# temperaturejump externalWallHeatFluxTemperature

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April 27, 2017, 16:14
temperaturejump externalWallHeatFluxTemperature
#1
New Member

Join Date: Jul 2014
Posts: 13
Rep Power: 11
Dear all,

I'm trying to verify the externalWallHeatFluxTemperature BC on a (geometrically) simple case using buoyantBoussinesqSimpleFoam in OF30x. The domain is a box of 2x2x2 m and heat is injected via the 'floor' boundary of T:

Code:
```floor
{
type            groovyBC;
value           uniform 293;
valueExpression "293";
fractionExpression "0";
variables
(
"heatFlux=1;"
"rho=1.225;"
"Cp=1000;"
"myNu=1.0e-5;"
"Pr=0.9;"
"alpha=myNu/Pr;"
);
}```
i.e. 1 W/m2 * 4m2 gives me 4 Watt (in controlDict this is monitored). At the top of the domain the temperature BC is:

Code:
```ceiling
{
type            externalWallHeatFluxTemperature;
kappa           lookup;
Ta              uniform 273; // external air temperature
h               uniform 2; // external heat transfer coefficient
// q uniform 1000;
//thicknessLayers (0.0); // thickness wall between in and outside
//kappaLayers     (0.01); // equivalent heat conductivity wall
kappaName       alphaEff;
value           uniform 273; // initial wall temperature
}```
Without the kappaLayers it's like a zero-thickness wall with just heat transfer between the wall and the outside domain (temperature Ta). So:

Code:
`Q = h*(T_wall - T_outside)*Area`
Q = 4W, area = 4m2 and h = 2 W/(m2*K), so I would expect a 0.5 degrees temperaturejump between the wall and the outside, meaning T_wall=273.5 K. It turns out to be around 274.6 K, see the attached image.

It would be great if someone could comment on this discrepancy (I have attached the case) and/or share experience using this BC.

Thanks!
Attached Images
 heatFlux.png (33.0 KB, 18 views) temperatureAlongVerticalLine.jpg (61.1 KB, 18 views)
Attached Files
 externalWallHeatFluxTemperatureTestCase.zip (22.7 KB, 5 views)

 April 28, 2017, 09:03 Woops #2 New Member   Join Date: Jul 2014 Posts: 13 Rep Power: 11 Woops, no. That's near the wall. The temperature of the wall itself is 273K. Hmmm...

 Tags boundary condition, heat transfer, verification

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