I understand mass diffusion. But what is the meaning of 'diffusion' which converts the kinetic energy to rise in pressure in a stator/diffuser?

  • $\begingroup$ I find this a good source: Engineering Thermodynamics, Work and Heat Transfer by Rogers and Mayhew. $\endgroup$ – Solar Mike May 23 '20 at 7:27
  • $\begingroup$ @SolarMike Thank you. But I don't have access to that book and am not finding any pdf version. $\endgroup$ – GRANZER May 23 '20 at 8:20
  • $\begingroup$ 4th edition easily available on Amazon.com, see amazon.com/Engineering-Thermodynamics-Work-Heat-Transfer/dp/… $\endgroup$ – Solar Mike May 23 '20 at 11:19
  • $\begingroup$ @SolarMike Yes and I am sure it's worth the price, but I can't afford it right now. $\endgroup$ – GRANZER May 23 '20 at 11:32
  • $\begingroup$ It explains what you are asking... so what value is that worth? $\endgroup$ – Solar Mike May 23 '20 at 11:45

The word "diffuse" is used in different contexts in both engineering and in the vernacular. A general definition would be similar to, as a verb, "spread out over a larger area, space, or number of participants or carriers."

With momentum diffusion, a more concentrated area of fluid momentum is spread out to a larger flow volume and to more fluid particles that have their mean velocity increased.

With heat diffusion, a concentrated area of molecular motion is likewise spread out, with larger numbers of molecules assuming more vibrational energy.

With mass diffusion, a concentration of molecular species among other species is spread out to a larger or more distant region, reducing the concentrations of the named species.

With a fluid diffuser, a concentrated area of kinetic energy of fluid motion gets directed to a region where the kinetic energy is converted (diffuses) to a higher static pressure. With subsonic flow, this requires an increase in flow area, but with supersonic flow, this requires a drop in flow area.


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