard that there should be a stronger design than the mechanical compressors and toxic gases used within the modern refrigerator. Together they set out in finding one.

And now, a quick primer on how your refrigerator works. Among the neat things about thermodynamics is that once you can create a giant enough differential – for instance, a gigantic difference in temperature between two compartments – you’ve got yourself a handy energy source to tap into should the will arise. Refrigerators work on an easy concept referred to as the Carnot cycle. Gas – usually ammonia or freon this present day, not the toxic gases more common during Einstein’s era – is pressurized in a chamber, said pressure causes that gas to heat up, this heat is then dissipated by coils on the back of the applying, and the gas condenses into a liquid. It’s still highly pressurized, sufficiently so that the liquid flows through a hole to a second low-pressure chamber.

That abrupt change in pressure makes the liquid ammonia boil and vaporize into a gas again, also dropping its temperature – thereby keeping your perishable foodstuffs nicely chilled. The cold gas gets sucked back into the first chamber, and the total cycle repeats without end – or a minimum of so long as the applying is plugged in. That’s always the catch, you spot. The refrigerator seriously isn’t a really ” closed system” : it gets a relentless influx of energy from the wall outlet that permits it to operate continuously. Left on its own, without that crucial influx, and the internal would cease to be nicely chilled, and the whole food therein would perish.

To address the toxic gas concerns, Einstein and Szilard focused their attention on absorption refrigerators, by which a heat source – in that time, a natural gas flame – is used to drive the absorption process and release coolant from a chemical solution, as opposed to a mechanical compressor. An earlier version of this technology were introduced in 1922 by Swiss inventors, and Szilard found the way to improve on their design, drawing on his expertise in thermodynamics. His heat source drove a mixture of gases and liquids through three interconnected circuits.

They still needed some version of a Carnot cycle. Anyone who lives at high altitudes (Denver residents, we’re watching you!) knows that water boils at lower temperatures when the air pressure is lower, as is the case within the Mile-High City. (Air pressures are higher at sea level.) The Einstein-Szilard fridge exploited this effect, using just pressurized ammonia, butane and water, while not having for electricity to operate the application (counting on your choice of heat source), and no moving parts – thereby eliminating the potential of seal failure.

One side contained a flask full of butane (the evaporator), which was then injected by a new vapor (the ammonia) just above the butane, creating that every one-important differential. This could decrease the boiling temperature, and as the liquid water boiled off, it sapped energy from its surroundings – chilling the compartment inside the process.

One of the components the two physicists designed for their refrigerator was the Einstein-Szilard electromagnetic pump, which had no moving parts, relying instead on generating an electromagnetic field by running alternating current through coils. The sphere moved a liquid metal, and the metal, in turn, served as a piston and compressed a refrigerant. Anything else of the process worked similar to today’s conventional refrigerators.

Einstein and Szilard needed an engineer to aid them design a working prototype, and they found one in Albert Korodi, who first met Szilard when both were engineering students at the Budapest Technical University, and were neighbors and good friends when both later moved to Berlin.

The German company A.E.G. agreed to develop the pump technology, and hired Korodi as a whole-time engineer. But the device was noisy simply by cavitation as the liquid metal undergone the pump. One contemporary researcher said it  ” howled like a jackal,” although Korodi claimed it sounded more like rushing water. Korodi reduced the noise significantly by varying the voltage and lengthening the number of coils within the pump. Another challenge was the choice of liquid metal. Mercury wasn’t sufficiently conductive, so the pump used a potassium-sodium alloy instead, which required a different sealed system because it really is so chemically reactive.

Despite filing more than 45 patent applications in six different countries, none of Einstein and Szilard’s alternative designs for refrigerators ever became a client product, although several were licensed, thereby providing a tidy bit of extra income for the scientists over time. And the Einstein/Szilard pump proved useful for cooling breeder reactors. The prototypes were not energy efficient, and the excellent Depression hit many potential manufacturers hard. Nevertheless it was the introduction of a new non-toxic refrigerant, freon, in 1930 that spelled doom for the Einstein/Szilard refrigerator. The economics supported the freon-based mechanical compressor technology, and that’s what most fogeys still use today.

Interest in their designs has revived lately, fueled by environmental concerns over climate change and the impact of freon and other chlorofluorocarbons on the ozone layer, in addition as the will find alternative energy sources. In 2008, a team at Oxford University led by Malcolm McCulloch (an electrical engineer who is obsessed on green technologies) built a prototype as component of a project to develop more robust appliances. They modified the design slightly, replacing the kinds of gases used, in hopes of quadrupling the efficiency of Einstein and Szilard’s original design. McCulloch may be toying with the notion of using a solar-powered heat pump to make the application even more energy efficient.

Meanwhile, other scientists at rival Cambridge University have explored cooling via magnetic fields, without needing for adding extra energy, in another modified design of the Einstein-Szilard fridge. ” Ours works similarly (to freon fridges) but in preference to using a gas we use a magnetic field and a different metal alloy,” project manager Neil Wilson told Green Optimistic in 2008. ” When the magnetic field is next to the alloy, it’s like compressing the gas, and when the magnetic field leaves, it’s like expanding the gas. This effect should be would becould very well be seen in rubber bands – whenever you stretch the band it gets hot and if you let the band contract it gets cold.”

And finally, a former graduate student at Georgia Tech, Andy Delano, also built a prototype of one of Einstein and Szilard’s designs as section of his master’s and doctoral thesis work. ” Literally, you heat one end and the alternative gets cold,” Delano explained at the time. He researched the refrigeration cycle and modeled it on a computer, using his own money to build the prototype. His then-roommate just happened to be majoring in civil engineering, and helped weld the prototype together, while his brother (another Georgia Tech alum) drew on his industrial design degree to create an animated version of Einstein and Szilard’s original patent diagram, bringing the movement of different fluids to life. Delano’s version used electric resistance heaters as the heat source, mostly for convenience, but a small gas burner or solar energy sources is also used.

It took months for Delano and his partners to complete building the prototype, but good news – it worked right off the bat. Well, almost: at the start, he got ice, so he tweaked the mixture of chemicals to get a chill, not not an outright freeze. It does bode well for the potential of creating a refrigerator/freezer combination – although that future is perhaps still pretty remote. Still, most of these prototypes are further proof of principle that Einstein and Szilard were clearly onto something – they were just 70-odd years too soon.

[Comic below: Saturday Morning Breakfast Cereal . Whenever you're not reading the strip regularly, why not?]

This post originally appeared on Cocktail Party Physics .

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This post is tagged: austro hungarian army, budapest technical university, energy efficient refrigerator, photoelectric effect, technological creativity