You ever see one of those drinking birds? I was combing through my feedback folder (truly, one of the highlights of my day – I just can’t get enough email) and I discovered a note from Lockergnomie Paul Curtis. Yes, the drinking bird toy is what I’m referring to… and it’s apparently very geeky:
The design is extremely clever, relying on phase changes in a volatile fluid (ie, high vapor pressure at room temperature) in a closed (sealed) environment, shaped like a dumb-bell with an off-center pivot point. The partition of material between the liquid and vapor phases is changed by exterior cooling of the bird’s head section due to endothermic evaporation of water as the nappy (ie, water-retaining) exterior coating on the bird’s head waves around after the bird “drinks”; the attendant change in center of gravity eventually causes the bird to over-balance and the head section again dips into the reservoir, getting wet and causing the cycle to repeat. Note that if you put the entire bird under a bell jar, creating a closed atmosphere where the water no longer evaporates from the head, the motion stops, proving that it is the repeated wetting of and evaporation from the head which powers the show.
The glass bulb and volatile fluid are indeed dangerous for children, but the physics is entrancing. Many years ago, the drinking bird was used (by the Rand Corporation, I think) as the basis for a solar-powered irrigation pump for places like Egypt. In this design, the fluid is a freon, highly optimized for phase change, and the “head” is a hollow scoop connecting to an internal channel in an extruded-aluminum body. No waving around here: one single cycle up, lifting water from an irrigation canal then which runs back down the body, then instant evaporative cooling of the head, followed by immediate overbalance and back down to get the next slug of water. The concept was beautiful, but the cost per unit was several hundred dollars back in the 1960s, and this was not economic in areas where a laborer to do the same work cost only pennies per day.
I’m gonna run out and buy me one of those drinking birds tomorrow. Everybody’s heard about the bird – bird, bird, bird – bird is the word. And if you think I’ve gone cuckoo, let me propose this: I’ll PayPal $100 to the first person to email me tonight. Ya know, just to say hello – or to tell me that you’ve linked to Lockergnome, my blog, or our comic, etc. First one’s the winner!
[tags]toys,drinking bird,toy,bird toy,pivot point,glass bulb,bird,endothermic,evaporation,freon[/tags]