Mixing efficiency analysis of mixing T geometry.

In this project, flow of air in T joint geometry also known as mixing T geometry is simulated in steady state for 3 cases to find the optimum conditions for maximum mixing effectiveness. T joint is a common joint used in AC units to moderate temperature so as to make the space thermally comfortable for living. Here the inlet parallel to y-axis is considered as cold air inlet and the inlet parallel to x-axis is considered as hot air inlet. Three cases considered for simulation are:

1) Short T pipe geometry with momentum ratio 2

2) Short T pipe geometry with momentum ratio 4

3) Long T pipe geometry with momentum ratio 2

where, momentum ratio = Velocity of cold air inlet/Velocity of hot air inlet.

For the first two cases same geometry and mesh is used as only the momentum ratio changes.

For all the cases velocity of hot air inlet is taken as 3m/s, the temperature of hot air inlet is taken as 25 degree celsius and the temperature of cold air inlet is taken as 10 degree celsius. In all the three cases the air volume to be simulated is extracted from these geometries shown below using Volume Extract function available in SpaceClaim and meshed using tetrahedral mesh taking element size as 0.005m.

Short T pipe geometry:

Short mixing T mesh:

Mesh metrics for short mixing T:

Now for momentum ratio 2:

The convergence plots:

Plot showing standard deviation of temperature at the outlet:

Plot showing area-weighted average of temperature at the outlet:

Post processed image showing temperature distribution over a cutplane along the middle of the pipe:

Post processed image showing velocity distribution over a cutplane along the middle of the pipe:

Now momentum ratio 4:

The convergence plots:

Plot showing standard deviation of temperature at the outlet:

Plot showing area-weighted average of temperature at the outlet:

Post processed image showing temperature distribution over a cutplane along the middle of the pipe:

Post processed image showing velocity distribution over a cutplane along the middle of the pipe:

Long T pipe geometry:

Long mixing T mesh:

Mesh metrics for long mixing T:

Now momentum ratio 2:

The convergence plots:

Plot showing standard deviation of temperature at the outlet:

Plot showing area-weighted average of temperature at the outlet:

Post processed image showing temperature distribution over a cutplane along the middle of the pipe:

Post processed image showing velocity distribution over a cutplane along the middle of the pipe:

Cases	Short mixing T with momentum ratio 2	Short mixing T with momentum ratio 4	Long mixing T with momentum ratio 2
Cell count	14247	14247	17771
Average outlet temperature in degree celsius	19.95	17.5	20
Number of iterations for convergence	50	100	60

From the above results we can easily conclude that increasing the velocity of cold air inlet or increasing the momentum ratio increases the mixing effectiveness quite considerably which is proved by average outlet temperatures obtained from the simulation. Further, using a long mixing T pipe does not improve the mixing effectiveness as results similar to short mixing T pipe is obtained in the simulation, so using a short mixing T pipe with high momentum ratio or high velocity of cold air inlet is advisable to improve the mixing effectivess.