Low-Temperature Stirling Engine Model – Runs on a Cup of Hot Water

Description

A heat engine that runs on a cup of hot water

This low-temperature-difference (LTD) Stirling engine turns heat into continuous rotation. Place it on a mug of hot water, wait about 20 seconds, give the flywheel a gentle turn, and it keeps running on the temperature difference between its warm base and the cooler top plate. It is a striking way to show thermodynamics on a desk or in a classroom.

How a Stirling engine works

• Hot water warms the base while the top plate stays cooler.
• The air inside moves between the hot and cold sides, expanding as it warms and contracting as it cools.
• That pressure change drives the power piston and connecting rod.
• The large flywheel stores momentum and keeps the cycle going: heating, expansion, cooling, compression.
• Invented by Robert Stirling in 1816, this external-combustion engine can, in theory, approach the efficiency of the Carnot cycle.

Highlights

• Low-temperature-difference design: hot water is enough, no open flame required
• Large, lightweight transparent flywheel with an iridescent rainbow sheen
• Low-friction precision shaft for easy starting and smooth running
• Aluminum alloy support and quartz heating cylinder
• Silicone diaphragm and high-strength connecting rod

How to use it

• Fill a cup with an opening of about 90 mm (3.5 in) with hot water and set it on a stable, level surface.
• Center the engine on the cup.
• Wait about 20 seconds, then flick the flywheel to start it.
• When you are done, lift it off carefully and let it cool before storing.

Good to know

• Hot water and warm metal can burn; an adult should handle the hot water.
• Do not oil the mechanism. Lubricant adds friction and can stop the engine.
• Handle the flywheel and quartz cylinder gently.