Heat pipe

A heat pipe is a building used to transmit heat between heat-producing and heat-consuming structures. It does not create heat on its own; instead, it stores and passes along thermal energy through connected pipes, forming the backbone of high-temperature setups such as nuclear power. Heat pipes can be chained into long straight runs, but each one has a finite throughput, so the temperature falls slightly along the line as heat power increases.

For a heat pipe with one input on one side and one output on the other, the temperature drop across that entity is 1 + (P / 15) °C, where P is the heat power flowing through it in MW. Because a heat exchanger must reach 500°C before it can produce steam, and a heat generator such as a nuclear reactor can reach up to 1000°C, the usable temperature difference between source and exchanger is at most 500°C. This gives a practical upper bound for a straight line of heat pipe of 500 / (1 + P / 15). For example, a single nuclear reactor outputting 40 MW can drive a heat-pipe line of about 136 tiles before the temperature loss becomes too large.

Heat pipes are also relevant when comparing them to nuclear reactors used as heat conductors. A reactor can transfer heat even when unfueled, but it is much larger than a pipe segment, so it must be compared against a 5-by-5 block of heat pipes rather than a single tile. As a result, a reactor lowers temperature far less efficiently than a compact pipe array when used purely for heat transfer. A long line of reactors can still move substantial heat, but it does so with significantly different space and efficiency characteristics than heat pipe networks.

In Space Age, heat pipes have an additional role on Aquilo. There, they are used to prevent entities from freezing by automatically transferring heat into nearby entities. Different entities consume different amounts of heat to stay warm, but unlike a heat exchanger they do not need to reach any special operating temperature. A heat pipe only needs to be at least 30°C to keep an entity warm. Heat pipes on Aquilo also do not lose heat to the environment; they only lose heat when feeding nearby entities that require warming.

Practical points:

• Heat pipes are best used in compact layouts when moving large amounts of heat over long distances.
• The effective length of a heat-pipe line depends on the heat power being carried; higher throughput shortens the safe distance.
• In nuclear setups, keeping the pipe run short helps preserve enough temperature for heat exchangers at the end of the line.
• On Aquilo, maintaining a minimum pipe temperature is enough to support nearby structures, since the pipe only transfers heat where needed.