Mixing Efficiency of mixing Tee using Ansys Fluent
OBJECTIVE:
In this project, we have to perform 3 steady state simulations on the mixing tee geometry of which two versions are short and one is long.
To set up steady state simulations to compare the mixing effectiveness.
- Case 1
- Short mixing tee with hot inlet velocity of 3m/s
- Momentum ratio of 2
- Case 2
- Long mixing tee with hot inlet velocity of 3m/s
- Momentum ratio of 2
- Case 3
- Short mixing with hot inlet velocity of 3 m/s
- Momentum ration of 4
- Momentum ratio = velocity at cold inlet / velocity at hot inlet
To compare the following values from the 3 cases:
- Cell count
- Average outlet temperature
- Number of iterations for convergence
Fluid Flow ( Fluent) is been used as an analysis system.
Ansys SpaceClaim utility was used for geometry model.
Mesh size used is 0.002m
The hot inlet temperature is 300K and cold inlet temperature is 283K.
Here X-direction inlet is the hot inlet and Y-direction inlet i.e. tee-inlet is the cold inlet.
Mesh Profile:
Case 1: Short mixing tee with hot inlet velocity of 3m/s and Momentum ratio of 2
Residuals Plots
Area Weighted Average of Temperature(k)
The Average Outlet temperature: 294.4k
Standard Deviation of Temperature
S.D. comes out to be 2.0
Temperature Plot
Here the tee is of the short version which helps the incoming cold air to travel to a significant distance.
As the inlet temperature is 283 k and the velocity is 6m/s, the cold air was not able to manipulate and mix with the hot air and we get a balanced outlet temperature which covers the whole range.
Velocity profile plot
Here at the outlet cross section, the velocity doesn't seem uniform throughout the cross-section of the pipe.
The highest velocity reaches up to 7.87 m/s at tee intersection.
Case 2: Long mixing tee with hot inlet velocity of 3m/s and Momentum ratio of 2
Residuals Plots
Area Weighted Average of Temperature(k)
The Average Outlet temperature: 294.4
Standard Deviation of Temperature
S.D. comes out to be 1.5k
Temperature Plot
Here the tee is longer than in case 1 and case 2, because of this the cold air reaches a short distance compared to case 1. Hence, the outlet temperature gets affected turning out to be higher and ranges within 292 to 297k.
Velocity profile plot
Here at the outlet cross-section, the velocity ranges between 3.91 to 5.86 m/s.
The highest velocity reaches up to 7.82 m/s at tee intersection.
Case 3: Short mixing tee with hot inlet velocity of 3m/s and Momentum ratio of 4
Residuals Plots
Area Weighted Average of Temperature(k)
The Average Outlet temperature: 291.5k
Standard Deviation of Temperature
S.D. comes out to be 1.0
Temperature Plot
Here as the cold air velocity is more (12m/s), it makes a significant mark throughout the pipe length reaching till the outlet and hence will provide cooler air compared to case 1 and case 2 outlet temperatures.
Velocity profile plot
Here we can see the velocity at the outlet almost becomes uniform, falling within the range of 3.65 to 7.30 m/s. Here as the cold inlet velocity is 12m/s, it reaches up to the bottom of the pipe covering the whole cross-section area.
The highest velocity reaches up to 14m/s at tee intersection.
Comparison of Cell Count, Average Outlet Temperature and No. of Iterations for Convergence for all three cases:
OBSERVATIONS and CONCLUSION:
- For the temperature plot, the inlet-x temp. is kept 300k and the cold temp. is kept being 283k and its intersection we see 2 different layers of temperature which makes an average of these two extreme temperatures.
- As the cold air velocity increases from the inlet y, the outlet air temperature obtained is cooler
- For the velocity profile plot as the hot and cold inlet velocity increases, the mixing efficiency increases and we get more uniform air at the outlet
- The velocity parameter plays an important role in determining the mixing efficiency
- The average outlet temperature depends upon the inlet hot and cold temperature. The less the temperature of the cold air, the less outlet air obtained.