To consider gravity or not ?

prince_pahariaa · March 31, 2015, 07:50

I have a vertical channel. From the bottom (say y=0) Deuterium and Oxygen gas flows inside the channel (D2-0.2 & O2-0.8 mass fraction) and from side inlet somewhere near the top (say at 4.12) helium gas enters into the domain. total length of domain is 4.7m

Velocity range for helium gas(He) is 0.12 m/s
for D2&O2 is in order of 10^-6 m/s

I have given mass diffsivity of each gases into mixture template in material section of fluent. i am using incompressible ideal gas equation for density estimation.

Here is my doubt..
Should i consider gravity in my problem ? Flow is upward
Temperature remains same and there is no heat source. so desnity variation is not a concern.
But density of D2&He is much lower than the O2. How to take that into account.

Any help is much appreciated. I have stuck to this problem for a long time.

pakk · March 31, 2015, 08:30

Quote:

Originally Posted by prince_pahariaa

I have a vertical channel. From the bottom (say y=0) Deuterium and Oxygen gas flows inside the channel (D2-0.2 & O2-0.8 mass fraction) and from side inlet somewhere near the top (say at 4.12) helium gas enters into the domain. total length of domain is 4.7m

Velocity range for helium gas(He) is 0.12 m/s
for D2&O2 is in order of 10^-6 m/s

I have given mass diffsivity of each gases into mixture template in material section of fluent. i am using incompressible ideal gas equation for density estimation.

Here is my doubt..
Should i consider gravity in my problem ? Flow is upward
Temperature remains same and there is no heat source. so desnity variation is not a concern.
But density of D2&He is much lower than the O2. How to take that into account.

Any help is much appreciated. I have stuck to this problem for a long time.

Maybe I am saying something stupid, but if you want to know if gravity is relevant for you problem, then do a simulation with gravity, and do a simulation without gravity, and compare the results.

prince_pahariaa · April 1, 2015, 00:54

Thanks for the reply.

Well, i did try that trick.
Only problem is without gravity my solution converges nicely and results can be explained with logics.

But with gravity on, results are not as expected. and it gives me some convergence problem. Though i think gravity should be considered in my problem as lighter gas should rise above the heavier gas.

March 31, 2015, 07:50	To consider gravity or not ?	#1
prince_pahariaa Member prince Join Date: Jun 2011 Posts: 56 Rep Power: 14	I have a vertical channel. From the bottom (say y=0) Deuterium and Oxygen gas flows inside the channel (D2-0.2 & O2-0.8 mass fraction) and from side inlet somewhere near the top (say at 4.12) helium gas enters into the domain. total length of domain is 4.7m Velocity range for helium gas(He) is 0.12 m/s for D2&O2 is in order of 10^-6 m/s I have given mass diffsivity of each gases into mixture template in material section of fluent. i am using incompressible ideal gas equation for density estimation. Here is my doubt.. Should i consider gravity in my problem ? Flow is upward Temperature remains same and there is no heat source. so desnity variation is not a concern. But density of D2&He is much lower than the O2. How to take that into account. Any help is much appreciated. I have stuck to this problem for a long time.

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April 1, 2015, 00:54		#3
prince_pahariaa Member prince Join Date: Jun 2011 Posts: 56 Rep Power: 14	Thanks for the reply. Well, i did try that trick. Only problem is without gravity my solution converges nicely and results can be explained with logics. But with gravity on, results are not as expected. and it gives me some convergence problem. Though i think gravity should be considered in my problem as lighter gas should rise above the heavier gas.