Tank of slurry, sealed air intake to generate flow

[camel80]

Hi,

I've been driving myself around the bend with this problem and feel its a simple solution that someone can comment on.

I have a flow experiment whereby i need to maintain a constant level in a tank. The problem is that the flow rate controlled by the exit value of this tank varies. I constructed a feeder tank similar to the antigravity water experiment whereby a glass is submerged in a bucket of water, filled then turned upside down and lifted whereby the water doesn't flow out of the glass until air is allowed to flow back in and water flows out. It works great for water as the viscosity is low, but i need to use this setup for slurries of high solids concentrations. Because this material is highly viscous, the air bubble takes a second or so to flow up the tank and allow more slurry to flow out. The lag time creates a variable level in the main tank which is not ideal. It also airates the slurry which is affecting the experiments.

See the diagram attached for the setup.

One solution, is how i can get air into the vacuum pressure area to allow the slurry to maintain its level in the primary tank. I'd like this to be automatic, so not someone controlling an air intake value. Obviously the level of slurry in the feed tank reduces as it maintains the level in the primary.

Any ideas?

MAny thanks in advance.

 

[StoneCold]

Why don't you just move the outlet level of the tank up to the desired level. Then liquid flows out when you are above that level?
Or is this really about your vacuum feed device?

Regards
StoneCold

 

[LittleInch]

Just add a separate level sensing air line to the top of your fill cylinder. If you size it right the initial "slump" will be limited, but still able to add enough air to match your outflow. Extend your tank line below the normal liquid level by a small distance to stop air gulping into the feeder tank as the main liquid level drops.

You may need to experiement with the size and position of the level sensing line and how far below the surface you need to put your main feed tube to stop it sucking up air when the man liquid level drops.

See attached mark up.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[camel80]

Hi

Thanks for the comments. I cant move the outlet to the same level as the pressure in the primary tank as I need a pressure to maintain a higher flow rate.

I like the idea of the line. I will think a little more on the pipe diameter and report back. I need a flow rate up to 2 litres a second.

Many thanks
Cheers

 

[LittleInch]

A 1" air line / level sensing line should be Ok for that flow, maybe 1 1/2". You could always put a valve on to dampen the flow a litle bit if it gets too fast.

Would be good to know if it works. Now I've thought about it a bit more, it might need a float and stopper arrangement rather than trying to suck up the liquid which would then create a bit of a slug in the sensing / filling line.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[camel80]

Hi LittleInch, after thinking about your tube, wont the slurry in the main tank be slowly sucked up the tube due to the vacuum pressure in the feeder tank?

I dont understand the float system design. Can you explain it a little more. Perhaps this prevents the slurry rising.

Looks good though. Will fabricate something and try it out.

Cheers

 

[LittleInch]

That's what I suddenly thought as well so the float idea is probably better but will need a very good seal. That's why your original idea is much simpler, but clearly runs into problems with slurry.

The float should sit on the slurry and have the opening above the slurry level to avoid sucking up slurry. A standard domestic ball cock as in your toilet may work very will with a bit of lag as it opens the valve for reverse flow but should seal very well.

Let me know if it works.

LI

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[camel80]

LittleInch,

I tried a slight variation to your idea. Basically it does not work fast enough. A little more rustic way is that the air intake pipe is left to atmosphere and someone controls the air intake by their thump trying to maintain a constant level in the tank. Not ideal i know, but i cant regulate the air intake correctly.

Will keep experimenting. Let me know if you have any other ideas.

Cheers

 

[LittleInch]

Sounds like you need a faster acting and wider opening valve which is acting on the liquid level or maybe double up the control air intake valve to increase air flow.

Maybe the air inlet pipe needs to be a bigger size.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way