Mixing efficiency

Aim:

Steady state of simulation of T joint mixing of hot and cold fluid.

Introduction:

In this project we have successfully simulated “Tee joint mixing of hot and cold fluid of steady state”

To be more specific study of flow and mixture of fluid of different temperature and we observe changes in its

parameters like is temperature , velocity , pressure e.c.t and we produce some result in the form of plot graph and

contour plot for different parameters .

Theory:

In any simulation we must have to design a geometry for simulate mixing efficiency of T-joint in which it have three

opening side. Two opening sides are co-inside with a line and another opening side is perpendicular to that line

whereas two opening sides are inlet and another one is outlet.

And we have to pass different temperature of fluid and compare the mixing effectiveness when hot and cold fluid

are mix together.

While using this simulation we have to use k-epsilon model. Because k-epsilon model of turbulence is capable of

solving parameter far from boundary or wall and k-omega model is used for solving turbulence near or very close

to the boundary. As we know our simulation is based on steady state of fluid flow and due to steady state fluid is in

laminar form near the boundary and where hot and cold fluid is mix together the fluid is in turbulence form, that’s

why we use k-epsilon model for t joint.

Formula:

Momentum ratio = Cold fluid velocity/Hot fluid velocity

Solving and modelling approach :

There are number of steps used to simulate a complete design , and these steps are :-

1}geometry:-

Step :1

Open workbench and select fluid flow (fluent)

Fig.1: Ansys workbench

Step:1.1

Firstly open space claim and open geometry file in space claim

Long pipe .

short pipe.

Fig:1.2 geometry

Step:1.2

Then we have to extract the volume by using selecting edge method and

create enclose volume by using selecting boundary option.

Long pipe

short pipe.

Fig:1.3 enclose volume of geometry

Step:1.3

And then we must have to click for supress for physick , due to which the other part of design

which is not used in simulation is hide and it will not making other effect for further process

Long pipe

short pipe.

Fig:1.4 volume use in simulation.

After this direct close space claim it will saved automatically

2} mesh:-

Step:2.1

Open mesh from workbench and the volume extracted in previous step is show hear.

Name the boundary of geometry. For naming the boundary we using [ctrrl+F] and then name the boundary 1) cold inlet

2) hot inlet

3) outlet

4) walls

long pope.

short pipe.

Fig:2.1 name the wall.

Step:2.2

Then generate mesh by clicking the generate mess option

Long pipe.

short pipe.

Fig:2.2 meshing.

Step:2.3

Check its mesh quality by using mesh matric

Long pipe.

short pipe.

Fig:2.3 mesh quality.

Step:2.4

After generating mesh we have to cut section-plane

Long pipe.

short pipe.

Fig:2.4 section plane

Then close the tab it will automatic save

the boundry condition are given in problem is

case: 1 Hot velocity = 3 m/s

Momentum ratio = 2

Cold velocity = 6 m/s

case: 2 Hot velocity = 3 m/s

Momentum ratio = 4

Cold velocity = 12 m/s

3} setup:-

Step:3.1

In this process we have to set up boundary condition and input all condition of fluid like its velocity , temperature , energy equation , viscous . we use k-epsilon model with realizable condition.

Then input temperature and velocity of fluid of hot and cold inlet and pressure at outlet boundary it Is always zero.

Long pipe.

short pipe.

Fig:3.1 setup boundry condition

Then go to solution and select new definition and select the graph or plot which is required. Usually hear two type of plot are selected

• Area weighted average
• Standard deviation

Then we do hybrid initialization and run calculation with 150 iteration, we can also use require number of iteration

Standard deviation plot

Long pipe.

short pipe.

Fig:3.2 standard deviation

Area weighted average of temperature (C).

Long pipe.

short pipe.

Fig:3.3 area weighted temperature

Over all.

Long pipe.

short pipe.

Fig:3.4

4} Result

Step:4.1

Insert the plane in xy direction and colure mood is on variable at temperature and click apply to show the effect

simulation

Long pipe.

short pipe.

Fig:4.1 temp distribution along the pipe.

In cross section view

Long pipe.

short pipe.

Fig:4.2 temp distribution across the pipe.

When we select for velocity varible

Long pipe.

short pipe.

Fig:4.3 veocity distribution along pipe

In cross sectional view.

Long pipe.

short pipe.

Fig:4.4 velocity across the pipe

and we plot some graph on the basis of its parameters like velocity , temperature , and pressure e.t.c

plot 1

long pipe.

short pipe.

Fig:4.1 temp along the pipe

plot 2

long pipe.

short pipe.

fig:4.4 velocity aong the pipe

plot 3

long pipe.

short pipe.

Fig:4.5 temp avross the pipe

plot 4

long pipe.

short pipe.

Fig: 4.6 velocity across the pipe.

Pre-processing and solver

5}Mesh

Doing an appropriate mesh depends on the physical parameter of simulation is the core concept of any CFD simulations. it is the most important part of a CFD simulation which has a tremendous impact on simulation results.

Although there is no specific rule for meshing, however, there are some parameters like skewness, aspect ratio, orthogonality e.t.c which play a vital rule in meshing.

Hear some setting in mesh by using this we can control the mesh quality

Fig:5.1

From this setting we can adjust mesh quality

Fig:5.2

6} Solver requirements

To simulate any geometry we have to apply boundary condition , energy equation , which type of flow is (laminar or turbulent).

First we have to apply some basic condition

Fig:6.1

Then apply energy equation

Fig:6.2

And we use k-epsilon equation because it capable of solving parameter far from boundary or wall.

Fig:6.3

Which type of material Is flow in the pipe

Fig:6.4

Then apply boundary condition at each wall of geometry. Hear we have to input temperature and velocity

temperature input

Fig:6.5

Apply definition

Fig:6.6

To produce result we must have to click hybrid initialize

Fig:6.7

And the last step is calculation with sone iterations

Fig:6.8

The table compares the following values from the above cases:

• Cell count
• Average outlet temperature and velocity
• Number of iterations for convergence

Effect of Momentum ratio in mixing:

In this section, the comparison between mixing in T-joint with short tube with 2 M.ratio and 4 M.ratio is carried out. This shows that increase in momentum ratio will show good result in temperature and velocity distribution along and across short tube which is shown below:

Temperature distributation

At 2M.ratio

At 4M.ratio

Velocity distributation

2M.ratio

4M.ratio

Temperature distribution across the pipe

2M.ratio

4M.ratio

velocity distribution across the pipe

2M.ratio

4M.ratio

Effect of length in mixing:

In this case study, the comparison between mixing between T-joint with short tube and long tube is carried. This shows that the increase in length will provide good temperature and velocity distribution near wall at end

temperature distribution

long pipe at 4.m ratio

short pipe at 4.m ratio

velocity distribution

.

long pipe at 4.m ratio

short pipe at 4M.ratio

Temperature distribution across the pipe

At 4M.ratio

4m.ratio

Velocity distributon across the pipe

4m.ratio

4M.ratio

conclusion

• In the above case study, k-epsilon realizable model is best against the k-epsilon standard and k-omega SST model.
• When the length of tube increases then it will provide good mixing near walls at end.
• When there is a decrease in mesh size, it shows good temperature and velocity distribution in mixing
• When velocity increases in flow then it will increase turbulences in flow thus it will result in better mixing and lower mixture temperature.