{
  "schema": "heat-recovery-functional-graph/v1",
  "scope": "Function-only natural-circulation arrangement; no engineering dimensions or adequacy",
  "nodes": [
    "steam drum",
    "downcomer",
    "heated water-side surface",
    "mixture riser",
    "contained hot-product path"
  ],
  "directed_connections": [
    {
      "from": "steam drum",
      "to": "heated water-side surface",
      "via": "downcomer",
      "phase": "water"
    },
    {
      "from": "heated water-side surface",
      "to": "steam drum",
      "via": "mixture riser",
      "phase": "water/vapor mixture"
    },
    {
      "from": "contained hot-product path",
      "to": "heated water-side surface",
      "relation": "heat across separating surface; no fluid mixing connection"
    }
  ],
  "mechanism": "Density/head difference can drive natural circulation; actual losses/levels/phase/heat input needed",
  "states": [
    "normal selected heat input",
    "startup",
    "shutdown",
    "alternative heat source where specifically designed"
  ],
  "not_supplied": [
    "height",
    "density",
    "duty",
    "flow",
    "circulation margin",
    "boiler/control acceptance"
  ]
}