Ellen Phiddian
What do 17th-century fire engines and arteries have in common? A physical effect that – until now – hasn’t been properly explained.
A pair of US physicists have been delving into museum artefacts to understand the Windkessel effect: a way to smooth the flow of a liquid when it’s being pumped out.
They’ve published a description in the American Journal of Physics.
“There are many fascinating physics problems hiding in plain sight within books and papers written centuries ago!” says co-author Dr Trevor Lipscombe, a researcher at the Catholic University of America.
“Recently we’ve been working on applying elementary fluid mechanics to biological systems, and came across a common description in medical journals: that the heart acts as a Windkessel.
“That begs the question of what, precisely, is a Windkessel?”
This question led Lipscombe and co-author Professor Don Lemons, a physicist at Bethel College, down a rabbit hole of innovations in fire engines.
Windkessel – German for “wind chamber” – has been used in English for over 100 years to describe how arteries turn pumps of blood from the heart into a smooth flow of fluid.
But historically, “wind chambers” were used to refer to an invention in firefighting technology, which happened in the decades following the Great Fire of London in 1666.
After this fire, water pumps began to emerge that could spray water in a continuous stream, despite being pumped by hand.
The researchers uncovered descriptions of one such innovation from Dutch-English inventor John Lofting, who patented a device called the “sucking worm” in 1690. The sucking worm – so-called because of its pump and leather hose – was drawn by contemporaries as producing a steady stream of water that could reach more than 49 metres high.
“This would require a ground-level water speed of at least 22 meters/second – a speed that, as we shall see, could be produced with a manually operated pump,” write Lemons and Lipscombe in their paper.
“However, without the addition of some device to regulate and smooth the stream of water, a piston-driven pump would produce water in spurts, rather than, as advertised, continuously. But no such regulating device is mentioned in Lofting’s sucking-worm patent.”
None of Lofting’s sucking worms have survived, but the researchers tracked down some other early firefighting vehicles, including one patented by English inventor Richard Newsham in the 1720s. Lemons inspected one of the Newsham’s wagons at the Hall of Flame firefighting museum in Arizona, US.
This wagon featured an airtight pressure vessel that the pumped water moved through before coming out of the hose. This is a Windkessel.
The researchers then developed a model to understand how the Windkessel could smooth water in this fire engine, and understand how fast it could produce water.
“When faced with Lofting’s design, or the Newsham fire engine, a physicist wants to sort out the basic science involved – simply because it’s there,” says Lipscombe.
“It’s the joy of doing physics. But also, there’s a pedagogical aspect. Our article builds a simple model that shows how a Newsham fire engine works. We’re partly answering the ‘when will I ever use this stuff?’ question.”
Next, the researchers are investigating how the Windkessel effect works in the aorta – the largest artery which carries blood away from the heart.
“We find it interesting that the simple physics of the Windkessel has been useful for over 300 years and yet, somehow, has escaped the notice of physics professors, textbook writers, and [American Journal of Physics] authors,” write the researchers in their paper.
