Week 6: Conjugate Heat Transfer Simulation

Conjugate heat transfer:

Conjugate heat transfer is used to describe the processes which involve variations of temperature within the solids and fluids,

due to thermal interaction between the solids and fluids. 

The CHT analysis is generally used in places where there is heat transfer taking place for example when a fluid flows through

a pipe and the heat of the fluid is transferred to the pipe by convection. CHT analysis is very much useful in analyzing the

areas where there are two bodies in which heat transfer takes place. when this analysis is used it is easy to calculate the heat

transfer coefficient temperature and velocity of a fluid flowing through a certain body.

This type of heat transfer corresponds to the combination of heat transfer in solids and heat transfer in fluids. heat transfer in

solids is called conduction and heat transfer in a fluid is 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 occurs.

The convection process is not happening alone. it is combined with the conduction or radiation. it occurs mostly in the cooling

process like Heat sink, Battery cooling, Airflow over the solid object for cooling.

SUPER CYCLING:

Super-cycling is a method used in converge studio for CHT problems with multiphase regions(solids and liquids). The solvers

for different fluids cannot run at the same speed for solving fluid it is much faster as compared to solids. If, this is done the

solution does not reach convergence. so, super cycling can be used to resolve this issue. This helps solver of fluid domain is

paused until the solver for solid converges.

Y+:

 Wall functions are useful in telling the solver how to approach the solution near the wall. this helps in predicting the

turbulence models for the coarse grid. no-slip condition is used if the flow is completely laminar that does not depends on

grid size. For turbulent flows, the laminar region is very small to get accurate results we need a very small grid size near the

boundaries. This is where the Y+ value helps. Y+ is a non-dimensional term that can be used to understand the grid is finer

or course. This can be used to determine if wall functions are used or not. In viscous sub-layer Y+ is less than 10 and in a

turbulent region, Y+ is greater than 30. 

SIMULATION AND SOLUTION:

In this project, we'll be running a total of 6 cases where 3 are based on mesh size and 3 are based on supercycle stage

intervals

Geometry:

Our geometry is created with a base radius of 0.015 m and a thickness of 0.005 of a cylinder.

Setup: 

Application Type	Time-based
MATERIALS:
1. Gas simulation	Standard
2. Global Transport Parameters	Standard
3. Solid simulation
4. Species	1. fluid: O2 and N2  2. Solid Aluminium
SOLUTION PARAMETERS
1. Run Parameters      Steady-state monitor:	Transient >Full hydrodynamic>Compressible
2. Simulation time parameters
3. Solver parameters	Navis-stokes solver scheme: PICO Navis-stokes solver type: density-based
BOUNDARY CONDITIONS
1. Inlet	Where, Re = (rho*V*D)/(Dynamic viscosity)   Given: Re = 7000 rho = 1.161 kg/m^3   D = 0.03 m Dynamic viscosity = 1.845e-5 kg/ms substituting  velocity = 3.708 m/s
2. outlet
3. Outer wall
4. Side-wall
5. Interface
INITIAL CONDITIONS AND EVENTS
1. Regions and initialization
PHYSICAL MODELS
1 Turbulence modeling	RNG- k-epsilon
2. Super cycling
GRID CONTROL
1. Base mesh	CASE 1 dx = 0.004, dy = 0.004 and  dz = 0.004 CASE 2 dx = 0.003, dy = 0.003 and  dz = 0.003 CASE 3 dx = 0.002, dy = 0.002 and  dz = 0.002
2. Fixed embedding
OUTPUT/POST-PROCESSING
1. Post variable selection	Add Y+
2. Output files:

Then Export the Files

Then continuing the setup in Cygwin :

leading to the folder where the exported files are saved

Then using mpiexec.exe -n 2 converge.exe restricted to simulate the setup

After the output is generated, we lead the Cygwin to the output folder, and by copying the post_convert folder and

Using mpiexec.exe -n 2 post_convert.exe and converting these files for processable output in ParaView.

BASED ON MESH

CASE 1: 

 VELOCITY COUNTER

 PRESSURE COUNTER

 TEMPERATURE COUNTER

 YPLUS

CASE 2

 VELOCITY COUNTER

 PRESSURE COUNTER

 TEMPERATURE COUNTER

 YPLUS

 

CASE 3

 VELOCITY COUNTER

 PRESSURE COUNTER

 TEMPERATURE COUNTER

 YPLUS

 

BASED ON SUPER CYCLING:

CASE 1 : Super cycling intervel= 0.01

CASE 2:Super cycling intervel= 0.02

CASE 3: Super cycling intervel= 0.03

 

FLUID REGION

SOLID REGION

CONCLUSION:

Refinement of grid results in clearer plots however at the expense of computational time

Decreasing the SUpercycling time interval results in a reduction of computational time

Irrespective of grid size, fluid values converge to a particular value.(380 K).