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Phys.org's To give astronauts better food, engineers test a fridge prototype in microgravity says:

Astronauts have been going to space since 1961, but they still don't have a refrigerator to use for keeping food cold on long missions to the moon or Mars.

[...]The researchers are not the first to attempt building a fridge like those used on Earth for space missions, but they are among the few who have tried since astronauts walked on the moon in 1969. Even though fridge experiments have been in space before, they either didn't work very well or eventually broke down.

In practice, the fridge design would cool food through a vapor-compression cycle, similar to the process that a typical fridge uses on Earth, but without the need for oil. Having an oil-free vapor-compression cycle removes concerns about oil not flowing where it should in zero gravity.

Question: Why did tests in space of refrigerators of the type we use at home fail? How many were tried? Which tests failed outright, which tests worked for a while then broke down and why?

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    $\begingroup$ Your quote doesn't seem to talk about "refrigerators of the type we use at home." It seems to mainly be concerned with refrigerators that are not lubricated with oil. I'm not an expert on the subject, but I'm reasonably certain that residential refrigerators, freezers, and air-conditioners all have oil mixed with the working fluid, and they may have oil in other parts of the sealed compressor unit. Totally reasonable to think that an oil-lubricated, stationary machine might only work when oriented with a certain side "up." $\endgroup$ May 31, 2021 at 0:19
  • $\begingroup$ @SolomonSlow "...the fridge design would cool food through a vapor-compression cycle, similar to the process that a typical fridge uses on Earth, but without the need for oil." Here "type" only means those that use "a vapor-compression cycle" to "cool food". $\endgroup$
    – uhoh
    May 31, 2021 at 0:22
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    $\begingroup$ @SolomonSlow The refrigerator manuals I have read always say that it must be upright for (x period of time) before being powered up. The only way that makes any sense is if they want to ensure the oil has drained to the lowest point. $\endgroup$ Jun 1, 2021 at 2:21
  • $\begingroup$ Wow. I never knew or even thought about this. What an interesting question. $\endgroup$
    – user39728
    Jun 1, 2021 at 4:09

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