Making bubbles and trying to use Trompe

[Tomimo]

Hi,

I am trying to create a device that would "simply" make a bubble under the water. What I am aiming for is production of small bubble but continuously and under the water. When I say continuously, it doeant have to be for extended periods of time, could be just for ~2 hours but the longer the better.

All my ideas about how to achieve it have some shortcomings and the easiest seem to have a chamber full of air and gradually taking air from that to create the bubble (=time limited supply)

All this had led me to something called "Trompe" my question is - can trompe device work under the water (no air supply? How to extract air from water without power) and how small could trompe device be? I am aiming at really small sizes here.

Thank you

 

[anorlunda]

After the device creates the bubble, what prevents the bubble from collapsing? Once the bubble leaves the device, the device had no more influence on it.

 

[Tomimo]

After the device creates the bubble, what prevents the bubble from collapsing? Once the bubble leaves the device, the device had no more influence on it.

Not sure what do you mean by bubble collapsing, but there is no need for any influence, all tjat is needed is for the bubble to float to the surface

 

[Baluncore]

I do not think the concept of a trompe is useful here. Your bubbles would be introduced at the top and be carried down to the drain at the bottom. As they travel down the trompe in the water flow, the hydrostatic pressure increases and the bubbles become smaller in diameter.

Consider the Bernoulli principle / effect. If there was some water velocity where you wanted to introduce the bubbles, a small orifice connected to external air could suck bubbles of air into the water.
What is the hydrostatic pressure or head where the bubbles will be introduced?

Alternatively, pack a small tube with baking soda, when it gets wet it will produce bubbles of CO2. Control the top vent tube size so bubbles are optimum size. Rate of water entry decides CO2 production rate.

Make a chamber that holds air that can be sunk to where you want bubbles. A narrow diameter capillary tube at the top allows small bubbles to vent, one at the time. A hole or horizontal capillary tube at the bottom regulates the water entry rate, (water has a higher viscosity than air). That sets the bubble rate from the top as the chamber slowly floods from the bottom where external hydrostatic pressure is slightly greater. Make the chamber low and flat and the top tube vertically longer to get better regulated bubble rate.

Or buy a fish tank aerator / bubbler from a pet shop.