Week 1- Mixing Tee

Mixing Tee

Aim:

To conduct a mixing Tee simulation through following cases

• Case 1 
  • Short mixing tee with a hot inlet velocity of 3m/s.
  • Momentum ratio of 2, 4. 
• Case 2 
  • Long mixing tee with a hot inlet velocity of 3m/s.
  • Momentum ratio of 2, 4.
• Momentum ratio = velocity at cold inlet / velocity at hot inlet
• Further comparison of following values from two cases (through table)
  1. Cell count
  2. Average outlet temperature
  3. Number of Iteration for convergence

Expected results:

1. Velocity and temperature contour plots on the cut planes along and across the pipe.
2. Velocity and temperature line plots along and across the length of the pipe.
3. Perform Mesh independent study for any one case.
4. Discuss the effect of length and momentum ratio on results. 

Procedure:

There are three major steps to perform any type of simulation as follows pre-processor includes meshing modal. Solving includes applying boundary conditions, initialize and convergence. Last step is post processor which includes generate plots, contours, vectors to analyse results. In this study we are going to follow all three steps to find out effectiveness of mixing tee. The following steps to be followed

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 Space claim, Ansys’s geometry 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.
5. Exit from Space claim 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.
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.
9. Exit mesh and open setup. First, Check mesh, it is throwing no error then only we can proceed further. We are going to do pressure based steady state simulation, so choose these options on task page.
10. Go to physics menu and select viscous model. It will open a menu, choose realizable k-epsilon and k-omega model and close it.
11. Click on material and choose air as working fluid. Check working fluid by clicking on cell zone conditions option, if it is air then proceed.
12. 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 parameters 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.
13. Repeat the same procedure for cold fluid coming, velocity 6 m/s and 12m/s, temperature 19C.
14. 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.
15. Now click on initialization to calculate approximate values of velocity and pressure.
16. Change the number of iterations to 250 and click on calculate. If solution is not converged, then iterations can be increased.
17. Exit setup and double click on result to open CFD post. Check boxes to see walls and other parts. Click on walls and go to render set transparency to inside of wall. Colour can also be changed to white for clear visibility.
18. Now insert a XY plane in wall by clicking on plane in location option of insert.
19. Go to colour of plane and change it by variable choose option temperature. Similarly, velocity contours can be created by just changing variable as velocity.
20. Right click on plane which we created and select streamline. Go to appearance and select temperature to see plot line on plane. Similar procedure can be repeated for velocity plot line.

RESULT:

Case 1 

• Short mixing tee with a hot inlet velocity of 3m/s.
• Momentum ratio of 2, 4. 
• In this simulation we use velocity of hot inlet is 3 m/sec and cold inlet is 6m/sec and given temperature of hot inlet is 36, and cold inlet is 19. we use k-epsilon model.
• In this simulation we use velocity of hot inlet is 3 m/sec and cold inlet is 12m/sec and given temperature of hot inlet is 36, and cold inlet is 19. we use k-epsilon model.
• In this simulation we use velocity of hot inlet is 3 m/sec and cold inlet is 6m/sec and given temperature of hot inlet is 36, and cold inlet is 19. we use k-omega model.
• In this simulation we use velocity of hot inlet is 3 m/sec and cold inlet is 12m/sec and given temperature of hot inlet is 36, and cold inlet is 19. we use k-omega model.

Case 2 

• Long mixing tee with a hot inlet velocity of 3m/s.
• Momentum ratio of 2, 4. 
• In this simulation we use velocity of hot inlet is 3 m/sec and cold inlet is 6m/sec and given temperature of hot inlet is 36, and cold inlet is 19. we use k-epsilon model.
• In this simulation we use velocity of hot inlet is 3 m/sec and cold inlet is 12m/sec and given temperature of hot inlet is 36, and cold inlet is 19. we use k-epsilon model.
• In this simulation we use velocity of hot inlet is 3 m/sec and cold inlet is 6m/sec and given temperature of hot inlet is 36, and cold inlet is 19. we use k-omega model.
• In this simulation we use velocity of hot inlet is 3 m/sec and cold inlet is 12m/sec and given temperature of hot inlet is 36, and cold inlet is 19. we use k-omega model.

Mesh Independent Study:

• For mesh independence test we select case (1) short tee momentum ratio 2 and we do the study for mesh element size 0.0195 and now it got 0.001. 
• From the above mesh independent study result we observed that is no large variation in output results.

Effect of length and momentum ratio on results:

• From the results of both the cases we can say that the output temperature is independent on length of mixing tee.
• Momentum ratio effects on outlet temperature, If momentum ratio increases then the outlet temperature is dropping suddenly.