# How to express a varible at a given point

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 March 14, 2011, 20:27 How to express a varible at a given point #1 Member   Ji Guozhao Join Date: Jan 2011 Posts: 42 Rep Power: 9 Hi All: How to express a varible at a specific point in CEL. for example, if i want to express the pressure at the point(x,y,z), is it p@(x,y,z)? or p_x_y_z_coord0? is there any kind hearted one who can tell me the answer? many thanks ahead!!! best regards Ji Guozhao g.ji@uq.edu.au

 March 15, 2011, 11:10 #2 New Member   Join Date: Oct 2010 Posts: 14 Rep Power: 9 If you use an expression that includes a variable at specific location, CFX calculates the variable at that location. If you express your problem in detail, we may find out a solution

March 15, 2011, 18:26
#3
Member

Ji Guozhao
Join Date: Jan 2011
Posts: 42
Rep Power: 9
Quote:
 Originally Posted by octavyo If you use an expression that includes a variable at specific location, CFX calculates the variable at that location. If you express your problem in detail, we may find out a solution
Dear Sir:
Thank you for your reply! I am super happy to that! because if i solved this problem, i can start my project.
let me express the problem in detail. I want to simulate gas mass transfer across membrane in a gas separation module.but to the best of my knowledge, only darcy's law is built in CFX, and it is not able to satisfy my requirement, so i have to introduce sink at feed side of membrane and source at permeate side. actually the quantity of sink or source is a function of both pressures at both sides.
to illustrate the problem clearly, i also attached a picture. for instance, I want to express the sink. sink_i=C*(P_j-P_i), C is a constant equal to 4.064e-9[kg m^-2 s^-1 Pa^-1]. In source tab-Fluid Mass Flux- CEL expression blank, I only wrote -p*4.064e-9[kg m^-2 s^-1 Pa^-1], treating P_j is equal to 0 pa. but in fact P_j is not constant, it is also changed with position.
Can you tell me how to deal with my problem. how can I introduce P_j to express the sink in element i?
Best regards

Ji Guozhao
g.ji@uq.edu.au
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