Rumoured "mini-nuke/diesel" Submarine SSK-N(?) thread

[tphuang]

If you're talking about Soyru class then sure nothing can beat pure battery in noise, but why don't you mention endurance then?

Again, larger sub -> more space for quieting technology -> quieter subs

Again, if sterling engine is the main source of noise then SSKN will have zero noise difference with a SSK that is powered by the same sterling engine, I don't know why you keep insisting nuclear powered sterling must be noisier than conventional sterling or am I misunderstanding you? If Yuan was perfectly fine with sterling AIP then why you have issue with nuclear sterling?

I never said nuclear powered stirling must be noisier than conventional stirling. I said when you have more noisy parts, you need to raft them and that takes up space.

Yuan needs just 1 320 kW stirling. It will need many 320 kW stirling if plugged into nuclear reactor and have these design requirements we talked about. And you will need to mount all of them, which takes up space

Which again, begs the question of why people think Stirling is the more logical choice here? You have a well established industry for steam turbines.

Yes rafting is necessary, but you can't apply the rafting requirement of a 100MW power plant to a 10MW power plant, smaller sub => smaller engine => less noise =>less rafting requirement.

We know Victor 3 class has smaller pressure hull diameter vs Akula and Yasen. We also know that with the smaller space, it doesn't have space for similar type of raft found in Akula or Yasen. That's why it's noisier despite having smaller power plant.

Noise from machine doesn't scale linearly with power of that machine. If you take a look at a steam turbine and a stirling engine, do you think a similar machinery half the size will generate half the amount of noise?

You say Yuan is cost effective, compared to what? Smaller sub built by the same shipyard will be even cheaper. I'm simply entertaining the possibility given the leak

We know shipyards in China already have production line & supply chain set up for something like Yuan. Building new subs of different dimension will take additional investment to scale. As such, the assumption all along is that a mini-nuke (assuming it exists) will be similar in dimension to Yuan

I thought that this SSKN won’t have steam at all, and potentially natural circulation means almost no noise from the reactor? In other words, there might not be any noisy machinery on this sub at all. If all your machines are quiet there is less need for sound insulation, and rafting could be simpler or simply done away with all together.

Lets say this is true, and also let’s say the reactor isn’t too large in size either, let’s say it’s man sized, then we have the potential to make a skinny sub which is virtually silent.

If it can be really skinny then maybe this mini-nuke could be more like a very large, manned, underwater vehicle than the subs we are used too. In other words, maybe this is not being developed from a Type 039, but rather an already fully automated battery powered very large UUV to which this new engine is being added along with a manned section. After all, this new engine is just a battery charger.

how do you generate electricity without steam? Most noise from nuclear sub does not come from coolant pumps

Could it be possible the 2500t version is just a POC/technology demonstrator? Any probability his configuration is being evaluated to see if it is viable for application on full sized SSN?

Do you think that's more likely or do you think it's more likely that a mini-nuke is strategic asset and we won't get real data on it until much later?

 

[BoraTas]

Icooling circuit is not the main source of noise on a nuclear sub. The biggest source of noise are the steam turbines, generators and reduction gears. So on a nuclear-electric boat like in this example, the loudest source of noise is with the steam turbines or stirling engine and with the eMotor. Think about anything that's mechanical and rotate. That probably causes a lot of noise.

Yeah. It is not known much but USN rarely uses natural circulation nowadays. Modern pumps are that quiet. Noise from the auxiliary machinery is very important nowadays as most noise related to propulsion was eliminated.

If this is truly a mini-nuke, it would be a strategic platform. I doubt they'd give us something as classified as engine power before first boat even gets launched. 10MWt delivery 1.2MWe would be 12% efficiency. That is stunningly low. Even 091's reactor going directly into shaft achieved like 18% efficiency.


Again, it's doable, but we have to think about what is the requirement here. Different requirement will lead to different sized propulsion unit.

Let's do some thought experiments here

If PLAN wants this to have real endurance/stealth, then it needs to have atmospheric control machinery, which takes power to operate. 300kw is required to keep lights on for Yuan sub and maybe move occasionally in deep waters. If we add more powerful equipment like atmospheric control, more computation power & sensors, the sub will also be a little larger. Maybe 600kW is needed to keep the lights on at low depth with everything you need and not moving.

Let's say for a 4000t sub, you need 25MWe to move at 30 knots under water (at reasonable depth) (basing this on VA needing 30+MWe to achieve some classified speed). I could be over or under-estimating things here.

To sustain 10 knots, you'd about 1MWe to do so. speed is correlated to power ^ 3

So, you probably need 1.6MWe. Now if we consider eMotor/Drive to be 80% efficient, then we need about 2MWe generated by steam turbine/Stirling to achieve at best 10 knots speed. This is actually better than I thought.

But it rests on my assumptions about speed/power being correct and keeping the lights on calculation to be correct. I could be entirely too optimistic about both here.

I don't think VA-class is a good measure here. Its top speed is classified and the power figure is non-dependable. Furthermore, pump-jets and high-speed are inefficient. You may want to look at the study I linked. 350 kW on water is enough for a 3000-ton submarine to reach 10 knots. The study uses the hull of the Collins class as example. At a 75% propeller efficiency and a 90% electrical transmission efficiency a 517 kW output by the engines would be enough. If we scale the sub up to 4000 tons at the same proportions we would have to increase that number by 21% as the required power scales mostly linearly with the wetted area. So I would say 4 x 320 kW engines are enough for 11 knots and non-propulsion loads for a 4000-ton sub.

 

[Andy1974]

@tphuang, check this..

A Stirling engine uses a working gas such as helium, which is housed in a sealed environment. When heated, the gas expands causing a piston to move and interact with a linear alternator to produce electricity. As the gas cools and contracts, the process resets before repeating again.

A linear alternator produces the electricity. The movement of the alternator is powered by heat on one side. The heat comes from the reactor chamber directly. You just have to point a Stirling engine towards a heat source and it starts generating electricity.

I think the key is to get as much heat to the stirling engine as possible, so you would position one end of it right next to the reactor chamber, where it is very hot. Perhaps, ideally, you would have one end of it sticking inside the reactor!

 

[Andy1974]

Guys, I think I just had an epiphany!

Stirling engines take heat out of the reactor, this means they can take the place of coolant and coolant loops. The Stirling engines can regulate the reactor chamber temperature, and not only can they take heat out but they can inject heat into the chamber too, because Stirling engines work in reverse.

So my question is, what components does this reactor actually need?

 

[tphuang]

I don't think VA-class is a good measure here. Its top speed is classified and the power figure is non-dependable. Furthermore, pump-jets and high-speed are inefficient. You may want to look at the study I linked. 350 kW on water is enough for a 3000-ton submarine to reach 10 knots. The study uses the hull of the Collins class as example. At a 75% propeller efficiency and a 90% electrical transmission efficiency a 517 kW output by the engines would be enough. If we scale the sub up to 4000 tons at the same proportions we would have to increase that number by 21% as the required power scales mostly linearly with the wetted area. So I would say 4 x 320 kW engines are enough for 11 knots and non-propulsion loads for a 4000-ton sub.

350kW at what depth?

And if you look at my calculations there, 600kW is needed just for all the machineries that you'd want to install in such a mini-nuke. Collins class is not expected to have Atmospheric control or carry similarly power intensive sensors & computational resources. After all, it's a 20 years old design

It really depends on what their design goals are. If they are looking for a sub with similar combat capability like Yuan (which needs about 250 kW for hotel load), then 4 x 320 might be enough. If they are looking for it to carry more power hungry machines and operate at lower depth, then they will need more.

I'm still not convinced why we need stirling here

 

[Blitzo]

The AUKUS map uses a 6.5 knot sustained transit speed for a SSK with limited fuel.
But if you plug in 14 knots, that's two-thirds of the SSN speed. Then add in unlimited fuel for the SSKN.
You get a radically different comparison map between an SSN and SSKN.

Yes, 6.5 knots as a sustained transit speed for a SSK.

We have no reason to believe at this stage that the SSKN is able to achieve a 14 knot transit speed indefinitely in the manner that a proper SSN is able to maintain transit or tactical speeds.

 

[para80]

For a start SSKs do need to snorkel to exchange air. This SSKN design would have to generate its own air supply from seawater same as modern SSN do to stay submerged and at cruise. This gets us into the whole "How much hotel load does the design provide"-debate, which is pretty crucial to SSN endurance vs SSK as well. As always things are far more complex than just replacing diesel and battery propulsion with just another form of AIP.

 

[BoraTas]

350kW at what depth?

And if you look at my calculations there, 600kW is needed just for all the machineries that you'd want to install in such a mini-nuke. Collins class is not expected to have Atmospheric control or carry similarly power intensive sensors & computational resources. After all, it's a 20 years old design

It really depends on what their design goals are. If they are looking for a sub with similar combat capability like Yuan (which needs about 250 kW for hotel load), then 4 x 320 might be enough. If they are looking for it to carry more power hungry machines and operate at lower depth, then they will need more.

I'm still not convinced why we need stirling here

Depth has an insignificant effect on power requirements once the sub is built. The density of water doesn't change much with depth. The rate is like 1% every 2200 meters. It has an indirect effect at the design stage. Subs designed for deeper operations have thicker hulls. Which means the sub has to be larger for the same internal equipment to have the same buoyancy, which increases the wetted area. As I wrote the study uses the Collins-class as example. 600 kW sounds too much for hotel load (which wasn't included in my previous message). Current SSKs use like 90 kW. Stirling engines are just a speculation. They would be more efficient than a steam turbine at the power level we are talking about. Which would enable a smaller reactor. That's it.

 

[tphuang]

Depth has an insignificant effect on power requirements once the sub is built. The density of water doesn't change much with depth. The rate is like 1% every 2200 meters. It has an indirect effect at the design stage. Subs designed for deeper operations have thicker hulls. Which means the sub has to be larger for the same internal equipment to have the same buoyancy, which increases the wetted area. As I wrote the study uses the Collins-class as example. 600 kW sounds too much for hotel load (which wasn't included in my previous message). Current SSKs use like 90 kW. Stirling engines are just a speculation. They would be more efficient than a steam turbine at the power level we are talking about. Which would enable a smaller reactor. That's it.

I'm not sure why Yuan is always transiting at PD if depth has such insignificant effect on power requirements then?

Yuan class right now has 320kW for its stirling engine. I'm basing hotel load on that. It's possible that for some smaller subs like 212, 90kW is enough. But boats with more sensors and computation power would require more. How much power does latest Intel CPU or Nvidia GPU consume? And atmospheric control (if they do chose to install it), would require quite a bit of power.

 

[lcloo]

Please accept my ignorance, I googled and found what "hotel load" means in electrical engineering, but what is "PD"? Is it Port of Destination?