All of the heat exchangers used everywhere in our engine are made of soft, pure, thin-wall copper. This is possible because of the low pressures and temperatures we employ. The thin walled copper is very effective in transferring large amounts of heat with little temperature loss.
Furthermore, all heat transfer passages are very slender, but very long relative to their slender width. This very high ratio of length to breadth of the passages causes the exchangers to exhibit a very high value of NTU - Number of Transfer Units - a commonly used figure of merit for heat exchangers. This in turn further greatly reduces the temperature differential across the exchangers.
Each heat exchanger is completely encapsulated inside an insulating material - usually an engineering thermoplastic. Again, this is only possible because of the low pressures and temperatures employed. The result is that the heat is trapped effectively inside the engine, rather than escaping to the surroundings.
High performance heat transfer fluids are employed, further improving the effectiveness of the heat transfer processes. This again is possible since the temperatures are low enough to permit their use.
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