Retired Physics Educational Specialist Rick Sorensen explores the difference between popular different drink containers using data-collection technology.
Teaching thermodynamics is an important part of the high school physics curriculum, but introducing students to this topic can be daunting. Here’s an investigation that involves a variety of drink containers and Vernier data-collection technology that will both pique students’ interest in thermodynamics and successfully introduce students to this crucial concept.
This experiment idea started with an interesting discovery. One evening I happened to fill up a Hydro Flask® with ice and water. The next morning it still had ice and water, and this happened without a lid. I was so impressed that I have since added a couple more of these containers to my cupboard. I began to wonder about the physics of vacuum insulated products.
As a retired Physics Educational Specialist at Vernier, and a high school physics teacher who spent many years in the classroom, I still think like an educator. I decided to create an activity focused on thermoses that could be easily replicated in a classroom setting to teach students about thermodynamics using Vernier technology.
History of Vacuum Insulation
It might help to give your students some historical context surrounding the invention, innovation, and commercialization of vacuum insulation. I’ve put together some dates that might be helpful in showing your students how vacuum-insulated products first got their start.
Cryogenic scientist Sir James Dewar invents a vacuum insulated goblet to keep liquids warm.1
Dewar exhibits a vacuum jacketed flask at the Royal Institution.
Dewar’s employees were manufacturing scientific glass devices.2 While producing flasks for Dewar, they also created a domestic vacuum flask with a protective metal casing.
Those same employees held a contest to name their patented invention. The winning name was “thermos,” a Greek word meaning heat.
American businessman William B Walker realized the potential for the thermos bottle in the United States.
Using imported technology and German glass blowers, he opened the first Thermos plant in Brooklyn, New York.
Thermos® was a world leader in glass vacuum technology and manufacturing.3
3 For more history of the Thermos Company, visit https://www.kitchenkapers.com/pages/history-of-the-thermos-company
Physics of the Vacuum Bottle
Vacuum bottles are effective because they reduce heat transfer caused by conduction, convection, and radiation. The vacuum between the two walls of the glass or metal vessel greatly reduces heat transfer due to convection and conduction. A tight fitting plastic lid seals off the vessel and eliminates heat transfer by convection and evaporation. Vacuum bottles made of glass contain silvered surfaces that reflect radiant energy back into the bottle. All-steel vacuum bottles are made of polished steel that also keeps the radiant energy in the bottle.
Is Newer Always Better?
Currently, double-wall stainless-steel vacuum bottles dominate the retail market. An important feature of these bottles is that they are almost indestructible. Glass-walled vacuum bottles are protected by metal or plastic exterior housings but are more susceptible to damage. Since the stainless steel versions do not need exterior protection, they are smaller; but are they better at keeping things hot or cold?
This was the question I wanted to answer in my investigation.
Part I: Preserving Heat
I used two Vernier Go Direct® Temperature Probes to monitor the cooling of hot water in a 16-ounce Thermos glass-walled vacuum bottle and a 16-ounce Hydro Flask Coffee Flask.
First, I poured sixteen ounces of boiling water into each bottle. Temperature probes were inserted and the bottles were sealed. I collected data for 24 hours.
Using the Graphical Analysis™ 4 app to view my data, I noticed that the 40-year-old Thermos cooled at a slower rate than the new stainless steel vacuum flask. The beginning temperature of the liquid in each bottle was about 87°C. After four hours, the temperature of the liquid in the Thermos bottle had dropped to 69.5°C, while the temperature of the water in the Hydro Flask had dropped to 61.3°C. After 24 hours, the liquid in the Thermos bottle had dropped to 34.4°C while the temperature of the water in the Hydro Flask had dropped to 28.8°C. (The room’s ambient temperature was about 21°C.)
Part II: Preserving Coldness
How would the two vacuum bottles compare if we measured the warming of water? The experiment was repeated with cold water. A slurry of ice chips and water was made. Cold water minus the ice chips was poured into each bottle and data were collected for 24 hours. The experiment started with the water in the Thermos bottle at 3.7°C and the water in the Hydro Flask at 3.9°C.
After four hours, the water in each bottle was at 6.8°C. The water in the Hydro Flask was warming faster than the water in the Thermos. After 24 hours, the water in the Thermos bottle was at 16.3°C and the water in the Hydro Flask was at 17.1°C. Again, the Thermos was the winner.
Part III: Further Points of Discussion for Your Class
Even though the double walls of the vacuum flask are evacuated, the space between the walls is not a perfect vacuum; heat energy is transferred from the inside wall to the outside wall. How would this transfer compare for the Thermos and Hydro Flask?
This can be answered by simultaneously measuring the temperature of the liquid in the bottle and the temperature of the outer wall of each vacuum flask. For each flask, the temperature of the liquid was measured with a Go Direct® Temperature Probe. The surface temperature of the outer wall was measured with a Surface Temperature Sensor that was taped to the wall and insulated from the room air by a patch of gauze.
The following graphs show the temperatures for each flask.
The following graph shows the temperature difference between the liquid and the flask outer wall.
The larger temperature difference for the Thermos shows that it is more effective at keeping the liquid in the flask hotter longer.
Another way to see the difference between the two is with an infrared photo. The photo below shows the Hydro Flask on the left and the vacuum flask portion of the Thermos. In each case a rubber stopper was used to seal the flask.
The brighter yellow sections are the hottest. The outside of the Hydro Flask is significantly warmer than the vacuum flask of the Thermos.
The next photo shows the two flasks as they are normally used. The flask portion of the Thermos has been put back into its metal housing. The rubber stoppers have been replaced with the supplied lids. Notice that the lid of the Thermos does a much better job of reducing the heat loss.
This activity can be easily replicated in the classroom, and it provides students with a great opportunity to use data-collection technology to explore their world.