Science and technology of the Tang dynasty
The inventor Ding Huan (fl. 180 AD) of the Han dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered. In 747, Emperor Xuanzong had a "Cool Hall" built in the imperial palace, which the "Tang Yulin" (唐語林) describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song dynasty, written sources mentioned the air conditioning rotary fan as even more widely used.
Regenerative cooling
Regenerative cooling is a method of cooling gases in which compressed gas is cooled by allowing it to expand and thereby take heat from the surroundings. The cooled expanded gas then passes through a heat exchanger where it cools the incoming compressed gas.In 1857, Siemens introduced the regenerative cooling concept with the Siemens cycle. In 1895, William Hampson in England and Carl von Linde in Germany independently developed and patented the Hampson–Linde cycle to liquefy air using the Joule–Thomson expansion process and regenerative cooling. On 10 May 1898, James Dewar used regenerative cooling to become the first to statically liquefy hydrogen.