Air Nozzles and Vacuum Chambers

... You no longer have a vacuum???

ROFL+GA

It all depends on what angle you place the nozzles in reference to the core of the unit and the angle of the equator in accordance with the directional flow of the vacuum reversal of the nozzle modules.

We all know, it could create a vortex, if an ionic charge is maintained of course, and reverse the roation of the earth or perhaps send you and all matter within 3.14159 meters (or simply 0.0019520935238208862 Miles) into another time and space.

But then again... It might simply release the vacuum.

Buy a Kirby!

JL Mealer

Mealer Companies LLC

I would say that we cannot release what is not there, and vacuum is absence of air, no? So we would just fill vacuum by air......

Since there would be expansion of air inside of vacuum chamber, probably there would be a temperature drop inside as consequence.

Yes, if properly designed, it may cause rotation also, but it depend how strong would be air flow and what is total mass that should be turned. Perhaps inertia would not let thing turn at all.....

I wonder why some people ask questions like this?

Sound like exam question for school :-))

Hi,

pressure in vacuum is a balance between leaks and pumps. Leaks let gas in, pumps bring gas out. Internal gas generation or absorption to be added.

So if the relation of air inlet by a precise nozzle and pumping out is ok, why not.

Air that is streaming through a nozzle will see different regimes of flow: first turbulent or laminar depending on pressure gradient and cross-section, then adiabatic decompression until reaching sonic velocity, then further expansion and cooling by Joule-Thomson effect until final velocity and pressure, impinging on walls or structures, finding its way to pump inlet.

This approach is used if airbearings are to be operated in vacuum.

As there are very small gaps where the air is expanding in gas bearings there are additional flow regimes: low pressure laminar, Knudsen (mix of laminar and molecular) and pure molecular flow.

Airbearings needed if need for very accurate rotation or linear movement with ultralow error-motions. (Magnetic is used too but much more complicated).

Airbearings are not often operated in vacuum as pumping may be a problem. Proper design is more difficult than with ordinary pressure levels.

Use is in modern semiconductor fabrication with UV exposure in vacuum UV scanners.

See Professional Instruments Co. at www.airbearings.com

RHABE

This would seriously depend on your application and how much air your using, what type of pumps are on the system (make and model please). Is this a Diffusion pump or a Turbo Molecular pump system? If it's a Diffusion pump system like in heat treating applications and you add to much air (under deep vacuum air is fluid not a vapor) then your going to quickly destroy thousands of dollars worth of Silicon diff oil and possibly whatever roughing and holding pumps you have. ie. rotary vane oil filled pumps run at .5 thou tolerance between rotor and stator inside the pump. If you jam lots of air (liquid under vacuum) through a space that small than your going to send the temperature through the roof, burn out your oil and loose vacuum and eventually seize the pump, once that happens your looking at a replacement pump or if you can find someone who knows how to fix it you might get lucky. Same goes for rotary piston pumps, if they are if a Kinney style you now have the world biggest and most expensive boat anchor. If you have Stokes style pumps then it's not that big of a deal other than it's going to cost pretty heavy. If your chamber is pulled down by a Turbo Molecular pump back with a Dry Scroll or Rotary Vane pump then the first thing that will happen is you flood the Turbo Pump with air (liquid under vacuum) and you end up destroying the pump ie. Aluminum blades spinning at 30 000 to 80 000 rpm at .5 thou, very unforgiving. If this happens you now have the world most expensive maraca. The Dry Scroll pump will eventually seize and have to be replaced or have major parts replaced if you can find someone who can do it. These parts CANNOT be fixed they MUST be replaced. The Rotary Vane pump will have the same thing happen as I stated before.

So I guess what I'm trying to say is find someone who knows what they are doing, ask them how to do this if you really must add an air nozzle to your chamber, then get him (or her) to do it for you. This is a very delicate science, too much and you have a big problem so be careful. Email me if you have anymore questions.

Hi,

"under deep vacuum air is fluid not a vapor"

Just the contrary is true: any liquid evaporates slowly or by boiling depending on vapor pressure below or above ambient (vacuum) pressure! So water at 20°C will boil if pressure drops below 18mbar.

Fast pressure rise by failing O-rings is an often occurring situation, I had also a cracking window and accidental opening of air or gas inlet valves: not recommended for turbo-pumps but survivable if not too fast. The pumps have a protection system built in that prevents excessive heating, and the motor-drives are not so powerful that the pumps are driven against too high pressure. You can test this if you switch on the pump at too high pressure, either switch on is not possible or run-up will not occur and after some time automatic switch-off is activated.

With diffusion pumps you will have some trouble with cleaning but not really much trouble.

RHABE

My point is that if your forcing a large amount of air into your pump or system the pump will over heat and cause the oil to lose lubricating properties due to oxidation, thus causing damage to occur to the pump. If your working with Turbo pumps usually there are 2 rotary vane or scroll pumps running with it. The fore pump brings the chamber or system down to a particular vacuum then the Turbo turns on then you have a holding pump to hold the system down. If you flood the system or chamber with air the pumps overheat causing damage. I fix vacuum pumps for a living and this is the main cause of most damage that occurs. When air is in a chamber that is under vacuum you are correct it does boil off relatively fast, this can be seen on a gauge, but if you run the system with a leak the air must be "out gassed" before the ultimate pressure is reached. If this is a constant leak then the pump never reaches optimal running pressure causing it to over heat and eventually fail. Most systems with Turbo pumps that I encounter run with with a 25 to 200 micron leak, all 2 stage vacuum pumps are designed to run at 1 micron or approximately 1x10-4 or so depending on the manufacturer. thus if your injecting any amount of air into the system the ultimate pressure drops causing the temperature to rise due to the air molecules being forced through .5 thou tolerance at 1780rpm 60Hz. I've always been told that at the molecular level air acts as a liquid. In regards to Diff pumps my remark was based on the impregnation of water molecules into the silicon fluid forcing you to replace the fluid at great cost. Cleaning is easy and relatively cheap, but the cost of silicon fluid is very expensive, that's why a vacuum booster pumps and rotary piston pump brings the system down to about 100 microns (depending on the system) then the Diff pump turns on bringing the vacuum pressure home thus reducing the amount of air that will impregnate the silicon fluid giving longer life to the silicon fluid.

In regards to the system shutting down I can show you pictures of pumps in mas-spec and chamber application were the pump has over heated and damage has been caused. most of the systems I see have Varian pumps in them and unfortunately they don't seem to stand up to the temperatures very well, on the other hand Leybold (Oerlikon) pumps seem to work better in high heat application. A Varian DS or HS 602 pump tends to run at 72 degrees C as opposed to the Leybold D16B pump that runs at 48 degrees C at ultimate running temperatures. so the higher temperature from the start already reduces the life of ones pumps drastically, thats one of the reasons I send all my rebuilt pumps back out with a semi-synthetic oil.

I hope I explained myself a bit better. Thank you for the information boiling points this is much easier to understand then what is printed in the book "Modern Vacuum Practice Third Edition" by Nigel Harris.

GA to both Simple1 and RHABE. While you guys argue out the minutia of the subject note that Varaharaju appears to be fairly naive about the technology of high vacuum. Perhaps he is only interested in a low vacuum application. He would have done well to tell us what torr level is his vacuum chamber operating at.

Ed Weldon

Ed Weldon made a good point, how deep of vacuum are you looking at, if it's anything more than 760 microns then completely disregard my previous 2 posts.

Dear Mr. Varadaraju, It's good question; answer is not as simple!