I fail to understand most of the reactor parts' physics. Please help.

Quote from Shimat

I'm fairly new to IC2. This whole mod is callenging, yet interesting, but recently I discovered the whole new game of nuclear engineering. Ever since I ran into reactor planner, I even almost stopped playing Minecraft itself, but still, my designs lack any true, in-depth understanding of how the components work. I've read Albaka's guides, but they only gave me the general idea of what's supposed to happen. So please, explain like i'm 5:

- The difference between core (heat) and hull (heat)?

I don't think there is any difference.

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- The copper and diamond heatswitch physics? I have no idea what the copper one is for, and I assume that the diamond one takes up to 24 heat from sides and 8 from core, divides the sum by 5 (4 sides+core) and sends the resulting heat back; The excess heat goes into it's own durability.

No; they calculate the heat level (heat / max_heat in percent) difference in the components beside itself first, and try to maintain a balance by moving the heat around, up to a variable total (depending on the type; diamond has 24, copper has 0, so copper will not attempt to balance heat between surrounding components). Afterwards, the calculate the heat level difference between itself and the reactor core by up to a variable total (depending on the type; diamond has 8, copper had 72).

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- Heat vents, especially the golden one? I assume that it takes x heat from up to 4 sides + up to 36 from the hull and then substracts 20; The excess heat goes into it's own durability.

Not exactly sure about this. However, I think it can transfer 36 heat points to itself but can only destroy 20 at the same time, so it will continue gathering damage.

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- How in the world is this different from this ? Why does simply copying it without using another reactor doesn't work either?

Reactors process the component on the top left, then across to the top right, then to the next row, and so on until it reaches the bottom right.

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Thank you in advance!

1.) None, just two words for the same thing.

2.) Try using the names you get when mousing over components in the reactor planner (or looking them up ingame), so we understand what you mean. Be exact, some components have very similar names. Alblaka's guide uses different names, because it was written before the system was finalized and those were the development names at the time.

3.) "Vents" never pull heat from surrounding components into themselves. Only "exchangers" do.

4.) During each "reactor tick", which is once a second, the internal components are processed one by one. It starts in the top left corner and goes left to right, top to bottom until the lower right corner. Because of this, the order of the components matters.

The design you linked there is in fact one of the most complex ones on the board, since it employs many different cooling design tricks all within a tiny 3x4 space. It's a masterpiece - don't underestimate it just because it's small. It cannot work when inverted or paired with itself, because then the underlying assumptions of when how much heat gets handled where are no longer true. If you can understand what exactly each individual part in that reactor does and why, you know most there is to know.

The following parts breakdown might help you, as it puts the important stuff from Alblaka's guide into a more condensed, clear format:

Vents
Basic: Dissipates 6 heat. Pulls nothing, transfers nothing.
Advanced: Dissipates 12 heat. Pulls nothing, transfers nothing.
Reactor: Dissipates 5 heat. Pulls up to 5 heat from the hull. Transfers nothing.
Overclocked: Dissipates 20 heat. Pulls up to 36 heat from the hull. Transfers nothing.
Component: Dissipates nothing, pulls nothing, transfers nothing. Has no durability and cannot accept heat. Each adjacent component that is capable of storing heat, however, dissipates 4 heat, even if it cannot normally do so.

Exchangers
Basic: Dissipates nothing. Attempts to balance its own heat level with that of the hull and that of all surrounding components by transfering up to 4 heat between itself and the hull, and up to 12 heat between itself and its neighbours.
Advanced: Dissipates nothing. Attempts to balance its own heat level with that of the hull and that of all surrounding components by transfering up to 8 heat between itself and the hull, and up to 24 heat between itself and its neighbours.
Reactor: Dissipates nothing. Attempts to balance its own heat level with that of the hull by transferring up to 72 heat between itself and the hull.
Component: Dissipates nothing. Attempts to balance its own heat level with that of all surrounding components by transferring up to 36 heat between itself and its neighbours.

Note: an exchanger only pulls as much from the hull as necessary to achieve balance, and will even return heat to the hull if necessary. A vent capable of hull transfer, on the other hand, only ever pulls from the hull. It will always pull, as much as it can, even to the point of its own destruction.

Other
Fuel rod (cell): Generates heat, and inserts it into any available adjacent component that can accept heat. If multiple are available, it is split evenly; if one is available, it gets all of it. If none is available, the hull takes the heat.
Condensator: Gobbles up all heat at the cost of durability. Can only be restored by crafting it with redstone/lapis.
Coolant Cell: Gobbles up all heat at the cost of durability. Can only be restored by pulling the heat back out (cooling it back down, essentially).
Reflector: Pretends to be a fuel rod but isn't. Raises fuel rod efficiency. Does not interact with heat in any way, shape or form.
Plating: Increases maximum hull heat and lowers explosion magnitude. Does not interact with heat in any way, shape or form.