Diffuser types question

[chertzyb]

just out of interest there are two basic diffuser types I've noticed that are used on centrifugal compressors. The first which seems to be the older style is one where the vanes radiate outwards and continue seamlessly around the 90 degree bend as re air takes on axial flow. The other and seemingly more contemporary configuration is where two sets of vanes are integrated so that an initial set of radial vans provide outward channelling followed by a set of axial vanes adorning the circumference of the diffuser plate.

The question is weather there is a name for each system? Furthermore does one system have advantages over the other. I always assumed the first system described here was easier to manufacture and the second more difficult but probably more efficient.

Just wondering as my first attempt many years ago employed the first system and my engine never ran. Regardless, I'm using the newer configuration now but would like to know if anyone can impart their knowledge / experience.

Thanks !

[racket]

Hi

I've made both types at different times , its simply been a preference thing for me , both types have worked .

The separated type with some radial and some axial is the prefered type by the commercial guys .

Cheers
John

[chertzyb]

Did you notice any performance differences ? Guessing not or you'd have mentioned it. Visually the second type appears as though it would be more efficiently. The current one we are working and already finished is the second type - I'll upload a picture later ...

[Johansson]

I´ve always considered the version with one continuous vane the more efficient one, it has a longer and smoother path of diffusion since it guides the air all the way around the corner instead of just dumping the air and let it find its own way around the corner and into the combustion section.

[chertzyb]

Kamps book says the same - the continuous vanes are more efficient whereas the two stage configuration is 'preferred' by manufacturers. I would venture to guess that construction methods are taken into consideration for example the ability to attach the outer housing to annular vanes is easier than via the funky curves of the continuous. Either way it's probably a very minor performance gain using continuous curved system

[jetjeff]

I have a KingTech 80 commercial turbine. The diffuser doesn't use the secondary axial vanes. The former is relatively easy to make on a mill with a rotary turntable.

Jeff

[jetjeff]

[smithy1]

I also have an old Kingtech K80E....small world. Also have a K180G and a very new K45G...the K45 is tiny, outer case diameter is only 3" (~75mm..!).

Cheers,
Smithy.