Mixing efficiency
AIM: To set up steady-state simulations to compare the mixing effectiveness when hot inlet temperature is 360C & the Cold inlet is at 190C.
Case-1:
Short mixing tee with a hot inlet velocity of 3m/s is used in this case.
We extract the volume by using ansys spaceclaim and resulted part shown below.
The meshed part is shown below. The coarse mesh generated initially and that is converted to fine mesh and mesh metrics are shown below.
Setup & Solution:
Ansys Fluent is used to setup the flow conditions.
Solver type is pressure based and velocity formulation is absolute.
K-Epsilon model is used in this process. K-epsilon model predicts well far from the walls where as k-omega predicts well near the walls.
inlet cold air = 6m/s at 36 celsius
inlet hot air = 3m/s at 19 celsius
Results:
The solution converged at 241 iteration.
Residuals, Area weighted average and standard deviation is shown below.
Velocity & Temperature variations:
Velocity(at momentum 2)
Velocity(at momentum 4)
Temperature:
Case-2:
Long mixing tee with a hot inlet velocity of 3m/s.
The volume is extracted and resulted tee is shown below:
Results:
The solution converges at more than 300 iterations.
Residuals, Area weighted average and standard deviation is shown below.
Velocity & Temperature variations:
Velocity(at momentum 2)
Velocity(at momentum 4)
Temperature:
The follwoing table shows the comparison of average temperature, iterations for both cases.
| No. of Elements | Average Temperature | Standard Deviation | No. of Iterations | |
| Case-1 | 105102 | 27.5 | 2.8 | 241 |
| Case-2 | 267702 | 27.5 | 2.3 | >>300 |
The better mixing observed by increasing the velocity of cold air. And increase in length of pipe leads to uniform flow and low standard deviation.