page_title: Degree of reaction
section_title: 50% reaction
hierarchical_section_title: Degree of reaction / Choice of reaction (R) and effect on efficiency / 50% reaction
caption_attribution_description: English: This figure shows the enthalpy vs entropy diagram for the case where degree of reaction is less than half in a compressor
context_page_description: In turbomachinery, Degree of reaction or reaction ratio is defined as the ratio of the static pressure drop in the rotor to the static pressure drop in the stage or as the ratio of static enthalpy drop in the rotor to the static enthalpy drop in the stage.
  Degree of reaction is an important factor in designing the blades of a turbine, compressors, pumps and other turbo-machinery. It also tells about the efficiency of machine and is used for proper selection of a machine for a required purpose.
  Various definitions exist in terms of enthalpies, pressures or flow geometry of the device.
  In case of turbines, both impulse and reaction machines, Degree of reaction is defined as the ratio of energy transfer by the change in static head to the total energy transfer in the rotor i.e.
  .
  For a gas turbine or compressor it is defined as the ratio of isentropic heat drop in the moving blades to the sum of the isentropic heat drops in the fixed blades and the moving blades i.e.
  .
  In pumps, degree of reaction deals in static and dynamic head. Degree of reaction is defined as the fraction of energy transfer by change in static head to the total energy transfer in the rotor i.e.
  .
context_section_description: The degree of reaction contributes to the stage efficiency and thus used as a design parameter. Stages having 50% degree of reaction are used where the pressure drop is equally shared by the stator and the rotor for a turbine. 
  This reduces the tendency of boundary layer separation from the blade surface avoiding large stagnation pressure losses.
  If R= ​¹⁄₂  then from the relation of degree of reaction,|C| α2 = β3 and the velocity triangle (Figure 4.) is symmetric. The stage enthalpy gets equally distributed in the stage (Figure 5.) . In addition the whirl components are also the same at the inlet of rotor and diffuser.
caption: Figure 6. Stage enthalpy for Reaction less than half
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