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Boundary condition help needed in ventilation problem

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Old   June 21, 2016, 08:41
Default Boundary condition help needed in ventilation problem
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Neha Sinha
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Dear Experts,
I am analysing a biotechnological equipment( a container) in which ventilation is required in order to reduce the biological contamination suspended in the container volume. I have modelled biological contaminant as an additional variable. Initially the container is filled with Argon with contaminant at certain known ppm level. At t=0, supply of fresh argon starts. Inlet flow rate is fixed at 10lpm. Outlet is maintained at slight negative pressure ( negative half inch of water column).
Experimentally I have online sampler that samples the contamination ppm passing through the outlet. In computational model, I have calculated this outlet contamination value by plotting expression areaAve(Contaminant)@outlet.
My computational results are close to experimental results. Both are decreasing trend from the same initial ppm value as expected. But there is slight difference in slope, which has resulted in deviation of about 25% (lesser) from the experimental result at the end of half an hour.
At inlet, flow sensor is situated near to the pressure regulator(output half kg), I suspect due to compressibility the inlet velocity is more that what I have calculated from the flowmeter value of 10lpm.
I changed to Ideal Gas Argon. My inlet pressure and outlet mass flow rate boundary condition is failing. My pressure-pressure boundary conditions are failing( I read somewhere pressure-pressure condition works in compressible flow).

Sorry for the long post.... but I am stuck....please suggest
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Old   June 22, 2016, 03:37
Default Please help in setting boundary condition in compressible flow
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Neha Sinha
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Sorry I think I didn't put my problem in precise way. Give me one more chance.

Regarding the same system, my problem is :
1. If driving force is inlet pressure (here 0.6 kg by pressure regulator), and I have assumed outlet mass flow rate same as inlet ( I have flowmeter at inlet and not at outlet) why my run fails.
2. I do know the pressure at inlet and at outlet, can it be solved for compressible flow(runs are failing).

Thanks in advance

Neha
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Old   June 22, 2016, 03:45
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please provide screenshots of your setup, your CCL and your out-file with the complete error message of the failed runs.
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Old   June 27, 2016, 03:29
Default Boundary conditions in compressible flow
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Neha Sinha
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Sorry I am afraid I will not be able to upload the screenshots as the simulations are carried out in a lab where there is no internet connection. I am summarizing the problem based on memory.
I just needed some expert to confirm that inlet pressure and outlet pressure boundary condition in compressible flow can give correct results.

Thanks in advance
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Old   June 27, 2016, 08:06
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Read the section in the documentation on well-posed boundary conditions (CFX Modelling guide, section 2.3.2 "Recommended configurations of boundary conditions"). This will answer your question and give you a useful background in the area.
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Old   June 27, 2016, 08:55
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Thanks Sir
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additional variable, cfx, compressible flow, hvac, ventilation

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