Steam Boilers, Engines, Nozzles and Turbines
Primary air is the air used to

Air delivered by forced draft fan
Convert CO (formed in lower zone of furnace) into CO₂ at higher zone
Transport and dry the coal
Provide air around burners for obtaining optimum combustion

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Steam Boilers, Engines, Nozzles and Turbines
For a Parson's reaction turbine, if α₁ and α₂ are fixed blade angles at inlet and exit respectively and β₁ and β₂ are the moving blade angles at entrance and exit respectively, then

α₁ = α₂ and β₁ = β₂
α₁ < β₁ and α₂ > β₂
α₁ = β₂ and β₁ = α₂
α₁ = β₁ and α₂= β₂

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