Bubble formation in 4 mm gap vessel

[wahaned]

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Hi,

I have a vessel I 3D printed to investigate single bubble rise. The vessel has a 4 mm gap separated by acrylic panels. This is essentially my viewing chamber where I can record the bubble motion. The vessel is open to atmosphere.

The bubble generation mechanism is composed of a syringe pump and glass capillary tube (Internal Diameter of 0.45 mm). I connect a 1/4” air line hose from the syringe to the capillary
The bubble is formed at the tip of the capillary and rises in water. I am using a 20 cc syringe and the flow rate for the pump is 30 ml/h. The distance from the capillary tip to the interface of the liquid is 160 mm

The issue I am currently having is consistent single bubble formation. It seems water wicks into the capillary and the air flow rate cannot displace the liquid. As a result I have included a check valve between the syringe and capillary to prevent this backfill of water into the capillary and I have also shortened the hose length from the capillary to check valve.

However I am still facing the issue of inconsistent single bubble generation. Even when I increase the flow rate I am unable to get consistent bubbles being generated.

Any advice on this will be greatly appreciated.

Regards
Wahaned

 

[berkeman]

Welcome to PF.

Can you attach some pictures and a diagram of the setup? Use the "Attach files" link below the Edit window to upload PDF or JPEG files. Thanks.

 

[wahaned]

Attached is a copy of the setup. I have located the position of the capillary and check valve

 

[Baluncore]

If you can dry the capillary tube, then flush it with some hydrophobic material such as silicone oil, that may allow the air to flow, while preventing the influx of water into the tube.

The check valve you show has a high capacity and is in the large tube, not at the tip of the capillary tube. Maybe think about the construction of a fuel injector valve, then use something like a Schrader tire valve, where a spring closes the passage during inflation. That would allow the bubble to form on the valve as air was pushed through, without water flowing back into the tube.
https://en.wikipedia.org/wiki/Schrader_valve

 

[wahaned]

Thanks loads for this insight.

I will look into this and update you.

Much appreciated

 

[Baluncore]

You might assemble the bubble in a horizontal capillary tube, level with the bottom of your viewing chamber. A linear scale, along the capillary tube length, would give an accurate air volume. The hydrostatic pressure there will be the same as at the bottom of the chamber, so the initial volume of the bubble will be predictable.

The horizontal capillary is part of a U-tube and is initially filled with water. It is connected to the chamber at both ends, on the left say through a check valve, while on the right, it passes directly to the bubble injection point. Since the system is filled with water, the bubble will stay at rest in the capillary tube while you take your time to adjust its length, and so set the bubble volume.

Two syringes are connected to the left-hand end of the capillary. One is small and contains the air for filling the bubbles, the other is used as a two-stroke water pump, to squeeze the measured bubble out of the capillary tube and into the chamber.

So as not to disturb the water in the display, use the minimum water volume to launch the bubble. Use the thinnest and shortest tube from the capillary to the injection point. You might consider mounting the horizontal capillary through the wall of the display chamber for direct injection with minimum water.

 

[Baluncore]

Further thoughts on a smoother operation, suggest replacing the syringes with two small peristaltic pumps, each controlled by hand. The diameter of the silicone tube used in the pump, sets the total volume per rotation.

Peristaltic dosing pumps are available on eBay for less than $20. They usually come with a geared electric motor for use with fish tanks. Either use the geared electric motor provided, or simply replace it with a knob or hand wheel.

One pump would replace the check valve on the inlet to the horizontal capillary tube, it would be used to prime the capillary with water, then later, to inject the water containing the bubble, into the chamber.
The other pump would inject free air into the capillary tube, preparing the volume of bubble to be released, when the first pump is again operated.

Because the pumps are reversible, smooth flow, positive displacement pumps, judicious use of the two hand controls would accurately meter air into the capillary and launch the prepared bubble into the chamber.

https://www.ebay.com.au/sch/i.html?...&LH_TitleDesc=0&_odkw=peristaltic+pump&_oac=1

https://www.aliexpress.com/w/wholes...?spm=a2g0o.home.auto_suggest.2.650c6278libc4P