MIXING TEE CFD SIMULATION IN ANSYS FLUENT
PROJECT OBJECTIVE:
Simulating the mixing tee to find out the outlet temperature and optimum design to get the desired temperature.
ABSTRACT:
Mixing tee is simulated using three various conditions to find the optimum design for desired temperature results.
The derived temperature at the outlet is the objective of this simulation.
METHOD:
SIMPLE method is used in solving the governing equations.
SOLVER:
A pressure based steady state solver is incorporated to simulate the flow.
The pressure based solver is generally used when the mach number is pretty low and there is no change of density associated with the flow.
A steady state solver has been used since we are only interested to look at the end temperature in this simulation.
We have to look at different cases since we have to decide which would be the optimum design to get the required temperature using minimum energy.
MATERIAL:
We have taken air as the fluid material in this simulation.
MODEL:
Since we are only interested in the fluid flow simulation, we have extracted the fluid model and suppressed the original model for physics.
CONVERGENCE CRITERIA:
1e-3 is taken aas the convergence criteria in this case and the simulation stops if the criteria has met.
END REPORTS:
The standard deviation of temperature at the outlet has been plotted and viewed to understand the effective mixing of the cold air with hot air and also to consider for the optimum design.
The area weighted temperature is plotted to understand the net average temperature at the outlet.
BOUNDARY CONDITIONS:
Hot atmospheric air at 25 degree celsius is fed through one inlet with a speed of 3m/s and cold air at 10 degree celsius is fed at a rate of 6m/s or 12m/s.
A pressure-outlet boundary condition is given at the outlet with a [0 Pa ]as gauge pressure since the outlet is exposed to the atmosphere.
The hot air is passed through inlet x and the cold air is passed through inlet y.
The boundary names are:
i)inlet x
ii)inlet y
iii)outlet
iv) walls
CASE 1:(momentum ratio: 2)
A short Tee joint is used in this case with a length of approximately 190mm.
The velocity of the hot air at the inlet is 3m/s.
A momentum ratio of 2 is used here.
The velocity of cold air at the inlet is 6m/s.
MODEL:
This is the solid model.
The fluid model used is:
The element size is kept as 3.5 mm.
The simulations is being run for 300 iterations and the plots are seen to converge by the time 300 iterations are completed.
RESIDUAL PLOT:
WEIGHTED AVERAGE PLOT:
STANDARD DEVIATION PLOT:
The standard deviation is seen to be nearly 1.5 which is low.Hence mixing is efficient and temperature is nearly uniform.
Temparature profile:
Velocity profile:
The average temperature is seen to be 19.9 degree celsius.
CASE 2:(momentum ratio: 2)
A long pipe is been used in this case with hot inlet air at 25 degree celsius entering the inlet at 3 m/s and cold air of 10 degree celsius entering at 6 m/s.
Fluid model:
The mesh size is kept at 4mm keeping in mind the constraints of Ansys Academic version.
The simulation is being run for 300 iterations.
SCALED RESIDUALS PLOT:
AREA WEIGHTED AVERAGE PLOT:
STANDARD DEVIATION PLOT:
The standard deviation is seen to be very low which suggests that the mixing has been very efficient and uniform temperature distribution is present.
TEMPERATURE PLOT:
VELOCITY PLOT:
The average temperature noted in the case of long tube at the outlet is nearly 20.2 degree celsius which is more than that of the small Tee joint.
CASE 3:(momentum ratio: 4)
A short tee joint similar to that of first case is used in this simulation but the invel velocity of cold air whichh is at 10 degree celsius is taken to be 12m/s and all other parameteers are kept same as in the first case.
Similar type of mesh as is used in first case is employed in this case simulation.
The simulation is being run for 300 iterations.
SCALED RESIDUALS PLOT:
AREA WEIGHTED AVERAGE PLOT:
STANDARD DEVIATION PLOT:
The standard deviation is seen to be very low which suggests that the mixing has been very efficient and uniform temperature distribution is seen to be present.
TEMPERATURE PLOT:
VELOCITY PLOT:
The temperature at the outlet is seen to be 17.5 degree celsius.
CONCLUSIONS:
The higher velocity has had a better mixing and as the mass flow rate of cold air is higher, the temperature at the outlet is also is less compared to other 2 cases.
Since there is a concern for the number of elements in the ANSYS academic version, a finer grid could not be used to perform the grid dependency test perfectly and mesh sizes coarser than the ones used is seen to yield not that good results as the values are seen to be dispersed.
It is seen that iterations more than 300 does not significantly change the results and convergence is easily achieved using 300 iterations. But at lower iterations like 250, it can be seen that the convergence is not fully achieved as gradients are seen to be very prominent.
1. Increasing the length of the model did not result in much change in temperature hence it is not a good option to select the long model as it increases the cost without much effect.
2.Increase in momentum ratio has resulted in decrease in average outet temperature and the time taken for convergence is also seen to increase.
The shorter model if found to be more optimal to use and the momentum ratio is seen to play a huge role in the oulet temperature and increase in momentum ratio has resulted in decrease in average outlet temperature.