Week 1- Mixing Tee

Aim: - To study nature and mixing effectiveness of a long & short mixing tee for different momentum ratio of inlets by CFD (computational fluid dynamics) using Ansys fluent where temperature of hot inlet is 36⁰C and cold inlet temperature is 19⁰C.

Introduction and importance: - mixing tee are a simple device used to mix fluids of different chemical/physical properties in the industries the are very much cost effective. In chemical process it used as diffuser or can be said as used in diffusion and mixing of fluids into one another. It utilizes its internal geometry to mix two fluid streams into one single stream. Moreover, to it is also used in HVAC systems to mix two different temperature fluids to maintain desired ambiance. It is used in various industries such as

• Waste management plants etc.

Mixing tees have very simple geometry but still works very effectively.

Modelling/Solving approach: - A study state analysis/simulation was performed to know the effectiveness of mixing and difference between short and long mixing tee with two different cases where momentum of ratio is different. The ratio is changed to understand function and behaviour of mixing tees more accurately.

Let us take short mixing see and process it for both the cases and then for long mixing tee.

Below are the steps involved in analysis of effectiveness of mixing tee:

Geometry: the mixing tee is either design or loaded in the Ansys design modeler or space claim I’m going to use space claim as it is very user friendly and tidy. In which I pre opened my files of mixing tee and extracted the volume by selecting the edge of the solid which will be interacting in the mixing process.

Short mixing tee: -

Long mixing tee: -

Meshing process: -

In meshing process first select the faces and name the selections as inlet, outlet and walls after that perform meshing and check quality of the meshing and give suitable grain size for both short and long tee.

Setting up physical parameters and solving: -

In this step the physical parameters can be set for the design and conditions in which they will be operating in after selecting all the parameters and setting up we can solve the problems after selecting required quantities to be measured such as temperature, standard deviation and velocity etc. after which we initialize the data and proceed with calculation by giving no of iteration.

	Case 1 momentum ratio	Case 2 Momentum ratio	Hot inlet velocity
Short tee	2	4	3
Long tee	2	4	3

Momentum ratio= cold inlet velocity/ hot inlet velocity

1) case 1 short tee: - 2 = x/3 2x3 = x x=6 m/sec

2) case 2 short tee: - 4 = x/3 4x3 = x x=12m/sec

3) case 1 long tee: - 2 = x/3 2x3 = x x=6 m/sec

4) case 2 long tee: - 2 = x/3 4x3 = x x=12 m/sec

Short tee:

	Case 1	Case 2	Temperature in oC
Hot inlet	3m/sec	3m/sec	36
Cold inlet	6m/sec	12m/sec	19

Case 1

For k- epsilon

For k -omega : -

The k-epsilon is the first order upwind where as k-omega uses second order upwind as we are computing behaviour of fluid flows away from the walls k omega is not required

Case 2:

Long tee:

	Case 1	Case 2	Temperature in oC
Hot inlet	3m/sec	3m/sec	36
Cold inlet	6m/sec	12m/sec	19

Case 1

Case 2

Results/postprocessing: -

After performing calculations in fluent we can close fluent window and open results where we can use required tools to display the calculation on the geometry with tools such as rendering, displaying legends, streamlines, vectors to show velocity etc. here with such tools I have shown velocity, mixing and temperature zones in short and long tee.

Short tee:

Case 1

Case 2

Long tee: -

Case 1

Case 2

Observation:

• The k-epsilon is the first order upwind where as k-omega uses second order upwind as we are computing behaviour of fluid flows away from the walls k omega is not required.
• Lesser the grain size more refined is the contour but calculation takes time as there more no of elements and calculation.
• the standard deviation comes closer to true value in case 2 from which we can conclude greater the inlet velocity at cool end lesser the deviation.
• By observing above results I suggest to use short tee with momentum ratio of 4 as it also has minimum backword streamlines, uniform mixture and handling will be easy.