CONJUGATE HEAT TRANSFER ANALYSIS ON EXHAUST MANIFOLD USING ANSYS

Conjugate Heat Transfer:

It is a coupled approach that solves for both the solid and fluid domains in a coincidental manner.

It helps in determining the temperature at fluid-solid interface through thermal coupling of the two domains.

The coupling involves three primary modes of heat transfer :Conduction,convection and radiation.

Heat transfer in a solid predominantly and most often occurs through conduction,whereas in fluids it takes place through convection which involves the the transport of fluid which in turn involves the transfer of energy transport also.

Coolers, heaters or heat exchangers are effective when there is an efficient combination of heat transfer between fluids and solids.Other examples involve wide range of applications like engines in bikes, cars,marine, agricultural equipment etc.,

In order to simulate the heat transfer between the solid and fluid domains which involves the exchange of thermal energy at the interface of both these domains CHT analysis is required.

Analysis properties:

Turbulent model is K-epsilon.

Steady state simulation is chosen to achieve the results without considering the effects that are involved during the simulation.

Domain:

In space claim the share topology option is set to avoid non -conformal mesh and both soid and fluid volumes are combined into a single final componant.

In mesher,the outer body which is the solid and inner volume of fluid are at first meshed using the default mesh size (without any refinement at the interface) and also on the outer surface for a baseline mesh simulation.

Later, mesh refinement is done using the inflation layers with a maximum thickness of 5 mm and growth rate of 1.2 which helps in arranging a body fitted mesh .Also, the outer body is refined to a element size of 10 mm using the body sizing.

Baseline mesh:

Number of elements:

Refined mesh:

Number of elements:

Body size fitted mesh/ inflation layers:

Boundaries:

Velocity inlet and pressure outlet condition is assigned for the inlets and outlet.

Outer wall is given convection boundary condition and the convection heat transfer coefficient is set to 20 w/m^2.K

Other solid surfaces are assigned to be adiabatic walls automatically by ANSYS .

Initial conditions:

In CHT analysis, the main physical parameters that are calculated are temperature distribution, velocity field, pressure and heat transfer co-efficient.

inlet velocity : 5 m/s.

Materials:

Fluid : air

Solid : alumminium

Baseline mesh simulation results:

plane in the exhaust port and results at that region:

1) Temperature

2)velocity streamlines

3)Heat transfer coefficient

Refined mesh simulation results:

1) Temperature

2)velocity

3)Heat transfer coefficient

Proving the accuracy of heat transfer co efficient obtained through simulation:

The baseline mesh and the refined mesh produce two different maximum values of heat trasfer co efficient.

This is because of the body fitted mesh that comes into picture in well refined mesh and this allows to capture the heat transfer coefficient accurately.

We can also caluculate the heat transfer co efficient of the outer wall using the theoritical formula of nusselt number and making a comparison with the numerical formula of nusselt number.

Nusselt - number (theoritical) = 0.023. (Re^0.8).(Pr^0.4)

Nusselt -number(numerical value) = (h.l)/k

where ,

Re - reynolds number

Pr - prandtl number

h - convective heat transfer

l - characterstic length

k -thermal conductivity of fluid