Hi, I am trying to solve a conjugated heat transfer problem that consists of an tube (1 1/2")and rectangular fins (100x100x2 mm) attached to tube (centered) and outside there is a flue gas stream. Actually this is a finned tube economizer bundle. I can not obtain the temperature contours on the fin surfaces, i give temperature value inside of the tube and fin surfaces seem completely the same temperature. Anyone have an opinion? Thanks a lot.

Check if the fins are attached to the cylinder.... check the heat balance at the interface of solid and gas...

Do you see contours on the tubes?

Try a simple geometry first and once you get good results move to real complex geometry...

What's material of the tube/fin? Do you have right thermal BCs, heat generation and or flow rate with temperature etc...

Is your enegery term ON in calculations?

I modeled fins on the tube surfaces seperately attached, and alternatively united tube and fins; then assumed tube inside temperature constant. Fluid and solid (tube and fin) materials are default materials (air and al.) Since i assumed tube temperature constant i just could examine temperature contours on the fin surfaces and this is problem. When i used heat flux balance, i saw very little amount of heat transfered to the tube surface. The energy therm is ON. Thanks for your interest.

Try applying heat transfer coefficient on the fin... The contour would depend on whats the max and minimum temperature on the fin and tube... many a times the material conductivity could be so high that you get almost isothermal condition... when you plot you see only small variation...

WHy don't you model the fluid as well to capture the thermal boundary layer then you might get better results...

Boundary conditions are important to predict thermal behaviour...

Best of luck... enjoy...

AJ