Date: Wed, 18 Aug 2010 11:03:44

Author: chuck britton

Subject: Re: "Ice Spikes" as art photography

Post:

My experience has been that the Leidenfrost Effect is quite effective
in keeping the LN2 from making contact with the mouthparts. The
temperature of the mouthparts is ~ four times higher than that of the
LN2. The Leidenfrost Effect is not a theoretical construct.

The layer of water should not be necessary for the Leidenfrost Effect to occur.

I say that one SHOULD ensure that the mouth is wet for two reasons:

The specific heat of H2O is high as is the Latent Heat of
Fusion for H2O,
so the time required for any (possible) freezing is increased.
and

The H2O serves as an indicator as to whether and freezing has occurred.
(My experience has always been - no freezing occurs)

My dentist has never observed any such cracking. (The plural of
anecdote is data?) ;-)

At 12:13 AM -0700 8/18/10, William Beaty wrote:
>On Mon, 16 Aug 2010, chuck britton wrote:
>
>>DO ensure that your mouth (teeth, tongue, lips etc.) are WET before drinking.
>> A wet surface will not get colder than zero C.
>
>A thin water film should have little effect, no? Wouldn't a soap
>bubble freeze in mSecs when touched with a droplet of LN2?
>
>I recall twenty years ago when the public warning went out in TPT:
>Paul Hewitt described his dentist's confusion at finding the enamel
>surfaces of Paul's back teeth to be covered with tiny fractures.
>The obvious cause was accumulated damage over many years during his
>quarterly "drink liquid nitrogen" lecture demos.
>
>So that's one data point to clarify any theoretical arguments. Of
>course it's possible that Paul's damage could be from a few outlier
>events such as rapidly repeated performances to chill teeth
>progressively, while the majority of demos were benign...
>
>I named the LN2 demo "worse" than ice-chewing because only a tiny
>tooth surface is needed to crush the dry ice pellets, and it takes a
>fraction of a second during contact. No need to actually chew them,
>just bite quickly so the chunks shatter, and simultaneously blow the
>pieces out as a white cloud. But with LN2, the fluid makes contact
>with relatively enormous tooth surface for a second or more. But
>perhaps with LN2 the tooth temperature falls slowly enough that the
>enamel surface won't fracture except during prolonged contact
>followed by rapid re-heating from tongue contact?
>
>Are your teeth safe as long as you only perform the demo once per
>minute, and only for less than two seconds at a time? Heh, obtain
>some human teeth and observe any cracks appearing during video
>time-lapse automated temp-cycling between LN2 and 37C water for
>increasingly long LN2 contact!



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