WHEN we think of the heroes of the current pandemic, frontline health workers and those who work on bringing effective vaccines to market come to mind.

But a Scotsman of the cloth and self -taught engineer born in the late 18th century is unlikely to be viewed as a prime candidate.

However, many experts believe the refrigeration technology of Robert Stirling, which he first patented in 1816, is making the vaccination programme possible. His work is, apparently, experiencing a renaissance.

Systems based on his findings are being employed in laboratory and hospital settings where a cold chain is required in the development of a vaccine and, in the case of some, to the point where it goes into a patient’s arm.

This is because Stirling coolers are about 75 per cent cheaper to run and are smaller than the liquid nitrogen and helium freezers in widespread use in science. Stirling technology directly facilitated the development of much else besides: for example, cryogenics, MRI scanners and stealth submarines.

Moreover, the economic viability of discoveries that seem to be futuristic, but which are already being trialled and developed – such as personalised medicine, stem-cell therapy and certain micro-energy machines – owe much to this modest man who courted neither fame nor fortune.

Little known outside academic circles, Stirling’s work continues to fascinate engineers, some of whom have dedicated their entire career to trying to penetrate the subtleties of how his inventions work.

Robert Stirling was born in Methven, Perthshire, in 1790.

The second of eight children, his father was a farmer and his grandfather, Michael Stirling, who was also in agriculture, is credited with inventing the first rotary threshing machine around 1756.

Details of Robert Stirling’s life remain quite sketchy because he was more of a doer than a writer.

However, he attended both Glasgow and Edinburgh universities and graduated in divinity studies in 1815, at which time he was appointed second charge in the parish of Kilmarnock before becoming minister of Galston in Ayrshire in 1824, where he was to serve his flock for more than 50 years.

Dr Allan Organ is a retired Cambridge academic engineer and a leading authority on Stirling technology who has designed several of his machines with potential commercial and military applications.

Dr Organ now lives in Wester Ross where he continues to write about his specialist subject. He says: “In 1816, Reverend Stirling was granted a patent for his ‘economizer’, subsequently called regenerator, and for an invention in parallel of the first ever reversible engine, capable of delivering power or, when driven by an external source, functioning with zero modification as a refrigerator.

“By convention, credit goes instead to a Frenchman, Sadi Carnot, who, eight years behind Stirling in 1824, described it – but neither designed nor built any engine.”

Stirling coolers are now helping to store vaccines across the world.

With Pfizer vaccines having to be stored at between minus 80C and minus 60C and the Moderna at -25C to -15C, they are being utilised to transport jags to the point of contact with patients.

How they work, in simple terms, is while an internal combustion engine relies on the burning of fuel and works in a sequence of suck, squeeze, bang and blow, a Stirling cooler operates within a closed system, so there is no bang or blow.

Rather, it takes advantage of the fact that the temperature of gases rise as they are compressed and fall when expanded.

Energy is applied and alongside parts which move in response to the action of the gases is the key component known as a regenerator.

It does not move.

Instead, its large surface area works like a thermal sponge which absorbs heat after the compression process, thereby cooling it on its way to the cool part of the refrigerator. This heat is then stored in the regenerator and recycled back to reheating the gas in the original compression space.

William Thomson, who was born in Belfast in 1824, was a keen student of Stirling engines. He is more widely known as Lord Kelvin – famous for describing the Second Law of Thermodynamics – but, according to Dr Organ, he owes much to the minister from Ayrshire.

He says: “Throughout the early 19th century debates raged within the learned societies as to how Stirling’s regenerator functioned. These played a key role in discrediting the caloric theory of heat and incrementally homing-in on the most far-reaching of all physical principles – the Second Law of Thermodynamics.”

Dr John Corey is a consulting engineer based in New York and an expert on Stirling Coolers. “Robert Stirling was a polymath who was capable across many disciplines,” he says.

“He could teach, preach and do science. His insights pre-dated the discovery of thermodynamics. He was amazing and intuitive.”

Another US-based engineer, Dr Dave Berchowitz, is the co- founder of the company Stirling Ultracold and is based in Ohio. His company has seen a huge upsurge in orders for cooling technology.

He says: “It’s changed this company overnight. We are doing very, very well.” which is one of the serious complications that sometimes results from Covid 19. Universal stem cells are also being trialled as treatment for people who have suffered ischemic stroke and the results so far are extremely promising.

Stem-cell therapy has many other applications currently being explored. Small portable Stirling coolers make these technologies available to patients who do not live close to major hospital facilities.

When it comes to modern computing, Reverend Stirling looms in the picture there too. Huge server farms generate a lot of heat and removing that heat is a problem.

Dr Berchowitz says: “The speed of a micro-processor is inversely proportional to its absolute temperature so that means the colder you make it, the faster it goes.

“So, if you cool a microprocessor to deep temperature you get a boost in the clock speed and the ability to calculate becomes faster. That is not valuable for the ordinary user but in the server business it is very valuable.

“They pay a lot of money to be able to run their computers faster”.

And there are more projects incorporating Stirling coolers currently being pioneered.

Dr Berchowitz says: “Where we are really going to benefit is with cell and gene therapy, which is an upcoming field that requires very deep temperatures. As you reduce the temperature of biological material you hold it in suspended animation. You slow it down until you can store it forever to temperatures of minus 135 degrees Celsius and below.”

Stem-cell therapy now involves the harvesting of so-called universal stem cells from the bone marrow of healthy volunteers. This is then used to treat patients suffering from acute respiratory disease, Stirling may remain relatively unknown, but to those familiar with his work, he continues to exert a magnetic attraction that bridges centuries.

Dr Berchowitz adds: “Everybody gets possessed by Stirling. It’s the craziest thing. I am not a superstitious person, but it is like you get infected by something. I’ve seen people’s lives get shattered by it because they get so devoted to it; it consumes people.”

So, how did a clergyman born before the industrial revolution gain such startling insights that continue to be of relevance to this day? One clue lies in the nature of the family into which he was born.

When his younger brother, James, died in 1876 an obituary notice stated that James “was descended from a highly respectable farming family, nearly every member of which, females included, possessed mechanical talent almost amounting to genius”.

Many would say Robert Stirling was a genius. He was also very humble.

In 1848 there was a cholera epidemic in Galston and Rev Stirling showed fearless dedication to his congregation by continuing to visit the sick. In 1849, 50 parishioners gathered in the Black Bull Hotel to present Stirling with commemorative tokens in thanks for his service.

On receiving some silver-plated items and a gold watch, Stirling, with typical modesty, said: “I said to myself, if the doctor and the other medical gentlemen examine and handle and come into the most intimate contact with their patients, and yet suffer no harm, what possible harm can I encounter when I only enter their dwellings and speak to them upon the words of Christian consolation?”

Nonetheless, it could be argued that Robert Stirling is a name with which all Scottish school children should be familiar.

Dr Organ puts it this way: “Robert Stirling is the unsung – arguably unrecognised – hero of thermodynamics, the theory behind modern weather forecasting, refrigeration and the design of gas turbines and internal combustion engines, the very motive power of modern life and the global economy.”