Week 1- Mixing Tee
Objective: To Analyze the Temperature profile, velocity profile and grid dependency on the mixing tee geometry.
About
`text(Mixing is a unit operation that involves the manipulation of a heterogeneous physical system with the intent to make it more homogenous. ixing is performed to allow heat and mass transfer to occur between one or more streams, components or phases. Industrial operation always involves some type of mixing.Mixing tee is a type of mixing mechanism. mixing tees utilize a specifically engineered internal geometry to efficient mix two fluid streams into one combined stream. Mixing tees are widely used in the petrocheical,HVAC etc. in which two fluid streams with different physical and chemical properties mix together.)`
Case: 1
Long Tee
a) hot inlet velocity 3m/s and momentum ratio 2
mesh size : 10mm
- Contour Temperature
- Contour Velocity
- Residuals Plot
- Temperature Plot
- Velocity Plot
b) hot inlet 3 m/s and momentum ratio 4
mesh size : 10mm
- Contour Temperature
- Contour Velocity
- Residuals Plot
- Temperature Plot
- Velocity Plot
Case : 2
Short Tee
a) hot inlet velocity 3 m/s and momentum ratio 2
mesh size = 10mm
- Contour Temperature
- Contour Velocity
- Residual
- Temperature
- Velocity
b) hot inlet velocity 3 m/s and momentum ratio 4
mesh size = 10mm
- Contour Temperature
- Contour Velocity
- Residual
- Temperature
- Velocity
Grid Dependence test
Short tee
Effect of grid on the velocity profile
- From above graph we can say that after some value of grid,there is no change in velocity profile whic shows that the parameters are depend on the grid point.
Effect of grid on the temperature profile
- Temperature is varing according the grid point but there is no much difference.
- It is consoldating in a finite range.
Comparision od cases :
| Case | Cell Count | Average outlet temp.(C) | No. of iteration for convergence |
| Long tee- momemtum ratio -2 | 34470 | 30.31 | 181 |
| Long tee- momemtum ratio -4 | 34470 | 27.488 | 225-250 |
| Shor tee- momemtum ratio -2 | 16359 | 30.2554 | 250-300 |
| Shor tee- momemtum ratio -4 | 16359 | 27.5379 | 225-250 |
Effect of length and momentum ratio on the result
- Fluid mix more efficiently as the length of the domain in increase as we have seen in the long mixing tee. Fluid mixes ore properly in the long tee domain as compared to the short tee domain.
- As fluid mixes properly, we will get the better temperature and velocity profile and it helps in the selection for application
- Momentum ratio helps to find out the velocity of cold inlet or hot inlet.
- Here, more high momentum ratio means mixixng is better because as the cold fluid move faster than the hot fluid, we will see the outlet temperature drops down singnificantly.
- If momentum ratio is less, cold inlet temperature is less and both the fluid will not mix properly and we will not get the better results.
- Hence momentum ratio will define the velocity of hot inlet or velocity of cold inlet
Conclusion
- Temprature at the outlet drops down significantly due to high velocity of cold air from the inlet.
- This is possible due to the turbulent mixing at the tee joint between hot air and the cold air because of the high velocity of cold air,which is not possible in case of low velocity cold air.
- The temperature contour at the outlet for long tee shows that the high temperature flow thoroughly mixes with the rest of the flow whereas in the short tee cases the high temperature flow sipd through without mixing with the flow.
- Hence we can say that recommendation of the long tee and high velocity inlet for the use.
- K-epsilon model predicts well far from the boundaries.
- K-omega model predicts well near the wall.