China's Shenzhou-15 mission crew onboard the China Space Station (CSS) has completed testing of a free-piston Stirling thermoelectric converter, the country's first successful in-orbit verification of such technology.
Stirling engine is basically a steam device, isn’t it?
No, stirling engines do not involve steam. They convert a temperature differential into mechanical energy by using the expansion and contraction of a gas to move a mechanism which displaces the gas from the hot side to the cold side and back. See https://en.wikipedia.org/wiki/Stirling_cycle and https://www.stirlingengine.com/animations/ for details.
When the temperature differential comes from burning fuel, the stirling engine is sometimes called an “external combustion engine”.
What benefits does that have over something like a radioisotope power?
The article doesn’t appear to say what heat source this stirling-engine-in-space test actually used; i suppose it could’ve been decaying radioisotopes. RTGs (Radioisotope Thermoelectric Generators) use solid-state thermocouples which operate by https://en.wikipedia.org/wiki/Thermoelectric_effect for the same purpose (as a stirling engine connected to a generator to convert the mechanical energy into electrical energy, that is).
I think the advantage of using Stirling engines over thermocouples is that they can be substantially more efficient, but the disadvantage is that they have moving parts and are constantly going through a heating-cooling cycle so they require some maintenance (albeit not as much as an internal combustion engine).
If i remember my college thermodynamics classes correctly, i believe the Stirling engine is interesting because in principle it can operate at the theoretical maximum efficiency (minus friction and other dissipative losses) which a thermodynamic system that converts heat into usable work can achieve. The disadvantage i believe is that they tend to be pretty slow and hard to scale to any practical applications.
No, stirling engines do not involve steam. They convert a temperature differential into mechanical energy by using the expansion and contraction of a gas to move a mechanism which displaces the gas from the hot side to the cold side and back. See https://en.wikipedia.org/wiki/Stirling_cycle and https://www.stirlingengine.com/animations/ for details.
When the temperature differential comes from burning fuel, the stirling engine is sometimes called an “external combustion engine”.
The article doesn’t appear to say what heat source this stirling-engine-in-space test actually used; i suppose it could’ve been decaying radioisotopes. RTGs (Radioisotope Thermoelectric Generators) use solid-state thermocouples which operate by https://en.wikipedia.org/wiki/Thermoelectric_effect for the same purpose (as a stirling engine connected to a generator to convert the mechanical energy into electrical energy, that is).
I think the advantage of using Stirling engines over thermocouples is that they can be substantially more efficient, but the disadvantage is that they have moving parts and are constantly going through a heating-cooling cycle so they require some maintenance (albeit not as much as an internal combustion engine).
Thanks for the rundown!
If i remember my college thermodynamics classes correctly, i believe the Stirling engine is interesting because in principle it can operate at the theoretical maximum efficiency (minus friction and other dissipative losses) which a thermodynamic system that converts heat into usable work can achieve. The disadvantage i believe is that they tend to be pretty slow and hard to scale to any practical applications.
Correct me if i’m wrong it’s been a long time.