[ExI] Help with freezing phenomenon

[Keith Henson]

On Thu, Jan 27, 2011 at 5:00 AM,  Jeff Davis <jrd1415 at gmail.com> wrote:

snip
>
> That should get you started.  Now here's my question.
>
snip

> I ask because I was expecting the reverse.  Somehow I got the notion
> that the outer shell of ice (conventional freezing) would slow the
> cooling rate, compared to the "shell" of fluid tissue kept unfrozen
> until the end point of the CAS process.
>
> ******************************************
>
> Water isn't tissue.  And convection, ...what about convection?!
>
> Make believe there is no such thing as convection.
>
>  I know, I know.

The current practice at Alcor is to load tissue with so much
cryoprotective solution and ice blockers that ice never forms at all.

Alcor uses burr holes in the skull to observe the brain for swelling.
We can reverse swelling in some cases by increasing the ramp of
cryoprotective addition (which dehydrates).  It all depends on how
much time/temperature the patient was subjected to before staring the
cryoprotective ramp.  Really fresh, cold brains don't swell at all.

Convection just doesn't apply to something like a slab of meat.  There
is no path for the liquid to circulate.

Gross reality check.  Long ago when I was working on the very first
computer controlled freezing system for heads, Hugh Hixon and I needed
a test heat load for it.  So we filled a head sized plastic bag with
water and froze that.

Boy what a mess.  It shell froze, then, as more inside froze, it
cracked, big cracks like half a inch wide.  Inside looked like crushed
ice.

Hugh Hixon had bags of the then current cryoprotective perfusate
around so the next test run we used those.  The stuff didn't actually
become a solid all the way down to dry ice temperature.  It looked
like milk and got stiffer than putty.

Keith

PS.  The system used a pump for silicon oil and a solenoid that
switched the flow of oil over dry ice or bypassed the dry ice to track
the desired temperature descent.  It evolved over time to what is used
today.