Settle down Cheech & Chong. It’s NOT what you think! That two-pot contraption is a refrigerator. As the water in wet sand in between the clay pots evaporates, it draws heat energy away from the smaller vessel, keeping the contents cool; via Greenupgrader.
The “Pot-In-Pot Cooler” is used MOSTLY in rural parts of the developing nations, where electricity is scarce. Reminds me of the camel-carried refrigeration! Researchers outfitted camels with solar-powered refrigerators to transport vaccines across the desert.