Week 1- Mixing Tee
Mixing Tee
Objective:
- To clean the geometry and mesh it in pre-processing.
- To solve the model with best solver in ANSYS solver.
- To generate contour and line plots and analysis it in postprocessor.
Introduction:
Computational fluid dynamic is a branch of fluid mechanics which uses mathematics, physics and computational software to visualize how fluid flows and affects its medium and its neighbors. In CFD mostly computers are used to predict the fluid flow phenomena based on some governing equation like conservation of momentum – Navier Stokes equation, conservation of energy etc. in this study we are going simulating effect of fluid using ANSYS fluent software. Is a very important tool in CAE domain, which is allows you to perform all the three major steps of any simulation pre-processing, solving and post-processing. ANSYS fluent facilitates for modelling flow, turbulence, heat transfer and chemical reactions. With ansys we can accomplice more in less and with less training.
Mixing tee is a device which uses specifically engineered internal geometry to mix two fluid streams into one steam, efficiently. In this study we are going to find effectiveness of mixing tee. Hot air and cold air are going to be mixed in mixing tee. They will have different velocities. We will use two different mixing tee distinguished with length and analyses the effect of length on mixing.
Procedure:
There are three major steps to perform any type of simulation as follows pre-processor – it includes geometry clean up and generate best quality mesh. Solving includes applying boundary conditions, initialize and convergence. Last step is post processor which includes generate plots, contours, vectors to analyses 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.
Now click on geometry to import mixing tee model. It will redirect to space claim, Ansys geometry model manipulator.
We are to analyses the mixing of two fluid, so there is role of parts other than two pipes. To suppress 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.
Hide solid by unchecking it from structure menu to see volume, which we have extracted. Suppress solid by clicking on option suppress for physics.
Exit from space claim and click on mesh to open mesh menu.
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 face.
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.
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
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 option on task page.
Go to physics menu and select viscous model. It will open a menu choose realizable k-epsilon model and close it.
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.
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 3 m/s and go to thermal parameter to set temperature as 36C, for hot fluid.
Repeat the same procedure for cold fluid coming, velocity = 6 m/s, temperature = 19C.
We want to generate temperature report of outlet and we want standard deviation of temperature also. Go to solution tab and select definition and select area weighted average. In the opened menu selected temperature as field variable, similarly selected standard deviation in definitions menu.
Now click on initialization to calculate approximate values of velocity and pressure.
Change the number of iteration to 250 and click on calculate. If solution is not converged, then iteration can be increased.
Exit setup and double click on result to open CFD post. Check boxes to see wall and other parts. Click on walls and go to render set transparency of 0.4 to inside of wall. Color can also be changed to white for clear visibility.
Go to color of plane and change it by variable choose option temperature. Similarly, velocity contours can be created by just changing variable as velocity.
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.
Results:
Case-1:
In this short mixing tee is used, which was mixing two fluid with temperature 36C and 19C. Velocity of hot fluid was 3m/s and cold fluid was 6m/s. we used different turbulent solvers for it first was realized K-epsilon and K – omega SST.
K – Epsilon model:
K–Omega model:
Temperature contour:
Velocity contour:
Temperature streamline:
Velocity streamline:
Case 1.1:
In this short mixing tee is used, which was mixing two fluid with temperature 36C and 19C. Velocity of hot fluid was 3m/s and cold fluid was 12m/s. we used different turbulent solvers for it first was realized K-epsilon and K – omega SST.
K-epsilon model:
Temperature contour:
Velocity contour:
Temperature streamline:
Velocity streamline;
K-Omega model:
Temperature contour:
Velocity contour:
Temperature streamline:
Velocity streamline:
Outlet temperature calculation:
- Numerical temperature value at outlet is 30.256 C.
- Analytical formula for Tmix value at outlet is.
Tmix = [(mhot * Thot) + (mcold + Tcold)]/(mhot + mcold)
Where,
m – Mass flow rate = ρ*A*V.
Tcold – Temperature at cold inlet = 19C.
Thot – Temperature at hot inlet = 36C.
Tmix – outlet temperature after mixing.
Ahot = 901.3138 mm2; Acold = 225.9823 mm2 ; Vhot = 3 m/s, Vcold = 6m/s.
Tmix = 30.322C.
Outlet temperature calculation:
- Numerical temperature value at outlet is 30.256 C.
- Analytical formula for Tmix value at outlet is.
Tmix = [(mhot * Thot) + (mcold + Tcold)]/(mhot + mcold)
Where,
m – Mass flow rate = ρ*A*V.
Tcold – Temperature at cold inlet = 19C.
Thot – Temperature at hot inlet = 36C.
Tmix – outlet temperature after mixing.
Ahot = 901.3138 mm2; Acold = 225.9823 mm2 ; Vhot = 3 m/s, Vcold = 12m/s.
Tmix = 27.4877C.
Case 2:
In this long mixing tee is used, which was mixing two fluid with temperature 36C and 19C. Velocity of hot fluid was 3m/s and cold fluid was 6m/s. we used different turbulent solvers for it first was realized K-epsilon and K – omega SST.
K-epsilon model:
Temperature contour:
Velocity contour:
Temperature streamline;
Velocity streamline:
K-Omega model:
Temperature contour:
Velocity contour:
Temperature streamline:
Velocity streamline:
Case 2.2:
In this long mixing tee is used, which was mixing two fluid with temperature 36C and 19C. Velocity of hot fluid was 3m/s and cold fluid was 12m/s. we used different turbulent solvers for it first was realized K-epsilon and K – omega SST.
K-epsilon model:
Temperature contour:
Temperature streamline:
Velocity streamline:
Outlet temperature calculation:
- Numerical temperature value at outlet is 30.256 C.
- Analytical formula for Tmix value at outlet is.
Tmix = [(mhot * Thot) + (mcold + Tcold)]/(mhot + mcold)
Where,
m – Mass flow rate = ρ*A*V.
Tcold – Temperature at cold inlet = 19C.
Thot – Temperature at hot inlet = 36C.
Tmix – outlet temperature after mixing.
Ahot = 901.3138 mm2; Acold = 225.9823 mm2 ; Vhot = 3 m/s, Vcold = 6m/s.
Tmix = 30.322C.
Conclusion:
- So we can prefer less number of elements mesh also for simulation.
- The main advantage of this study is to decrease the computational time for solving.