STEADY STATE ANALYSIS OF EXHAUST PORT

STEADY STATE ANALYSIS OF EXHAUST PORT

Conjugate Heat Transfer (CHT)

Conjugate heat transfer (CHT) is a process of heat transfer between solids and fluids. Conjugate heat transfer (CHT) Analysis means analysis of both solid and fluid heat transfer and fluid flow. Conjugate heat transfer (CHT) analysis can accurately predict heat transfer by simultaneous solving all the relevant solid and flow field heat transfer processes, for example: conduction through solids, free and forced convection in the fluids and thermal radiation.

The CHT approach has an advantage over Finite Element Analysis in that wall heat transfer coefficients and their local variations on surfaces are directly calculated within the model rather than based on simplified empirical calculations. The CHT approach therefore has benefits for those applications where heat transfer is either non-uniform or difficult to calculate empirically.

Examples of CHT Analysis:-

Aerospace, Nuclear reactors, Thermal goods treatment, Food processing, HVAC, IC Engines, Heat Exchanger, Boiler, Heat Sink etc.

Objective:- To perform steady state analysis of exhaust port.

Case 1:

A STEADY STATE ANALYSIS of exhaust port is done using ANSYS FLUENT. Inlet velocity= 5 m/s, Temperature= 700 K.

Model

The model was imported in Spaceclaim.

Mesh

The model was meshed using ANSYS mesher with element size of 0.15 m which the BASELINE mesh.

A mesh metric that identifies elements according to their quality was employed and it can be seen that the elements of lowest quality are minimal. Most of the elements have very high quality in the range of 0.7-1. Hence, the mesh is of acceptable quality. The meshed model is shown in image below. Number of Elements= 138571, Nodes= 27609.

Convergence

Iteration= 300 were ran. The residual plot is plotted in ANSYS FLUENT shown below.

Result

Temperature Contour

Streamline Temperature Plot

Streamline Velocity Plot

Plane Velocity Plot

Heat Transfer Coefficient on the Plane

Case 2:

A STEADY STATE ANALYSIS of exhaust port is done using ANSYS FLUENT. Inlet velocity= 5 m/s, Temperature= 700 K.

Model

The model was imported in Spaceclaim.

Mesh

The model was meshed using ANSYS mesher with element size of 0.0075 m. Inflation layer= 5 were employed around the interior of the with growth rate of 1.2. Total thickness of the layers= 0.005 m.

A mesh metric that identifies elements according to their quality was employed and it can be seen that the elements of lowest quality are minimal. Most of the elements have very high quality in the range of 0.5-1. Hence, the mesh is of acceptable quality. The meshed model is shown in image below. Number of Elements = 494177, Nodes =137092.

Convergence

Iteration= 300 were ran. The residual plot is plotted in ANSYS FLUENT shown below.

Result

Temperature Contour

Streamline Temperature Plot

Streamline Velocity Plot

Plane Velocity Plot

Heat Transfer Coefficient on the Plane

Difference in results in case 1 & case 2

	CASE 1		CASE 2
	MAX	MIN	MAX	MIN
TEMPERATURE (K)	700	464	700	504
VELOCITY (m/s)	37.23	0	39.16	0
HEAT TRANSFER COEFFICIENT (W/m2 K)	105.4	0	215.6	0

From the above table we can see the following:-

• The maximum temperature in both the cases remain the same but the minimum increases in case 2.
• With refinement there is some increase in the maximum velocity occurred in the flow.
• With refinement the maximum Heat Transfer Coefficient occurred in the flow gets doubled.

Verification of HTC predictions from the simulation:-

• To verify the results we can use Nusselt Number

The Nusselt number is the ratio of convective to conductive heat transfer across a boundary. The convection and conduction heat flows are parallel to each other and to the surface normal of the boundary surface, and are all perpendicular to the mean fluid flow in the simple case.

Nu = `(Convective heat transfer)/(Conductive heat transfer)`

Nu = `(hl)/k`

• We can also perform grid dependency test for verification. The simulations are performed for various mesh sizes till there is no change in the results value

Factors on which the accuracy of the prediction depends on are:-

• The accuracy of the simulation results depend upon the mesh quality, finer the mesh more accurate are the results.
• Type of mesh element being used also be used as prediction for accuracy as hexa mesh give better results.
• Inflation layers are also used around edges to correct uniform meshing.
• The experience of the Engineer also plays an important factor for choosing the above mentioned factors.

Conclusion

The refinement done in the mesh gives accurate results which can be verified using the mentioned methods.