Date: Mon Apr 23 20:23:23 2007

Author: Richard Berg

Subject: Re: Big, loud, impressive demos


What are you going to do when it does not explode?


On Mon, 23 Apr 2007, Bernard Cleyet wrote:

> (Only about 20 mL of LN2 as I recall is about 40 L(?) of gas--we can
> calculate this of course) [ D.S.] And:
> Can the LN2 bottle explosion damage a 50-gallon steel drum, as well? That's
> what I was hoping to use. [Scott S.]
> lN2 S.G ~ 0.8 therefore, 20 ml is ~ 16 gm or ~ 1/2 mole. At STP this would
> make ~ eleven litre (Critical pressure is ~ 500 PSI.)
> Work done in boiling (expansion at constant pressure) is ~ one kilo joule.
> [~0.01 m^3 * 101 kPa]
> 55 ga ~= 208 litre adding ~ 11 litres would increase the p only about 5%.
> However, if a sig. portion of the energy of the expanding gas were
> transferred to a hard missile, it could puncture the drum.
> bc, thinks something wrong; not near enuff energy.
> David Sturm wrote:
>> With a resounding boom, I'll echo Jerry Zani and Dick Berg... Exploding
>> small soda bottles containing LN2 is extremely dangerous, and it only
>> takes one "unplanned consequence" to cause injury.
>> I remember the 1999 Summer AAPT meeting... the garbage cans used at the
>> big demo show were not of a rubbery plastic. The cans shattered from the
>> explosion and sent out shrapnel consisting of sharp plastic shards of can.
>> Also, I've saved pieces of previous 20 oz bottle explosions, and have
>> noticed that the neck of the bottle often ends up with very sharp edges.
>> The soundblast I think is the most impressive part of the demonstration,
>> and as Jerry points out, the 55-gal drum crushed by atmospheric pressure
>> (and condensation of steam to water, too) is a superb outdoor
>> demonstration that makes a big boom.
>> If one must do the LN2 in a 20oz bottle, I'll add how I prefer to do it:
>> NEVER with garbage cans. Take a copy paper box (without the reams of
>> paper, of course!)... lay the lid down on the ground, place a thin plastic
>> can liner (cat litter bags
>> work well too) in the lid... fill it with water. Set the box itself up at
>> an angle, ready to be knocked down when you insert the bottle. Prepare
>> the bottle with one round of duct tape around the top: as I mentioned
>> before, the thickest part of the
>> bottle could produce sharp shrapnel. I prefer to pre-cool the bottle in a
>> nearby dewar. Just an ounce'll do inside. The cap should be tight.
>> (Only about 20 mL of LN2 as I recall is about 40 L(?) of gas--we can
>> calculate this of course). Be
>> sure everyone and everything is clear... set the bottle in, drop the box
>> fully over the lid... and get out of the way quickly. Something like 30
>> meters distant is certainly good. This method will create lots of flying
>> wet cardboard... but of
>> course there's always the issue of the bottle fragments: but no chance of
>> breaking a garbage can from the blast.
>> ====================================================
>> David E G Sturm - - 1.207.581.1241
>> --Physics & Astronomy Instructional Laboratories
>> --Bennett Hall Lecture Demonstration Facilities
>> --Mainely Physics Road Show --PIRA VP '06-07
>> Dept of Physics & Astronomy -- University of Maine
>> 5709 Bennett Hall -- Orono ME 04469-5709
>> ====================================================

Dr. Richard E. Berg, Professor of the Practice
Director, Physics Lecture-Demonstration Facility
U.S. mail address:
Department of Physics
University of Maryland
College Park, MD 20742-4111
Phone: (301) 405-5994
FAX: (301) 314-9525