STIRLING WORK

Dick Pountain /Idealog 326/ 06 Sep 2021 11:11

If there’s an underlying theme to this column (which may be doubted) then it’s the difference between the physical and the digital worlds, summed up in an aphorism I’ve employed far too many times “You can order a pizza online but you can’t eat it online”. I’ve been living in this gap between worlds for 40 years now: my first toe in the digital water was via a Commodore PET in 1981 at the very start of the personal computer revolution, though it wasn’t until the coming of WWW that we all got properly connected together. 

Of course I was born into the physical world, and inhabited it with increasing curiosity throughout a childhood filled with Meccano (I built the travelling gantry!) and model aeroplanes with glow-plug engines (I was in a control-line combat team). At school I excelled in science and my college lab days were pretty physical: hot, smelly and toxic in organic chemistry; warm, wet, salty and mildly radioactive in biochemistry. I dropped out of science and stumbled into the digital world by accident when Dennis Publishing acquired Personal Computer World magazine, merely because I was the most numerate person present, though my previous experience had been handing a sheaf of printout out to a man in a brown lab-coat and getting the results back Tuesday.The physical world is filled with palpable, even edible, objects made of atoms and molecules that whizz around subject to rules we were taught in physics and chemistry, while the digital world consists of bits with which we construct representations of those physical objects to calculate and simulate their relationships. More precisely, bits live between the physical and yet another world, the quantum world, which follows different, weirder, rules that allow ‘entanglement’ to eradicate distance and separation. Bits are electrical charges stored in silicon capacitors or similar, and at today’s tiny feature sizes they begin to feel that weirdness. My scepticism toward the current hype over quantum computers grows from a suspicion that many quantum enthusiasts believe  ‘quantum’ is going to free us from the confines of boring old physicality, which it isn’t. 

We in the physical world are ruled by the laws of thermodynamics. For me the most readable account of those laws is Professor Peter Atkins 1984 book The Second Law, in which he explains that many things in the world are engines that take in energy, turn some (never all) of it into work, and expel the ‘waste’ as heat. For example we take in glucose and run around thinking, while chips steer electrons to perform boolean operations. 

I was first introduced to Atkins book by my brother-in-law Pip Hills, who like me was fascinated from childhood by motors and machines – we once drove to Prague together in his 1937 Lagonda, fitted with a large Gardner diesel engine (http://www.dickpountain.co.uk/home/journalism/the-classic-motoring-review). Pip studied philosophy rather than chemistry, but we share that faith in thermodynamics as a way to understand the limits of the physical world. A few years ago while visiting us in London, he bought a rather fine old working model of an odd-looking engine on Portobello Road market: we took it home, plonked it on a lit gas ring and it just started running. 

Once back home in Scotland Pip began to study the history of this unusual type of heat engine, becoming so intrigued that he’s written his own book about it called The Star Drive (Birlinn 2021). He explains how the engine was invented by a Scottish parson Robert Stirling in 1816, and it runs by expanding hot air rather than steam. It differs from internal combustion, petrol or diesel, engines by using an external heat source. Simpler and with fewer moving parts than steam engines, Stirling engines nevertheless lost out during the industrial revolution because the high temperatures they worked at broke available materials like cast iron and leather, and also because their speed isn’t easy to control. But more recently, their ability to operate completely sealed from the outside world except for a heat source has opened up several interesting niche applications. 

The Swedish navy operates small non-nuclear submarines powered by Stirling engines burning liquid oxygen and diesel fuel catalytically to charge batteries for long, silent underwater periods. One of these humiliated the US navy’s aircraft carrier USS Ronald Reagan during 2005 war games in San Diego, by penetrating its sophisticated defences to ‘paintball’ it. NASA employs closed-cycle Stirling engines heated by small nuclear reactors to generate electricity in spacecraft travelling to the outer solar system where they must operate for years without sunlight, lubrication or maintenance. And miniature Stirling engines driven backward by external electromagnets make highly efficient heat pumps for cryogenic cooling, perhaps to keep some future quantum computer within its own chilly world.    

[Dick Pountain nowadays expels most waste heat via the top of his head]