Mixing efficiency

Aim: To perform steady-state simulations for both short & long Tee at hot inlet temperature 36⁰C & the Cold inlet 19⁰C and comparing mixing effectiveness Using the k-epsilon and k-omega SST turbulence models.

Case 1 (short mixing tee at Momentum ratio of 2)

Geometry: (short mixing tee)

Named selections of short tee:

1.Hot inlet

2.Cold inlet

3.Hotoutlet

Wall:

Meshing:

Section plane:

Quality of mesh:

Element size: 0.002

Nodes: 28551

Elements: 141599

Setup:

General

Check Mesh Quality

Solver : pressure based

Velocity Formulation : Absolute

Time : Steady

Models:

Energy on

viscous-K-epsilon-Realizble-Standard wall

Materials:

Fluid: Air

Solid: Aluminium

Cellzone conditions:

Fluid: Air

Boundary conditions:

• hot inlet velocity of 3m/s.
• Momentum ratio= coldinlet velocity/Hotinlet velocity (Taken Momentum ratio =2)
• cold inlet velocity=6m/s.
• hot inlet temperature 36⁰C
• Cold inlet 19⁰C
• hot outlet Temperature =30.26⁰C (Caliculated using Tmixture formula)

Report profiles:

Average weighted temperature

Average weighted velocity

standard deviation temperature

scaled residuals

Solution intialization:

Hybrid intialization

Run caliculations:

no of iterations =100

Average weighted temperature:

Average weighted velocity:

standard deviation temperature:

scaled residuals:

Results:

Contours of temperature:

Contours of Velocity:

Contours of Temperature across length:

Contours of Velocity across length:

Line plot Temperature:

Line plot Velocity:

Case 1 (short mixing tee at Momentum ratio of 4)

Geometry and meshing for short tee is same except change in boundary conditions

setup:

General

Check Mesh Quality

Solver : pressure based

Velocity Formulation : Absolute

Time : Steady

Models:

Energy on

viscous-K-epsilon-Realizble-Standard wall

Materials:

Fluid: Air

Solid: Aluminium

Cellzone conditions:

Fluid: Air

Boundary conditions:

• hot inlet velocity of 3m/s.
• Momentum ratio= coldinlet velocity/Hotinlet velocity (Taken Momentum ratio =4)
• cold inlet velocity=12m/s.
• hot inlet temperature 36⁰C
• Cold inlet 19⁰C
• hot outlet Temperature =26.78⁰C (Caliculated using Tmixture formula)

Report profiles:

Average weighted temperature

Average weighted velocity

standard deviation temperature

scaled residuals

Solution intialization:

Hybrid intialization

Run caliculations:

no of iterations =100

Average weighted temperature:

Average weighted velocity:

standard deviation temperature:

scaled residuals:

Results:

Contours of temperature:

Contours of velocity:

Contours of Temperature across length:

Contours of Velocity across length:

Line plot of Temperature:

Line plot of Velocity:

Case 2 (Long mixing tee at Momentum ratio of 2)

Geometry: (Long mixing tee)

Meshing:

Section plane:

Quality of mesh:

Element size: 0.002

Nodes: 28372

Elements: 140525

Setup:

General

Check Mesh Quality

Solver : pressure based

Velocity Formulation : Absolute

Time : Steady

Models:

Energy on

viscous-K-epsilon-Realizble-Standard wall

Materials:

Fluid: Air

Solid: Aluminium

Cellzone conditions:

Fluid: Air

Boundary conditions:

• hot inlet velocity of 3m/s.
• Momentum ratio= coldinlet velocity/Hotinlet velocity (Taken Momentum ratio =2)
• cold inlet velocity=6m/s.
• hot inlet temperature 36⁰C
• Cold inlet 19⁰C
• hot outlet Temperature =31.56⁰C (Caliculated using Tmixture formula)

Report profiles:

Average weighted temperature

Average weighted velocity

standard deviation temperature

scaled residuals

Solution intialization:

Hybrid intialization

Run caliculations:

no of iterations =100

Average weighted temperature:

Average weighted velocity:

Standard deviation:

Scaled residuals:

Results:

Contours of temperature:

Contours of velocity:

Contours of temperature across length:

Contours of Velocity across length:

Line plot of Temperature:

Line plot of velocity:

Case 2 (Long mixing tee at Momentum ratio of 4)

Geometry and meshing for long tee is same except change in boundary conditions

setup:

General

Check Mesh Quality

Solver : pressure based

Velocity Formulation : Absolute

Time : Steady

Models:

Energy on

viscous-K-epsilon-Realizble-Standard wall

Materials:

Fluid: Air

Solid: Aluminium

Cellzone conditions:

Fluid: Air

Boundary conditions:

• hot inlet velocity of 3m/s.
• Momentum ratio= coldinlet velocity/Hotinlet velocity (Taken Momentum ratio =4)
• cold inlet velocity=12m/s.
• hot inlet temperature 36⁰C
• Cold inlet 19⁰C
• hot outlet Temperature =28.85⁰C (Caliculated using Tmixture formula)

Report profiles:

Average weighted temperature

Average weighted velocity

standard deviation temperature

scaled residuals

Solution intialization:

Hybrid intialization

Run caliculations:

no of iterations =100

Average weighted temperature:

Average weighted velocity:

Standard deviation:

Scaled residuals:

Results:

Contours of temperature:

Contours of velocity:

Contours of temperature across length:

Contours of Velocity across length:

Line plot of temperature:

ine plot of velocity:

Charts for long Tee /Short tee along line=4:

Tempareture chart

Velocity chart:

Pressure Chart:

Charts for long Tee /Short tee across line:

Tempareture chart:

Velocity chart:

Pressure chart:

Grid dependence test:

For short tee at momentum ratio=2

Grid size (mm)	T actual(C^o)	T numerical(C^o)
4	30.32	30.295
3	30.32	30.328
2	30.32	30.37

Case type	Turbulence model	Cell Count	Iterations for convergence	T(outlet temperature)
Short Tee (Momentum Ratio=2)	K-epsilon-Realizable-Standard wall function	141599	100	29.897
Short Tee (Momentum Ratio=4)	K-epsilon-Realizable-Standard wall function	141599	100	26.667
Long Tee (Momentum Ratio=2)	K-epsilon-Realizable-Standard wall function	140525	100	30.234
Long Tee (Momentum Ratio=4)	K-epsilon-Realizable-Standard wall function	140525	100	27.023

Convergence criterion:

Residual levels of 1E-4 are considerd lossely converged for 1E-5 are considerd well converged for1E-6 are considerd Tightly converged. in this simulation for converging faster residuals are taken 1E-6. so converging happend at 100 iterations.

Turbulence model	Case type	Iterations for convergence	Avergae outlet temperature(C)
K-omega-Standard wall function	Short Tee (Momentum Ratio=2)	130	30.566
K-omega-Standard wall function	Short Tee (Momentum Ratio=4)	130	27.89
K-omega-Standard wall function	Long Tee (Momentum Ratio=2)	130	30.578
K-omega-Standard wall function	Long Tee (Momentum Ratio=4)	130	27.892