CHT ANALYSIS ON EXHAUST PORT
CONJUGATE HEAT TRANSFER:
This type of heat transfer corresponds to the combination of the heat transfer in solids and heat transfer in fluids. Heat transfer in solid called as conduction and heat transfer in fluid called convection.
Conduction occurs due to the direct molecular collision. The faster kinetic energy collides with the low-speed kinetic energy and the heat transfer occur.
Convection process is not happed alone. It combined with the conduction or radiation. (CONDUCTION + ADVECTION=CONVECTION).
So, the Conjugate heat transfer occurred mostly in the cooling process like HEAT SINK, BATTERY COOLING, AIRFLOW OVER THE SOLID OBJECT FOR COOLING.
Whenever the solid and fluid interface appears, this type of CHT analysis can be done to find the optimum result by using the Ansys. It allows the simulation of the heat transfer between solid and fluid domains by exchanging the thermal energy at the interface between them.
CHT ANALYSIS ON A MODEL OF AN EXHAUST PORT:
Here we use the inline four-cylinder engine exhaust manifold, where the conjugate heat transfer is analyzed to find the optimum heat transfer coefficient. Fluid volume is extracted from the port and consider as the fluid region where the air enters into the region. Since it has the interface of the solid and fluid domain so this type is called as CHT analysis.
When we generate the baseline mesh, the non-conformal mesh is generated which affect the result. To make a Conformal mesh Share topology option is used which make the perfect mesh.
SETUP:
Pressure based solver is used for this analysis. Steady state and enable the energy to measure the temperature. The turbulent k-epsilon method is used to run the analysis.
BOUNDARY CONDITION:
Material- air.
Inlet- velocity Inlet- 5m/s, Temperature-700k.
The outer wall of the port - convection, Heat Transfer coefficient-20w/m^2k.
Free stream Temperature-300 k.
Outlet- Pressure outlet.
Use the hybrid initialization and run the analysis to get the result.
RESIDUAL:
The process is slowly converged around 400 iterations. Even in 120 iterations, the solution is slowly converged which is easily observed from the animation of the velocity contour.
TEMPERATURE CONTOUR:
VELOCITY PLOT:
Observe that, the velocity at is low and high at the outlet.
Because of mass conservation, A1V1=A2V2. Since the dia for both the inlet and outlet are the same. Since the flow enters from the different port and exit at the same outlet. So the velocity at the exit is maximum.
Because of high velocity, we have high Reynolds Number.
Re=pvd/u
p=density.
v=velocity.
d=diameter.
u=dynamic viscosity.
Because of high Reynolds number , Nusselt number is increased. Nusselt number is proportional to the heat transfer coefficient which increases convective heat transfer at the outlet which shown by the below diagram.
VELOCITY PLANE:
TEMPERATURE PLANE:
WALL HEAT TRANSFER PLANE:
REFINING MESH:
To make the mesh more refine, reduce the size of the element in the solid region and add the inflation layer which the replica of the part.
ELEMENT SIZE=0.15m and match the zone with respect to the domain.
ELEMENTS=482383. NODES=132818.
Body sizing for the outer body of the port is 10mm.
FINE MESH:
INFLATION LAYER:
The inflation layer is generated on the outer layer of the fluid domain to get the optimum wall heat transfer coefficient.
RESIDUAL:
The fine mesh gives the result more accurate. The above residual shows that the solution is slowly in a converging manner.
TEMPERATURE CONTOUR:
Compare above the refining and baseline mesh where the result is more optimum around the outlet.
VELOCITY STREAMLINE:
The velocity of the outlet is increased which is compared with the baseline mesh Because of the inflation layer the region is compressed which give the more accurate result.
VELOCITY PLANE:
TEMPERATURE PLANE:
WALL HEAT TRANSFER COEFFICIENT PLANE:
Compare the result with the baseline mesh. The refining mesh model gives the result more accurate and optimum. Adding the inflation layer give the benefit which is shown above diagrams. The bending of the outlet area produced more Temperature and wall heat transfer coefficient because of high velocity at that region.
HTC VERIFICATION:
HTC-HEAT TRANSFER COEFFICIENT.
Already mentioned above the Reynolds number. Reynolds number used to find whether the flow is laminar or turbulent. In CHT Conduction and Convection are occurred. Here in this process, we use the natural cooling where Reynolds number depends on Nusselt Number.
where Nu=hl/k
Increasing h, it increases the Qconvection.
So whenever increasing the velocity it increases the HTC which result in increasing the Q.
The factor depends by HTC are
PROPERTIES OF THE FLUID
MOVEMENT OF THE AIR.
GEOMETRICAL DOMAIN.