Week 6: Conjugate Heat Transfer Simulation
Conjugate Heat Transfer
The term conjugate heat transfer (CHT) is used to describe processes which involve variations of temperature within solids and fluids, due to thermal interaction between the solids and fluids. The exchange of thermal energy between the two physical bodies is called study of Heat Transfer, the rate of transferred heat is directly proportional to the temperature difference between the bodies. This 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 for example liquid water to vapor phase change.
Heat transfer in solids and heat transfer in fluids are combined in the majority of applications. This is because fluids flow around solids or between solid walls, and because solids are usually immersed in a fluid.
To perform a Conjugate Heat Transfer Simulation through a pipe with grid dependancy test and varing supercycle stage intervals.
Calculations for Velocity
Re= 7000
Dynamic Viscosity - 1.81*10^-5 `(kg)/(ms)`
Density- 1.225 `(kg)/m^3`
Diameter- 0.03 m.
Re = (rho*V*D)/(Dynamic viscosity)
V=`(7000*1.81*10^-5)/(1.225*0.003)`
V= 3.447 m/s.
Geomerty
Above is the geometry that isused for the CHT simulation.
Boundary Conditions
Soild_outer_wall
Velocity BC- Wall Motion type-Stationary, Surface movement-Fixed
Temperature BC- Heat Flux- -1000 `W/m^2`
Solid_side
Velocity BC- Wall Motion type-Stationary, Surface movement-Fixed
Temperature BC- Zero Normal Gradient
Inlet
Pressure BC- Zero Normal Gradient
Velcity BC- 3.447 m/s
Temperature BC- 300 K
Outlet
Pressure BC- 101325 Pa
Velocity BC- Zero Normal Gradient
Interface
Velocity BC
Forward
Region- Fluid Region
Wall Treatment- Law of Wall
Temperature BC- Law of Wall coupled
Reverse
Region- Solid Region
Wall Treatment- Slip
Temperature BC- Specified Value Coupled
Region and Initialization
Fliud Region
Temperature- 300 K
Pressure- 101325 Pa
Species- O2 and N2
Solid Region
Temperature- 300 K
Species- Aluminum.
Super-Cycle Modelling
For Grid Dependancy test the super-cycle stage interval is set to 0.05 seconds.
Then for the variations the intervals are set to 0.01 sec ,0.02 sec and 0.03 sec.
Base Grid
For Grid Dependancy test the grid size is set to 0.004 m base grid size, 0.003 m and 0.002 m.
Then for the super-cycle intervals the grid size is set to 0.004 m that is base grid size.
Grid Test
Below are the meshs of the varing grid size from 0.004m to 0.002m.
Base Grid of 0.004 m
Grid Size of 0.003 m
Grid Size of 0.002 m
Cell Count of the Meshs
Above is the cell count for the varing grid sizes.The largest is for the 0.002m grid size which is above 36000 cell count.
Temperature Plots
Above plot is the Temperature Plot at the outlet. Maximum temperature at the outlet is for the base grid which is almost at 900 K and the finer grid has temperature of 750 K at the outlet.
Temperature Contours of different Grids
Base Grid
0.003m Grid
0.002 m Grid
In the above graphs of different grid sizes the heat transfer rate varies differently with respect to the grids meaning the heat follow rate is more smother and clearer in the 0.002 m grid size when comparing to other grid sizes. The tempeature is more at the outlet raning in between 500 to 600 K.
Y+ Contours
When looking at the Y+ contours we can see a turbulent region for the 0.004 m and 0.003 m meshes are extending from the inlet region till the middle region meaning it has greater value of Y+ more than 30. But in the finer mesh case the laminar region is in the begining meaning the case is more refined when compated to the other two grid sizes and also the Y+ values is in the Laminar regions.
Super-Cycle Intervals
0.01 Interval
0.02 Interval
0.03 Interval
Above are the temperature plots with 0.004 m grid size with varing interval of supercycle stages. The temperature of the grids are same throughout the cases with minimum temperature of 300 K at the inlet to a max temperature of 700 K within the solid and for the solid walls the temperature is about 850K.
Super-Cycle Plot
Above the supercycle plot where the temperature converges 650 K for all the intervals at the end of the simulation.
Y+ Contour
The Y+ contour for this case irrespective of the intervals are the same at the begining the region is turbulent but as it progressed the region is in laminar at the end of the simulation.
Simulation Time
Super-Cycle Interval
| SGS | Simulation Time(sec) |
| 0.01 | 319.766577 s |
| 0.02 | 346.576104 s |
| 0.03 | 351.808274 s |
Grid Size
| Grid Size (m) | Simulation Time(sec) |
| 0.004 | 398.281962 s |
| 0.003 | 1193.781407 s |
| 0.002 | 5840.229973 s |
Conclusion
From the simulation we can see that varing the grid size varies the temperature distribution and Y+ function is also varies.
In terms of simulation time finer the mesh longer the simulation time and also the simulation time varies with the SGS parameter.