I need advice to choose proper thermal boundary condition on the wall of furnace and burners of pulverized coal combustion boiler. I am not sure that t=constant is satisfied condition which is used in many cfd computations. Insted I think using heat transfer coefficient is better? I found in literature just a few works, but value of coefficient is very different from 150 to 10000 and more.
In case an outer wall is of interest then this would be better to specify the heat flux which would incorporate the convective heat transfer (1st term) and the radiative heat transfer (2nd term). The 1st is calculated indeed with the use of COH, which could be evaluated using e.g. Chu and Churchill expression. The later comes from the Stefan-Boltzmann law.
If you are modeling only steam generation inside tubes then you can use heat flux boundary condition
If you are modeling only coal combustion inside furnace then you can use negative heat flux (energy taken by fluid e.g. water/steam)
and If you are modeling both then boundary condition will be coupled
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