UDF sources for energy equation

el

Dear all, Who can help me? I study flow in 2D geometry (plane channel) with zero- initial and boundary conditions (velocity=0, temperature=300K at the inlet and at the channel end). I add a source to the energy equation in the form of -coskx. As a result I get temperature distribution along the channel in the form of -coskx. However, if solving analytically, the result will be +coskx, because only second derivative of temperature with respect to y (or r in axisymmetrical case)remains in equation and the derivative and the source enter the same side of the equation. el