Conjugate Heat Transfer Simulation
Objective:
To setup Conjugate heat transfer flow simulation with different conditions. Reynolds number must be 7000 at inlet. To perform grid dependence test. To determine the effect of supercycle stage interval.
Geometry and case setup:
The pipe constructed has an inner diameter of 15 mm and outer radius of 20 mm with length of the pipe being 200mm. The pipe is heated with a constant heat flux of 10000 W/m^2. The simulation was run using transient solver with RNG k - `epsilon`turbulence model.
calculation of velocity:
Re = (rho*V*D)/(Dynamic viscosity)
as we know that reynold\'s nmber at the inlet = 7000
velocity (v) = (Re*Dynamic viscosity)/(rho*D) = (7000*18.63*10^(-6))/(1.165*0.03)
velocity (v) = 3.73m/s
Grid dependence test:
The simulation was tested for three different meshes 0.004,0.003,0.002 respectively. Super cycling stage interval was taken 0.05 seconds for all these three cases.
Results:
Base Grid 0.004m:
Mesh:
Temperature:
Velocity:
Yplus:
y+ is a non-dimensional distance. It is often used to describe how coarse or fine a mesh is for a particular flow pattern. It is important in turbulence modeling to determine the proper size of the cells near domain walls. The turbulence model wall laws have restrictions on the y+ value at the wall. As the simulation runs for different mesh sizes we can observe that y plus value increases with increase in grid size
Base Grid 0.003m:
Mesh
Temperature:
Velocity:
Yplus:
Base Grid 0.002m:
Mesh:
Temperature:
Velocity:
Yplus:
Effect of supercycle stage interval:
supercycle stage interval 0.01s:
supercycle stage interval 0.02s:
supercycle stage interval 0.03s:
Plots:
Grid dependence test:
The base grid simulation (4mm) was repeated for different grid sizes (3mm,2mm) in order to study the effect of grid. The below plots shows the mean temperature in fluid region and in solid region.
Variation of mean temperature in fluid region
From the above plot we can observe that in fluid region as we increase the grid size (more finer grid) the mean temperature increases.
variation of mean temperature in solid region
From the above plot we can observe that in solid region as the grid becomes more finer the mean temperature decreases. From the above plots it is evident that the simulation is grid dependent as reduction grid sizes has resulted in changes in output.
Effect of Supercycle stage interval:
The base grid smulation was run with a supercycle stage interval of 0.05s. To study the effect of supercycle stage interval, the simulation was repeated with different supercycle stage intervals 0.03,0.02,0.01s.
Variation of mean temperature in fluid region
Variation of mean temperature in solid region
From the above plots both fluid region and solid region we can observe that the simulation shows non dependence on super cycle stage interval as all converges to a definite value so irrespective of supercycle stage interval the simulation converges to a definite value