Re: [Phys-L] Garbage can explosion

[Chuck Britton <cvbritton@mac.com>]

In a similar vein - I have used Dry Ice to explode a soda bottle which has the added advantage of letting folks actually see liquid CO2 before the bottle fails.

My scheme (which has been successful several times with no failures) uses a 10 oz plastic soda bottle for the pressure vessle.

For containment i use a nested set of four larger bottles that  have had their top sections cut off - leaving just the cylindrical sides (with the bottoms intact).

A three liter cut-off bottle holds a two liter cut-off bottle which holds a one liter, which holds a half liter cut-off bottle.

This set of four cut-off bottles does a fine job of directing the blast upwards.
Yes, the cap and neck section of the pressure vessle make a dangerous projetile at first but it literally flutters back down to the ground with much reduced liability.  ;-) 

The pressure bottle is most efficiently filled with finger sized cylindrical Dry Ice but this form factor is not as easily available as the blocks/slabs found in local grocery stores.
For blocks/slabs you need to use a large flat blade screw driver or such and a hammer to help you break it up into chances that will  fit into the bottle.
Stuff the bottle as full as possible to minimize the wait time.

Have the bottle collection resting on a flat surface to keep it from falling over before it pops.


Experience shows that the outer shield (three liter bottle) has never been breached while the inner shields will shred to varying degrees.



On Aug 3, 2013, at 4:52 PM, David Willey <dwilley@pitt.edu> wrote:

> This may be a repeat, my apologies if it is, my server told me the first version was "undeliverable".
>
>
> *BLOWING UP A GARBAGE CAN USING A SODA BOTTLE AND LIQUID NITROGEN.***
>
> *The soda bottle.***
>
> A 2 liter soda bottle works well, although I have used smaller bottles, e.g. 1 liter Seltzer bottles. The newer "reduced plastic" water bottles will work, but produce a less energetic explosion as the bottle bursts more easily than the thicker walled bottles. Recycled bottles are fine, but, as I recently discovered, they should not have liquid nitrogen, LN2, put in them until the demonstration is performed. I thought that putting a desert spoon of LN2 in bottles before shipping them would prevent them from damage when shipping. It turns out, as far as I can tell, that this actually weakens the bottle and causes it to leak at the site where the plastic is injected, rather than exploding. A friend of mine who works for Pepsi Cola assures me that this is the weakest point on the bottle. I'm fortunate that both Pepsi Cola and Coca Cola are willing to donate virgin bottles (never had soda in them, nor a label on them) to me. I have never had one of either of these brand's new bottles fail. The lid of the bottle needs to be screwed on tightly, but be careful not to over tighten it and strip the screw threads. I usually take the plastic ring off the bottle cap before use. I use a small funnel to pour about 300 mL (about a cup) of LN2 in the bottle. I do not wear gloves while doing this. It seems that using more nitrogen makes it take a longer time for the bottle to explode, although I have not timed how long varying amounts take. I have timed it a few times for approximately 300 mL and it took about six minutes usually.
>
> *The garbage can.***
>
> If you do this outdoors you can just let the "naked" bottle explode, but I would very strongly recommend that you do not do this. The frozen shards of plastic especially the section around the cap of the bottle constitute dangerous shrapnel, but if you insist on doing it this way, no one should be within 100 meters of the bottle when it does explode.
>
> To make this demonstration safer I place the bottle under an inverted plastic, never metal, garbage can. I have found the smooth sided 44 gallon BRUTE cans by Rubbermaid work well and have a longer life expectancy than thinner cans or ones with folds in the plastic.
>
> http://imageshack.us/photo/my-images/706/l1h2.jpg/
>
> Figure 1. BRUTE trash can by Rubbermaid
>
> To extend the life of them, these days I cut off the bottom ten centimeters of an old can that has holes or splits in its sides and put that inside the bottom of the new can and duct tape it in place. Without this a can seems to last for about ten explosions before the bottom ruptures, with the reinforcement the can last three to four times as long and it is usually splits in the side that cause its demise. Small slits in the side of a can may be repaired with a large patch cut from an old can duct taped inside the new can.
>
> http://imageshack.us/photo/my-images/266/aor0.jpg/
>
> Figure 2. Can with a patch and a double bottom.
>
> Just having a can over the bottle however does not ensure safety, as some of the bottle pieces can still escape from under the can. The cap and neck of the bottle are particularly nasty shrapnel. To prevent them from escaping and to direct the rest of the bottle up into the can, I use a base to hold the bottle.
>
> *The base.***
>
> http://imageshack.us/photo/my-images/849/s4x7.jpg/
>
> Figure 3. Base for exploding soda bottle, photograph.
>
> http://imageshack.us/photo/my-images/199/1xc8.png/
>
> Figure 4. Base for exploding soda bottle, drawing.
>
> To make this base fasten a stainless steel mixing bowl to a two inch thick piece of plank, both of which have a four centimeter hole cut centrally in them. As can be seen in Figure 3. I reinforced the bowl where it fastens to the wood with a large washer held in place by smaller washers on the bolts. This assembly is in turn is fastened to two pieces of plywood. Bolts hold all of this together, as they do not pull out as easily as wood screws.
>
> The resulting explosion is quite spectacular, the bowl tends to direct the gas upward resulting in the can being launched about 20 meters into the air, see figure 5.
>
> http://imageshack.us/photo/my-images/825/86qk.jpg/
>
> Figure 5. Soda bottle explosion.
>
> Notice the piece of green soda bottle to the right of the garbage can. If the demonstration is done on level ground the can usually lands within about ten meters of the launch position. I have placed the whole arrangement on a sheet of inch thick plywood, angled to the horizontal to direct the can away from the audience.
>
> For indoor shows I tie one handle of the barrel to some relatively immovable object, e.g. a door knob, stair hand rail, or even the concrete block later to be broken on me. I make the rope short enough so that the barrel can neither hit an audience member, nor any breakable objects, e.g. ceiling tiles, or the other apparatus.
>
> Outdoors I sometimes use an alternative to the bowl, which launches the can even higher. This base is made from a piece of eighth inch thick, six inch diameter, eight inch long brass cylinder, surrounding a sixteenth inch thick, sixteen inch long aluminum cylinder. Both cylinders were salvaged from scrapped equipment.
>
> The aluminum tube fits inside the brass tube. The screws at the bottom fasten both tubes to a two inch thick, six inch diameter piece of wood, in turn fastened to a piece of plywood. Sometimes I line the inside of the tubes with a plastic trash bag and then pour in about half a gallon of water. This reduces the time for the bottle to explode from about six minutes to less than one minute usually.
>
> http://imageshack.us/photo/my-images/834/zvul.jpg/
>
> Figure 6. Alternative base for higher launches.
>
> I recently measured the sound pressure level at a distance of 3.5 meters from the garbage can, using a Model 370 Triplett sound pressure level meter. For a 2 liter, fluted bottom Coke bottle, filled with about 300 mL of LN2, the reading was 105 ± 1 dB. From what I read, this is not a dangerous level for a sound of short duration. I still recommend that parents with babies or very young children sit considerably further away. Startled children are no fun for anyone.
>
>
> I hope that this may be of some use to some of you. If you have questions I may be reached at dwilley@pitt.edu
>
> Comments are welcomed,
> cheers,
> David
>
>
>
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