energy absorption instead generation
 

Hello there,

I face ti very interesting thing. My problem is related to viscous dissipation. My job is 2d axisymmetric tube. The non-newtonian fluid is the flowing medium. The inlet temperature is 19°C. The tube external wall is cooled by water (temp of 5 °C). In the core of flow, where there is almost no velocity gradient, I can clearly see drop temperatures about 2°C. In near wall region, there is heat generation, thus temperatures are more than 19°C.
Could anybody please explain to me this strange artificial heat absorption. I cannot even mathematically imagine, how it is even possible.
many thanks!!
Honza

viscous heating
 

any idea, please!! ?? come on, guy. I do know..