A Common Debate: Axial or Radial Turbine?

Comparison of efficiency against power output for axial flow and radial inflow turbine configuration

The question always remains, which is better: axial or radial? But with that question are sub questions: Which application? Which fluid? What results are you looking for exactly?

In automobiles for waste heat recovery, we believe that radial inflow turbines are more suited for use. Here’s why:

  • Radial inflow turbines are highly efficient at very low power output with efficiency as high as 90%.
  • The pressure ratio in Radial stages used for ORC turbines are very high and working temperatures are very low.
  • The volume flow rates are high relative to steam cycles.

This month and next month we are hosting our brand new turbomachinery course on Design of Waste Heat Recovery Systems scheduled for February 17-21 in Bangalore, India and March 3-7 in Boston, USA. We dive deeper into these results and more. Why not join us?

8 thoughts on “A Common Debate: Axial or Radial Turbine?

  1. Questions:
    1) What are the reasons for efficiency differences at low power?

    2) Do these curves apply to hydraulic turbines? Where is their crossover?

    1. Hi Jim,

      Thank you for your questions! At low power (due to the small channel size), secondary losses are much higher for axial turbines than for radial. Also the power loss due to the leakages is more significant for small axial turbines.

      This curve was obtained for compressible fluid (R245fa fluid in superheated region). Thus it may be applicable for other superheated fluids (steams), though only qualitatively (the efficiency scale may be different).
      The application of them to hydraulic turbines is hardly possible due to the different nature of fluid (compressible and incompressible). To obtain such curves for hydraulic turbines, a similar study needs to be performed. But keep in mind that the type of hydraulic turbine is also important. What type are you interested in? As you can see the charts crossover at around 1.2MW.

  2. Why for the same inlet conditions for both, we experienced higher efficiency for the axial and higher power out for the radial?
    How it is possible to have higher power output and lower efficiency at the same time?

  3. The plot is not comparing the same turbines running at different pressure ratios. It is comparing different turbines designed for the RATED power. Does that make sense?

    1. Hi Colin,

      Thanks for the comment! Yes, this is correct. Each point on the graph that define both curves are different turbines to evaluate the potential max. efficiency attainable for different power requirements.

  4. And so an appropriate set of comparison curves for hydraulic turbines would be?

    1. Thanks for the comment Jim! It’s hard to say without more information about the specs, application, etc. If you had something specific in mind, we’d be more than happy to check into it for you. You can contact us at Info@Softinway.com. Hope this helps!

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