October 23, 2023 at 7:35 amAbdullah HassanSubscriber
I am new to ANSYS and doing an Implicit VOF transient simulation on single tube parrallel heat exchanger.
K-Epsilon with realizable and Enhanced wall function
Primary phase = water liquid (as I don’t need it to put in boundry condition volume fraction)
Secondary phases = water vapor, ammonia liquid, ammonia vapor.
Tube side = Hot fluid =water that converts from vapor to liquid with VOF Lee’s Model at frequency 180/s.
Shell side = Cold fluid = ammonia that converts from liquid to water with Lee’s model frequency 89/s.
Velocity inlet and pressure outlet.
Tube side = I put water vapor Volume fraction = 1
Shell side = I put ammonia liquid volume fraction = 1
Piso Scheme with all second order upwind
Initially all are at 1 UR factor and then reduced the convergence UR till 0.7.
Water vapor VF = 1 in tube domain
Ammonia liquid VF = 1 in shell domain.
I am facing two big issues.
1- Continity residual is showing a straight line. It is not converging to 1e-3 or 1e-4. it stays at 1e-1 as a straight line. All other residuals are below 1e-6.
2- As water liquid is primary phase so I can’t assign it to any domain. I did the patch to avoid any water liquid in shell domain. After the simulation. What I find out through volume fraction surface and volume intergrals is that “the water liquid is present in both the tube and shell domain”. In tube domain it is condensed from water vapor but from where it comes to shell domain.
Can you guide me on this?
October 24, 2023 at 11:45 amAbdullah HassanSubscriberHello, Can you please suggest me some solution?????
October 24, 2023 at 4:05 pmRobForum Moderator
I suspect you need two phases, one for the liquid and a second for gas. Each is a mixture. You then need to transfer ammonia and water from/to their respective phases.
October 25, 2023 at 2:23 amAbdullah HassanSubscriber
I have chosen four phases.
And in boundary conditions, from phases, I assign Water Vapor volume fraction =1 to Tube inlet,
Ammonia liquid volume fraction = 1 to Shell Inlet. and then after initialization,
I patch the water vapor VF = 1 at tube domain and Ammonia liquid VF =1 at shell domain.
Above is the geometry.
And if you want to see the traces of water liquid, please refer below image.
October 25, 2023 at 8:33 amRobForum Moderator
Did you set all of the boundary conditions, including outlet and patch the zones?
October 26, 2023 at 2:38 amAbdullah HassanSubscriber
Yes, I have put an outlet guage pressure = -0.15
and patch volume fraction of ammonia liquid = 1 in Shell domain.
and patch volume fraction of water vapor = 1 in tube domain.
October 26, 2023 at 10:33 amRobForum Moderator
Assuming all bc's are set correctly, if convergence is initially poor you could be getting some of the wrong material in the channel.
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