Look back at this thread. Read the posts.
To everyone else reading this thread: FG and I have tussled on this topic several times before. I am not even going to bother presenting my side of the argument again except to note that this: http
/www.fishforums.net/index.php?/topic/377186-a-rational-discussion-on-oxygen-transfer-from-an-airstone-bubble/ is a thread that contains links to both sides of the discussion. Feel free to peruse it at your leisure.
I actually read the posts finally. And the only argument there is that the air bubles themselves don't provide enough aeration while travelling upward to the surface.
But presuming this is true based on some reasearch regardless whether it is from 1956 or 2011, I can't see proof that the bubbles themselves don't oxygenate the water by moving the surface when bursting. Especially when combined with another device like the filter outflow pipe, as both together will create more vigorous waves in different directions, therefore increasing the surface movement signifficantly. Also it creates an additional vertical movement of the water on top of the horizontal filter flow, thus spreading the aerated water better, and also contributing to the efficient heating in tropical setups.
So the statement that air pumps are completely unnecessary is not true, as this depends a lot on the setup. No one denies that air pumps are more flexible and are used in CO2 pressurised systems at night, otherwise fish will suffer and die due to lack of oxygen, not to mention many other uses. So the usage of one, does not exclude the necessity of the other in most cases.
As far as to decide which scientists are the best and who is right or wrong, Einstein, Newton, Mr paper 1956, etc..that is a a never ending debate and research. Some scientists write theories based on presumption, which may prove right or wrong. Others base their theories on scientific attempts, rather than presumption.
Even Nikola Tesla, whose scientific discoveries have made it possibe for us to even have aquariums at home, has said about Einstein's theory of relativity:
Einsteins relativity work is a magnificent mathematical garb which fascinates, dazzles and makes people blind to the underlying errors. The theory is like a beggar clothed in purple whom ignorant people take for a king... its exponents are brilliant men but they are metaphysicists rather than scientists.
We don't all agree. They didn't all agree either. So nothing has changed
The question that I've always answered is: how much oxygenation do bubbles provide compared to the surface oxygenation. I have always noted that rising bubbles help circulate the tank and help disturb the surface, both of which drive the tank to equilibrium faster.
But look, take a bubble of 0.5 mm radius. This will have a surface area of 3.1416 * 10^-6 m^2. A 20 gallon tall tank has dimensions of 24 in wide * 13 in deep. This is equal to 0.20129 m^2 of area. Dividing the two, the surface is equal to over 64,000 0.5 mm bubbles. There is no airstone that puts out 64,000 bubbles. And, the surface is always refreshed, whereas the bubbles -- if there was time to exchange much gas (which there isn't since they get to the top very quickly) -- would be constantly depleted.
In short, the surface is dominant in terms of gas-exchange. It is just a matter of scale.
Now, regarding your Tesla quote, it is a total non sequitur. Because no matter how ugly Tesla, or you, or I or anyone things the theory of relativity is, it works. It is proved correct millions of times every single day because our GPS devices work. That's right, the calculations based on the theory of relativity are used every time you ask your device for directions. If relativity was wrong, your device wouldn't know where you are exactly, and wouldn't be able to give good directions (the quality of the map notwithstanding).
And THAT is ultimately the crucible in which science is judged: does it work. That is how a paper gets peer-reviewed and the decision is made on whether it is printed or not. I don't know what you mean by "Some scientists write theories based on presumption, which may prove right or wrong.", but scientific papers are judged on whether the author(s) provide ample evidence on if their ideas work or not. A paper written on presumption without evidence that that presumption is correct would be rejected by any journal of any scientific quality. This doesn't mean that everything published is right -- most of our knowledge today will probably be proved to be at the very least incomplete. But, we do know that what is published is the best knowledge at the time. And, a lot of times, that same knowledge is relevant forever.
Back to relativity, the theory of relativity superseded Newtonian mechanics. Note, that relativity did not prove Newtonian mechanics wrong, relativity just the answers right where it was known Newtonian mechanics break down. Situations like when an object is travelling near the speed of light, or undergoing a strong acceleration. But, in situations away from the speed of light, or not strong accelerations, Newtonian mechanics are the same they have always been. We also know that relativity is incomplete, there are situations where its predictions don't agree with experimental results. The neutrinos reportedly travelling faster than the speed of light as reported in the last two months will also be outside the predictions of the theory of relativity if confirmed correct. But, that won't stop Newtonian mechanics from being right when used correctly -- to build every single bridge, road, building, etc.
This is the same with that paper from the 1950's that calculates the mass transfer of a gas from bubble into a liquid. The laws of mass transfer have been known for a very long time. They were first formalized by a man named Adolf Fick in 1855. They are based on the first principle that mass cannot be created or destroyed. And while we have learned that there are other cases other than Fickian diffusion, we also know where Fick's Laws don't work. Like we know where Newtonian mechanics don't work. The vast, vast majority of the time, the mass transfer is within just a few percent of what is predicted from Fickian diffusion.
So it is with this case. Just like relativity is proven right every day with all the successful uses of GPS devices, the predictions for the mass transfer of a gas from bubble into a liquid are proven right in every distillation tower and bubble reactor at every refinery and chemical plant around the world. If that derivation from the 1950's was grossly wrong, it wouldn't have made its way into one of the most used and common texts in engineering. It wouldn't be published in every text on mass transfer since the 1950s. It wouldn't be derived as a homework problem in almost every mass transfer class taught across the world. It is proven correct because it works -- the experimental results match the predictions made by the mathematics.
As above, that is the crucible in which science is judged: the predictions match the experimental results. No matter how beautiful or ugly the idea may seem to any person, the science is sound when the predictions agree well with the results. There really is nothing more to it. I have always agreed that the exact number predicted can have a few nits picked on it: the diffusion coefficient is a strong function of temperature. It is also a weaker function of pH, and whatever else is dissolved in the water, etc. But, its value also isn't going to change by more than a few percent over the range at which the vast, vast majority of fishtanks are kept (room temperature to very warm tropical temps). Which is why I believe that the estimate is probably with 5%, 10% at the worst. And, a 10% change doesn't change the major conclusion -- that the mass transfer from the bubbles is very tiny compared to the mass transfer from the surface.
So, I used this well-verified equation to estimate the mass-transfer of oxygen from an air bubble into water, and posted the results. Unless it can be shown that the estimate is flawed in some significant way (that is, the rules of Fickian diffusion are not valid in this case), why such a reluctance to believe an equation that has shown itself to be right millions of times over?
