CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   Mass flow rate (

Neser February 12, 2004 07:22

Mass flow rate
Hi there,

In CFX5.6 post, when I used calculter panel to calculate pressure, temprature, mass flow rate, velocity, etc. I asked it to calculate all inlet condition, there was no any problems. However, when I asked it to calculate the out put conditions, I got the following answers:

Mass flow rate 0.0 max. Velocity 5.698 m/s

How I can have a velocity with out mass folw rate!!!. How outlet mass flow rate is zero, while inlet mass flow rate is 19.8198 kg/s.

please help me, what is the problem!!

Glenn Horrocks February 12, 2004 17:28

Re: Mass flow rate
Hi Neser,

If the flow is leaving the domain it is a negative mass flow rate. Velocity magnitude is a scalar, and so is always positive. I suggest you find the minimum of the mass flow rate instead and you should get a sensible answer.


Neale February 13, 2004 00:43

Re: Mass flow rate
From previous posts it looked to me like you are attempting multiphase calculations. Maybe the volume fraction is zero at your outlets for the phase with a 5.68 m/s velocity?


Neser February 13, 2004 06:03

Re: Mass flow rate
Yes, It two phase flow, water and air. However, the program gave me zero mass flow rate for the two outlets I have this for total, water and air. It is imposible to have zero volume fration for all fluids at outlets.

Jeff February 14, 2004 01:27

Re: Mass flow rate
If you look at a plot of the vectors are they all leaving the domain? For both phases?

It is possible to have a finite maximum velocity (which is direction independent and indicates the maximum vertex velocity on the plane, not the mean signed velocity) and still have an eddie at the outlet plane which results in a zero mass flow rate. Thus, even though the maximum velocity is 7.6 m/s, there may be an equal vector in the opposite direction (which will also be positive) resulting in a net zero mass flux.

Just a thought.


All times are GMT -4. The time now is 20:53.