Graduation of air flow inside a vacuum chamber

[kaigoss69]

TL;DR Summary

Is it possible to graduate the amount of air low and/or vacuum level inside a vacuum chamber

Hi there. I would like to start saying that I am not an engineer or scientist, and that my knowledge about vacuum and vacuum systems, in general, is limited, and I would like to apologize in advance if I am not describing the problem accurately.

The application I am posing this question about is very simply, and amateurly, depicted in the attached sketch. I will try my best to describe it as follows:

In the industry, a continuous wet fabric belt, for this example 100 inches wide, is running over a series of vacuum boxes for the purpose of removing water from the fabric. The vacuum box in question, for this example, is 12 inches wide, in the direction of the fabric run, and spanning 100 inches across. On top of the vacuum box sits a thick metal plate, that is perforated with small holes. The hole diameters are 1/4" and the holes are evenly spaced, yielding 25% open area. The thickness of the plate is 2". This design cannot be changed.

The vacuum chamber has a depth of at least 5x the thickness of the plate, so in this case 10". The vacuum chamber is connected, via piping, to a vacuum pump. The typical level of vacuum inside the vacuum chamber is -60 kPa. The fabric traverses over the vacuum chamber at 50 mph.

The dewatering process is dependent mainly on air flow through the fabric, meaning the more air flow, the higher the dewatering rate. The objective of the process is to get the fabric as dry as possible, but the fabric is sensitive to "damage" from water flow, and it has been shown that using a number of these vacuum chambers in series, each one with a slightly higher vacuum load applied, creates the best results. So, for example, there would be 5 vacuum chambers in series, with vacuum loads starting at 20 kPa, and increasing 10 kPa per chamber, resulting in 60 kPa in the last chamber. The last 3 vacuum chambers have 40, 50 and 60 kPa vacuum, respectively.

Since the use of multiple chambers requires multiple vacuum pumps, my "idea" is to combine the graduation of vacuum (and/or air flow) in one single chamber.

Now here is my question: Is it possible to "graduate" the vacuum level (and/or air flow) from the beginning (left side) to the end (right side) of the chamber, with the introduction of some sort of obstacle, in this case a curved "plate" as depicted in the sketch? If not, is there another way to do it? - My theory is that the air flow inside the chamber would increase towards the end, and therefore creating more "drag", resulting in more air flow through the fabric near the end of the box, compared to the beginning of it.

This may very well be a stupid question, and totally outside the realm of possibility, but I have to ask...thanks in advance for the valuable insight and advice from this community.

 

[Arjan82]

Something like this?:
https://www.equilibar.com/vacuum-regulators/about-vacuum-regulators/

 

[jrmichler]

It's not a stupid question, and is well within the realm of possibility.

Vacuum regulators are designed for clean gas flow, not an air and water mixture. But you could use vacuum transmitters, industrial control valves, and pressure controllers to control the vacuum. The downside is that you would have to size the vacuum pump for 60 kPa, then regulate it down to 20 kPa. The total energy consumption (pump power) would about double.

A complete analysis requires a comparison of both capital cost and operating cost. One large pump plus a number of transmitters, controllers, and control valves vs several smaller pumps.

 

[kaigoss69]

Thank you gentlemen for your answers. I think I may not have described this well enough...I am looking to have a pressure and/or air flow gradient within one vacuum chamber, from one side to the other, i.e. low vacuum/airflow on ingoing side, and high vacuum/airflow on outgoing side.

 

[Limebat]

Ah apologies my friend for going outside your question, but from my also non-engineering standpoint (I just come here for some physics fun), I propose this instead:

If the fabric belt is compressible, and assuming it springs back to normal shape after compression, what if you have several heavy hot roller made of non-absorbent material in rotation to the belt instead? (See example sketch)

So here's the theory I have. It might be dumb, but hey. Let's learn together, eh?
Squeeze a wet paper towel. It releases its water contents relatively well, leaving a good bit less of its water contents within. I believe the cellulose (recall paper is from hardy plant material) that traps the water is compressed to such an extent as to squeeze the water from its pockets.

Perhaps the same can be applied to the fabric. If we compress the speeding fabric in question, then perhaps we can compress the water prior to the vacuum process. To help with the physics of that, see how far you can compress this fabric belt before it cannot spring back to its original form (perhaps Young's modulus can help with that, although I feel as though this is more for material tensile strength, so I am not sure). Probably faster to just calculate it by hand and some screw clamps, along with a jolly good lass / lad to record time and camera.

Heat can also help via the latent heat of vaporization in water. If you can turn the water contents to steam, then that'd probably help a tad with fabric water contents. But that's just another guess.

If this is one-and-done and we only need the fabric to dry, then perhaps salt can help. Recall osmosis and all that jazz.

Increasing the ambient air pressure around the belt might also help with the vacuum process (air pressure to vacuum increases, causing more pressure to build and subsequently get sucked), although this might also overwork the vacuums. Or worse, kill an unprotected floor worker if pressures are significant. Perhaps if you increase the local pressure of the local environment, it'd best be in a smaller enclosure without human input. A small enclosure would lessen the energy requirements to pressurize a chamber, and the lack of humans is going to make OSHA happy.

Speaking of ambient air pressure:
Maybe try to remove humidity from the air when possible. Might introduce some water back into system. Maybe a dehumidifier? Airflow? Vents?

I digress. In any case, if water contents are sufficiently low, then perhaps the vacuum system would be provide the necessary remainder of pressure to "grab" the rest of the water.

Also note that a vacuum doesn't necessarily have to be generated from a generator. A weak vacuum can actually be accomplished via a piston!:

Notes:
It should also not be hot enough to let dried materials "stick" to the cycling cylinders.
Do not let cylinders "eat" the cloth when rotating in tandem with the 50 mph belt.
Heat can cause wear and tear in fabrics. Not entirely sure if your company is keen on doing that if you plan to use these belts multiple times. However, if this is a one-and-done deal, then maybe it'll work?
Maybe consider using salts with the fabric to help? (Perhaps not regular ole' table salt...?)
An interesting experiment or two that might help:
https://www.scientificamerican.com/...specially absorbent,and fill the empty spaces.
https://www.explainthatstuff.com/ho...t=Heat a liquid and you,with no liquid at all.