Phil and Kevin,

This analysis is very interesting and hopeful.  Two thoughts:

a) There is the question of the cooling of the rest of the shell, which Phil and I talked about on Friday.  It looks to me like the coil cooling may need to the bulk of this, and may be capable of doing it. But it should be analyzed, likely by extending Kevin's model.

b) This calculation assumes a cooling rate of 0.08 W/cm^2 into the gas.  This will imply a calculable temperature rise in the gas, given the length of tube, the pressure and pressure drop, and temperature.  The cooling tube is 0.19 in diameter => 1.516 cm inside circumference.  The specific heat of N2 gas is almost independent of temperature at ~1.05 J/g/K and the density of N2 gas is 1.25 g/liter at 1 atmosphere and 283K.  If we assume an inlet pressure of 150 psia and a 14.7 psi drop, we can calculate flow rates using http://www.pipeflowcalculations.com/pressuredrop/index.htm .  I don't know the cooling pipe lengths, so I'll calculate several representative lengths.  I get


length   heat     gas    mass     delta T
         flow    flow    flow 
(m)      (W)     (CFM)   (g/s)     (K)
-----------------------------------------------------------
for 283K:
-----------------------------------------------------------
2        24.      1.4     8.0      2.9
3        36       1.1     6.4      5.4
4        49       0.93    5.5      8.5

for 150K:
----------------------------------------------------------
2        24               11       2.2
3        36               8.7      4.0
4        49               7.4      6.3


So, in order for the gas flow to carry away 0.08 W/cm2, the temperature rise along the flow and along the coil will be several degrees and thus comparable to the temperature variations you are trying to control across the pack and structure.  If the tubes are longer than ~2m, the variations along the pack are significant and may determine the cool down rate.

As expected, the heat carrying capacity of the gas improves as the temperature decreases, due to the  change in density.


Mike.





At 04:05 PM 5/16/2008, Phil Heitzenroeder wrote:

 
Mr. Philip Heitzenroeder
Head, Mechanical Engineering Division
Princeton Plasma Physics Laboratory
Princeton, NJ 08543
e-mail:  pheitzen@pppl.gov
Phone:  609-243-3043
Fax:  609-243-3030
 

From: Phil Heitzenroeder
Sent: Friday, May 16, 2008 2:47 PM
To: David Gwinn
Cc: Steve Raftopoulos; Don Rej; Hutch Neilson
Subject: Kevin Freudenberg's thermal modeling
 
Dave,
Attached is Kevin’s latest effort on thermal modeling.  Please let  me know if you think a conference call would be useful to compare thoughts. 
Phil
 
 

From: Freudenberg, Kevin D. [mailto:freudenbergk@ornl.gov]
Sent: Friday, May 16, 2008 2:38 PM
To: Phil Heitzenroeder
Subject:
 
 
 
Kevin D. Freudenberg
Mechanical Design and Analysis
Oak Ridge National Laboratory
US ITER Team
(865) 574-1310