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flux magnitude

Posted Aug 26, 2015, 12:44 p.m. EDT 5 Replies

Anwer Mhannawee
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Hi

I try to find the total flux magnitude along line in flow channel, it gives result with units (kg/m^2.s), which depends on area , any idea how it defined the area along that line?

Regards
Anwer
5 Replies Last Post Aug 27, 2015, 5:52 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 9 years ago Aug 26, 2015, 1:10 p.m. EDT
Hi

are you in 2D or 3D ?
I assume 2D since you talk about lines ... COMSOL always assumes 3D, even for 2D, but for 2D models mostly the "depth" is set to 1[m] so all fluxes along a "line" = Boundary in 2D remains fluxes in units/m^2.

Which means you must integrate along the "line" = boundary in 2D and multiply by the fixed depth, or accept the results in per m "depth"

--
Good luck
Ivar
Hi are you in 2D or 3D ? I assume 2D since you talk about lines ... COMSOL always assumes 3D, even for 2D, but for 2D models mostly the "depth" is set to 1[m] so all fluxes along a "line" = Boundary in 2D remains fluxes in units/m^2. Which means you must integrate along the "line" = boundary in 2D and multiply by the fixed depth, or accept the results in per m "depth" -- Good luck Ivar
Anwer Mhannawee
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Posted: 9 years ago Aug 26, 2015, 1:57 p.m. EDT
Thank you Ivar

I am in 3D module , the depth magnitude defined , so the result i found considered the surface area along the depth of flow channel ?
Thank you Ivar I am in 3D module , the depth magnitude defined , so the result i found considered the surface area along the depth of flow channel ?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 9 years ago Aug 27, 2015, 1:44 a.m. EDT
Hi
OK in 3D, then I probably missed the concept of Line in your case.

Could it be that you want to define a "Results - DataSet - Cut Line 3D" and plot spf.U*spf.rho thereon ?
If so I have joined two images below for a simple fluid in a tube case

But I'm not sure I got your question 100% right ;)

--
Good luck
Ivar
Hi OK in 3D, then I probably missed the concept of Line in your case. Could it be that you want to define a "Results - DataSet - Cut Line 3D" and plot spf.U*spf.rho thereon ? If so I have joined two images below for a simple fluid in a tube case But I'm not sure I got your question 100% right ;) -- Good luck Ivar
Anwer Mhannawee
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Posted: 9 years ago Aug 27, 2015, 2:07 a.m. EDT
yes right , that exactly what I have,
in the plot, the unit is in (kg/m^2.S) , and we measure flow along the Line which is one dimension,so I was asking about how defined flux ( which is depends on area) along one dimension line

regads
yes right , that exactly what I have, in the plot, the unit is in (kg/m^2.S) , and we measure flow along the Line which is one dimension,so I was asking about how defined flux ( which is depends on area) along one dimension line regads
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 9 years ago Aug 27, 2015, 5:52 a.m. EDT
Hi

well it's on the image, no?: spf.U*spf.rho

which gives the local mass flux in kg /(m^2)/s : mass [kg] per perpendicular surface Area [m^2], per second [s]

if you want the total mass per second [kg/s] you need to integrate over the section surface, and define correctly which "normal" to use. i.e. integrate over the outflow surface check the equations under the hood (Preferences Equation View) => search for COMSOL internal variable "spf.out1.Mflow"

--
Good luck
Ivar
Hi well it's on the image, no?: spf.U*spf.rho which gives the local mass flux in kg /(m^2)/s : mass [kg] per perpendicular surface Area [m^2], per second [s] if you want the total mass per second [kg/s] you need to integrate over the section surface, and define correctly which "normal" to use. i.e. integrate over the outflow surface check the equations under the hood (Preferences Equation View) => search for COMSOL internal variable "spf.out1.Mflow" -- Good luck Ivar

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