| 165 / | HD | HEAT EXCHANGE |
| DIG 9 | DD | HAVING A SOLID HEAT STORAGE MASS FOR ABSORBING HEAT FROM ONE FLUID AND RELEASING IT TO ANOTHER (I.E. REGENERATOR) {5} |
| DIG 30 | DD | .~ Mass formed of modules arranged in three dimensional matrix ("Checkerwork") {4} |
| DIG 36 | | .~.~ Distinct passages formed in individual modules |