Week 1- Mixing Tee

Aim:-

• Set up steady-state simulations to compare the mixing effectiveness when the hot inlet temperature is 36C, and the cold inlet is 19C.
• Simulate each case for the given velocity and momentum ratio.
• Compare results from the 4 cases about cell count, average outlet temperature, and the number of iterations for convergence.
• Plot the velocity and temperature contour plots on the cut plane along and across the pipe.
• Also, plot the velocity and temperature line plots along and across the length of the pipe.
• Perform Mesh independent study for any one case.
• Moreover, discuss the effect of length and momentum ratio on results.
• Lastly, for each simulation, show the convergence plot.

Objective :

• hot inlet temperature is 36⁰C & the Cold inlet is at 19⁰C.

  Use the k-epsilon for the first case and based on your judgment use the more suitable model for further cases. Giving the reason for choosing a suitable model is compulsory.

Problem Setup

Understand k-epsilon

Case-1

Short mixing tee

a - Simulation-1

hot Inlet velocity - 3m/s

Momentum ratio - 2

case-2

b - Simulation-2

hot Inlet velocity - 3m/s

Momentum ratio - 4

Case-3

Long mixing tee

a - Simulation-3

hot Inlet velocity - 3m/s

Momentum ratio - 2

case-4

b - Simulation-4

hot Inlet velocity - 3m/s

Momentum ratio - 4

procedure:

1. Open new project, by clicking on Fluid flow (Fluent) in Ansys workbench.

2. Now click on geometry to import mixing tee model. It will redirect to Spaceclaim, Ansys’s geometry model manipulator.

fig. Mixing Tee Model

3. We are to analyse the mixing of two fluid, so there is role of parts other than two pipes. To supress that we need to extract volume of tee. Go to prepare menu and click on volume extract. Switch to edge selection and select three outer edges and click on green check button.

4. Hide solid by unchecking it from structure menu to see volume, which we have extracted. Supress solid by clicking on option supress for physics.

Fig. Extracted Volume

5. Exit from Spaceclaim and click on mesh to open mesh menu.

6. Select outer face and press right click of mouse, it will open a menu. Click on option create named selection and write suitable name for face. Repeat for other faces.

7. Now click on mesh option and choose generate mesh. It will generate mesh according to some predefined criteria. Element size can be selected but it is going to affect simulation time. Section plane can be created to see inner portion of geometry.

Fig. Generated Mesh

8. Select the option element quality to see, how many elements are defying quality. Quality is measured on the scale of 0 to 1. In our graph most of the element are near to 1 so we can say it is good quality.

Fig. Number of Elements vs Element Metrics

9. Go to physics menu and enable energy equation select viscous model. It will open a menu, choose realizable k-epsilon model and close it.

Fig. Viscous Model Parameters

10. Click on materials and choose air as working fluid. Check working fluid by clicking on cell zone conditions option, if it is air then proceed.

11. Now go to boundaries option to set boundary conditions. Select inlet_x and click on option edit. It will open a menu, where all the parameter can be set whether it is thermal, radiation, momentum etc. Put the value of velocity as 3m/s and go to thermal parameter to set temperature as 36C, for hot fluid.

Fig. Applying Boundary Conditions

12. Repeat the same procedure for cold fluid coming, velocity –6 m/s, temperature – 19C.

13. We want to generate temperature report of outlet and we want standard deviation of temperature also. Go to solutions tab and select definition and select area weighted average. In the opened menu select temperature as field variable. Similarly select standard deviation in definitions menu. Now insert a XY plane in wall by clicking on plane in location option of insert.

14. Now click on initialization to calculate approximate values of velocity and pressure.

15. Change the number of iterations to 200 and click on calculate. If solution is not converged, then iterations can be increased.

Results:

case1

Short mixing tee

Inlet velocity - 3m/s

Momentum ratio - 2

Inlet velocity of cold air = 3x2 = 6m/s

Fig. Residuals

Fig. Average Temperature

Fig. Standard Deviation

Fig. Temeprature Contour

Fig. Velocity Contour

Fig.vector Velocity

Fig. Temparature planes

Fig. values computed

chart temparature:

velocity chart:

Case-2

Short mixing tee

Inlet velocity - 3m/s

Momentum ratio - 4

Inlet velocity of cold air = 3x4 = 12m/s

Fig. Residuals

Fig. avg-temp

Fig. std- deviation

Fig. Temparature contour

Fig. velocity contour

3 Fig. vector velocity

Fig. Temparature planes

Fig. velocity planes

Fig. values computed

comparion of short tee MR=2 and MR=4

Case-3

long mixing tee

Inlet velocity - 3m/s

Momentum ratio - 2

Inlet velocity of cold air = 3x2 = 6m/s

Results

Fig. residuals

Fig. avg-temp

Fig. std- deviation

Fig. Temparature contour

Fig. velocity contour

Fig. vector velocity

.

Fig. Temparature planes

Fig. velocity planes

Fig. values computed

Case-4

Long mixing tee

Hot Inlet velocity - 3m/s

Momentum ratio - 4

Inlet velocity of cold air = 3x4 = 12m/s

Fig. residuals

Fig. avg-temp

Fig. std-deviation

Fig. Temparature contour

Fig. velocity contour

Fig. velocity velocity

Fig. temparature planes

Fig. velocity planes

Fig. values computed

comparison of velocity chart:

comparison of temp chart:

Comparison table

Parameters	Cell Count	Average outlet temperature	Number of iterations to converge
Case 1	12812	30.202064	122
Case 2	15588	27.54591	154
Case 3	17812	30.26080	184
Case 4	19588	27.47814	400

Conclusion:

Ansys fluent is high performance CFD software recognized for accuracy, robustness etc. it is not confined to only aerospace and mechanical domain, it has various application like to simulation of calculation of air flow on air craft wing, combustion in furnace, bubble columns in oil refineries, combustion in IC engine etc. In this study we performed simulation on simple geometry of mixing tee and got insights of various feature of fluent. we can conclude by analysing graph that If momentum ratio is increased, outlet temperature will decrease and there is no effect of velocity even though length is increased.