Discussion Forum

Hi

I assume you are in 2D ? and your units are not flow/m^2 but /m ?
If so yes, in 2D everything is "per meter" so you need to multiply by the appropriate depth (d or "Z value)
Note that several physics in 2D allows you to define a thickness along Z to get absolute values (sometimes you can add a "change thcikness" sub-node

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Good luck
Ivar

Hi,
thanks for reply dear Mr. Ivar
I'm in 2D axisymmetric, and my unit is (kg/s).
I still do not understand how to specify and enter the "Channel thickness" ! just enter the "d= ... [m]" in Variables?
best regards

Hi

In 2D-axi you have no "depth" but a "loop length" of 2*pi*r hence varying depending how far you are from the axis.

When you integrate over the domain in 2D-axi you have the additional option to have COMSOL automatically multiply by 2*pi*r for you check on the option, or add it by yourself. THis adds a "m" on the units and transform a surface integral into a volume (of revolution) integral

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Good luck
Ivar

thanks a lot for reply
Unfortunately I didn't understand ...! didn't know how to solve this problem! My model consists of Plasma module and Lamir flow. My mass flow rate 1e-7 kg/s.
Inlet thickness 2 mm.
how can I add a mass flow rate?
I integrated over the inlet boundary

Integration1 (Intop1) > "inlet boundary"
Variable > mass = intop1(2*pi*r*u*spf.rho)

this integral depends on the velocity!
what should I do?

Please help somebody ...

Hi

first of all, in 2D-axi you should have no geoemtry on the r<0 side of the axis, only the cut line along the r=0 symmetry axis.

if you have an flow rate of [kg/s] this should be intop1(2*pi*r*u,rho) over the inlet, as "r" is in meters, u in [m/s], rho in [kg/m^3] and the dr of the integration argument (implicit not written out in COMSOL) adds a "m" hence you have

m*m/s*kg/m^3*m = kg/s

, no ?

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Good luck
Ivar

yes! I understand it! this is not problem!
Problems another! how I can to add mass flow rate integration when I dont know velocity (u)? I just know mass flow rate=1e-7 [kg/s]
if I add the integral as a variable, I need to know the velocity (u).
density changes with time in the chamber.
how can I achieve a concrete mass flow rate?
how can I add 1e-7 [kg/s] ?

thanks...

Hi

but if the gas is entering in laminaire mode a parabolic profile is quite usual, then you have fixed values.

However you can also add a dependent variable: the local input velocity field across the inlet, and bind it through your fomula to impose the total flux, then COMSOL will adapt it "in a means square" approach

u(x,y,z,t) defined such as => intop1(...) - 1E-7 = 0

where the =0 is implicit in the COMSOL notation

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Good luck
Ivar

thanks you very much Mr. Ivar !! We love you ...