Artificial gills, what is the hold up?

[Deseoso]

I love seeing how a lot of scientific advancement is first seen in science fiction but later ends up as a reality. Just look at the iPhone. If you had an iPhone in the 80's people would have thought you just stepped off the USS Enterprise.

 

One piece of science fiction that I have seen used in many films, books and computer games is the idea of creating artificial gills that can filter oxygen out of sea water. It would be great if you could use an artificial gill instead of an oxygen tank when diving but one has never been invented and it made me start to ask why?

 

My thoughts are this, please tell me if you think it is wrong. Fish are cold blooded right? If my understanding is correct about the difference between cold blooded and warm blooded creatures, cold blooded creatures don't require the same amount of oxygen in their systems as warm blooded creatures. This being the case, even if we could create an artificial gill of the size that you would expect to find on a human sized fish, it would not be able to filter the amount of oxygen that we, as warm blooded creatures, require to breath.

 

Any thoughts?

[CaptainPanic]

First of all, there are 3 problems:

1. Extract oxygen from water, and into an inert gas (nitrogen is probably easiest).

2. Remove CO2 from the nitrogen.

3. The partial pressure of oxygen in water may be too low.

 

All of this can be built. All the necessary thermodynamic data is available from public sources, and common design methods are available. But I doubt you want to carry the resulting factory on your back. The most basic method would be to bring the oxygen-poor gas into direct contact with oxygen-rich water (bubbling or spraying). The rate at which the oxygen will go into the gas is low, so that is a large machine.

You can also use some oxygen-selective membrane. You still need a very large surface area for that, and I am not sure that anyone can build that using membranes (you would have to fold it up to create a really large surface). A negative side effect of using a membrane is that the partial pressure of oxygen on the gas side is even lower than with direct contact. You'll need some way to improve that (e.g. a compressor).

 

And I did not even address the problem of removing the CO2 (which is probably easier though).

 

All in all, it is probably cheaper and easier to bring some compressed air.

[Ringer]

Where would they fit it to the circulatory/nervous system? The support system necessary for gills wouldn't be worth the cost unless you planned on living underwater constantly. Then you would have a host of other problems such as buoyancy control, osmotic regulation, etc.

[John Cuthber]

Among the problems is that we are adapted to breathe a mixture of oxygen with some other gas- nitrogen.

You would need to make gills that exchanged O2 and CO2 but conserved N2.

Good luck.

 

Also, tanks full of gases work quite well, so there's not that much incentive to produce gills.

(Though I accept they would be great for "snorkelling".