[ashghan]

Hey Guys,

I am using the externalWallHeatFlux boundary condition on one of my walls in a room and here is how I give the condition.

wall
    {
            type            externalWallHeatFluxTemperature;
            kappa           fluidThermo;       // fluidThermo, solidThermo or
                                               // lookup
            //q               uniform 1000;      // heat flux / [W/m2]
            Ta              uniform 273.15;     // ambient temperature /[K]
            h               uniform 25.0;      // heat transfer coeff /[W/K/m2]
            thicknessLayers (0.1); // thickness of layer [m]
            kappaLayers     (0.05);          // thermal conductivity of
                                               // layer [W/m/K]
            value           uniform 294.15;     // initial temperature / [K]
            kappaName       none;

About the case. I have a room with an inlet and outlet and I supply air with a temperature of 285K at 0.25 m/s velocity at the inlet and would like to investigate how the temperature distribution is affected with that and with the external wall. To my surprise I get a temperature of less than 273K on the externalwall-patch. How can this be possible as the minimum temperature specified is 273.15K.

Does anybody know where am I going wrong? I am using buoyantSimpleFoam solver for my case. Here is the attached picture of the wall. Hope someone here has got an idea

Best
Ashwin

[vasava]

Can you post your temperature file here?

[ashghan]

dimensions      [0 0 0 1 0 0 0];

internalField   uniform 294.15;

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform 285;
    }
    outlet
    {
        type            zeroGradient;
    }
    box
    {
        type            zeroGradient;
    }
    wall
    {
            type            externalWallHeatFluxTemperature;
            kappa           fluidThermo;       // fluidThermo, solidThermo or
                                               // lookup
            //q               uniform 1000;      // heat flux / [W/m2]
            Ta              uniform 273.15;     // ambient temperature /[K]
            h               uniform 25.0;      // heat transfer coeff /[W/K/m2]
            thicknessLayers (0.1); // thickness of layer [m]
            kappaLayers     (0.05);          // thermal conductivity of // layer [W/m/K]
            value           uniform 294.15;     // initial temperature / [K]
            kappaName       none; 
    }
}

[vasava]

Originally Posted by ashghan

....I supply air with a temperature of 285K at 0.25 m/s velocity at the inlet .... I get a temperature of less than 273K on the externalwall-patch. How can this be possible as the minimum temperature specified is 273.15K.

Your inlet temperature is 293.15 K (20 C) and ambient temperature is 273.15 K (0 C). Also you have given value uniform 294.15; I think you meant to use 294.15 K and used 273.15 K instead.

[ashghan]

Hi vasava,

Sorry I replaced it with the correct file now. Since it's been a long time I got confused with the files.

Best
Ashwin

[ntn]

Is Ta must be less than bulk fluid temperature?
I have tried externalWallHeatFluxTemperature boundary condition in simple pipe flow. Simulation run perfectly when ambient temperature is less than bulk fluid temperature.
When ambient temperature greater than bulk fluid temperature simulation get diverged.

Please help me .

Regards
Nitin Chauhan