CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   Phoenics (http://www.cfd-online.com/Forums/phoenics/)
-   -   Mass flux and mass flow rate (http://www.cfd-online.com/Forums/phoenics/51811-mass-flux-mass-flow-rate.html)

us October 12, 2004 01:05

Mass flux and mass flow rate
 
Hi,

Can anybody tell how to retrieve the mass flux and mass flow rate data at any given plane ?

Thanks in advance.

US

Rami October 12, 2004 04:35

Re: Mass flux and mass flow rate
 
Here is an answer (with certain omissions) I had received from Mick Hughes of CHAM a long time ago and implemented successfully (with some modifications) in my GROUND (I had plugged it in group 19, section 8. In my case - BFC grid and compressible flow is assumed). I hope it will work for you too.

Date: Tue, 03 Feb 1998 16:58:24 GMT From: support@cham.co.uk (CHAM User Support) Subject: mass fluxes

I am not aware of any earth array that stores the actual mass fluxes. I imagine that there is more than one way to approximate these mass fluxes.

Just for my own piece of mind I will think aloud .....

Thinking about it from Gausses law :

Int_over_volume (div F) dVol = int_over_faces (F.n) dArea

therefore dF/dn *Vol = (Sum_of F.n*area) i.e the flux could possible be approximated as a function of differentials *Vol, (df/dx+df/dy+df/dz)*vol or the addition of the products of F.normal_to face*face_area.

I think the lattere of these two is the most natural way to calculate the fluxes.

For cell i,j,k mass flux at east face is rho*UVEL_IN_DIR_OF_GRID_LINES*PROJECTED_AREA_OF_FA CE_IN_DIR_OF_GRID_LINES

which is rho1*UCMP*APROJE

In Q1 put store(ucmp,vcmp,wcmp) to have the components of velocities perpendicular to grid lines calculated. You will then be able to access these from within ground using normal L0f's. Look in the result file at the name commands, if NAME(16)=UCMP, then you can access it directly by using the earth index 16.

The projected areas are APROJE,APROJN and APROJH have bfc indexes 1,2 and 3 respectively, they can be accessed in ground by using LOB's, access to all BFC geometric quantities is through l0B's

So for example to calculate the sum of east face fluxes at iz = 17, the code in ground might be something like.

if(iz.eq.17)then

l0u1=l0f(16) c could try l0u1=l0f(lbname('UCMP'))

l0A=l0B(1) c for east area projections 2 -> north, 3- high

l0den=l0F(den1)

rsum=0.0

do iy=1,ny

do ix=1,nx

icell = iy+(ix-1)*ny

rsum=rsum+(f(l0den+icell)*f(l0u1+icell)*f(l0A+icel l)

enddo

enddo

write(14,*)'sum of east dir fluxes at iz = 17 is',rsum

Regards

Mick

us October 12, 2004 08:42

Re: Mass flux and mass flow rate
 
Dear Rami,

Thanks for your reply. I have worked out the problem using INFORM. Somehow succeeded as below I have used the V402 case and altered it for width of 0.5 m (i.e., Y) instead of 1.0 and as well as made it 3D by giving the grid divisions along Y.

Then, stored some variables (i.e., in Q1 STORE(DEN1,MFX ,MFY ,MFZ ,MRX ,MRY ,MRZ ) Where MFX stands for X directed mass Flux and MFY and MFZ for Y and Z.

MRX stands for Cell Mass Rate along X direction and similarly others for Y and Z.

To refer the Inform Formula to some location, I have created a User_defined patch in the name of MASS, with a CELL type of patch named MASS, to cover the whole domain.

The following are the formulas used which are self-explanatory.

Echo InForm settings for Group 23

inform23begin

CHAR(MFLX,MFLY,MFLZ,CMFX,CMFY,CMFZ)

MFLX=DEN1*(U1)

MFLY=DEN1*(V1)

MFLZ=DEN1*(W1)

CMFX=DEN1*(U1)*(DYG*DZG)

CMFY=DEN1*(U1)*(DXG*DZG)

CMFZ=DEN1*(U1)*(DXG*DYG)

(STORED OF MFX AT MASS IS MFLX)

(STORED OF MFY AT MASS IS MFLY)

(STORED OF MFZ AT MASS IS MFLZ)

(STORED OF MRX AT MASS IS CMFX)

(STORED OF MRY AT MASS IS CMFY)

(STORED OF MRZ AT MASS IS CMFZ)

inform23end

For the full forms of the variable like DXG, refer the reserved names. Here instead of storing all thro' the solution process, you can store the mass flux values after the last sweep by adding one more conditional statement like (STORED OF MFX AT MASS IS MFLX with IF(ISWEEP.EQ.LSWEEP)) .

You can also see some of the reserved variables like CNE1 : outward convection flux (kg/s) of phase 1 through east cell face

CNN1 : outward convection flux (kg/s) of phase 1 through north cell face

CNH1 : outward convection flux (kg/s) of phase 1 through high cell face

I hope these variables (cell mass flow rates for all the three directions, equivalent to MRX, MRY and MRZ in my INFORM case)can readily be stored and used for visualisation when the flow is highly dominated by convective fluxes and where the diffusive fluxes are negligible.

This is how I incorporated data retrieval of mass flux. Correct me if I am wrong.

Thanking you once again.

US.


johnnie nwokoro August 23, 2005 06:34

Re: Mass flux and mass flow rate
 
Am a student of chemical engineering at the enugu state univesity tech.am have problem in understanding mass and volume flow rates.please could you help me by sending a detailed explanation of what is all about. thank you.

johnnie.

Mike September 8, 2005 04:52

Re: Mass flux and mass flow rate
 
The question is rather vague, but a simple answer is mass flow rate = density * velocity * flow area, and volume flow rate = velocity * flow area.

Mark Russell September 8, 2005 16:52

Re: Mass flux and mass flow rate
 
... where the flow area is normal to the velocity.


Yen Chang Yu October 14, 2005 14:48

Re: Mass flux and mass flow rate
 
i am a student of chemical engineering, Malaysia. i would like to ask the correlation between the mass flux and mass flow rate. if i have a membrane with 30cm2 effective area, so, how can i calculate the mass flow rate with the flux at 2kg/m2-hr? thanks

Jelle October 27, 2005 11:22

Re: Mass flux and mass flow rate
 
30cm2 * 2kg/m2-hr = 3E-3 kg/h or does this require some more sophisticated math?

Jelle October 27, 2005 11:28

Re: Mass flux and mass flow rate
 
The correct answer of course should be

30cm2 * 2kg/m2-hr = 6E-3 kg/h

sorry, primary school has been some time ago :S

ciunel stefanita March 11, 2006 19:11

can I simulate heat and mass transfer?
 
I am engineer in Craiova, Romania, Europe. I have a question for you: What software help me to simulate-modulate heat and mass transfer at thermo-chemical treatments. Especially for powder sintering pieces.Thanks for your answers!


shuaib March 31, 2006 02:06

Re: Mass flux and mass flow rate
 
please send some notes on the mass flow and flux


All times are GMT -4. The time now is 02:34.