I was struggling to think of what to write about today.
And then... suddenly... it came to me. I have no clue why because I wasn't thinking about anything particular... but once this flashed into my mind I HAD to feature it.
I think it's very 70s... though they may have been around after that too. It seems to have come from an idea back in the 18th century which was refined over the years.
According to Wikipedia it's a heat engine that exploits a temperature difference to convert to a pressure difference within the device, and performs mechanical work."
But we just knew it as the Drinking Bird...
Again... according to Wikipedia... it worked like this:
- The water evaporates from the felt on the head.
- Evaporation lowers the temperature of the glass head (heat of vaporization).
- The temperature decrease causes some of the dichloromethane vapor in the head to condense.
- The lower temperature and condensation together cause the pressure to drop in the head (governed by Equations of state).
- The higher vapor pressure in the warmer base pushes the liquid up the neck.
- As the liquid rises, the bird becomes top heavy and tips over.
- When the bird tips over, the bottom end of the neck tube rises above the surface of the liquid in the bottom bulb.
- A bubble of warm vapor rises up the tube through this gap, displacing liquid as it goes.
- Liquid flows back to the bottom bulb (the toy is designed so that when it has tipped over the neck's tilt allows this). Pressure equalizes between top and bottom bulbs
- The weight of the liquid in the bottom bulb restores the bird to its vertical position.
- The liquid in the bottom bulb is heated by ambient air, which is at a temperature slightly higher than the temperature of the bird's head.
I didn't ever have one... did you?