Week 6: Conjugate Heat Transfer Simulation

Introduction

Conjugate Heat Transfer (CHT)

Conjugate Heat transfer (CHT) is when heat transfer occurs simultaneously within & between fluid and solid regions

The predominant mode of Heat transfer in a fluid is convection

The predominant mode of Heat transfer in Solid is conduction

Converge solves the fluid heat transfer using the energy equation

Converge solves the solid heat equation using the solid heat equation

`C_p ρ(∂T)/(∂t)=∇∗(k∆T)+s_h`

SUPER CYCLING

Super-cycling (recommended for combination with combustion): converge iterates between fully coupled transient & SS methods for the solid only

Converge use transient solver for fluid

Time control: Super-cycling

1. Solves the fluid & the solid together with a transient solver
2. Stores the instantaneous HTCs & temperature with transient solver
3. Freezes the fluid solver
4. Time averages the HTCs & temperatures & applies them as BC at the interface
5. Solves the solid temperature until it reaches SS
6. Updates the solid temperature field and unfreezes the fluid solver
7. Repeats until the solid temperature converges

ANALYSIS CASES

Cases	Mesh size dx,dy,dz	SuperCycle Stage interval
case1	0.004	0.05
case2	0.003	0.05
case3	0.002	0.05
case4	0.002	0.01
case5	0.002	0.02
case6	0.002	0.03

Calculation of velocity

Re=7000
rho=1.225 #kg/m3
D=0.015 #m
mu=0.000017894 #ns/ms
u=Re*mu/(rho*D)

Boundary condition

Material

SolidSimulation

Fluid-Air

Species

Solid-Aluminum

Fluid-N2, O2

Run Parameter

Simulation Parameter

Run Parameter

Simulation Time Parameter

Region

Fluid-Air

Solid-Aluminum

Boundary

solid_outerwall- Solid

Q=-10000W/m2

Solid_sidewall- Solid

inlet-Fluid

outlet-Fluid

Interface

Forward side- Fluid Region

Reverse Side- Solid Region

Physical Model

Turbulent- K-Epsilon RANS

Super-Cycle Modelling

This is changing to the case by case

Base Grid

this is changes by case by case

Result

Case1

output

Mesh

Temperature

Velocity

Pressure

Y Plus

Mean Temperature

Super-cyclic Stage

Case2

output

Mesh

Temperature

Velocity

Pressure

Y Plus

SuperCyclic Stage

Mean Temperature

Case3

output

Mesh

Temperature

Velocity

Pressure

Y-Plus

SuperCyclic Stage

Mean Temperature

GRID TEST Case 1 to 3

SUPERCYCLIC COMPARISON

MEAN TEMPERATURE

Case4

output

Mesh

Temperature

Velocity

Pressure

Y-PLUS

Super-cyclic

Mean Temperature

Case5

output

Mesh

Temperature

Velocity

Pressure

Y-Plus

SuperCyclic

Mean Temperature

Case6

Output

Mesh

Temperature

Velocity

Pressure

Y-Plus

SUPERCYCLIC

MEAN TEMPERATURE

SCS comparison Cases 4 to 6

SUPERCYCLIC COMPARISON

Mean Temperature

From the analysis Yplus=30 case6 we can find the boundary layer

Program

""" 
Conjucated Heat Transfer
Program by Jagaveerapandiyan
"""
import numpy as np

Re=7000
rho=1.225 #kg/m3
D=0.015 #m
mu=0.000017894 #ns/ms
yplus=30 # from analysis
u=Re*mu/(rho*D)

cf=0.026*pow(Re,((1/7)))
#friction
tow_w =(1/2)*cf*rho*pow(u,2)
#frictional velocity
u_t=np.sqrt(tow_w/rho)
# boundary layer
y=(yplus*mu)/(u_t*rho)
# uplus
uplus=u/u_t

print('velocity')
print('U=',u,'m/s')
print('Boundary layer')
print('y=',y,'m')

dy calculation

Conclusion

Study of conjugated heat transfer is done using Super cyclic stage

Case1 to 3

From Grid independent study finer mesh, mesh size=0.002 at SCS=0.005 whereas the response of change in Temperature is 630 with the same time.

Saturated mean temperature=700 changes from 0.1s to change in Temperature with 0.05s time difference

Accuracy of result is greater in finer mesh 0.002 m mesh size with same setup finer mesh accuracy result with more computation time

Case4 to 6

From Supercyclic Stage 0.01s the stage of response in Temperature difference in more to obtain until steady-state Temperature

Mean temperature function of Supercyclic Stage 0.03s response of time is more with change in temperature gradient response is lesser

Super cyclic Stage=0.001s stage of the Temperature gradient is more untile obtain SteadtState temperature

Finer mesh with SCS lesser condition the temperature Boundary layer capture in CHT is accuracy so it better to create a boundary layer to obtain accuracy result with least time

Reference

https://www.pointwise.com/yplus/index.html

https://www.learncax.com/knowledge-base/blog/by-category/cfd/basics-of-y-plus-boundary-layer-and-wall-function-in-turbulent-flows

https://www.simscale.com/forum/t/what-is-y-yplus/82394

Skill Lynk

https://skill-lync.com/knowledgebase/what-is-super-cycling