Please, somebody know web pages about fundamentals, theory, design about heat transfer and Flow of hot gases in ducts and stacks. I am studying a practical problem about those areas. Thanks.
I did consulting in this area for years. Check power plant publications for papers on this. The pressure drop is from the hydrostatic head inside the stack. You need to do a thermodynamic balance to calculate the temperature drop inside the stack according to that pressure drop. Don't forget to include heat loss to the environment throughn the stack walls. You also need to watch for condensation and account for the heat released if you have condensation.
If there is no condensation and no heat loss, the temperature drop is the adiabatic lapse rate. I hope this helps