CFD-post function calculator- wrong area

namandoshi · April 10, 2018, 11:04

I want to do mass balance, there are 2 vents (on the wall) and a cooler(rectangular area inside room) all of the dimensions 0.5*0.5m while using CFD-post function calculator area both vent comes to be 0.25m^2 while area for cooler is 0.5 m^2

Q1. how is it possible??

Q2. how do i do mass balance analysis? simulations are done on cfx.

both vents are given as opening.
cooler as inlet with 5m/s velocity.
fulid is - humid air.
sst model used

please help.
thanks in advance

edit- i found the reason for the wrong area basically it is taking both faces of the area hence 0.25+0.25m^2= 0.5m^2

also in function calculator mass is coming of order 10^-5 which suggest that #mass going in that area of cooler =mass going out that area of cooler.

AtoHM · April 10, 2018, 11:37

Can you add an image and maybe which expressions you used?

Gert-Jan · April 10, 2018, 11:51

It is very good that you check mass balance.

But you should already check your mass balance during the calculation. Therefore open the run in the solver manager, create a new monitor and select to plot all imbalances (mass & momentum). These should all go to zero, to assure mass balance. Alternatively create a monitor in the same way and plot the mass flows through the inlets and outlets. The sum should be zero.

All these data are stored in each results file by default. So, also if you open a finished run, you can retrieve these data very easily. Much easier than in fluent, where I find this impossible ;-)

namandoshi · April 10, 2018, 12:18

Quote:

Originally Posted by AtoHM

Can you add an image and maybe which expressions you used?

i am directly using functions which are prensent in cfd-post (mass_conservation ,avg etc..)

image-http://www.afs.enea.it/project/neptunius/docs/fluent/html/cfd/node11.htm

namandoshi · April 10, 2018, 12:22

Quote:

Originally Posted by Gert-Jan

It is very good that you check mass balance.

But you should already check your mass balance during the calculation. Therefore open the run in the solver manager, create a new monitor and select to plot all imbalances (mass & momentum). These should all go to zero, to assure mass balance. Alternatively create a monitor in the same way and plot the mass flows through the inlets and outlets. The sum should be zero.

All these data are stored in each results file by default. So, also if you open a finished run, you can retrieve these data very easily. Much easier than in fluent, where I find this impossible ;-)

Sir can you please explain step by step as I am working on cfx first time are this options in cfx-pre or solver?

Gert-Jan · April 10, 2018, 17:29

I expect my explanation regarding the imbalances is clear enough since I didn't mention the word CFX-Pre.
Just go through the steps I described. Read my text.

April 10, 2018, 11:04	CFD-post function calculator- wrong area	#1
namandoshi Member naman doshi Join Date: Oct 2017 Posts: 35 Rep Power: 8	I want to do mass balance, there are 2 vents (on the wall) and a cooler(rectangular area inside room) all of the dimensions 0.50.5m while using CFD-post function calculator area both vent comes to be 0.25m^2 while area for cooler is 0.5 m^2 Q1. how is it possible?? Q2. how do i do mass balance analysis? simulations are done on cfx. both vents are given as opening. cooler as inlet with 5m/s velocity. fulid is - humid air. sst model used please help. thanks in advance edit- i found the reason for the wrong area basically it is taking both faces of the area hence 0.25+0.25m^2= 0.5m^2 also in function calculator mass is coming of order 10^-5 which suggest that #mass going in that area of cooler =mass going out that area of cooler. Last edited by namandoshi; April 11, 2018 at 04:35.*

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April 10, 2018, 11:37		#2
AtoHM Senior Member M Join Date: Dec 2017 Posts: 692 Rep Power: 12	Can you add an image and maybe which expressions you used?

April 10, 2018, 11:51		#3
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,885 Rep Power: 27	It is very good that you check mass balance. But you should already check your mass balance during the calculation. Therefore open the run in the solver manager, create a new monitor and select to plot all imbalances (mass & momentum). These should all go to zero, to assure mass balance. Alternatively create a monitor in the same way and plot the mass flows through the inlets and outlets. The sum should be zero. All these data are stored in each results file by default. So, also if you open a finished run, you can retrieve these data very easily. Much easier than in fluent, where I find this impossible ;-)

April 10, 2018, 17:29		#6
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,885 Rep Power: 27	I expect my explanation regarding the imbalances is clear enough since I didn't mention the word CFX-Pre. Just go through the steps I described. Read my text.