Just stumbled upon this little beauty on Banggood.com:
It’s a low temperature Model Stirling Engine and is completely unnecessary but the perfect desk toy for your inner geek. Imagine the work you could procrastinate away watching the brass look wheel turn! Nodding ducks (aka dipping birds) are so very 1940’s where as the mechanism for this funky looking engine was invented way back in 1816 by the Scottish Minister Robert Stirling. Now, as with all these “Want-not-need” category products, I haven’t seen or used this in real life so can’t comment on the build quality but I think it would look great on an engineers desk.
How does it work?
Um, magic? Probably but turning to Wikipedia tells us:
A Stirling engine is a heat engine that operates by cyclic compression and expansion of air or other gas at different temperatures, such that there is a net conversion of heat energy to mechanical work. More specifically, the Stirling engine is a closed-cycle regenerative heat engine with a permanently gaseous working fluid. Closed-cycle, in this context, means a thermodynamic system in which the working fluid is permanently contained within the system, and regenerative describes the use of a specific type of internal heat exchanger and thermal store, known as the regenerator. The inclusion of a regenerator differentiates the Stirling engine from other closed cycle hot air engines.
So magic then… All you need to know is that if you put it over a cup of hot water, or cool the base, it will turn and only a small temperature difference is required to get this little engine moving quite rapidly.