Efficiency of longer heat pipes

[Ranayna]

Just a small question about nuclear power. I was not able to find a conclusive answer in the wiki.

TL;DR: Does the temperature of a heatpipe connected to a heat exchanger actually matter, as long it is above 500 degrees?

As far as i understand, turbine need 500 degrees steam made in a heat exchanger, and if the heatpipe connected to the heat exchanger is not at least 500 degrees hot, it does not do anything.
But do higher temperatures at the heat exchanger matter?

If they do matter, i assume it would be better to pipe steam to the turbines and make the exchanger setup more compact.

At the moment my setup is as follows: From each reactor i have a single heat pipe going to a douple row of heat exchangers, and to each exchangers i have directly connected two turbines. This makes somewhat long heat pipes, at the furthest away i am at ~850 degrees,
According to the power statistics this seems to be able to produce the full amount, but i do not consume nearly enough at the moment to verify.

[Khagan]

Higher temperatures don't affect the heat exchanger. But you do need the heat pipes close to the reactor to be hotter so that heat flows to the further ones, and keeps them above the magic 500°.

[Fletch]

This makes somewhat long heat pipes, at the furthest away i am at ~850 degrees,

As long as the furthest exchanger is greater than 500° then you are fine (for now) -- the exchanger will produce steam. Heat exchangers need at least 500° to work, and any heat above that is buffered in the exchanger (up to the max 1000° the system can ever get to).

However, if the turbines are idle'ing -- not consuming steam / not producing electricity because there is not enough electrical demand (which is exactly how your coal-based steam engines work too), then the entire nuclear system (reactors, heat pipes, and exchangers) will get hotter and buffer/store that extraneous heat if your reactor stays fueled.

I think the best test of your reactor design is when it is under max load (stress testing). That is when you'll see the system draw down on all those stored heat buffers and eventually reach its "lowest continuous operating temperature". At that point you might find that your furthest exchangers no longer work because they are simply too far away and the heat pipes don't have the throughput to keep them at 500°.

Recommend studying the wiki here: https://wiki.factorio.com/Tutorial:Nuclear_power

Generally, I think it is better to keep your exchanges as close to the reactors as possible, and then pipe the generated steam away to your turbine field. Heat pipes have a "heat throughput" (that degrades based on distance from heat source), whereas steam pipes are practically infinite throughput.

[Defektiv]

It does on Aquilo, but that's because heat pipes double as defrosters there. But I'm pretty sure you do not get more power from hotter steam.

[Z0MBE]

why doesn't it work the same way pipes do where there is always the same amount throughout the pipe - I feel like it's not a unreasonable ask but i guess it's about the thermodynamics

[Ranayna]

Originally posted by Fletch:

This makes somewhat long heat pipes, at the furthest away i am at ~850 degrees,

As long as the furthest exchanger is greater than 500° then you are fine (for now) -- the exchanger will produce steam. Heat exchangers need at least 500° to work, and any heat above that is buffered in the exchanger (up to the max 1000° the system can ever get to).

However, if the turbines are idle'ing -- not consuming steam / not producing electricity because there is not enough electrical demand (which is exactly how your coal-based steam engines work too), then the entire nuclear system (reactors, heat pipes, and exchangers) will get hotter and buffer/store that extraneous heat if your reactor stays fueled.

I think the best test of your reactor design is when it is under max load (stress testing). That is when you'll see the system draw down on all those stored heat buffers and eventually reach its "lowest continuous operating temperature". At that point you might find that your furthest exchangers no longer work because they are simply too far away and the heat pipes don't have the throughput to keep them at 500°.

Recommend studying the wiki here: https://wiki.factorio.com/Tutorial:Nuclear_power

Generally, I think it is better to keep your exchanges as close to the reactors as possible, and then pipe the generated steam away to your turbine field. Heat pipes have a "heat throughput" (that degrades based on distance from heat source), whereas steam pipes are practically infinite throughput.

Now i feel stupid :D
I totally did not consider that a fully loaded heat exchanger will pull more heat from the heatpipe.

I will test this under load by isolating one part of my plant while disconnecting the coal burners. That should put it under full load.
So as long as under full load the heatpipe at the end stays above 500 degrees, i should be fine, right?

[Fletch]

Originally posted by Ranayna:

So as long as under full load the heatpipe at the end stays above 500 degrees, i should be fine, right?

I believe that is correct.

...isolating one part of my plant while disconnecting the coal burners...

You can use a circuit to automatically turn on/off the coal boilers, which in effect makes your coal boilers your "emergency power supply". A very simple way to do this is to wire a circuit between an accumulator and the offshore water pump feeding the boilers -- then set a condition on the water pump to only run when "A < 50" (or whatever number you choose). If accumulator charge gets too low, then the boilers kick back on as your emergency backup.

[Ranayna]

Ok...
I isolated one of the 120 MW reactors at the end of the double row and it's turbines. All other turbines where disconnected from the grid.
This was now running on full electrical load for a couple of minutes and i think the system has reached equilibrium,

The heatpipe at the end constantly sits at 501.17 degrees, and the two heat exchangers are at 500 degrees flat and are still producing 32 Steam per second.
So it is close, but just out of reach of full efficiency... I am producing 116 MW of electrical power, while the reactor outputs 120 MW of heat.

Ah well, i can live with that design for now. My next plant will be build differently :D

EDIT: Slight miscalculation, i accidentally left 2 Turbines connected to the grid. I produced only 104 MW at full load

[Ranayna]

And - for now - final update:

I rebuilt the part under test, made the heat pipe not a line anymore but a "T", and was able to make it 5 elements shorter.
Under full load the system has not fully reached thermal equilibrium, but with a heat exchanger temperature of currently 533.72 it takes several seconds to go down by .01 degrees.

[Chindraba]

It bears testing in 2.0 as things may have changed, but if you have the space available a parallel run of heat pipes used to enable the heat to flow farther from the reactors. That could very well be different now, though a mild search in the notes about heat pipes didn't show anything which looked like it would change that.

Even if that 'trick' hasn't changed, fluid flow has. The old reactor designs probably still work well, perhaps even as well as they did in 1.1. The constraints, however, are much less and the pipe placement is no longer a major source of odd behavior. Any design from 1.1 should, in my view, considered suspect, at best. Similarly, any advice with a 1.1 frame reference ought to be well tested to ensure that it is still valid as well as being useful. (I don't have any 2.0 experience with nuclear reactors, so I'll not give any direct advice for the new designs.)

[Fletch]

Originally posted by Chindraba:

It bears testing in 2.0 as things may have changed, but if you have the space available a parallel run of heat pipes used to enable the heat to flow farther from the reactors. That could very well be different now, though a mild search in the notes about heat pipes didn't show anything which looked like it would change that.

Even if that 'trick' hasn't changed, fluid flow has. The old reactor designs probably still work well, perhaps even as well as they did in 1.1. The constraints, however, are much less and the pipe placement is no longer a major source of odd behavior. Any design from 1.1 should, in my view, considered suspect, at best. Similarly, any advice with a 1.1 frame reference ought to be well tested to ensure that it is still valid as well as being useful. (I don't have any 2.0 experience with nuclear reactors, so I'll not give any direct advice for the new designs.)

Good points on doubling up the heat pipes -- probably a requirement when you are running all the exchangers off one side (instead of both sides), and especially as you scale up with more of the neighbor bonuses to have the more powerful reactors (even if you have exchangers on both sides).

From the wiki: https://wiki.factorio.com/images/Heat_exchangers_per_pipe.png
The example showing 42 exchangers is the style I lean towards.

[Chindraba]

Originally posted by Fletch:

Good points on doubling up the heat pipes -- probably a requirement when you are running all the exchangers off one side (instead of both sides), and especially as you scale up with more of the neighbor bonuses to have the more powerful reactors (even if you have exchangers on both sides).

From the wiki: https://wiki.factorio.com/images/Heat_exchangers_per_pipe.png
The example showing 42 exchangers is the style I lean towards.

Been so long since I did a reactor I couldn't even remember how I did it. Made me look.
https://steamcommunity.com/sharedfiles/filedetails/?id=3408278157
With the change in water to steam ratio and the new fluid system in 2.0 I'm not sure what I'm gonna do. It's gonna be different, though.

[Khagan]

Originally posted by Chindraba:

Any design from 1.1 should, in my view, considered suspect, at best.

Yes, lots of changes. The new fluid dynamics means you don't need (or want) pumps. The combination of that with the changed ratio of water to steam means you don't need to build on water (though being near to water is still a Good Idea). Being able to read the temperature of the reactor means you can control fuel usage without needing any steam tanks. Overall the designs can be much simpler and more flexible.

[Chindraba]

I love the new fluid system over the old. It is, however, a mixed blessing. I'll definitely take the change and roll with it. The benefits, and reduced obscure behavior are very welcome. I do lose, however, my easy wall setup. I could place a solar-powered pumpjack in the middle of nowhere and fuel the flamers for nearly 2000 tiles of wall without a pump needed anywhere on the wall, and unless using a backup turret not even needing power to the wall. Now, for the same wall, I'd need 6 or 7 pumps and a line of power poles to run them, for the same wall. Certainly a minor inconvenience compared to the mysterious performance of the old system. Just not 100% sweetness and light.

[Khagan]

Originally posted by Chindraba:

I love the new fluid system [...] The benefits, and reduced obscure behavior are very welcome. I do lose, however, my easy wall setup.

Yes, not being able to connect together an unlimited line of flame turrets is a drawback. But it's the only one I've noticed.

[Chindraba]

Well, another big hit is the pump drop from 12,000/s to 1,200/s. That's probably going to be a problem for many of the mega-basers. I know I did a few spots were I was pushing 5+k and those are going to be broken. That map's so broke that it won't matter to me, but the hit to existing 'plans' will give others something to complain about.

It's so broke it don't matter, but I "fixed" my wall of flame. Only had to add 55 pumps to it. The power shouldn't be an issue since I really should have repair bots covering the wall anyway. Real damage was rare, and easily handled in person when it was important. While off-planet, however, personal intervention won't be quite as simple, or rapid.

For now I'm just inching my way through things. As long as I get to the Shattered Planet before Thanatos gets to me it's all good.