Conjugate Heat transfer simulation by CONVERGE CFD
Title: Conjugate Heat transfer simulation by CONVERGE CFD
Objective: 1. Preapare model of hollow pipe with thickness & Setup in CONVERGE Studio.
2. Grid indepance test & see effect on pressure, temprature & velocity
3. Effect of supercycle stage interval on computation time & cycle
Theory :
What is CHT analysis
Computaational fluid dynamic (CFD) and more specifically conjugate heat transfer (CHT) analysis can accurately predict heat transfer by simultaneous solving all the relevant solid and flow field heat transfer processes, for example: conduction through solids, free and forced convection in the gases/fluids and thermal radiation.
Conjugate heat transfer corresponds with the combination of heat transfer in solids and heat transfer in fluids. In solids, conduction often dominates whereas in fluids, convection usually dominates. Efficiently combining heat transfer in fluids and solids is the key to designing effective coolers, heaters, or heat exchangers. Forced convection is the most common way to achieve high heat transfer rate. In some applications, the performances are further improved by combining convection with phase change.
Problem understanding
for this challenge hollow pipe with thickness of 0.005m is provided on outer side Aluminium material is provided. the heat flux -1000w/m2k is provided on solid wall through this it transfer to interface & from this it transfer to fluid region (air).
For inlet turbulent flow is considered with Reynold No 7000 & velocity is 3.71m/s
Inlet velocity calculation
`Re= (rho.v.D)/(mu)`
Re is given 7000
D=0.03m
density of air=1.161kg/m3
dynamic viscosity of air= 1.85 Ns/m2
`V= (Re. mu)/(rho.D)`
V=3.71m/s its used for inlet of velocity
Geometery
Geometery create
1. Prepare fluid region
2. Solid Region
3. Delete the intersections
Repari>delete>triangle>Any angle 20
4. Loft the for create the solid region & interface
Create>triangle>loft edge>lof edge by arc
5. Identify the inlet & outlet by patch
Repair>patch>list of edge by arc
CASE SETUP
1. Application type> Time based
2. Material>air
- Turn on Gas simulation & solid simulation (Aluminium material select)
- Species for Air> N2 & O2 For Solid > Aluminium
3. Simulation time parameter
- solver> Transient , Simulation mode> Full hydrodynamic
- Start time>0 sec , end time>0.5sec
- Initial & minimum time step=1e-7
- Maximum time step=1
- Navier stroke solver> Density based
4. Boundry name & Region name
1.Solid wall
heat flux apply on solid material -ve sign indicate heat transfer in to the solid body
2. solid thickness
3. Inlet
inlet velocity provide is 3.71m/s
4.outlet
for outlet static press. provided
5. Interface
interface where two region is created for forword side is liquid region & reverse side is for solid side
5. Region & Intialization
1. liquid Region>Pressure>101325pa & material>air
2.Solid region> material>Aluminium
6.Physic model
RNG>K-Epsilon model
7.Super cycling modeling
The basic idea of super-cycling is that the solver for the fluid domain is paused until the solver for the solid domain converges. This pausing is done in intervals that can be set by the user
8. Base grid >0.004m for grid dpendance test 0.003m ,0.002m
9.post variable selection > Y+criteria
10 0utput file
Grid Depedancy test
for grid depedancy test 0.004, 0.003, 0.002m mesh size is uses
Mesh
Mesh size: 4e-3m
Mesh size: 3e-3m
Mesh size: 2e-3m
CASE 1: 4e-3m
Temprature contour
for solid outer wall -1000w/m2k Heat flux & inlet velocity is 3.71 m/s is provided , so we can see that on outer side around 860 degree celcius temp. at the interface of outlet side is 500 degree celcius.
Velocity contour
As we provide the inlet velocity is 3.71m/s , but as air is pass from left to right side velocity is increases & which is higher up to 5m/s its due to the lower static pressure at outlet
Pressure contour
As at inlet neumann Boundry condition is provide for Pressure . so, we can see that at the inlet higher pressure up to 1bar & lower pressure at outlet.
Y PLUS
y + criteria is important for capture the good result nearest the solid wall boundry. basically y+ crtieria is decide the mesh should be fine or coarse near wall boundry. if y+ is in the range of 0-10 we can capture laminar flow. if y+ is in the range of 30-100 we can capture the turbulent flow.
CASE II: 3e-3m
Temprature contour
due to mesh size is decrease the y+ criteria is below the 10 , which is good for capture the temp. near the wall region . so, we can see that at the middel section temp is capture
Velocity contour
As we provide the inlet velocity is 3.71m/s , but as air is pass from left to right side velocity is increases & which is higher up to 5m/s its due to the lower static pressure at outlet
Pressure contour
As at inlet neumann Boundry condition is provide for Pressure . so, we can see that at the inlet higher pressure up to 1bar & lower pressure at outlet.
Y PLUS
CASE III: 2e-3m
Temprature contour
Velocity contour
Pressure contour
Y PLUS
Y+ is below the 7 . so, its good to capture the result near the wall surface.
Mean Temprature Solid Region
from the below plot we can see that as mesh size is decrease , it capture the correct temp for .002 m around 700 degree celcius the temp is steady state. There is main resaon for capture good result is due to refine mesh & y+ criteria is less than 10 which is good
Mean Temprature Fluid Region
for fluid region the mean temp. is steady at 350 degree celcius. so, for mesh 0.002m capture good result
Total cell count
for mesh 0.002m there is highest total cell is 35500 because of as mesh size is decrease the domain size is divide in to the small cell. for mesh 0.004m there is lowest total cell is 5000
Temprature animation
Pressure animation
Velocity animation
Grid depedancy test
from below table we can see that as mesh size is decrease the computation time , no. of cycle & total cell is increase
Supercycle stage
The basic idea of super-cycling is that the solver for the fluid domain is paused until the solver for the solid domain converges. This pausing is done in intervals that can be set by the user
Mean Temprature Fluid Region
as supercycle stage is increase it reaches in to steady state early .
Mean Temprature Solid Region
as supercycle stage is increase it reaches in to steady state early .
Super cycle stage test
from below table we can observe that as supercycle stage is increases the computaton time & no. of cycle is decreases. as pause time increases for fluid region the solid region is easily converge which help for reduction of computation time.
Overall conclusion
1. Conjugate heat transfer analysis is uses for analysis the heat transfer from solid to fluid through interface region.
2. Y+ criteria is very important in CHT analysis ,as it help for capture accurate temprature & heat transfer coeff.
3. It is observed that as supercycle stage is increases the computaton time & no. of cycle is decreases
4. As mesh size is decrease the computation time , no. of cycle & total cell is increase