CHT analysis of an exhaust port

CHT:- The term conjugate heat transfer is used to describe processes which involve variations of temperature within solids and fluids, due to thermal interaction between the solids and fluids.

The analysis type Conjugate heat transfer (CHT) allows the simulation of the heat transfer between Solid and Fluid domains by exchanging thermal energy at the interfaces between them. It requires a multiregion mesh to have a clear definition of the interfaces in the computational domain. Such a mesh can be created with the Hex-dominant parametric operation in the mesh creator.

The CHT analysis is performed on electronics cooling in devices like Graphic card, Heat-sink, Turbocharger, Boilers etc.

CAD model of the exhaust port:-

Fig. 1- CAD model of Exhaust port

Boundary conditions:-

Inlet velocity:- 5 m/s at temperature of 700 k.

Outlet:- 1 atm.

Convection at outlet wall:- 20 W/m^2 k.

Fluid:- Air.

Solid:- Almunium.

Pressure-based solver was used with k-epsilon. 5 inflation layers were used to get accurate result.

Case 1- Baseline mesh.

No. of nodes:- 88681.

No. of elements:- 253348.

Meshing:-

Fig. 2- Baseline mesh.

Temperature contour:-

Fig. 3- Temperature contour of exhaust port.

Velocity streamline:-

Fig. 4- Velocity streamline inside exhaust port.

Velocity distribution plane:-

Fig. 5- Velocity distribution at throat.

Wall heat transfer cofficient:-

Fig. 6- Wall heat transfer cofficient at throat.

Case 2- Refined mesh.

No. of nodes:- 130824.

No. of elements:- 473162.

Meshing:-

Fig. 7- Refined mesh.

Temperature contour:-

Fig. 8- Temperature contour of exhaust port.

Velocity streamline:-

Fig. 9- Velocity streamline inside exhaust port.

Velocity distribution plane:-

Fig. 10- Velocity distribution at throat.

Wall heat transfer cofficient:-

Fig. 11- Wall heat transfer cofficient at throat.

Observation:-

• There was increase in value of wall heat transfer cofficient and velocity as the mesh were refined so it can be concluded that as the mesh get refined more accurate valure can be achieved.
• As the the mesh were refined, more smoother and accurate graphs of velocity and wall heat transfer cofficient were obtained

Verification of HTC obtained from simulation:-

Verification can be done using two ways:-

1. Physical experiment.
2. Analytical Method.

Analytical method:-

First we can find the Reynolds no. and then we can find the nusselt no. using the formula,

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

where, Nu= Nusselt number;

Re= Reynolds number;

Pr= prandlt number(ratio of momentum diffusivity to the thermal diffusivity);

After calculating Nusselt number wall heat thansfer cofficient can be calculated using the relation,

Nu=hD/k.

Where, h= Wall heat transfer cofficient.

Thus one can calculate the Wall heat transfer cofficient and verify the predicted result.

Accuracy Factors:-

• Mesh quality and mesh refinement.
• Inflation layer.