Week 1- Mixing Tee

Mixing Efficiency of Tee

Aim:

1. To compare

Case 1 : Short Mixing Tee

Case 2 : Long Mixing Tee

and perform the following

1. Velocity and temperature contour plots on the cut planes along and across the pipe.
2. Velocity and temperature line plots along and across the length of the pipe.
3. Perform Mesh independent study for any one case.
4. Discuss the effect of length and momentum ratio on results.

Given Data:

Hot inlet temperature is 36⁰C & the Cold inlet is at 19⁰C.

Case 1:

• Short mixing tee with a hot inlet velocity of 3m/s.
• Momentum ratio of 2, 4.

Case 2 :

• Long mixing tee with a hot inlet velocity of 3m/s.
• Momentum ratio of 2, 4

Solution:

1. Geometry

Case 1 :

Case 2 :

2. Meshing

Mesh settings are kept default. Tetramesh is applied by default.

Case 1:

Each element size is 1.0219e-002 m

Case 2:

Each element size is 1.3853e-002 m

3. Working Fluid: Air

4. Turbulence Model used : K epsilon

Reason: K-omega is used for near wall modelling and particularly in case of low Re number. In our case, both of them are not required. Hence K epsilon is chosen.

5. Parametric Study for Grid Independence and Momentum Ratio

Case 1 :

• In this study the mesh element size is varied from 10mm to 2 mm at a step of 2 mm . There was no significant change in the result, initial 10mm mesh element size is good enough for an accurate result.
• Momentum Ratio is altered between 2 and 4 by altering the parameter 6 (cold inlet velocity) from 6 to 12 m/s.
• DP 0-5 shows MR 2 , DP 6-10 shows MR 4.

Case 2:

• Momentum Ratio is altered between 2 and 4 by altering the parameter 6 (cold inlet velocity) from 6 to 12 m/s.
• DP 0-5 shows MR 2 , DP 6-10 shows MR 4.

Comparision between Case 1 and Case 2:

	Cell count	Average outlet temperature	Number of iterations for convergence
Case 1	12657	MR 2, 303.39 K MR 4, 300.68 K	159
Case 2	15610	MR 2, 303.46 K MR 4, 300.64 K	181

6. Residual Plot

Case 1:

Case 2:

7. Area Avg. Temperature Plot for Entire Domain:

Case 1:

Case 2:

8. Area Avg. Temperature Plot for Outlet:

Case 1:

Case 2: 30.03 deg.C

9. Temperature Contour:

Case 1:

Case 2:

10. Velocity Contour:

Case 1:

Case 2:

Inference:

1. As the length is increased, number of mesh elements is increasing and the iterations increases. Temperature also drops faster than the short length as the fluid needs a travel farther than the short tee.
2. As the momentum ratio is increased, the temperature falls rapidly due to higher velocity.