Steam Boilers, Engines, Nozzles and Turbines
Water tube boilers are those in which

Flue gases pass through tubes and water around it
Water passes through the tubes and flue gases around it
Change in enthalpy
Work is done during adiabatic expansion

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Steam Boilers, Engines, Nozzles and Turbines
In designing air preheaters, the important design consideration is that

Handling and maintenance should be easier
Approach temperature should be as low as possible
Heat transfer area should be optimum
Stack gases should not be cooled to the dew point

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