Exhaust Port Challenge

AIM :- To perform a conjugate heat transfer (CHT) analysis on an exhaust manifold.

QUE.1) Give a brief description of why and where a CHT analysis is used.

ANS.:- The term CHT is used to describe processes which involve variations of temperature within solids and fluids, due to thermal interaction between the solids and fluids. The exchange of thermal energy between the two physical bodies is called study of heat transfer , the rate of transfered heat is directly proportional to the temperature difference between the bodies. A typical example is the heating or cooling of a solid object by the flow of air in which it is immersed and some other example includes conduction through solids, free and forced convection in the gasses/fluids and thermal radiations.

Conjugate heat transfer corresponds with the combination of heat transfer in solids and heat transfer in fluids. In solidsa, conduction often dominates where as in fluids, convection usualy dominates. Efficiently combining heat transfer in fluids and solids is the key to designing effective coolers, heaters or heat exchangers. Force convection is the most commen way to achieve high heat transfer rate. In some applications, the performances are further improve by combining convection with phase change ( for example liquid water to vapour phase change ).

Heat transfer in solids and heat transfer in fluids are combined in the majority of applications. This is because fluid flow around solids or between solids wall, and because solids are usualy immersed in a fluid.

Modes of heat transfer :-

1. Conduction :- diffusion of heat due to temperature gradients. A measure of the amount of conduction for a given gradient is the heat conductivity.
2. Convection :- When heat is carried away by moving fluids. The flow can either be caused by external influences, forced convection or a buyoncy forces, natural convection. Convective heat transfer is tightly coupled to the fluid flow solution.
3. Radiation :- transfer of energy by electromagnetic waves between surfaces with different temperatures, seperated by a medium that is at least partially transparent to the (infrared) radiations. Radiation is especially important at high temperatures, e. g. during combustion processes, but can also have a measurable effect at room temperatures.

An accurate description of heat transfer modes, material proparties, flow regimes, and geometrical configurations enable the analysis of temperature fields and heat transfer.

Typical design problems involve the determination of :-

• Overall heat transfer coefficient, e. g. for a car radiator.
• Highest (or lowest) temperature in a system, e. g. in a gas turbine, chemical reaction vessels, food ovens.
• Temperature distribution (related to thermal stress) e.g. in the walls of spacecraft.
• Temperature responses in time dependent heating/cooling problems, e.g. engine cooling, or how fast does a car heat up in the sun and how is it affected by the shape of the windshield ?

The fluid flow and heat transfer problems can be tightly coupled through the convection term in the energy equation and when physical proparties are temperature dependent. While analytical solutions exist for some simple problems, we must rely on computational methods to solve most industrially relevant applications.

CHT can be performed to improve cooling performance of the water jacket and increase engine life. Advancement in cooling for applications such as gas turbine components require improved understanding of complex heat transfer mechanisms and the interactions between those mechanisms, which our engineers can perform without hassle. Critical cooling applications often rely on multiple thermal protection techniques, including internal cooling, external film cooling...etc. Which are efficiently used by our analysis to cool components and limit the use of coolent. We do extensive support for motor and battery CHT analysis to get optimized designfor high voltage systems. Conjugate heat transfer analysis provides the temperature distribution in solids and coolents of the engine and clear insight on velocity distribution and mechanism of heat transfer of coolent. Results of CHT analysis become input to structural simulations as thermal loads.

We have a wide experience in Engine CHT analysis for various type of engine like bikes, passenger cars, racing cars, commercial vehicles, marine, Agricultural equipments and earth moving equipments...etc.

QUE.2) Perform a CHT analysis on a model of an exhaust manifold. We need to compare solutions for the 2 sizes of meshes. The first one should be the baseline mesh and the second one should have a finer mesh on the solid zone and also with inflation layers. Show the velocity, temperature and heat transfer coefficient plots and explain if refining the mesh produced any changes to the results.

ANS.:- the commen geometry for whole project is as follows-

1) Geometry of exhaust manifold :-

This is the solid volume geometry, which get after, volume -> edge, slection tool.

2) Fluid volume of exhaust manifold :-

This is the fluid volume geometry, also which get after, volume -> edge, selection tool.

I provide here 2-parts, in which first is baseline mesh and second is manual mesh which get after putting certain number of body sizing edge values. In second part there have more cases, which define the quality of mesh as follows-

PART-1 :-

Body & element size = 150mm

Number of elements = 15752

Number of nodes = 4880

1. Baseline mesh :-

This mesh is for body and mesh element size = 50mm, I cant provided here inflation layer because here shows the error that, inflation layer is only for stair size mesh, but this is traingular mesh thats why it can\'t be allow.

Some basic quantities are-

viscosity = k-epsilon,

solid material = aluminium,

inlet velocity = 5 m/s,

temperature = 700k

pressure = 0 guage pressure

heat transfer coefficient = 20 watt/(m^2*k)

velocity and temperature contours for all boundary, and heat transfer coefficient is only for wall provided.

From this mesh I find out some plots and contours are as follows -

2. Scaled residuals :-

Here, as iterations increases residuals must be decreases.

3. Temperature Contours :-

This temperature contours is for 700k.

4. Velocity contours :-

This velocity contours for the temperature of 700k.

5. Tempereature outer wall :-

From this figure we can say that inlet temperature is less than outlet temperature, because inlet temperature is combined at throat and increases the temperature value.

here at inlet temperature is 458.4k and outlet temperature is 579.2k.

6. Velocity outer wall :-

Here velocity is same at every where, only the heat should somewhat increase at throat point.

7. Temperature plane :-

Here we can see that temperature plane which is maximum at middle side i.e. 700.1k and minimum at face side i.e. 518.8k.

8. Velocity plane :-

This is velocity plane where velocity is maximum at middle which is 29.12 m/s and minimum at face which is 0 m/s.

9. Pressure plane :-

This is the pressure plane where pressure is maximum at face which is 629.3 pascals and minimum at throat point which is -390.2 pascals.

10. Streamline :-

This is the streamline which shows velocity at outer wall convections. Streamline are minimum at inlet and maximum at outlet due to the increase in velocity.

11. Heat transfer coefficient plane (HTC) plane :-

Here shows wall heat transfer coefficient at plane. The HTC is maximum at inside the wall which is 100.9 watt/(m^2*k) and minimum at the outer face of wall which is 0 watt/(m^2*k).

12. Report :-

a.

b.

This is the report which describe the elements boundary, nodes, domain, different types of wall...etc.

PART-B :-

Here I describe total 7-different cases which are shows different mesh types and there plots, contour, results ...etc.

Case-1 :-

Body & Mesh size = 20mm

Total Number of nodes = 34023

Total number of elements = 132333

1. Mesh :-

2. Scaled residuals :-

3. Temperature contours :-

4. Velocity contours :-

5. Temperature outer wall :-

6. Velocity outer wall :-

7. Temperature plane :-

8. Velocity plane :-

9. Pressure plane :-

10. Streamline :-

11. Heat transfer coefficient (HTC) Plane :-

12. Heat transfer coefficient contour :-

13. Converge solution :-

Here, solution is converged at 294 iterations at 3 minute 20 seconds.

14. Report :-

a)

b)

Case-2 :-

Body & Mesh size =50mm

Total number of elements = 15033

Total number of nodes = 4644

1. Mesh :-

2. Scaled residuals :-

3. Temperature contours :-

4. Velocity contours :-

5. Temperature outer wall :-

6. Velocity outer wall :-

7. Temperare plane :-

8. velocity plane :-

9. Pressure plane :-

10. Streamline :-

11. Heat transfer coefficient (CHT) plane :-

12. Report :-

a)

b)

Case-3 :-

Body & Mesh size = 100mm

Total number of elements = 15786

Total number of nodes = 4892

1.Mesh :-

2. Scaled residuals :-

3. Temperature contours :-

4. Velocity contours :-

5. Temperature outer wall :-

6. Velocity outer wall :-

7. Temperature plane :-

8. Velocity plane :-

9. Pressure plane :-

10. Streamline :-

11. Heat transfer coefficient (CHT) plane :-

12. Report :-

a)

b)

Case-4 :-

Body & Mesh size =150mm

Total number of elements = 15752

Total number of nodes = 4880

1. Mesh :-

2. Scaled residuals :-

3. Temperature contours :-

4. Velocity contours :-

5. Temperature outer wall :-

6. Velocity outer wall :-

7. Temperature plane :-

8. Velocity plane :-

9. Pressure plane :-

10. Streamline :-

11. Heat transfer coefficient (CHT) plane :-

12. Report :-

a.

b.

Case-5 :-

Body & Mesh size =200mm

Toata number of elements = 15761

Total number of nodes = 4881

1. Mesh :-

2. Scaled residuals :-

3. Temperature contours :-

4. Velocity contours :-

5. Temperature outer wall:-

6. Velocity outer wall :-

7. Temperature plane :-

8. Velocity plane :-

9. Pressure plane :-

10. Streamline :-

11. Heat transfer coefficient (CHT) plane :-

12. Report :-

a)

b)

Case-6 :-

Body & Mesh size =300mm

Total number of elements = 15762

Total number of nodes = 4881

1. Mesh :-

2. Scaled residuals :-

3. Temperature contours :-

4. Velocity contours :-

5. Temperature outer wall :-

6. Velocity outer wall:-

7. Temperature plane :-

8. Velocity plane :-

9. Pressure plane :-

10. Streamline :-

11. Heat transfer coefficient (CHT) plane :-

12. Report :-

a)

b)

Case-7 :-

Body & Mesh size = 500mm

Total number of elements = 15762

Total number of nodes = 4881

1. Mesh :-

2. Scaled residuals :-

3. Temperature contours :-

4. Velocity contours :-

5. Temperature outer wall :-

6. Velocity outer wall :-

7. Temperature plane :-

8. Velocity plane :-

9. Pressure plane :-

10. Streamline :-

11. Heat transfer coefficient (CHT) plane :-

12. Report :-

a)

b)

Results :-

1. From the above meshing part its clear that when the body size increases then number of nodes and number of elements decreases and vice versa.
2. As iteration increases convergence plot decreases.
3. At body element size = 20, the solution is converge at very fast rate and we get finer results.
4. Temperature contours including external area, shows less temperature at inlet and higher temperature at outlet.
5. Velocity contours only for the given boundary, shows less at inlet equal to zero and maximum at outlet.
6. Temperature outer wall contours show that temperature s low at inlet and moderate at outlet ut maximum at throat.
7. Velocity outer wall also zero at inlet, moderate at outlet and maximum at throat.
8. In temperature plane, temperature is higher everywhere inside the wall and lower at outside the wall but, at face it is moderate.
9. In velocity plane, velocity is higher everywhere inside the wall, and decreases towards outer wall.
10. In pressure plane, pressure is maximum at front face, moderate at on the wall and less at throat.
11. Streamline is directly proportional to the velocity, means at inlet velocity is less it means streamline also less but velocity at outlet is maximum it means streamline also maximum at outlet and throat also.
12. In results show that number of elements and number of nodes from given mesh quality.
13. Domain results for geven module, i.e. fluid volume type and solid volume type.
14. Domain and various boundaries like inlet, oulet, outer wall convection and their types.

Observations :-

Parameters Baseline case-1 case-2 case-3 case-4 case-5 case-6 case-7

mesh

Temperature

(minimum) 458.4 458.4 458.4 458.4 458.4 458.4 458.4 458.4

(maximum) 700.1 700.1 700.1 700.1 700.1 700.1 700.1 700.1

Velocity

(minimum) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

(maximum) 29.12 29.12 29.12 29.12 29.12 29.12 29.12 29.12

HTC

(minimum) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

(maximum) 100.9 102.3 102.3 100.9 100.9 100.9 100.9 100.9

From the above table, we clear that,

1. We can infere that refined mesh produces more accurate results near the walls due to propar interpolations.
2. The heat transfer coefficient calculate in part-B has little difference as compare to part-A.

QUE.3) How would you verify if the HTC predictions from the simulations are right ?

On what factors does the accuracy of the prediction depends on ?

ANS. :- As we know that, HTC is fully depends on the materials and its walls, as the temperature increases, HTC also incraeses and vice versa and if temperature get constant then HTC also constant.

In other words accuracy of prediction is depends on mesh quality, as mesh is finer then our accuracy get high. Mesh quality is depends on body element size. If body element size is small then we get finer mesh and convergence solutions.

Varification of results :-

We can varify simulation results by performing grid independency test, where simulation will be running for various grid sizes untill the results obtain are independent of the grid sizes.

OR

By calculating the nusselts number by using the formula-

Nu = 0.023*(Re)^0.8*(Pr)^0.4.

and equating it to

Nu = (h*l)/k

where,

Re = reynold number

Pr = prandtl number

h = convective heat transfer coefficient

k = conductive heat transfer coefficient

l = length of the rod

Factors affecting the simulations :-

1. Number of elements in the mesh :- finar mesh gives more accurate results.

2. Inflation layer around the boundary :- Inflation layers which provide accurate analysis of geometry.

3. Accurate fitting of mesh around the geometry :- Mesh needs to accuratly accomodate the geometry around the curvatures.

4. Setting share topology :- Mesh should be conformalfor smooth transfering of mesh in different zones.

Conclusion :-

In this way, I describe CHT in details, by giving different cases through different grid independency test and compare the each result carefully. Also, showing some contours and different plots like temperature, velocity, CHT ...etc. Varify if the prediction from the simulations are right or not. and which factors does the accuracy of the prediction depends on. Also give the appropriate results for all cases.

So, I completed successfully exhaust port challenge.