Can Magnetohydrodynamic Propulsion Revolutionize Silent Submarines?

[chayced]

Slight change in topic, but I am amazed that the US hasn't invested in Stirling engines for sub propulsion. It seems pretty logical to me, you have primary coolant providing heat directly to the heat engine with a piston and hydrogen between it and the circ water. Maybe it's cost, maybe its size requirements.

Read about a Swedish company that builds Stirling powered submarines, but they are liquid 02 cooled and probably have a high temperature differential.

Oh and the 20 year lifespan of a reactor core is based around alternating at sea times of low power and in port periods of shutdown. If a boat is running at high power for extended periods of time that number can quickly fall. Then again if a boat was driven that hard for that long, it would be time for a complete overhaul anyway.

 

[mgb_phys]

Read about a Swedish company that builds Stirling powered submarines, but they are liquid 02 cooled and probably have a high temperature differential.

They aren't liquid oxygen cooled, they burn diesel fuel and the liquid oxygen is just a compact way of storing O2. The stirling engine can run from the diesel and stored O2 while submerged - the exhaust is dissolved directly into the sea water.
When the O2 runs out you still have a regular diesel electric boat. I assume they could also carry plants to make more LOX while at sea and surfaced. The advantage is that you get much better submerged endurance combined with diesel electric quiet, and you don't have any of that icky nuclear stuff to dispose of.

Nuclear boats are never completely quiet because of the coolant circuit. The Polaris boats were described by an-ex submariner technician as sounding like a "pair of skeletons ****ing in a metal trash can" - I assume they have improved since then.

 

[taylaron]

downside to that technique is you can track a submarine that is cooled by the surrounding water by measuring the surrounding temperature of the water. kind of like a hunting dog does a scent. without using the surrounding water to dissipate the heat from the source, you would need a lot of liquid He or O2 or N2 to do anything practical.

 

[chayced]

I believe the Stirling's in question were liquid oxygen cooled, just diesel and oxygen fired. It would be a waste to do it otherwise. Guess my comment was a bit ambiguous.

The coolant loop in a nuclear sub is only loud at high driven flowrates. In a natural circulation mode the loudest thing would be the reduction gear and main engine followed by the generators and pumps.

So yes, they have improved since the Polaris boats. From what I understand Trident boats are silent and easier to find by looking for the quiet spot than by looking for the noise they make. Until sonar technology improves its pretty pointless in making a quieter boat, unless of course it can go quietly at high speeds.

 

[mgb_phys]

The Swedish boats are only 1300Hp and supposedly because the exhaust dissolves into the sea water the temperature diffuses away form the boat quickly. Yes - it would make sense to arrange the cold side of the Stirling to be the LOX pre-heater.

I don't know how a nuclear boat cools the condensers but with a 30-50MW reactor something has to dump a lot of heat.

 

[MATLABdude]

Like, fill the submarine with oxygenated Flourinert?

http://en.wikipedia.org/wiki/Flourinert

Then train all the submariners to breath the stuff, and give them special glasses so that they can focus on the displays and see still. Kind of like (what was the name of that movie...something like The Deep or The Chasm?...with the John Glenn actor guy?)

Is this for real? I know it was in the movie, and the Wiki indicates tests with rats, but wow. Or are you going to be receiving a visit from some gentlemen with dark glasses and suits?

 

[russ_watters]

No, it isn't for real. People can't breathe liquid.

 

[MATLABdude]

No, it isn't for real. People can't breathe liquid.

Ah. I read the 'then' as 'they'!

EDIT: And skimmed over the part where the rats later died of lung trauma after being removed from the solution.

 

[Morbius]

I don't know how a nuclear boat cools the condensers but with a 30-50MW reactor something has to dump a lot of heat.

mgb-phys,

They sure do cool the condensers with sea water. They run a normal Rankine cycle.

A colleague of mine is a former US Navy submarine engineering officer. He related his experience
in the following. Because the condensers are exposed to seawater - they have sacrificial anodes -
a replaceable plug that is allowed to corrode in order to minimize corrosion of the main body of the
condenser. The plug screws into an approximately 1 inch hole in the condenser and is supposed
to have a wire through the cap to make sure it doesn't get loose.

My colleague was standing an engineering watch when one of those plugs popped out and they had
a 1 inch hole open to seawater pressure. There was a loud bang and a roar as water poured in via
that 1 inch hole. My colleague immediately hit an emergency button to close a valve to stop the influx
of seawater into the engine compartment.

Even though the hole was only 1 inch in diameter, and the whole incident lasted only a few seconds -
the time it took for him to hit the button and close the valve - the water level in the engineering space
was a couple feet deep. A LOT of water poured in during a very short period of time.

Dr. Gregory Greenman
Physicist

 

[mgb_phys]

The plug screws into an approximately 1 inch hole in the condenser and is supposed to have a wire through the cap to make sure it doesn't get loose.

And presumably a label saying - "do not remove" !

 

[OmCheeto]

In regards to fishing, I doubt that they want to open the hull to bring anything inside.
You also don't want to have anything "passing through" the pressure hull; otherwise
you are asking for trouble.

The sub could fish on the surface, but a Trident stays underwater pretty much thourgh out
the mission in order to avoid detection by satellite.

Utilizing the subs sonar, torpedo tubes, and a bit of ingenuity, I believe fishing would be quite possible underwater. They might even be able to fabricate a crab pot. Now that I could eat for 20 years. Although you would then have to solve the "how are we going to store that much butter" problem.

OC
Ex-Submariner

 

[Morbius]

And presumably a label saying - "do not remove" !

mgb_phys,

In this case, nobody removed the plug - it worked loose by itself.

However, it was not properly wired with a wire through the head to prevent rotation.

Dr. Gregory Greenman
Physicist

 

[mgb_phys]

mgb_phys,
In this case, nobody removed the plug - it worked loose by itself.

Yes I know - I'm just picturing a big cork in a hole in the side of the sub with a note saying 'do not remove'

Rather like this (about 15 sec in)

 

[IAMOLBG]

whats dielectrophoresis and could you do anything with that? regarding movement through water...