Brayton cycle

A heat engine moves heat from a high temperature area (Th), to a lower temperature sink (Tc), in order to generate power. The Brayton cycle is a thermodynamic engine that can be used for power (usually electric) generation. It uses a gas as a working medium. (Some more efficient cycles require gas to liquid phase changes.)

• An airplane turbo engine is an example of an open Brayton cycle.

• A nuclear reactor power plant using helium cooling is an example of a closed Brayton cycle.

• The ideal equation for a Brayton cycle is efficiency(ef) = 1-Tc/Th.

• An actual Brayton engine has a number of inefficiencies and non-reversible, so the actual efficiency is significantly lower.

So for a high efficiency Brayton cycle, Th needs to be significantly higher than Tc.

• For example, with an efficiency of 40% Tc/Th is 0,6. If Tc is 500K, then Th is 830K.

• For the same example at 60% efficiency, Tc/Th=0,4, and for a TC of 500K Th is 1250K.

If applied to a closed cycle used on Mars, Tc is the radiator temperature, and Th would be the temperature of the reactor core. Note that Mars has large cold sinks, so in principle, heat engines would be more efficient on Mars than on Earth. However, dumping heat on Earth is easier (into the air and rivers), so it may be an engineering challenge to dump large amounts of waste heat on Mars.