Energy From Thorium Discussion Forum

It is currently Sep 24, 2018 2:17 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 318 posts ]  Go to page Previous  1 ... 18, 19, 20, 21, 22
Author Message
PostPosted: Jun 29, 2013 9:42 pm 
Offline

Joined: Feb 05, 2013 5:24 am
Posts: 108
Since the PB-AHTR uses an open bed the pebble density as you approach the edge drops due to the wall interaction. This extra porosity will allow some larger flow fraction in this lower power density region and thus robbing the center of flow. For a large bed compared to ball size this wil be small, and over flowing the core can compensate at a pumping power price. I hope they accounted for this properly in their scaled down flow model.

Also, didn't the graphite balls in the German reactor get sticky/tacky at the temperatures they operated at? Balls sticking together some, which makes the funnel scenario worse. Also, balls sticking together reduces relative motion between balls, thus keeping the low cooling regions together longer and creating a higher risk of failure region ( i.e. constantly higher temperature, compared to balls eith relative motion). That does not explain the stuck ball in the pipe unless it was also sticking to the metal walls.


Top
 Profile  
 
PostPosted: Jun 30, 2013 3:15 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
Yes, the friction coefficient for graphite increases greatly above 300 degree Celsius or so. At HTGR operating temperatures it's close to 1!

With fluoride salt the opposite effect will be true. The salt becomes a better lubricant at higher temperatures, so friction will decrease with temperature.


Top
 Profile  
 
PostPosted: Dec 19, 2013 12:41 am 
Offline

Joined: Dec 31, 2008 12:09 am
Posts: 236
Location: Berkeley, CA
Cyril R wrote:
Yes, the friction coefficient for graphite increases greatly above 300 degree Celsius or so. At HTGR operating temperatures it's close to 1!

With fluoride salt the opposite effect will be true. The salt becomes a better lubricant at higher temperatures, so friction will decrease with temperature.



This is correct. Friction experiments were performed by the UCB NE-170 senior design class in 2009 showing that fluoride salts act as good lubricants for graphite at high temperature, see Chapter 5 in

http://www.nuc.berkeley.edu/pb-ahtr/pap ... Design.pdf

-Per


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 318 posts ]  Go to page Previous  1 ... 18, 19, 20, 21, 22

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group