Week 1- Mixing Tee

Aim : The simulation of thermal mixing tee junction using Ansys fluent.

Introduction: 

          In this practical we can study the CFD simulation of thermal mixing tee test are performed to obtained the themperature using k-epislon and k-omega sst model. In this practical we can use the long mixing tee and the short mixig tee

          In long mixing tee we can use k-epislon model  for free-shear layer flows with relatively small pressure gradients as well as in confined flows where the Reynolds shear stresses are most important. It can also be stated as the simplest turbulence model for which only initial and boundary conditions needs to be supplied.

          In short mixing tee model we can use the k-omega model The k-omega model is well suited for simulating flow in the viscous sub-layer. The k-epsilon model is ideal for predicting flow behavior in regions away from the wall. 

         Theory:

        Temperature fluctuations occur due to thermal mixing of hot and cold air, In the T-junctions of the piping system in power plants. Temperature fluctuations cause thermal fatigue of piping system. In the present work, thermal mixing experiments are carried out on a T-junction with water hot air. Velocity and temperature fields are measured using hot film anemometer (HFA). Three dimensional steady state computational fluid dynamics (CFD) simulations have been carried out to predict the velocity and temperature fields. The predicted velocity and temperature fields are in good agreement with the experimental measurements.

solving and modeling approch :

       In thermal mixing tee the hot air is provided through horizontal pipe at a temperature of 36 °C and the cold air is provided through vertical pipe at a temperature of 19 °C. The inlet velocity rates of hot and cold air are 3 m/s and the momentum ratio is  2,4 we can find the outlet temperature using CFD simulation.

       we can solving the probleam using the formula given below...

Tmix= (2*309)+(4*292)/4+6

Tmix= 298.27 k 

the average temperature is...

tmix= 298 k

pre-processing:

        we can design the geometry of long mixing tee and short mixing teeusing space claim geometry go to prepare and extract volume, then we can extend it.

after geometry we are go to mesh and we can meshing it an gives the name inlet-x, inlet-y,and outlet resp.

       after meshing we can go to the solver and taking the tempperature in kellvin first and and we can go to the inlet-x and put the value of pressure 6 m/s and tempture 309 k momentum ratio is 2,4 then we can go to the physics and we can gives the name the cell zones and use the fluid as air and we can give the boundry condition.and viscus model we can use k-epsilon, we can go to the surface defination in area weighted average and crete report file. and inilizing the problem. no. of iterations for convergence  is taken 150 and get calculated. After calculation we can have the graphs and simulation model.

Result:

      After solving calculation we can have the result, the outlet average themperature is 298 k .

the cell count of long tee is 15530 and the cell count of short tee is 12613

the following graph show the result...

The final CFD  simulation image is following below...

conclusion: 

      In this  way we can solve the long and short mixing tee problem and the outlet average temperature is 25 °C .