Aeration Using Bubbler

[hollanda88]

I was just wondering if aerators such as air pumps actually allow for the diffusion of gasses through the bubbles as many people say that they don't but i don't see why not as they are simply increasing the surface area of caontact between tank water and air.

andrew

 

[fatheadminnow]

After reading this, I did a little research, just to see what I could find.

I found that when air bubbles traverse through the water column, they do put a small amount of oxygen into the water.

The larger the bubble, the greater the surface area, but the faster it will rise to the surface.

The smaller the bubble, the smaller the surface area, but the bubble will travel slower, allowing for the air/water connect time to be greater, which will allow for some diffusion of oxygen into the water.

Overall, surface agitation is going to be the most significant, just because you are having a greater period of time in which the water is going to be in contact with the air.

The more time water and air are in contact with each other, the more oxygen is going to be diffused into the water, that is if only there is surface agitation.

just my 2 cents.

-FHM

 

[hollanda88]

After reading this, I did a little research, just to see what I could find.

I found that when air bubbles traverse through the water column, they do put a small amount of oxygen into the water.

The larger the bubble, the greater the surface area, but the faster it will rise to the surface.

The smaller the bubble, the smaller the surface area, but the bubble will travel slower, allowing for the air/water connect time to be greater, which will allow for some diffusion of oxygen into the water.

Overall, surface agitation is going to be the most significant, just because you are having a greater period of time in which the water is going to be in contact with the air.

The more time water and air are in contact with each other, the more oxygen is going to be diffused into the water, that is if only there is surface agitation.

just my 2 cents.

-FHM

Thanks FHM, although the total surface area of the bubbles produced by a 15cm air stone will surpass the surface area of the surface of most tanks,

andrew

 

[fatheadminnow]

You are true about that, but they are not going to be in contact with the water as long as the air that is at the surface of the tank.

It take like 1-2 sec for the bubbles to rise to the surface.

But than again, there are going to be a constant stream of bubbles all the time....mmmmmmmmmmmmmmmmmmmmm...

I guess we will have to see what other members will say?

I am sure there will be many other good replies to your question soon as more members come on.

-FHM

 

[hollanda88]

You are true about that, but they are not going to be in contact with the water as long as the air that is at the surface of the tank.

It take like 1-2 sec for the bubbles to rise to the surface.

But than again, there are going to be a constant stream of bubbles all the time....mmmmmmmmmmmmmmmmmmmmm...

I guess we will have to see what other members will say?

I am sure there will be many other good replies to your question soon as more members come on.

-FHM

Yeah thats exactly what i thought there will always be the same number of bubbles in the tank (give or take), therefore there is always the same surface area for gas exchange from the bubbler.

Come one sciencey people tell us why they don't aerate the water, or is it simply a common misconseption?

andrew

 

[Curiosity101]

Maybe it's a bit like Chinese whispers.
People used to think you HAD to have bubbles to aerate --> Then someone said - actually you only need surface agitation ---> Then someone mis interpreted and started saying that bubbles don't aerate?

I suppose that could be the explanation, cause I've gotta admit...you make a good point. I guess the only question is, how long does the gas exchange take? I'm pretty sure it's instantaneous... So in theory you're correct I guess.

 

[hollanda88]

Maybe it's a bit like Chinese whispers.
People used to think you HAD to have bubbles to aerate --> Then someone said - actually you only need surface agitation ---> Then someone mis interpreted and started saying that bubbles don't aerate?

I suppose that could be the explanation, cause I've gotta admit...you make a good point. I guess the only question is, how long does the gas exchange take? I'm pretty sure it's instantaneous... So in theory you're correct I guess.

As there is a direct contact between air and water the gas exchange should be instant its just how much gas is exchanged, but thats not a problem as the bubbles are in a continuous stream therefore they have a combined time of a long time to exchange gas.

andrew

 

[BenPursglove]

Diffusion is not such a great word to describe this as diffusion mainly relates to light (but we all use the word related to your question to communicate the same thing lol).

What you are really asking is about dissolving gas (air) into water, which I have seen an an experienced plant keeper describe as akin to "herding cats" : )

Air bubbled in a tank consists of (generally): 78% Nitrogen, 21% Oxygen, 1% Others (being many different elements and chemical compounds in small percentages)

Because each constituent part of "air" have different atomic masses each will be dissolved at different rates in the water, whether bubbled or not. I guess the bubble has the best chance of dissolving all it's parts sooner than surface agitation has of dissolving the same as it is in contact with the water longer and is generally spherical so it gets the most contact with the surronding water for it's size, with one caveat; The bubble rises quickly and is not around long enough to have chance to diffuse very much (the reason why CO2 aquarists use diffusers or reacters)

When the rising air bubble hits the surface it breaks causing surface agitation which allows for the surface air dissolving through temporal breaking of the meniscus.

I am guessing this is why most say that surface agitation (larger area than a / many bubble(s)) is the best way to aerate a tank. An airstone will aid to create this agitation and will, no matter how small the result, also help to dissolve the air in it's rise to the surface.

Pressurised CO2 heavily planted tanks create good oxygen levels despite having higher than "normal" dissolved CO2 levels. This is because the plant consumes the dissolved CO2 as fuel for photosynthsisis which as a bi-product produces Oxygen from the plants surface = instant Oxygen dissolving.

I am by no means a scientist so the above is subject to my own assumptions, observations and general meanderings. Best place to look / post an answer to this is in the scientific section as I am no expert. BigNose would clear this up right away I'm sure : )

 

[fatheadminnow]

Good write up, but actually diffusion is the process by which molecules spread from areas of high concentration, to areas of low concentration.

The air molecules in the air bubbles are going to be closer together, creating an area of high concentration.

While the water, which has air molecules that are not as close to each other, meaning an area of lower concentration.

Light on the other hand is not in an area of high nor low levels of concentration, unless the object emitting a light source (photons) is either moving away from the observation point, at any speed, up near the to the speed of light ( 3.0x10 m/s^2) creating what is called a "Red Shift." Or if the object emitting the light source is moving closer to the observation point at any speed up to/near the speed of light, will be producing what is called a "Blue Shift."

A "Red Shift" is going to be where the light waves are farther apart, which will cause the light that they emit to be Red, hence the name "Red Shift."

A "Blue Shift" is going to be where the light waves are closer together, which will cause the light that they emit to be Blue.

This is how astronomers can figure out if galaxies are moving further or closer from us.

A galaxy that produces a red light is going to be moving away, where a galaxy is producing a blue light is going to be moving closer to us.

-FHM

 

[tenohfive]

I haven't the energy for a scientific debate, so I'm going to participate in that great TFF tradition of ignoring everything posted above and giving my opinion:

I was under the impression bubblers work by increasing the surface agitation, and hence aeration. As for why that matters, I have no idea - I always keep enough surface agitation using my powerhead that the only time I'll add a bubbler is if treating with certain med's, as I do believe they increase the amount of oxygen etc in the water.