Heat Exchangers are a material used by Engineers, introduced in v2.1.
Component found in ships: frequently used by haulage vessels. Destroyed haulage vessels can be scavenged from the aftermath of combat in shipping lanes. Known to be salvaged from signal sources in anarchy systems.
Heat exchangers transfer heat between separate systems.
— In-game description
It is often dropped by Type-9 Heavy transport vessels after they have been destroyed. They can also be found as salvage items in some Unidentified Signal Sources (e.g. Encoded Emissions, or Combat Aftermath), especially systems with Anarchy governments.