Heat Engine: Drinking Bird

The drinking bird (AKA “Dippy Bird”) illustrates the conversion of thermal energy into mechanical energy. The bird consists of two hollow glass chambers (head and bottom) which are coupled by a double walled glass tube. The outer tube provides mechanical support, and the inner tube extends into the bottom chamber below the surface of a colored fluid with suitably high vapor pressure. The head of the bird is coated with a fuzzy material, and is initially soaked in water so that it will begin to cool by evaporation. This provides the temperature difference from head to tail necessary to run the heat engine. As the head cools, the colored fluid rises from the bottom of the bird through the neck, gradually shifting the center of gravity of the bird toward its head. The bird bends at the hips and dips its bill into a glass of water (thus keeping the head wet and cooler than the tail). As the fluid continues to rise into the head, the fluid level in the bottom of the bird eventually drops below the end of the connecting tube. This allows vapor to be pulled up through the neck to equilibrate the pressure. The fluid runs back down into the bottom of the bird, the bird stands up again, and the cycle repeats providing the bird has enough to drink.