Laser heating and laminar flow

I'm trying to build a model to study the temperature distribution within a microfluidic channel. Liquid flows through the channel and heated by a laser beam. I used NITF for my modeling, and enter Q expressed in Gaussian equation as heat source. But the results I got looks odd. It seems no heat generated, the temperature remained as the initial temperature all over the channel. Is there anyone has idea on how to combine the laser heating with laminar flow properly?

Thanks.