Are there other ways to cool an object to 77 K (−196 °C; −321 °F) without use of cryogenic fluids, like liquid nitrogen?

 I am looking for a way to be able to keep an object below 77 K, while maintaining an airtight container. This cannot be obtained with cryogenic fluids like liquid nitrogen, as it becomes highly explosive and dangerous. Therefore, I need a way to keep an object below 77 K in an airtight container, safely.

kebmoore6 years ago
Acetone can be cooled with dry ice to -78 °C without freezing; acetone/dry ice baths are commonly used in laboratories to conduct reactions at low temperatures. To get below that, I think you have to go to a cryogenic fluid. Any sealed, airtight container would have to have a valve to vent the pressure of the sublimating solid or evaporating liquid, or else there could be explosive results from high pressure gasses.
Liquid Nitrogen sure as heck isn't explosive at any temperature. Its co,mpletely inert.

The only other method is a Stirling heat engine, and they COST.