https://www.techpowerup.com/319892/wieland-pumpless-aio-cpu-cooler-tested Wielend AIO CPU cooler is a prototype closed-loop liquid CPU cooler that lacks a pump, or any form of active coolant flow between the heat-source (the CPU block), and the sink (the radiator). The cooler works on the principle of thermosiphon, where the temperature differential between the source and sink cause coolant flow. This is essentially how solar water heaters work, as they drive coolant (water) between the heating panels and a storage tank. It's not like the cooler is without any moving parts, the radiator still needs ventilation from fans.
Der8auer tested a prototype Weiland cooler, and compared its cooling performance to that of a typical 240 mm AIO CLC (with a pump), on a machine with an AMD Ryzen 9 7950X processor with a 170 W TDP. During a 20-minute Cinebench R23 multithreaded stress test, the 240 mm AIO held temperatures to around 70 °C, while the Wieland AIO managed 78 °C. The power draw with the regular 240 mm AIO was higher, as the processor probably utilized the lower temperature to hold onto higher boost frequencies.
It's an interesting concept.
