why is resultant temp higher than surrounding fluid

[geping.song]

I am performing a transient thermal analysis using ANSYS Workbench for a round metal plate with several openings. The boundary conditions are convections through one side of the plate in contact with a fluid and through other sides in contact with air. The fluid is heated up in three steps from 70 deg.F to 250 deg.F.

I am surprised that the resultant maximum temperatures on the surface in contact with the fluid are higher than the fluid temperature, e.g. in step 3, the fluid is 250 deg.F, the resultant maximum temperature on that surface is 254.8 deg.F. and occurs on the edges of the openings.

The film coefficients used are 50 BTU/hr.in2.F for the fluid and 0.01 BTU/hr.in2.F for air.

Does anyone know why this occurs ?
I would appreciate any advice on this.

Thank you.

Geping Song

GE Hitachi Nuclear Energy Canada