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-   -   chtMultiRegionFoam violates energy balance (https://www.cfd-online.com/Forums/main/244760-chtmultiregionfoam-violates-energy-balance.html)

MattiaGalanti August 26, 2022 11:24

chtMultiRegionFoam violates energy balance
 
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Hello everyone. During the past couple of weeks I was working on a heat transfer problem.

I'm using "chtMultiRegionSolver" but the problem is that using the function "wallHeatFlux" to calculate the overall energy input, my energy balance is not closed.

Here's my setup:

The system consist in CO2 flowing in a box which is heated by the walls and a rectangle which is also heated by the walls. I'm running on a 300x300 orthogonal grid.

--------------------------------------------For FLUID region---------------------------------------------------

FVSCHEMES:
ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
}

divSchemes
{
default none;

div(phi,U) Gauss limitedLinearV 1;
div(phi,Yi) Gauss limitedLinear 1;
div(phi,h) Gauss limitedLinear 1;
div(phi,K) Gauss limitedLinear 1;
div(phi,p) Gauss limitedLinear 1;
div(phi,epsilon) Gauss limitedLinear 1;
div(phi,k) Gauss limitedLinear 1;
div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear orthogonal;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default orthogonal;
}

FVSOLUTION:
solvers
{
"(rho|rhoFinal)"
{
solver PCG;
preconditioner DIC;
tolerance 1e-7;
relTol 0;
}

p_rgh
{
solver GAMG;
tolerance 1e-7;
relTol 0.01;
smoother GaussSeidel;
}

p_rghFinal
{
$p_rgh;
tolerance 1e-7;
relTol 0;
}

"(U|h|k|epsilon|R)"
{
solver PBiCGStab;
preconditioner DILU;
tolerance 1e-7;
relTol 0.01;
minIter 1;
}

"(U|h|k|epsilon|R)Final"
{
$U;
tolerance 1e-07;
relTol 0;
}
}

PIMPLE
{
momentumPredictor no;
nOuterCorrectors 1;
nCorrectors 2;
nNonOrthogonalCorrectors 0;
pRefCell 0;
pRefValue 1e5;
}

relaxationFactors
{
equations
{
"h.*" 1;
"U.*" 1;
}
}

--------------------------------------------FOR SOLID REGION----------------------------------------------
FVSCHEME
ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
}

divSchemes
{
default none;
}

laplacianSchemes
{
default none;
laplacian(alpha,h) Gauss linear orthogonal;

}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default orthogonal;
}

FVSOLUTION
solvers
{
h
{
solver PCG;
preconditioner DIC;
tolerance 1e-7;
relTol 0.01;
}

hFinal
{
$h;
tolerance 1e-07;
relTol 0;
}
}

PIMPLE
{
nNonOrthogonalCorrectors 0;
}


As boundary conditions I'm using the "compressible::turbulentTemperatureRadCoupledMixed ".


On a qualitative way, the results are quite nice, but the energy balance after 300s is not fullfilled. From a python script I'm able to extract:
TEMPERATURES
Phi averaged outlet temperature is 363.05374938 K
Fluid To Solid Temperature: 499.89102129 [K]
Solid To Fluid Temperature: 499.89102129 [K]

ERROR on Solid Interphase Temperature: 0.00000000 % (this check is ok)

MOLAR FLOWS
Inlet molar flow is 0.00000030 kmol/s
Outlet molar flow is 0.00000030 kmol/s

ERROR on molar flows is 0.00006608% (this check is kinda ok)

WALL HEAT FLUXES
Heat flux from left wall to fluid: 0.30404273 W
Heat flux from right wall to fluid: 0.15984328 W
Total heat provided to fluid: 0.46388601532
Heat flux from right wall to solid: 0.11319697 W
Total heat provided to system: 0.57708298679

ENTHALPIES
Inlet fluid Enthalpy : 0.24258751 W
Outlet fluid Enthalpy : 0.74487901 W
Fluid delta H: 0.50229150 W
Fluid calculated delta H: 0.49567707 W (with cp(T) integration)
ERROR on fluid heat balance: 12.96026541 %
ERROR on fluid heat balance (calculated): 14.10644877 %

INTERPHASE HEAT FLUXES
Fluid To Solid heat flux: 0.14793788 W
Solid To Fluid heat flux: -0.14803772 W
ERROR on interphase duty: -0.06744383 %

HEAT BALANCES HEAT FLUXES
Solid heat balance: solid wall - interphase = -0.03484075 J/s
Fluid heat balance: fluid walls + interphase - deltaH: 0.10953239 J/s
Global heat balance: fluid walls + solid wall - deltaH: 0.07479149 J/s
0.57708298679

Have you experienced the same? I really don't know what to do with that.


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