Hydrate Formation in Multiphase (Mixture) Flow in Elbow Pipe
The present problem simulates hydrate formation flow inside a tube with a 90-degree elbow using ANSYS Fluent software.
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The present problem simulates hydrate formation flow inside a tube with a 90-degree elbow using ANSYS Fluent software. Hydrates are organic substances that contain water. Hydrates are formed by adding water. The hydrate in this project is a combination of three different materials of water, water vapor, and methane. Therefore, to define this hydrated material, the multiphase mixture model is used. Also, between the liquid water phase and water vapor, mass transfer is defined as the evaporation-condensation process. This evaporation-condensation process will occur at the saturation temperature, which is defined as a polynomial function of the pressure value.
It is assumed that hydrate is obtained by converting the water vapor phase to the liquid water phase in the condensation process. The inlet stream enters the elbow in the form of a mixture of water vapor and methane at a speed of 2 m.s-1 and a temperature of 315 K; So that the inlet flow consists of 80% methane and 20% water vapor. After the mixture enters the knee and due to the convection heat transfer, the condensation phenomenon occurs. As a result, some water is produced and added to the existing composition to form a hydrating substance.
Geometry & Mesh
The present model is designed in three dimensions using design modeler software. The current model is for a tube with a 90-degree elbow; So that the diameter of this pipe is equal to 2 cm.
We carry out the meshing of the model using ANSYS Meshing software, and the mesh type is structured. The element number is 55040. The following figure shows the mesh.
Hydrate CFD Simulation
We consider several assumptions to simulate the present model:
- We perform a pressure-based solver.
- The simulation is unsteady (Transient Solver).
- The gravity effect on the fluid is equal to -9.81 m.s-2 along the Y-axis.
The following table represents a summary of the defining steps of the problem and its solution:
|near wall treatment||standard wall functions|
|number of eulerian phases||3 (water,vapor,methan)|
|velocity magnitude – water||0 m.s-1|
|velocity magnitude – vapor||2 m.s-1|
|velocity magnitude – methan||2 m.s-1|
|volume fraction – vapor||0.2|
|volume fraction – methan||0.8|
|gauge pressure||0 pascal|
|wall motion||stationary wall|
|convection||heat transfer coefficient||15 W.m-2.K-1|
|free stream temperature||269 K|
|momentum||first order upwind|
|turbulent kinetic energy||first order upwind|
|turbulent dissipation rate||first order upwind|
|volume fraction||first order upwind|
|energy||first order upwind|
|gauge pressure||0 Pascal|
|velocity (x,y,z)||0 m.s-1|
|vapor volume fraction||0.2|
|methane volume fraction||0.8|
Results & Discussions
After the solution process, two-dimensional and three-dimensional contours related to the pressure, methane velocity, temperature, and volume fraction of the liquid water phase are obtained. These results are obtained at different simulation process times (between 0.06 s to 0.24 s). As can be seen from the pictures, as the simulation process progresses, the volume fraction of liquid water produced increases.
There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.