| 62 / | HD | REFRIGERATION |
| 600 | DF | CRYOGENIC TREATMENT OF GAS OR GAS MIXTURE {4} |
| 606 | | .~ Liquefaction {6} |
| 607 | DF | .~.~> Hydrogen |
| 608 | DF | .~.~> Helium |
| 51.2 | DF | .~.~> Utilizing Joule-Thomson effect {1} |
| 611 | DF | .~.~> Natural gas {3} |
| 615 | DF | .~.~> Air |
| 616 | DF | .~.~> Heat exchange with liquid cryogen |