[hjasak]

That's because you're in the code you are setting the patch value of the fixedGradientFvPatchScalar field:

fixedGradientFvPatchScalarField& buffer=
refCast<fixedgradientfvpatchscalarfield>(T.boundar yField()[patchI]);
forAll (buffer, faceI)
{
buffer[faceI] = 0.1*(293.-T.boundaryField()[patchI][faceI]);
}

and you should be setting the gradient() instead. Have a look at fixedGradientFvPatchField.H.

So:

fixedGradientFvPatchScalarField& buffer=
refCast<fixedgradientfvpatchscalarfield>(T.boundar yField()[patchI]);
scalarField& grad = buffer.gradient();

forAll (grad, faceI)
{
grad[faceI] = 0.1*(293.-T.boundaryField()[patchI][faceI]);

}

(if that is what you want).

Enjoy,

Hrv