| 165 / | HD | HEAT EXCHANGE |
| DIG 327 | DD | THERMOSYPHONIC HAVING VERTICAL AIR DRAFT PASSAGE {3} |
| DIG 331 | | .~ Air draft passage confined entirely by heat transfer surface {2} |
| DIG 332 | DD | .~.~> Coaxial ducts define air draft passage and annular passage for heat exchange fluid {1} |
| DIG 335 | DD | .~.~> Plural air draft passages enclosed by casing {1} |