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

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

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Steam Boilers, Engines, Nozzles and Turbines
The effect of friction on the flow of steam through a nozzle is to

Decrease the mass flow rate and to decrease the wetness of steam
Increase the exit temperature without any effect on mass flow rate
Increase the mass flow rate and to increase the exit temperature
Decrease the mass flow rate and to increase the wetness of steam

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