Physics just got delicious.
Have you ever wondered why a chocolate doesn’t flow like water? I have... but only after gorging myself on as much chocolate as humanly possible.
Chocolate fountains are delicious examples of Newtonian and non-Newtonian fluid dynamics, but they have left many people (scientists included) wondering why the flowing walls of chocolate pull inward between piers rather than falling straight down.
Adam Townsend, a former mathematics graduate student from University College London, and co-author of the paper, decided to tackle that question for his Master’s thesis in fluid dynamics. "Chocolate fountains are just cool, aren't they!" says Townsend. "But it's also nice that they're models of some very important aspects of fluid dynamics."
To determine why the chocolate behaves this way, Adam and his supervisor Dr. Helen Watson, co-author of the paper, looked at previous work on “water bells”. According to Watson, you can easily create a water bell at home by fixing a pen under a tap with a coin placed on top and what you will see is a “beautiful bell-shaped fountain of water."
You can easily create a water bell in your kitchen sink by fixing a coin to the end of a pen. Photo credit: Adam K Townsend and Helen J Wilson/Institute of Physics
The physics behind the chocolate fountain turns out to be exactly the same as the water bell, and the reason that the chocolate flows inward toward the centre between piers is mainly due to surface tension.
Both Townsend and Watson were happy that their research allowed them to engage with the public. "It's serious maths applied to a fun problem," said Townsend. While the flow between piers was determined to be from surface friction, there is still a lot to learn from looking at the way the flow of the chocolate walls change over time.
They examined the flow of the entire chocolate fountain system, including not only the flow over the tiers, but the flow up the center pipe. "Thankfully, individual strands — like the screw-pump flow up the pipe — have applications well beyond chocolate, and international teams are working on them now." concludes Wilson.
Townsend is currently finishing his PhD investigating suspensions of solid particles in fluids, supervised by Wilson. You can read their research paper on chocolate fountains for free right here.
