Mixing Efficiency Using Ansys Fluent in a Tee Joint

I. Introduction :  

Tee joint is a type of pipe fitting which is T-shaped having Either 1 inlet 2 outlets or 2 inlet 1 outlet combination, The Inlet/Outlet in the Y direction is in perpendicular with the X direction. It is a Common piping component, typically used to combine or seperate flow of fluid. This project is aimed at learning the mixing effectivenes of one such T joint pipe having Two inlets, one inlet from X-dir recieves hot fluid and Y-dir recieves cold fluid. Seperate conditions are given and study is done for a short and longer T joint pipe and its results are compared. 

II. Objective :

1. Performing 3 steady state simulations on the mixing tee geometry. 

   1.1. Short mixing tee with hot inlet velocity of 3m/s with a Momentum ratio 2.

   1.2. Long Mixing tee with hot inlet velocity of 3m/s with a Momentum ratio of 2.

   1.3. Short mixing tee with hot inlet velocity of 3m/s with a Momentum ratio of 4.

   (Momentum Ratio = velocity at cold inlet / velocity at hot inlet)

2. Comparing Results.

III. PreProcessing in SpaceClaim :

1. Volume Extraction : 

After loading the geometry in Ansys fluent, We first extract the volume of the Geometry we need to perform the simulation in. This helps us reduce the geometry to true usable size and define the end faces bascially within which the simulation wil be performed. Other edges and non-required geometry is supressed. We use edge volume extraction option here. 

A. Defining Edges for volume extraction: 

B. Extracted Volume and other geometry suppressed. 

2. Meshing : 

A. Short Tee :                                  

An element size of 0.004 is choosen for short tee. 

Half Section Mesh and Mesh Metric Generated :  

   We can see that majority of the element quality comprises of 80-95% quality.

B. Long Tee :

     An element size of 0.003 is choosen for Long tee. 

     Mesh Metric Generated.

IV. Case Setup & Processing : 

A. General Case conditions : 

1. Solver Type - Pressure Based.

2. Velocity Formulation - Absolute. 

3. Time - Steady. 

4. Boundaries and Cell zones defining.

5. Definiations of the plots and reports required.

6. Physics - Energy 

7. Viscous Model : k-epsilon : Realizable model. 

B. Case Wise Conditions: 

1.1. From objective 1.1, in short mixing tee, hot inlet velocity of 3 m/s is set and to obtain a momentum ratio of 2, Cold inlet velocity is set 6 m/s. Temperature range for hot inlet is set to 45 degree and cold is set to 15 degree celcius.

1.2. From objective 1.2, In long mixing tee, hot inlet velocity of 3 m/s is set and to obtain a momentum ratio of 2, Cold inlet velocity is set 6 m/s. Temperature range for hot inlet is set to 45 degree and cold is set to 15 degree celcius.

1.3. From objective 1.3, In short mixing tee, hot inlet velocity of 3 m/s is set and to obtain a momentum ratio of 4, Cold inlet velocity is set 12 m/s. Temperature range for hot inlet is set to 45 degree and cold is set to 15 degree celcius.

After initializing the solver, It is run for 300 iterations, after which we get some following plots we defined for. The solution obtained is then post-processed in Cfd Post .

V. PostProcessing & Results on Case Basis : 

 A. Case 1 : Short Mixing tee with Momentum ratio 2. 

Residuals plot : 

We can observe that values and step formation on the plot are repeating after 230 iterations hence the solution has converged.

Temperature Plot : Outlet. 

The Temperature Drop at the outlet weights at an average of 34.75 degree approx

We can Further post process the plotted Temperature data, we can see how the temperature variation takes place in the T joint. The diffusion observed is created because of a little coarse mesh.

Velocity Plot : Outlet. 

We observe that the velocity at outlet weights at 4.950 m/s where the hot inlet was 3m/s and cold inlet was at 6m/s

We can observe the post processed velocity distribution 

 B. Case 2 : Long Mixing tee with Momentum ratio 2. 

Residuals plot : 

We can observe that values and step formation on the plot are repeating after 250 iterations hence the solution has converged.

Temperature Plot : Outlet. 

The Temperature Drop at the outlet weights at an average of 35 degree approx

We can Further post process the plotted Temperature data, we can see how the temperature variation takes place in the T joint. 

Velocity Plot : Outlet. 

We observe that the velocity at outlet weights at 4.4895 m/s where the hot inlet was 3m/s and cold inlet was at 6m/s

We can observe the post processed velocity distribution 

 C. Case 3 : Short Mixing tee with Momentum ratio 4 . 

Residuals plot : 

We can observe that values and step formation on the plot are repeating after 300 iterations.

We observed the solution for further more 300 iterations and the litte curve and rest of the steps kept repeating.  Hence the solution is Converged.

Temperature Plot : Outlet. 

The Temperature Drop at the outlet weights at an average of 30 degree approx

We can Further post process the plotted Temperature data, we can see how the temperature variation takes place in the T joint. 

Since the Cold inlet velocity is increased we see the there is more temperature drop than case 1. About nearly 5 degree temperature drop just by doubling the cold inlet velocity from 6m/s to 12 m/s

Velocity Plot : Outlet. 

We observe that the velocity at outlet weights at 6.015 m/s where the hot inlet was 3m/s and cold inlet was at 12 m/s

Post Processed Velocity Distribution: The velocity has increased because of higher Cold inlet velocity. 

VI. Comparisons & Conclusions : 

1. Comparing just the short tee joints together we can conclude that for the same geometry we observe a higher temperature drop nearly by 5 degree's by doubling the velocity from 6 m/s to 12 m/s. 

2. Short tee & Long tee joints with same momentum ratio observe very little temperature difference between the two, however it takes more execution time for the Longer tee to solve and produce about same results, which makes the shorter Tee joint more useful in this very specific observation. 

3. We can observe more mixability when the cold inlet speed is a little high in case 3 as we can observe in its temperature post processing, it pierces till the end of the pipe having the entire flow of hot inlet coming inside collide with it but with other two we can observe as the velocity is less it didnt quite do that. However this conclusion also can change/depend upon the mesh, finer the mesh the better the observation. 

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