What is a drinking bird?
A drinking bird, also known as a dipping bird, is a popular novelty item that demonstrates thermodynamics in action. It’s a toy that dips its beak into water repeatedly. The most popular style is the classic glass drinking bird with a felt “hat” and red “feet” at the bottom. It’s also known affectionately as the “Alfie drinking bird”, named after Alfred Dunnett who is credited with inventing it in 1945.
The drinking bird is an interesting example of heat transfer and phase changes. It uses evaporative cooling to drive the repeated motion of dipping its beak into water. Let’s take a closer look at how the drinking bird works!
How does the drinking bird work?
The drinking bird has a glass bulb body filled with a volatile liquid, usually methylene chloride. Inside the hollow glass bulb are two tubes – a short one at the bottom acts as the beak, and a longer curved tube connects to the body. The tubes are filled with the volatile liquid as well.
At the top of the longer tube is a fabric cover soaked with the volatile liquid. The fabric acts as a wick to spread the liquid around and help it evaporate faster. This is the “hat” portion typically colored red.
The evaporation cycle
When the bird is placed on a glass of water, here is the cycle that takes place:
1. Evaporation occurs from the wick, which cools the vapor inside the top bulb. The cooled vapor condenses and reduces pressure inside the top bulb.
2. The higher pressure of the vapor in the bottom bulb forces the liquid up into the top bulb through the long neck. This shifts the center of gravity and causes the bird to dip forward.
3. As the fluid in the top bulb warms again from the ambient air temperature, the vapor pressure increases, forcing the fluid back down into the bottom bulb through the long neck.
4. This shifts the center of gravity backwards, causing the bird to tilt upright again.
5. The cycle then repeats as evaporation continues cooling the vapor at the top!
How the drinking bird stays balanced
The drinking bird is weighted at the bottom so that when empty, it stands upright with its beak out of the water. The red feet help keep it stable.
As evaporation occurs in the top bulb, the increasing mass of liquid in the upper bulb causes the center of gravity to shift forward. At a critical point, the center of gravity moves in front of the pivot point and the bird tips forward. When the liquid flows back down, the center of gravity shifts back over the feet and it tips back up.
When positioned properly, capillary action will pull a small amount of water into the beak so it looks like the bird is “drinking”. The fluid remains trapped in the beak and rolls back down into the glass as the bird tips back up.
The thermodynamics behind it
The drinking bird operates using a heat engine, exploiting the temperature difference between the ambient air and the evaporated vapor to repeatedly lift and dip the beak. Here are the key thermodynamic principles at work:
Evaporative cooling
Evaporation of a liquid requires an input of energy to overcome the intermolecular forces between the molecules. This energy input leads to cooling. In the case of the drinking bird, evaporation of the volatile liquid in the wick cools the vapor in the top bulb.
Vapor pressure
The vapor pressure depends on the temperature – as temperature increases, vapor pressure increases. In the top bulb, the cooled vapor condenses and the vapor pressure decreases. This causes a pressure difference that forces liquid into the top bulb.
Phase changes
The drinking bird exploits vapor-liquid phase changes of the working fluid. Evaporation, condensation, boiling, and cooling occur in the cyclic process. These phase changes are key to creating the self-oscillating motion.
Optimizing the drinking bird
Choosing the right liquid
The rate of evaporation depends heavily on the type of liquid used:
– It should have a high vapor pressure to evaporate easily. Methanol and chloroform work well.
– A low boiling point allows evaporation at room temperature. The boiling point should be just below room temperature.
– Higher molecular mass and low toxicity are also preferred. The original drinking bird used dichloromethane but methanol is more common today.
Wick design
The wick must be optimized to provide effective evaporation:
– Fabric density and weave affects the wicking action and evaporation rate.
– The wick should hold enough liquid to sustain evaporation while not being overly soaked.
– A larger wick surface area increases evaporation but also the thermal mass, potentially slowing the oscillation rate.
Beak design
– A narrow beak opening reduces the flow rate back down into the lower bulb. This helps maintain the pressure differential.
– The beak shape ensures that liquid rolls back into the glass as it tips upwards. Round beaks work best.
– A straight beak allows liquid to flow out, so a curved shape is preferred.
Center of gravity
– The center of gravity must shift significantly for the bird to tip. Longer necks provide greater shift.
– The bottom weight helps keep the center of gravity near the pivot point when empty.
– Lighter glass bulbs reduce the overall weight and allow greater center of gravity shift.
Troubleshooting issues with drinking birds
If your drinking bird isn’t oscillating or functioning properly, here are some common issues and remedies:
Not oscillating
– Add more of the volatile liquid to the bulbs to increase vapor pressure.
– Check for leaks allowing vapor to escape, use sealant if needed to plug leaks.
– Insufficient evaporation can cause insufficient cooling – ensure good airflow over the wick.
– Clean any oil/dirt from the wick limiting evaporation. Replace wick if needed.
Tips over and doesn’t right itself
– Center of gravity is too far forward, add weight to feet or shorten neck.
– Pivot point friction is too high, lubricate with graphite powder.
– Base is uneven, stabilize base or use shims to level.
Beak leaks fluid
– Filing the beak tip or bending can fix minor leaks.
– Check for cracks and replace beak if damaged. Be careful not to overfill.
– Wipe dried fluid from beak interior which can trap excess liquid.
Not drinking
– Beak may not be immersed deep enough into water.
– The orifice where liquid enters beak may be clogged – try flushing with water.
– Reduce beak opening size to increase suction of liquid.
The history of the drinking bird
While the drinking bird became a popular novelty item in the mid 1900s, the basic concept is much older:
Ancient Greece and Rome
The drinking bird’s concept of heat transfer and hydraulics dates back over 2000 years ago to the Aeolipile, a device used in ancient Greek and Roman times. It used steam power directed at turbine blades to cause rotation.
Da Vinci’s observations
Leonardo da Vinci observed the basic principles of heat transfer that enable the drinking bird in his journals in the 1500s. He noticed temperature differences between air and water created vapor pressures that could drive motion.
First patented in 1945
The drinking bird was first patented in 1945 by Miles V. Sullivan and Alfred W. Dunnett. Dunnett observed the basic operating principles while working in a British explosives lab during World War II.
The patent was filed under the name “artificial fountain drinker powered by vapor” and licensed to B.I.F, who manufactured and sold them as novelties in London stores. Dunnett’s brother dubbed it the “Alfie Drinker”.
Pop culture prominence
The drinking bird received prominence in popular culture being featured in cartoons, TV shows, movies, and advertising during the 1950s-60s heyday of novelty items. Millions were sold during the timeframe.
While other novelty items faded, the affordable drinking bird remains popular today as a captivating example of thermodynamics that anyone can own on their desk.
How drinking birds are made
The original drinking birds were made from glass but more recent versions use plastic. However the components and manufacturing process remains similar:
Blown glass method
– Glass tubes are joined to form the bottom bulb and beak, bent into shape, and attached to the body.
– The top bulb is blown from glass, colored, and attached.
– A glass tube connects the two bulbs.
– The feet and wick are attached last.
Injection plastic molding
– The two bulb pieces and beak are injection molded from plastic.
– Holes are molded in to allow filling with liquid.
– The feet and wick are also molded plastic pieces.
– The components are joined and sealed together.
– Liquid is added through the holes which are then sealed.
QA and packaging
– Drinking birds are tested to ensure proper operation and sealing.
– Any additional paint or dye is applied and allowed to dry.
– Instructions are included on usage and troubleshooting.
– They are packaged in boxes or blister packs to protect and display them.
Interesting facts about drinking birds
The drinking bird has captivated audiences for decades with its charming appearance and seeming ability to drink perpetually. Here are some fascinating facts about these kinetic art pieces:
– They were originally called “dipping birds” since they don’t actually drink but just dip their beaks. |
– Inventor Dunnett was inspired while working with liquid explosives that evaporated and cooled their containers. |
– The liquid was switched from carcinogenic benzene and chloroform to methanol for safety. |
– In hot & dry conditions, they can operate up to 2 hours continuously. |
– The world record for longest continual operation is over 3 hours. |
– A 4 foot tall drinking bird was constructed using 6 gallons of methylene chloride. |
– To prevent damage, drinking birds should only “drink” from glass containers. |
– Thousands are still manufactured each year and sold as novelty items. |
Conclusion
The drinking bird is a captivating example of heat transfer and thermodynamics. First patented in 1945, these toys exploit the cooling power of evaporation to repeatedly dip their beaks. Inside the two glass bulbs, changes in vapor pressure from evaporation and condensation drive the oscillating motion. Optimizing the wick and beak designs allows fine tuning of the operation. While originally made of glass, most today are injection molded plastic for durability and affordability. The drinking bird remains popular as a fascinating desk toy after over half a century of making people smile.