Converging Diverging Nozzle

[Edson]

As being fresher to this industry curious to know lot more subjective things in this field. While reading about hvof technology i have heard about converging-diverging nozzle, but not clear about the concept of this nozzle! Can anybody clear my thought? How differently this kind of nozzle works?

Experts are requested to put their thoughts as now less replies are being observed on technical things which is mostly expected from a reputed online forum like this. People now are more interested in commercialization here rather than being part of some interesting technical discussion. I request please participate.



Regards
Dany

[djewell]

A converging-diverging nozzle is used to accelerate the gas flow above sonic velocity. This, in turn, accelerates the particles more, but reduces their dwell time in the flame. When particles hit the surface of a part with this higher velocity, they pack together more tightly and form a more dense coating.

There is a limit to this. Accelerating the gas by expanding it also cools it, so particles get cooler. If they get too cool, they do not bond to the coating surface. They simply bounce off and get sucked into the dust collection system in your spray booth.

[Parat Tech]

Dear Friend,

Let me make the principle of working very simple, water going through a tube if you pinch it somewhere in between speed gets increase. Similarly this type of nozzle works where velocity of particles is increased to supersonic speed. dense & less porous coatings is obtained as a result.

This nozzle is used in rocket engine & same is been used in hvof process.



Thanks

Harish Dhandiya
https://www.parattech.com

[loriolo]

Hi Daniel
In a supersonic HVOF system, there is a simple design, it consist of a high pressure chamber, where a mix of gases is ignited, then gases at high pressure enter a special like Laval-nozzle or barrel, which is a tube with a pinch inside, before the barrel pinch, there is a convergent zone, in order to create a supersonic pressure wave, so while gasses enter the barrel , it accelerates as it is compressed, at the pinch zone, gases matches about sound speed, and after which hole is divergent, gases speed becomes supersonic as it expand inside the divergent zone of the barrel. So convergent at the beginning, then quite cylindrical at the pinch zone, and divergent at the end of the barrel.