Week 1- Mixing Tee

AIM:-

• Sovling Mixing Tee Simulation Using Ansys.

OBJECTIVE:-

• To set up steady-state simulations and compare the mixing effectiveness when the hot inlet temperature is 360 °C and the cold inlet temperature is 190 °C.

  Use the k-epsilon and k-omega SST model for the first case and based on your judgment, use the more suitable model for further cases.

  1. Case 1
     • Short mixing tee with a hot inlet velocity of 3 m/s.
     • Momentum ratio of 2, 4.
  2. Case 2
     • Long mixing tee with a hot inlet velocity of 3 m/s.
     • Momentum ratio of 2, 4.

  Momentum ratio = velocity at cold inlet / velocity at hot inlet

• For momentum ratio 2, the cold inlet velocity is 6 m/s.
• For momentum ratio 4, the cold inlet velocity is 12 m/s.

PROCEDURE (MIXING TEE):

INTRODUCTION.

• A tee is formed by two pipe sections joined at a right angle to each other.
• The hot fluid (air) is flowing through the main pipe, while the cold fluid enters the main pipe through the branched pipe.
• There have been traditionally developed empirical design equations to solve mixing problems, but they do not take into account the complexity of turbulent flow.
• With respect to all the other industries, the nuclear industry is the one where the efficiency of the mixing of fluids in the mixing chambers is very critical. There has been much research regarding the thermal stresses arising in the T-joint due to the large temperature difference and also due to frequent changes.
• Mixing tee possess two inlets and one outlet. The momentum ratio for this type of tee is the ratio of velocity of cold fluid to velocity at mixed fluid at outlet.
• Turbulence model differs in how it is computed by augmenting the Navier-Stroke Equation with additional terms which consists of some parameters like local fluid velocity, wall distance, additional transport equations, eddy viscosity, turbulent kinetic energy, turbulent kinetic energy, turbulent intensity, etc.
• K – EPSILON Model.
• K – OMEGA Model.

DIFFERENCE BETWEEN K-OMEGA AND K-EPSILON:

K -EPSILON.

• It has two equational models. All functions are used in this model.
• It relates the rate of kinematic to the turbulent viscosity.
• Suitable for high Reynolds number flow or free stream flow. Predicts are well far from the boundaries for all.

K-OMEGA.

• K-omega is also a two-equation model. It requires the y+ calculation near the wall.
• It is similar to the k-epsilon model, but it solves for (omega), the specific rate of dissipation of the kinetic energy.
• Good for highly non-linear or drastic change in flow gradient.
• When deployed with SST-k-omega turbulence model, it can be switched between the low and high Reynolds number.

SETUP:-

• GEOMETRY.
• MESHING/SOLVING/RESULTS.
• POST-PROCESSING

Assume Vc1, Vc2 ,Vc3, Vc4 as cold inlet velocity and Vci as Hot inlet velocity . Hot inlet temperature is 36 degrees and cold inlet temperature is 19 degrees.

1.Short Tee.

CASE1: Momentum =2, Vc1=6m/s , Vci=3m/s ,Ti=36,To=19 .

CASE2: for momentum 4, Vci=3m/s , Ti=36,Vc2=12m/s, To=19

2.Long Tee

CASE3: Momentum =2, Vc1=6m/s , Vci=3m/s ,Ti=36,To=19 .

4. Case 4:for momentum 4, Vci=3m/s , Ti=36,Vc2=12m/s, To=19

Results:

refer to the table below which contains comparision between 4 cases

s.no	type	description	cell count	avg outlet temperature	no of iterations for convergence
1	short tee	momentum 2 Vc=6m/s Vh=3m/s	12780	31.15 degree celsius	150
2	short tee	momentum 4 Vc=12m/s Vh=3m/s	12780	27.65 degree celsius	150
3	long tee	momentum 2 Vc=6m/s Vh=3m/s	15727	30.83 degree celsius	150
4	long tee	momentum 4 Vc=12m/s Vh=3m/s	15727	27.3 degree celsius	150

Consequently, we can identify the following details from the above table:

1. A difference in momentum causes a different outlet temperature for the same cross section.

2. The outlet temperature is also impacted by variations in length for the same momentum.

3. Every temperature contour plot displayed above makes it abundantly evident that temperature changes with length as a result of air mixing.

Conclusion:

Thus, flow analysis in a mixing tea with various cross sections and momentum types is covered.