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Re: deep water = less ejecta?



Well, (ahem!), the following is actually, uh, er, backwards. "Also 
as 
the 
the 
vapor 
condenses 
it  
> 
extracts 
heat 
from 
the 
atmosphere". Should read "releases heat". I guess as the _condensate_ falls, it 
might extract heat

Anyhow, what I was thinking re impactors is that the rock vapor fraction of the 
ejecta will have a much higher 'boiling point' and change phase fairly quickly, 
therefore carrying further and cooling more slowly (due to geometry and 
density) than the water fraction which as a vapor will lack momentum and 
dissipate it's heat quickly. But whatever. It is out of my depth, anyway (pun 
intended).

Don

----- Original Message ----
From: Mike Habib <habib@jhmi.edu>
To: d_ohmes@yahoo.com
Cc: dinosaur@usc.edu
Sent: Sunday, January 27, 2008 7:12:02 PM
Subject: Re: deep water = less ejecta?


On 
Jan 
27, 
2008, 
at 
1:50 
PM, 
don 
ohmes 
wrote:
> 
Not 
qualitatively, 
according 
to 
my 
understanding; 
the 
heat 
of 
the  
> 
vapor 
obviously 
dissipates 
quickly 
relative 
to 
liquid 
due 
in 
part 
to  
> 
the 
many 
point 
sources 
involved. 
Also 
as 
the 
the 
vapor 
condenses 
it  
> 
extracts 
heat 
from 
the 
atmosphere.

True.  
The 
specific 
heat 
capacity 
of 
water 
vapor 
is 
still 
quite 
high,  
though.  
It 
much 
lower 
than 
that 
of 
liquid 
water 
(assuming 
standard  
pressure 
and 
temperature) 
but 
the 
heat 
capacity 
of 
water 
vapor 
is  
greater 
than, 
for 
example, 
solid 
silicious 
clay.  
Your 
point 
about  
point 
sources 
for 
dissipation 
is 
well 
taken; 
this 
applies 
to 
both 
the  
water 
vapor 
and 
the 
vaporized 
rock, 
however.

>
> 
A 
jet 
of 
steam 
is 
devastating 
at 
close 
range, 
but 
cools 
quickly,  
> 
whereas 
a 
jet 
of 
liquid 
water 
(or 
molten 
rock) 
will 
hold 
it's 
heat  
> 
much 
further/longer...

True, 
but 
this 
is 
largely 
because 
of 
the 
mass 
differences: 
a 
jet 
of  
liquid 
water 
will 
usually 
have 
more 
mass 
than 
a 
jet 
of 
steam.  
If 
the  
mass 
of 
the 
hypothetical 
jets 
of 
material 
are 
all 
the 
same, 
then 
the  
liquid 
water 
would 
hold 
the 
energy 
the 
longest, 
followed 
by 
the 
water  
vapor.  
The 
particulate/vaporized 
rock 
would 
probably 
cool 
off 
the  
most 
quickly, 
though 
I 
say 
this 
with 
some 
hesitation 
as 
I 
do 
not 
have  
heat 
capacity 
data 
for 
molten 
substrates 
handy.  
We 
should 
also 
keep  
in 
mind 
that 
the 
superheated 
ejecta 
would 
have 
higher 
heat 
capacity  
than 
at 
standard 
temperature; 
water 
vapor 
at 
1000 
K, 
for 
example, 
has  
a 
heat 
capacity 
of 
2.288 
kJ/kgK 
(compared 
to 
1.954 
kJ/kgK 
at 
500 
K).

Cheers,

--Mike


Michael 
Habib, 
M.S.
PhD. 
Candidate
Center 
for 
Functional 
Anatomy 
and 
Evolution
Johns 
Hopkins 
School 
of 
Medicine
1830 
E. 
Monument 
Street
Baltimore, 
MD 
21205
(443) 
280-0181
habib@jhmi.edu