# Determining alpha and beta for porous baffle

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Search this Thread Display Modes
 October 25, 2000, 18:28 Determining alpha and beta for porous baffle #1 Liaqat Khan Guest   Posts: n/a I am a new user of Star-CD, and not sure how to determine alpha and beta values of porous baffle. The porous baffle in my case represent a screen. When I run the model without the baffle, the solution converges in less than 100 iterations. However, when the baffle is included, and if I use arbitrary values of alpha and beta the solution does not converge in 1000 iterations, and the convergence parameters never fall below 100. I have tried various combinations of alpha and beta, changing their values by order of magnitude, with the same result. From field and physical model studies, the head loss across the screen is approximately given by HL = 0.125 V^2, where velocity is in ft/s and HL is in feet of water, and the porosity is 0.755. I would like to use the following equation (equation(8-6) in Methodology) delP = -rho*(alpha*V+beta)*V to determine alpha and beta. From equation for head loss: For V = 1 ft/s (0.3048 m/s), HL = 0.125 ft = 0.054 psi = 373.463 Pa. For V = 2 ft/s (0.6096 m/s), HL = 0.500 ft = 0.217 psi = 1493.85 Pa Using these estimates of head losses, equations for delP can be written as (rho = 998.2 kg/m^3) 373.463 = -998.2*(alpha*0.3048+beta)*0.3048 1493.87 = -998.2*(alpha*0.6096+beta)*0.6096 If I solve these equations for alpha and beta, I get negative value of alpha and beta is almost zero. Obviously, something is not right. I will appreciate if some one can give me suggestions how to approach this issue. Thanks. Liaqat A. Khan

 October 27, 2000, 04:44 Re: Determining alpha and beta for porous baffle #2 Brian Guest   Posts: n/a Alpha is coming out negative because your pressure drop should be negative. The way you have formulated it, the baffle causes a pressure INCREASE! But whatever the values, remember to test them against the allowable limits for alpha and beta. You can find these limits in the manual.

 Thread Tools Search this Thread Search this Thread: Advanced Search Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Guy Siemens 3 December 21, 2008 10:59 Aga Siemens 0 July 24, 2007 01:58 azmir Siemens 0 February 9, 2006 19:25 Nirmal Siemens 1 November 9, 2005 00:50 Jan Siemens 0 June 8, 2002 09:23

All times are GMT -4. The time now is 08:44.

 Contact Us - CFD Online - Privacy Statement - Top