Physics-wise, if there's a useful working fluid in the temperature and pressure range you want, it can be done.
The problem then is power. Refrigerators are power hungry. Space exploration tends to be desperately short on power-- there's not a lot of sources of electricity that are happy to spend ten years at -100C and then spring forth to produce volts at quantity and with minimal mass. A heat engine is right out. (Where would the cold sink come from?) Batteries are tough. RTGs have terrible engineering challenges-- plus they'll use up a lot of half-life during the coast phase to Venus.
Given that design space, a Venus lander (that isn't built to operate at Venus temps) would probably have a battery and a store of internal coolant that undergoes phase change and is dumped overboard. A big block of water ice, or depending on the constraints, something more exotic.
>drops to 20C
Don't have to get that cold, fortunately. There is a considerable domestic demand for ultrahot electronics for wellhead sensors in oil exploration. (The head of a drill string needs to have some smarts for remote sensing-- figuring out if the rock you're drilling through has any oil in it. If you've got the money, you can buy a microcontroller than can run all day and night at 220 Celsius!https://www.digikey.com/en/products/detail/texas-instruments...
The problem then is power. Refrigerators are power hungry. Space exploration tends to be desperately short on power-- there's not a lot of sources of electricity that are happy to spend ten years at -100C and then spring forth to produce volts at quantity and with minimal mass. A heat engine is right out. (Where would the cold sink come from?) Batteries are tough. RTGs have terrible engineering challenges-- plus they'll use up a lot of half-life during the coast phase to Venus.
Given that design space, a Venus lander (that isn't built to operate at Venus temps) would probably have a battery and a store of internal coolant that undergoes phase change and is dumped overboard. A big block of water ice, or depending on the constraints, something more exotic.
>drops to 20C
Don't have to get that cold, fortunately. There is a considerable domestic demand for ultrahot electronics for wellhead sensors in oil exploration. (The head of a drill string needs to have some smarts for remote sensing-- figuring out if the rock you're drilling through has any oil in it. If you've got the money, you can buy a microcontroller than can run all day and night at 220 Celsius! https://www.digikey.com/en/products/detail/texas-instruments...
Fun fact: one of the handful of commercial applications for nuclear fusion reactors, today, is as a source for downbore neutron excitation gamma spectroscopy https://www.slb.com/-/media/files/drilling/brochure/neoscope... )