Liquid Nitrogen Trash Can
Publication information:
Abstract
What it Shows
An inverted trash can is launched into the air by an exploding bottle of liquid nitrogen.
Link to Liquid Nitrogen Trashcan video can be found here https://harvard.hosted.panopto.com/Panopto/Pages/Viewer.aspx?id=6f33f468-528c-4ab5-acd6-b1af00cd80f1
How it Works
A plastic soda bottle is filled with LN2 (liquid nitrogen), placed in a bowl of room temperature water, then covered with an upside trash can. The water greatly increases the evaporation rate of the LN2 by increasing heat transfer. Gaseous N2 has approximately 800 times the volume of LN2, therefore pressure builds up inside the bottle and causes the bottle to explode. The force of the explosion hits the inside of the trash can, launching it up into the air. We have seen the 10 gallon trash can to surpass the height of Jefferson Laboratory at Harvard University, which is about 40 feet!
As the LN2 evaporates, the gas is confined to the headspace above the liquid, causing an increase in pressure. Eventually, when the pressure surpasses the burst pressure of the plastic bottle, the bottle explodes. The rapidly expanding pressure wave of nitrogen gas pushes against the inverted trash can, lifting it off the ground. We have three sizes of trash cans: 10 gallon, 20 gallon, and 32 gallon. In our lecture halls, the energy from the exploding bottle is enough to lift the 32 gallon trash can to a height of approximately 5 meters (~16 feet)!
There are several approaches to calculating the amount of energy that is generated in the explosion. Before explaining the calculations, some information needs to be listed. We typically use a plastic PET 20 oz. Coca-Cola bottle which has a burst pressure of about 150 psi (10.2 atm), according to the Coca-Cola customer service line (see Reference 1). It is unclear whether this is the actual burst pressure or one that has a safety factor included. We fill the bottles approximately 1/3 of the way up, so the head space volume is 2/3 of the 20 oz volume. Our trash cans are yellow Rubbermaid Brute trash cans with masses of 1.297 kg (10 gal), 2.564 kg (20 gal), and 3.332 kg (32 gal). The physical quantities for the calculations can be obtained here (Reference 3).
First, let's consider the moles of gas in the head space volume at the burst pressure of 10.2 atm. We assume constant temperature and moles at the burst pressure. When the LN2 is first poured in, the head space volume is 0.3943 L (2/3 of 20 oz). As the LN2 evaporates, however, the head space increases. To account for the increase in head space, we use the following volume equation in the ideal gas law to calculate the moles of gas in the head space:
V = V0 + nM/D where V0 is the initial volume of 0.3943 L, n is the moles of gas, M=28.0 g/mol, D = 662 g/L at 10.2 atm and 105K
To account for the non-ideal conditions (high pressure and low temperature), Z, the compressibility factor of N2 gas is added into the ideal gas law to account for the volume and intermolecular forces between the gas molecules. As a result, the moles of gas are calculated as 0.644 moles N2 using the following equation:
n = PV0D / (ZRTD - MP)
For more accuracy, you could use the van der Waals equation of state to calculate the moles, but the difference is small based on Tom Kunzleman's calculations (see Reference 2).
Now that the moles of N2 that are involved in the explosion have been calculated, we can use the 0.644 moles to find the initial head space volume using V = V0 + nM/D = 0.4215 L. The final volume of the gas at 1 atm is calculated as 5.499 L using the ideal gas law at constant temperature and moles. Using the initial and final volumes, the PV work from the explosion is:
w = nRT ln(Vf/V0) = 1431 J
The explosive energy goes mainly into the following:
1) Breaking the bottle
While it has been reported that approximately 50% of the energy goes into breaking the bottle, this is for metal containers. For plastic, we will follow Tom Kunzleman's estimate of 10%. Subtracting off 10%, we get:
1431 J - 143.1 J = 1288 J
2) Expansion of the gas against the atmosphere
Using w = PΔV, 514 J is used to expand the gas against the atmosphere.
3) Launching the trash can
Subtracting off the work for the expansion, 1288 J - 514 J = 774 J is left for the launch. Based on experimental evidence that the 32 gallon trash can reaches a height of 5 m, we can use mgh to calculate the amount of potential energy gained by the trash can.
E = 3.332 kg * 9.81 m/s2 * 5 m = 163 J
This means that about 11% of the initial explosive energy is used to launch the 32 gallon trash can. For the 10 gallon and 20 gallon trash cans, if we assume everything is constant, they would reach heights of 6.5 m (21.3 ft) and 12.8 m (42 ft), respectively. What a blast!
We are making numerous assumptions in the calculations (see Reference 2 for a more detailed discussion), but hopefully this provides some quantitative context for this exciting demonstration. In addition, there is a great deal of variability - see the Comments section for more details. As long as safety precautions and consistent setup procedures are followed, you will launch your classes to new heights!
Setting it Up
Safety
Wear ear protection and safety glasses. We recommend doing this demonstration outside where is plenty of clearance. If you are doing this in a lecture hall, use the 32 gallon trash can and make sure there is at least 5 meters of clearance. Before each demonstration, inspect the stainless steel bowl for leaks and the trash can for cracks. The audience should be at least 15 feet away. Tell the audience to cover their ears. Once the trash can is inverted over the bowl of water with the bottle, do not go near it until the trash can explodes. If there is no explosion, leave the trash can for at least 30 minutes before uncovering it to be completely safe (the LN2 will have evaporated by then).
Demonstrating it
Equipment: Obtain an empty 20 oz soda bottle with cap, preferably Coca-Cola, a 1 L water bottle with water, a stainless steel bowl large enough to hold a 20 oz soda bottle, cryogenic gloves (leather gloves work), small funnel, ear protectors, and a Rubbermaid Brute trash can (10 gallon, 20 gallon, or 32 gallon depending on how high you want it to go). Get at least 1 liter of LN2.
Procedure: Make sure there is enough of clearance overhead (5 meters for the 32 gallon trash can, more for the smaller sizes) before placing the bowl - you don't want anything to get hit! Place the stainless steel bowl on the ground and pour the water into the bowl. Put the trash can upside down on the ground. Get your ear protectors ready to go. Put on gloves, place funnel in bottle, and fill the bottle with LN2 about 1/3 full (to the bottom of the label on the bottle if using Coca-Cola bottle). Put on your ear protection. Screw the cap on the bottle as tightly as possible. Place the bottle in the bowl of water, and immediately cover with the trash can. Stand back, be patient, and wait for the explosion to occur!
Cleanup and Disposal
Pick up and throw away the pieces of plastic in the trash. The pieces may be very sharp so be careful.
Comments
In the lecture hall, we use the 32 gallon large trash can, which typically flies about 10-15 feet high on average. Soda bottles have a lot of variability in terms of thickness of plastic and the tightness of the cap. In addition, the bottle is filled with a slightly different amount of LN2 each time, and humidity and temperature can affect heat transfer rates. Sometimes the trash can will jump only a few feet, but it can also jump 15 feet with the same amount of LN2. There is also variability in the amount of time required for the evaporation depending on the heat transfer. This is probably due to factors like temperature and how much of the soda bottle is exposed in the bowl.
The main failure mode is that the screw cap is not on tightly enough so the LN2 leaks out. You will see a stream of condensed water vapor seeping out under the trash can. Wait at lease 30 minutes before uncovering to be completely safe. The other failure that can occur is a leak in the bowl with the water. In this case, it takes a long time for the explosion or it may not explode at all if the bottle develops a leak. Safety wise, never remove the trashcan for at least 30 minutes to ensure that the LN2 has all evaporated.
A more detailed discussion of the calculations is provided in Tom Kuntzleman's post about this demo (Reference 2). It would also be interesting to calculate heat transfer rates and amounts.
References
Daniel Rosenberg has provided safe and practical guidance in the procedure of this demonstration.
Narkive Newsgroup Archive https://alt.home.repair.narkive.com/rFSc9123/at-what-psi-does-a-plastic-soda-bottle-explode-home-co2-carbonation. This reference claims that some Coca-Cola bottles have a burst pressure of 250 psi.
Kuntzleman, Tom and Wildman, Randy. (2015, January 9). Liquid Nitrogen, Gas Laws and Rocket Science. ChemEdX https://www.chemedx.org/blog/liquid-nitrogen-gas-laws-and-rocket-science
Wischnewski, B. (2007, June). Peace Software. Publication Name. http://www.peacesoftware.de/einigewerte/stickstoff_e.html
(When using this site, be certain to use the calculator designated for nitrogen in the saturated state).
Full text
What it Shows
An inverted trash can is launched into the air by an exploding bottle of liquid nitrogen.
Link to Liquid Nitrogen Trashcan video can be found here https://harvard.hosted.panopto.com/Panopto/Pages/Viewer.aspx?id=6f33f468-528c-4ab5-acd6-b1af00cd80f1
How it Works
A plastic soda bottle is filled with LN2 (liquid nitrogen), placed in a bowl of room temperature water, then covered with an upside trash can. The water greatly increases the evaporation rate of the LN2 by increasing heat transfer. Gaseous N2 has approximately 800 times the volume of LN2, therefore pressure builds up inside the bottle and causes the bottle to explode. The force of the explosion hits the inside of the trash can, launching it up into the air. We have seen the 10 gallon trash can to surpass the height of Jefferson Laboratory at Harvard University, which is about 40 feet!
As the LN2 evaporates, the gas is confined to the headspace above the liquid, causing an increase in pressure. Eventually, when the pressure surpasses the burst pressure of the plastic bottle, the bottle explodes. The rapidly expanding pressure wave of nitrogen gas pushes against the inverted trash can, lifting it off the ground. We have three sizes of trash cans: 10 gallon, 20 gallon, and 32 gallon. In our lecture halls, the energy from the exploding bottle is enough to lift the 32 gallon trash can to a height of approximately 5 meters (~16 feet)!
There are several approaches to calculating the amount of energy that is generated in the explosion. Before explaining the calculations, some information needs to be listed. We typically use a plastic PET 20 oz. Coca-Cola bottle which has a burst pressure of about 150 psi (10.2 atm), according to the Coca-Cola customer service line (see Reference 1). It is unclear whether this is the actual burst pressure or one that has a safety factor included. We fill the bottles approximately 1/3 of the way up, so the head space volume is 2/3 of the 20 oz volume. Our trash cans are yellow Rubbermaid Brute trash cans with masses of 1.297 kg (10 gal), 2.564 kg (20 gal), and 3.332 kg (32 gal). The physical quantities for the calculations can be obtained here (Reference 3).
First, let's consider the moles of gas in the head space volume at the burst pressure of 10.2 atm. We assume constant temperature and moles at the burst pressure. When the LN2 is first poured in, the head space volume is 0.3943 L (2/3 of 20 oz). As the LN2 evaporates, however, the head space increases. To account for the increase in head space, we use the following volume equation in the ideal gas law to calculate the moles of gas in the head space:
V = V0 + nM/D where V0 is the initial volume of 0.3943 L, n is the moles of gas, M=28.0 g/mol, D = 662 g/L at 10.2 atm and 105K
To account for the non-ideal conditions (high pressure and low temperature), Z, the compressibility factor of N2 gas is added into the ideal gas law to account for the volume and intermolecular forces between the gas molecules. As a result, the moles of gas are calculated as 0.644 moles N2 using the following equation:
n = PV0D / (ZRTD - MP)
For more accuracy, you could use the van der Waals equation of state to calculate the moles, but the difference is small based on Tom Kunzleman's calculations (see Reference 2).
Now that the moles of N2 that are involved in the explosion have been calculated, we can use the 0.644 moles to find the initial head space volume using V = V0 + nM/D = 0.4215 L. The final volume of the gas at 1 atm is calculated as 5.499 L using the ideal gas law at constant temperature and moles. Using the initial and final volumes, the PV work from the explosion is:
w = nRT ln(Vf/V0) = 1431 J
The explosive energy goes mainly into the following:
1) Breaking the bottle
While it has been reported that approximately 50% of the energy goes into breaking the bottle, this is for metal containers. For plastic, we will follow Tom Kunzleman's estimate of 10%. Subtracting off 10%, we get:
1431 J - 143.1 J = 1288 J
2) Expansion of the gas against the atmosphere
Using w = PΔV, 514 J is used to expand the gas against the atmosphere.
3) Launching the trash can
Subtracting off the work for the expansion, 1288 J - 514 J = 774 J is left for the launch. Based on experimental evidence that the 32 gallon trash can reaches a height of 5 m, we can use mgh to calculate the amount of potential energy gained by the trash can.
E = 3.332 kg * 9.81 m/s2 * 5 m = 163 J
This means that about 11% of the initial explosive energy is used to launch the 32 gallon trash can. For the 10 gallon and 20 gallon trash cans, if we assume everything is constant, they would reach heights of 6.5 m (21.3 ft) and 12.8 m (42 ft), respectively. What a blast!
We are making numerous assumptions in the calculations (see Reference 2 for a more detailed discussion), but hopefully this provides some quantitative context for this exciting demonstration. In addition, there is a great deal of variability - see the Comments section for more details. As long as safety precautions and consistent setup procedures are followed, you will launch your classes to new heights!
Setting it Up
Safety
Wear ear protection and safety glasses. We recommend doing this demonstration outside where is plenty of clearance. If you are doing this in a lecture hall, use the 32 gallon trash can and make sure there is at least 5 meters of clearance. Before each demonstration, inspect the stainless steel bowl for leaks and the trash can for cracks. The audience should be at least 15 feet away. Tell the audience to cover their ears. Once the trash can is inverted over the bowl of water with the bottle, do not go near it until the trash can explodes. If there is no explosion, leave the trash can for at least 30 minutes before uncovering it to be completely safe (the LN2 will have evaporated by then).
Demonstrating it
Equipment: Obtain an empty 20 oz soda bottle with cap, preferably Coca-Cola, a 1 L water bottle with water, a stainless steel bowl large enough to hold a 20 oz soda bottle, cryogenic gloves (leather gloves work), small funnel, ear protectors, and a Rubbermaid Brute trash can (10 gallon, 20 gallon, or 32 gallon depending on how high you want it to go). Get at least 1 liter of LN2.
Procedure: Make sure there is enough of clearance overhead (5 meters for the 32 gallon trash can, more for the smaller sizes) before placing the bowl - you don't want anything to get hit! Place the stainless steel bowl on the ground and pour the water into the bowl. Put the trash can upside down on the ground. Get your ear protectors ready to go. Put on gloves, place funnel in bottle, and fill the bottle with LN2 about 1/3 full (to the bottom of the label on the bottle if using Coca-Cola bottle). Put on your ear protection. Screw the cap on the bottle as tightly as possible. Place the bottle in the bowl of water, and immediately cover with the trash can. Stand back, be patient, and wait for the explosion to occur!
Cleanup and Disposal
Pick up and throw away the pieces of plastic in the trash. The pieces may be very sharp so be careful.
Comments
In the lecture hall, we use the 32 gallon large trash can, which typically flies about 10-15 feet high on average. Soda bottles have a lot of variability in terms of thickness of plastic and the tightness of the cap. In addition, the bottle is filled with a slightly different amount of LN2 each time, and humidity and temperature can affect heat transfer rates. Sometimes the trash can will jump only a few feet, but it can also jump 15 feet with the same amount of LN2. There is also variability in the amount of time required for the evaporation depending on the heat transfer. This is probably due to factors like temperature and how much of the soda bottle is exposed in the bowl.
The main failure mode is that the screw cap is not on tightly enough so the LN2 leaks out. You will see a stream of condensed water vapor seeping out under the trash can. Wait at lease 30 minutes before uncovering to be completely safe. The other failure that can occur is a leak in the bowl with the water. In this case, it takes a long time for the explosion or it may not explode at all if the bottle develops a leak. Safety wise, never remove the trashcan for at least 30 minutes to ensure that the LN2 has all evaporated.
A more detailed discussion of the calculations is provided in Tom Kuntzleman's post about this demo (Reference 2). It would also be interesting to calculate heat transfer rates and amounts.
References
Daniel Rosenberg has provided safe and practical guidance in the procedure of this demonstration.
Narkive Newsgroup Archive https://alt.home.repair.narkive.com/rFSc9123/at-what-psi-does-a-plastic-soda-bottle-explode-home-co2-carbonation. This reference claims that some Coca-Cola bottles have a burst pressure of 250 psi.
Kuntzleman, Tom and Wildman, Randy. (2015, January 9). Liquid Nitrogen, Gas Laws and Rocket Science. ChemEdX https://www.chemedx.org/blog/liquid-nitrogen-gas-laws-and-rocket-science
Wischnewski, B. (2007, June). Peace Software. Publication Name. http://www.peacesoftware.de/einigewerte/stickstoff_e.html
(When using this site, be certain to use the calculator designated for nitrogen in the saturated state).