Mixing efficiency

AIM:

Steady state simulations to compare the mixing effectiveness for following 3 different cases

• Case 1.
  • Short mixing tee with hot inlet velocity of 3m/s.
  • Momentum ratio of 2 ( i.e., inlet cold velocity of 6m/s.)

Geometry:

The Geometry has been provided in the challenge interface. The first case in simulated with the short T-joint with the momentum ratio 2.

Meshing:

I have used the mesh refinement by using the following changes in the values in the Mesh properties dialogue box.

• element size = 2mm
• Max mesh size = 2mm
• Mesh Defeaturing size = 2mm
• Statistics
  • Nodes = 17541
  • Elements = 84468

The bar chart for element quality is given below

After creating the Mesh file, I applied boundary conditions in fluent. The details of the boundaries conditions are as follows

• Energy equation using k-epsilon, realisable turbulence model
• inlet cold velocity = 6m/s and 10 C temperature
• inlet hot velocity = 3m/s and 25 C temperature

Converge plots after 450 iteration

Now, from post processing the simulation here are the plots for Templerature distribution and Velocity variation throughout the t-joint

We have defined air as the working fluid, hence the outlet temperature of air is 20.15C.

• Case 2.
  • Long mixing tee with hot inlet velocity of 3m/s.
  • Momentum ratio of 2 ( i.e., inlet cold velocity of 6m/s.)

Geometry

The Geometry has been provided in the challenge interface. The first case in simulated with the Long T-joint with the momentum ratio 2. The Following solid volume geometry is created after preparing in space claim.

Meshing:

I have used the mesh refinement by using the following changes in the values in the Mesh properties dialogue box.

• element size = 2mm
• Max mesh size = 2mm
• Mesh Defeaturing size = 2mm
• Statistics
  • Nodes = 50200
  • Elements = 271225

The bar chart for element quality is given below

After creating the Mesh file, I applied boundary conditions in fluent. The details of the boundaries conditions are as follows

• Energy equation using k-epsilon, realisable torbulence model
• inlet cold velocity = 6m/s and 10 C temperature
• inlet hot velocity = 3m/s and 25 C temperature

Converge plots after 450 iteration

Now, from post processing the simulation here are the plots for Templerature distribution and Velocity variation throughout the t-joint

We have defined air as the working fluid, hence the outlet temperature of air is 20.20C.

• Case 3.
  • Short mixing tee with hot inlet velocity of 3m/s.
  • Momentum ratio of 4 ( i.e., inlet cold velocity of 12m/s.)

Geometry

The Geometry has been provided in the challenge interface. The first case in simulated with the short T-joint with the momentum ratio 4.

Meshing

Here, I have taken same mesh details as of case first. Hence, I would like to skip the Geometry, Meshing and Quality graph as these being same as the First one.

After creating the Mesh file, I applied boundary conditions in fluent. The details of the boundaries conditions are as follows

• Energy equation using k-epsilon, realisable turbulance model
• inlet cold velocity = 12m/s and 10 C temperature
• inlet hot velocity = 3m/s and 25 C temperature

Converge plots after 450 iteration

Now, from post processing the simulation here are the plots for Templerature distribution and Velocity variation throughout the t-joint

We have defined air as the working fluid, hence the outlet temperature of air is 17.50C.

Overall Conclusion

Remark on Number of iteration for convergence

As we solely concern with the outlet temperature of different geometry and inlet flow regime, the number of iteration doesnot make any significant difference with the results after 300 iteration, even when we increase the number of cells counts i.e reducing the mesh element size we can get attractive profiles of plots, of course which is directly proportional to the computational time and computer hardware configurations. Hence, we can examine clearly that 450 iteration holds good enough for the converged results.

In overall conclusion

• We can examine the effectiveness of mixing my standard deviation plots, a high deviation means mixing is bad whereas a low deviation in curve indicate the outlet temperature mixing is good. Hence a longer configuration is not at all helpful as it gives almost same outlet temperature as of short one of same inlet air velocity.
• By doubling the chilled air velocity at inlet results in better outlet mixing temperature which pretty much acceptable result for us.