Air Mixing efficiency in Tee-Joint Pipe using Ansys Fluent

Air Mixing efficiency in Tee-Joint Pipe

Aim:

To perform 3 steady-state simulations on a short & long mixing tee geometry using Ansys Fluent.

Procedures:

1. Extracting the Fluid volume data from the CAD Model using Ansys SpaceClaim plugin.
2. Mesh Processing.
3. Setting up the boundary conditions & Setup steady-state simulations to compare the mixing effectiveness for the below cases
   
   • Case 1
     • Short mixing tee with hot inlet velocity of 3m/s
     • Momentum ratio of 2
   • Case 2
     • Long mixing tee with hot inlet velocity of 3m/s
     • Momentum ratio of 2
   • Case 3
     • Short mixing with hot inlet velocity of 3 m/s
     • Momentum ration of 4
4. Post Processing output files.

1:- Pre-Processing:

1.1 CAD Prep for case1 & case3:

In these cases, the length of the mixing pipe is short which is of 192.4mm

1.2 CAD Prep for case2:

In this case, the length of the mixing pipe is longer than the previous cases which is of 268.3m

2:- Mesh Processing:

2.1 Meshing for case1 & case3:

Launch the mesh generator from the project schematic window. In Mesh Quality section enable the Mesh Metric by element size to verify the mesh generated is above 10%. In order to increase the accuracy of the simulation, the element sizing is set to 0.002m.

2.2 Meshing for case2:

The same Mesh configuration processing done for cases1&2 is repeated for this case too.

3.1- Setting up BCs:

Following criteria to be set up for the respective cases.

• For Case1:
  • Inlet along X-Axis which carries hot air of 25°C at 3m/s. The momentum ratio is 2. We know Momentum Ratio is the ratio of the velocity of cold air to the velocity of hot air. So the velocity of cold air (10°C) from the inlet along the Y-axis is set to be 6m/s.
  • The fluid medium considered for this case is Air.
• For Case2:
  • Inlet along X-Axis which carries hot air of 25°C at 3m/s. The momentum ratio is 2. We know Momentum Ratio is the ratio of the velocity of cold air to the velocity of hot air. So the velocity of cold air (10°C) from the inlet along the Y-axis is set to be 6m/s.
  • The fluid medium considered for this case is Air.
• For Case3:
  • Inlet along X-Axis which carries hot air of 25°C at 3m/s. The momentum ratio is 4. We know Momentum Ratio is the ratio of the velocity of cold air to the velocity of hot air. So the velocity of cold air (10°C) from the inlet along the Y-axis is set to be 12m/s.
  • The fluid medium considered for this case is Air.

These cases are solved using pressure-based solver as the flow is determined as non-variable with Reynold number found to be below 4000 with low Mach number. The time steps for these cases is calculated by steady-state as the flow attains steady state after some time.

In setting up physical models we use realizable k-epsilon under the Viscous model section. This will provide us a stable solution with less computational time.

For these cases, the mixing tube wall is set to have No-slip under shear condition.

4.1- Case1 Post-Processing:

This case took around 600 number of iterations to attain steady-state flow. This can be known from the above chart as the velocity, energy & continuity curves attain a varied stable state.

The above plot shows us the temperature at the outlet with respect to the number of iterations. In this case, the outlet temperature is found to be 19.96°C.

The above plot shows us the effectiveness of cold & hot air mixing through the standard deviation of temperature at the outlet with respect to the number of iterations.

The above figure shows us the simulation of the mixing of hot air & the cold air for case1.

Case1_Simulation_Clip:

4.2- Case2 Post-Processing:

This case took around 500 number of iterations to attain steady-state flow. This can be known from the above chart as the velocity, energy & continuity curves attain a varied stable state.

The above plot shows us the temperature at the outlet with respect to the number of iterations. In this case, the outlet temperature is found to be 20.04°C.

The above plot shows us the effectiveness of cold & hot air mixing through the standard deviation of temperature at the outlet with respect to the number of iterations.

The above figure shows us the simulation of the mixing of hot air & the cold air for case2.

Case2_Simulation_Clip:

4.3- Case3 Post-Processing:

This case took around 775 number of iterations to attain steady-state flow. This can be known from the above chart as the velocity, energy & continuity curves attain a varied stable state.

The above plot shows us the temperature at the outlet with respect to the number of iterations. In this case, the outlet temperature is found to be 17.55°C.

The above plot shows us the effectiveness of cold & hot air mixing through the standard deviation of temperature at the outlet with respect to the number of iterations.

The above figure shows us the simulation of the mixing of hot air & the cold air for case3.

Case3_Simulation_Clip:

Case Report: