Week 6: Conjugate Heat Transfer Simulation

Aim- CHT analysis on solid pipe

Objective:

• To study of effect of super cycling on simulation
• Perform grid independency test for three different grid size

Introduction:

Conjugate heat transfer is coupled, fluid structurer, heat transfer where conduction heat transfer in solid wall interacts with fluid flow and convection heat transfer in fluid flow interacts with solid boundary

Steps

• First create geometry by one by taking following dimension

Inner Radius =0.015

Length=0.2

Outer Radius=0.02

• Then check the diagnosis for any geometry error
• Setup the simulation
• Run the simulation in Cygwin
• Post process results in paraview

Geometry

Diagnosis

Calculation of inlet velocity:

Inlet Reynolds number =7000

Diameter of pipe=0.03 m

Dynamic viscosity of air=1.7894*10^-5

density=1.225 kg/m3

Re=rho*v*D/μ

v= (7000*1.7894*10^-5)/1.225*0.03

v=3.40 m/s

Case setup-

Applications-

-General flow (Time Based)

.

Gas Simulation:

Materials-

Gas: Air

Solid: Aluminium

Global Transport parameters

Species

Species-Gas-O2, N2

Solid- Aluminium

Run parameters:

-Transient solver

-Start time-0, End time-0.5 s

-Initial time step=minimum time step=1e-7 s

-Maximum time step=1 s

Density Based solver

Boundary conditions

• Inlet- INFLOW-velocity-3.40 m/s
  
  Outlet- OUTFLOW-Total pressure-101325 pa
  
  Solid outer wall- WALL, Heat flux= -10000 W/m2
  
  Solid wall -WALL velocity-slip , Temperature-zero normal gradient
• Interface- INTERFACE
  
  Forward boundary-velocity and temperature-Law of wall ,region-fluid
  
  Reverse boundary-velocity and temperature-slip and specified value ,region-solid
  

Region and initialization:

Results

Totals cells

Total cells at different grid size

Grid Size Total cells (approximate)

0.004 m 5000

0.003 m 10000

0.002 m 35000

Grid size=0.004m

Mesh

Temperature contour

Velocity Contour

Y-plus

The maximum range is 15 for the mesh size 0.004m

Grid size=0.003m

Mesh

Temperature contour

Velocity contour

Y-plus

The maximum range is 13 for the mesh size 0.003m

Grid size=0.002m

Mesh

Temperature Contour

Velocity contour

Y-plus

The maximum range is 10 for the mesh size 0.002m

Mean temperature in fluid Region vs time:

The mean temperature for fluid region converged to around Approx 346 k for 0.004 m and approx 348 k for 0.003 m grid size. Whereas for 0.002m size the value is 360 K.

Mean temperature in Solid Region vs time:

The mean temperature for solid region converged to around 900 k for 0.004m grid size. Whereas for 0.003m and 0.002m size the value is 800 K and 750 k respectively.

Mean temperature at monitor point vs time

The outlet temperature converged to around 850 k for 0.004m grid size. Whereas for 0.003m and 0.002m size the value is 820 K and 730 k respectively

Effect of super cycling stage interval

Super-cycling is a method used by CONVERGE in the case of conjugate heat transfer problems with a solid and liquid region. The solver for fluid and solid doesn’t run at same speed as heat transfer in fluid region is faster than solid region.
This causes problems during the solution given that the solid side solver would not have reached a steady state/convergence in the time the liquid solver does. This is where the concept of super-cycling can be used. Super-cycling is only meant to speed up the simulation

Three supercyle stage interval was set for comparison 0.01,0.02 and 0.03 respectively.

Mean temperature in fluid Region vs time:

The mean temperature for fluid region converged to around Approximate 345 k

We can see from the below graph that supercyle stage interval of 0.01 converged faster than stage interval with 0.02 and 0.03.

Mean temperature in Solid region Region vs time:

The mean temperature for solid region converged to around 850 k

We can see from the below graph that supercyle stage interval of 0.01 converged faster than stage interval with 0.02 and 0.03.

Mean temperature at monitor point vs time

The temperature at outlet monitor point converged to 850 k.

We can see from the below graph that supercyle stage interval of 0.01 converged faster than stage interval with 0.02 and 0.03.

supercyle stage interval of 0.01 the convergence is the fastest in all the cases followed by 0.02 and 0.003 stage interval. So it can be concluded that lower value of super cycle stage interval gives faster convergence.

• Results:
  Time of simulation for different super cycle stage interval
  
  Super cycling Stage interval Time of simulation
  
  0.03 977.10 s
  
  0.02 960.8 s
  
  0.01 899.1 s

Animation:

For Grid size:0.004m:https://www.youtube.com/watch?v=lAGiflBl2C4

For Grid size:0.003m:https://www.youtube.com/watch?v=x26iVoaduwY

For Grid size:0.002m:https://www.youtube.com/watch?v=_mVmWHIC9q8

Conclusion

1. Conjugate heat transfer simulation for flow through a solid pipe was successfully performed.

2. The grid dependency test showed that the temperature values approached a closed value when we decreased the mesh size and the solution was almost grid independent.

3.supercyle stage interval of 0.01 the convergence is the fastest in all the cases followed by 0.02 and 0.003 stage interval. So, it can be concluded that lower value of super cycle stage interval gives faster convergence.