Steam Boilers, Engines, Nozzles and Turbines
In recuperative air preheaters, the heat is transferred

Heat is transferred by bleeding some gases from furnace
From a metal wall from one medium to another
From heating an intermediate material and then heating the air from this material
By direct mixing

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Steam Boilers, Engines, Nozzles and Turbines
Degree of reaction is defined as the ratio of

Heat drop in moving blades to the heat drop in fixed blades
Heat drop in fixed blades plus heat drop in moving blades to the heat drop in moving blades
Heat drop in fixed blades to the heat drop in moving blades
Heat drop in moving blades to the heat drop in fixed blades plus heat drop in moving blades

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

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