Week 1- Mixing Tee

Aim:

 to set up steady-state simulations to compare the mixing effectiveness in a mixing tee when hot and cold air was passed through different inlets respectively at different velocities

Given:

hot inlet temperature is 36⁰C & the Cold inlet is at 19⁰C

1. Case 1 
   • Short mixing tee with a hot inlet velocity of 3m/s.
   • Momentum ratio of 2, 4. 
2. Case 2 
   • Long mixing tee with a hot inlet velocity of 3m/s.
   • Momentum ratio of 2, 4.

Momentum ratio = velocity at cold inlet / velocity at hot inlet

introduction:

mixing tee is a part that mixes fluid of different temperatures to one. an example for this type of assembly is mixing of air in AC vent.

it shows clearly at the end of temperature diffusions by two diagrams

in this challenge we gonna isolate the inner volume and we mesh it.

then we need to apply boundary condition and initialize it.

We can calculate the fluent and simulate it.

Theory:

Mixing tee is a T joint which mixes fluids at 90 degree angle.

it is more effective and easier to understand precisely.

we can isolate inner volume  to work on it because air flows through the inner volume.

finite volume method is an approximation process. it may vary practically.

we can use some of energy equations to solve it precisely.

Process:

Case 1:

open ansys work bench

drag and drop fluent model in screen

double click on geomentry

open short tee from downloaded files

outer geomentry has only heatflux and so for flow simulation we does not need it hence we can extract only inner volume in space claim.

click prepare >> volume extract >> select edges ( openings of pipe) >> click green mark

hide and suppress for physics the component .

it wil shows like this.

close the window the component will save automatically

now double click mesh which opens mesh module

select each faces and right click to name it as inlet x ; inlet y; outlet  and wall

now generate mesh

it will create mesh accordingly

Cell count will be 12780 and 15727 for short and long tee

mesh quality will be taken by default by software.

click section plane >> create lines >> it will cut geomentry in xy plane

we can see that mesh is so dense at connection area

check quality and also at graphs the quality will not be lower than 5%.

now close the window.

double click setup and it will launches ansys fluent.

in console we can check for run time errors and other warnings.

click setting up physics

click on energy dialog box click on steady state.

click viscous model>>k epsilon>>realizable>> std wall function>> ok

assign boundary condition>> parameters like inlet x and inlet y

give detais such as velocity as 3 m/s and temp 36 degree celsius for inlet x 

by solving momentum ratio we get factor of 2 by that  we can obtain inlet y velocity as 6m/s and temp as 19 degree celsius

click definitions >> new>> area weighted avg>>temp>> outlet>>report file; report plot>> ok

click definitions >> new>> std deviation>>temp>> outlet>>report file; report plot>> ok

click initialization>>hybrid>>initialize

click calculate with  150 iterations

it will solve model and plot respective graphs automatically

close window

close ansys fluent and double click results it will take you to cfd post.

active all parts 

click on wall and make it fully transparent

click insert>>location >> plane 1 >> at middle >>okay

click colours as variable >> temp >> to see the temperature mixup 

by that we can see all factours by diferent colours.

by same procedures we can solve case 2 and we can compare results 

let us gone through the challenges

let take short tee first

let us compare results between momentum 2 AND 4

 above scalar plaot for momentum 2 in short tee

 

above is scalar plot for momenttum 4 in short tee

hence by above plot we can tell for convergence to achieve we need 130 iterations

 

temperature difference across pipe for momentum 2

temperatur across pipe for momentum 4

velocity contour for momentum of 2

velocity contour for momentum 4

lets see about long tee

scalar plot for momentum 2

scalar plot for momentum 4

temperature along pipe for momentum 2

temp along pipe for momentum 4

velocity differnce across pipes momentum 2

velocity differnce across pipes momentum 4

Results:

refer to the table below which contains comparision between 4 cases

s.no	type	description	cell count	avg outlet temperature	no of iterations for convergence
1	short tee	momentum 2  Vc=6m/s Vh=3m/s	12780	31.15 degree celsius	150
2	short tee	momentum 4 Vc=12m/s Vh=3m/s	12780	27.65 degree celsius	150
3	long tee	momentum 2  Vc=6m/s Vh=3m/s	15727	30.83 degree celcius	150
	long tee	momentum 4 Vc=12m/s Vh=3m/s	15727	27.3 degree celsius	150

thus from the above table we can recognize following details,

1. for same cross section differnce in momentum results in  diffrent  outlet temperature

2. also for the same momentum differnt in length also affects the outlet temperature.

3. all the temperature contour plots given above its clearly shown that temperature varies in according to length due to mixing of air.

Conclusion:

Thus flow analysis in a mixing tee with different crosss section and  with differnt momentum are discussed.