[Beryl]

Hi,
I am having some problems of fluent to accurately model the following unsteady heat transfer model:

I have a fluid-solid interface problem: a steel pressure vessel (diameter:10mm, length:50mm) containing water and a thin metal wire(diameter:25um,length:30) put in the middle of the vessel. Heat is applied to the suface of the thin metal wire,then the heat transfer will cause natural convection of the water in the vessel.

however,after running the simulation with 100 time steps of approximate 4seconds,the temperature of the surface of thin metal wire increases linearly with time,but from my experiment the temperature should be increase lower and lower. And the residual of x,y velocity is no less than 10e-2,the residual of continuity is stable in 10e-3.

I am using the following conditions in fluent:
2D Axisymmetric Segregated unsteady 2st order Implict Solver, energy equation, laminar viscous flow, Boussinesq for density, PISO pressure-velocity,standard Pressure discretization, second order Upwind for Momentum and Energy.
Boundary condition: the same heat flux in solidwall(the thin wire surface) and solidwall-shadow. My boundary condition right?

Am i missing something? Any suggestions?

Thank you very much!