Monotube Flash Boiler Design

[Steamchick]

Just a word on caution.
Corderite has a long life up to 900deg.C.
Stainless steel, should be good up to 1100deg.C. maybe even 1200 C?
Nickel, chrome and Tungsten for higher temperatures?
K2

 

[Toymaker]

Just a word on caution.
Corderite has a long life up to 900deg.C.
Stainless steel, should be good up to 1100deg.C. maybe even 1200 C?
Nickel, chrome and Tungsten for higher temperatures?
K2

I'm pretty much limited to what I can find on eBay, AliExpress, etc. and at the moment the only ceramic discs I can find are Alumina ceramic, aka: aluminum oxide (Al2O3). A few Google searches say it's a good choice for my restrictor disc/plate as it's max temp can go up to 2000 C and can only be machined with diamond tooling. Maybe I'll buy a piece just to see how it holds up.

 

[Steamchick]

That ceramic is beyond my experience.
K2

 

[Toymaker]

I finally took a video of the Air-Oil separator. The first silicone tube shown in the video is from the compressor and shows the suspended oil moving through the yellowed tube. The second tube shown is the output from the Air-Oil separator, and as the video shows, very little oil is present.

Photo is for reference:

 

[Steamchick]

But is that air clean enough? Does it need a secondary separator? Unfortunately, there is a pressure drop at the separator... Have you put pressure gauges in line to see what pressure drop yours produces?
I am sure in due course you'll quantify the air-flow and pressure at the final output to be sure you have adequate clean (Oil-free) air.
I think you previously described the return of oil from the separator to compressor. Is this working OK?
I like the sphere!
K2

 

[Toymaker]

But is that air clean enough? Does it need a secondary separator? Unfortunately, there is a pressure drop at the separator... Have you put pressure gauges in line to see what pressure drop yours produces?
I am sure in due course you'll quantify the air-flow and pressure at the final output to be sure you have adequate clean (Oil-free) air.
I think you previously described the return of oil from the separator to compressor. Is this working OK?
I like the sphere!
K2

The fuel nozzle I use is sold for use in waste-oil burners, so no worries about whether the oil might clog the nozzle, it should not. The tiny amount of oil left in the compressed air feeding the fuel nozzle will be mixed in with the B7 Diesel fuel and promptly burned in the combustion chamber,... so no problem there.

There's a small submersible fuel pump inside the sphere, half submerged in the oil reservoir, which pumps oil into the center section of the compressor through a 1/8" OD silicone tube. Oil separated from the air continuously runs down the inside walls of the sphere and into the oil reservoir where it gets pumped back into the compressor. It's all working very well.

 

[NapierDeltic]

Hi Toymaker. I know you mention a swirl movement of air inside sphere, but have you thought about maximizing it?
Swirl effect separators are among the best in what concerns efficiency and reduced losses; and the trick is to lengthen as much as possible the travel of stream in spiral.
Personally I would see air admission in the spere in horizontal plane, tangent to the sphere's wall (not 90 degree), at the height where you have already fitted it; and exhaust vertical at the top (maybe continued inside sphere towards center) so not to affect swirl's movement and collect potential droplets.
Clean air has to make a steep turn at the bottom to go out upwards and you have (as much as possible) a general, coordinated movement of particles, which should be better.

 

[Toymaker]

Hi Toymaker. I know you mention a swirl movement of air inside sphere, but have you thought about maximizing it?
Swirl effect separators are among the best in what concerns efficiency and reduced losses; and the trick is to lengthen as much as possible the travel of stream in spiral.
Personally I would see air admission in the spere in horizontal plane, tangent to the sphere's wall (not 90 degree), at the height where you have already fitted it; and exhaust vertical at the top (maybe continued inside sphere towards center) so not to affect swirl's movement and collect potential droplets.
Clean air has to make a steep turn at the bottom to go out upwards and you have (as much as possible) a general, coordinated movement of particles, which should be better.
View attachment 155246

What you've shown & described is very close to what I've done. As shown in the photo labeled "90 Degree Air Nozzle" in post #419, the brass fitting directs the air flow tangentially along the inside walls of the sphere, just above the sphere's "equator", which is also just above the oil pool inside the sphere. The ideal exit point for the clean air would be through the cap at the top of the sphere, but the cap already had the electrical connector for the submersible oil pump, and the 1/8" silicone tube which carries the pumped oil to the compressor, so a compromise was made to locate the exit air fitting as close to the top as was reasonably possible.

Although your design would likely extract a bit more oil from the air, it would also require a separate oil reservoir.

 

[NapierDeltic]

I see. Only because of view direction I could not notice the tangential orientation of intake nozzle.

 

[Steamchick]

There are a couple of significant differences between the "ideal" and real separator here: (and may be insignificant?):

1. Entering gases at the top of the sphere will accelerate as the gases expand and also as the diameter increases, creating more space for expansion... Then decreasing diameter towards the bottom will accelerate the gases further to try and maintain the rotational momentum at a constant. (I think that's the Physics?).
2. Gases entering "at the equator" can only accelerate as the gases expand, and as they move away either side towards the top and bottom poles, they will be slowed a bit by compression, compensated somewhat by the smaller radius accelerating the gases (as with an ice skater who pulls her arms close to speed-up her spin).
3. Domestic vacuum cleaner makers use tapering/conical venturis to accelerate the gases as they pass through the cone such that the centrifugal forces move particles to the outside and cleaner gases pass up the centre.

https://www.google.com/search?q=cyc...ate=ive&vld=cid:e2c190a6,vid:3fB_uH5k6RQ,st:0
ANY use?
K2 - a mine of useless junk.

 

[The Ignoble Troll]

There are a couple of significant differences between the "ideal" and real separator here: (and may be insignificant?):

1. Entering gases at the top of the sphere will accelerate as the gases expand and also as the diameter increases, creating more space for expansion... Then decreasing diameter towards the bottom will accelerate the gases further to try and maintain the rotational momentum at a constant. (I think that's the Physics?).
2. Gases entering "at the equator" can only accelerate as the gases expand, and as they move away either side towards the top and bottom poles, they will be slowed a bit by compression, compensated somewhat by the smaller radius accelerating the gases (as with an ice skater who pulls her arms close to speed-up her spin).
3. Domestic vacuum cleaner makers use tapering/conical venturis to accelerate the gases as they pass through the cone such that the centrifugal forces move particles to the outside and cleaner gases pass up the centre.

https://www.google.com/search?q=cyclone+separator+working+principle&sca_esv=59018620b3723b92&sxsrf=ACQVn0-V3G8TI_6Ytu9gg3UqPFxnkIYo0g:1712991555004&ei=Qi0aZqzvPNiFhbIPo_-_qAM&oq=how+do+cyclones+work+in+cleaners?&gs_lp=Egxnd3Mtd2l6LXNlcnAiIWhvdyBkbyBjeWNsb25lcyB3b3JrIGluIGNsZWFuZXJzPyoCCAAyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEdI9SRQtwdYtwdwAXgCkAEAmAEAoAEAqgEAuAEByAEA-AEBmAICoAINwgIKEAAYRxjWBBiwA5gDAOIDBRIBMSBAiAYBkAYIkgcBMqAHAA&sclient=gws-wiz-serp#fpstate=ive&vld=cid:e2c190a6,vid:3fB_uH5k6RQ,st:0
ANY use?
K2 - a mine of useless junk.

There is a highly detailed paper on the web about the oil/air bubble seperator on the F4 phantom. Great read on separating oil and air in a dynamic environment.


Where this seperator will not be used in a orientation static set up, it might be good to toss in some fine stainless mesh cylinders to act as baffles and increase oil separation.

 

[Toymaker]

There are a couple of significant differences between the "ideal" and real separator here: (and may be insignificant?):

1. Entering gases at the top of the sphere will accelerate as the gases expand and also as the diameter increases, creating more space for expansion... Then decreasing diameter towards the bottom will accelerate the gases further to try and maintain the rotational momentum at a constant. (I think that's the Physics?).

I'm fairly certain that a few seconds after the compressor has been running, and filling the sphere with compressed air, the pressure of air entering the sphere will be nearly the same as the pressure inside the sphere, resulting in minimal expansion of the air sent swirling around the inside of the sphere. The primary force causing the air to swirl is the air's momentum, as the air's expansion is minimal.

2. gases entering "at the equator" can only accelerate as the gases expand, and as they move away either side towards the top and bottom poles, they will be slowed a bit by compression, compensated somewhat by the smaller radius accelerating the gases (as with an ice skater who pulls her arms close to speed-up her spin).

Again, the air cannot expand inside the already pressurized sphere.

1. Domestic vacuum cleaner makers use tapering/conical venturis to accelerate the gases as they pass through the cone such that the centrifugal forces move particles to the outside and cleaner gases pass up the centre.

https://www.google.com/search?q=cyclone+separator+working+principle&sca_esv=59018620b3723b92&sxsrf=ACQVn0-V3G8TI_6Ytu9gg3UqPFxnkIYo0g:1712991555004&ei=Qi0aZqzvPNiFhbIPo_-_qAM&oq=how+do+cyclones+work+in+cleaners?&gs_lp=Egxnd3Mtd2l6LXNlcnAiIWhvdyBkbyBjeWNsb25lcyB3b3JrIGluIGNsZWFuZXJzPyoCCAAyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEcyBBAAGEdI9SRQtwdYtwdwAXgCkAEAmAEAoAEAqgEAuAEByAEA-AEBmAICoAINwgIKEAAYRxjWBBiwA5gDAOIDBRIBMSBAiAYBkAYIkgcBMqAHAA&sclient=gws-wiz-serp#fpstate=ive&vld=cid:e2c190a6,vid:3fB_uH5k6RQ,st:0
ANY use?
K2 - a mine of useless junk.

 

[Steamchick]

Thanks. "I missed the obvious", thinking of vacuum cleaners, where the pressure drop (a few mbars) across the device develops the flow and gas velocity.... But isn't that the same with yours? If there was no pressure drop from inlet to outlet, the gas would not flow?
I am confused now...
K2

 

[Toymaker]

Thanks. "I missed the obvious", thinking of vacuum cleaners, where the pressure drop (a few mbars) across the device develops the flow and gas velocity.... But isn't that the same with yours? If there was no pressure drop from inlet to outlet, the gas would not flow?
I am confused now...
K2

I believe this is where Bernoulli's equation comes into play; If you think of pressure energy and kinetic energy as being inversely proportional then it begins to make sense.
In the picture below, the decreased area section would be the nozzle inside the sphere. The pressure energy at the nozzle is lower than the pressure inside the sphere, but the kinetic energy of the air flow is able to overcome the greater pressure inside the sphere.

Yes, I know that intuitively it doesn't seem to make sense, but the math says this is how it works.

 

[The Ignoble Troll]

Air flow means you must have higher air pressure at the source then the receiver. That's easy to agree with.

If the pressure is high enough then you get flow. Depending on nozzle design, the flow accelerates and thermal energy becomes kinetic and the pressure in the air stream drops regardless of the gauge pressure. Having multiple pressures in a receiver is nothing special.


I'm thinking that the location of the injector will turn the incoming low pressure air stream into an aspirator as the oil sloshes while driving.


Then the fast moving tangential air flow will be able to peel off the oil forming an ultra fine mist.

I used just such an action in a failed burner aspirator for heavy oils.

The spinning air was able to make a dense theatrical fog, which is impossible to separate without layers of mesh or a spinning disc seperator.


If the air flow is too low for this to happen, it may still entrain larger droplets.


I used to design hydraulics stuff and baffles to cut sloshing are always a must in moving receivers.

The mesh number is critical for success and I plain forget it sorry.

 

[Steamchick]

Thanks. Beyond my education (my Physics degree was beyond my imagination too!).
I have always struggled a bit with injectors too.... pushing water uphill?
For forgive my lack of knowledge and I'llp try and understand Bernoulli!
K2

 

[The Ignoble Troll]

I believe this is where Bernoulli's equation comes into play; If you think of pressure energy and kinetic energy as being inversely proportional then it begins to make sense.
In the picture below, the decreased area section would be the nozzle inside the sphere. The pressure energy at the nozzle is lower than the pressure inside the sphere, but the kinetic energy of the air flow is able to overcome the greater pressure inside the sphere.

Yes, I know that intuitively it doesn't seem to make sense, but the math says this is how it works.


View attachment 155253

There is a critical point where the down stream pressure must be low enough or a working injecting gas be hot enough.

Check out boiler injectors.

That energy has to come from some where in order to increase P2.

Check out de laval nozzles.


If the down stream pressure = the upstream and you have no injection or heating, then you will only have a restrictor not a venturi.

 

[Steamchick]

I think Bernouli says that in the steam powered injector, the temperature and pressure of steam is converted to kinetic energy, then add cold water, and the resulting kinetic energy of the warmer water is converted to pressure to overcome the clack and fill the boiler... smoke and mirrors to me! Seems you are getting more into the boiler than you are taking out.... But Bernouli worked it all out so I accept it.
K2

 

[Steamchick]

All I can figure (simply) is that there is constant mass flow of air.... but it is carrying the mass (and velocity) of the oil as well. The line tic energy in is the combined kinetic energy of air and oil. The kinetic energy out is only the air.... so the sacrificial energy of the oil could be the concession to maintaining the pressure constant between input and output. Or something?

 

[The Ignoble Troll]

I think Bernouli says that in the steam powered injector, the temperature and pressure of steam is converted to kinetic energy, then add cold water, and the resulting kinetic energy of the warmer water is converted to pressure to overcome the clack and fill the boiler... smoke and mirrors to me! Seems you are getting more into the boiler than you are taking out.... But Bernouli worked it all out so I accept it.
K2

Might "click" for you if you look up how a De Laval nozzle works.

The restriction is just a simple machine (inclined planes) so imagine the inducting fluid is placed into a piston and is pushing a mass up a hill instead of gasses moving around.

The thermal to kinetic energy is very much like the thermal to kinetic energy of an engine taking expanding gas and moving something with that force.

Does that help?