Document SteamHeater0D unit model

[aryanputta]

Fixes #1825.

Summary

• Add a technical reference page for SteamHeater0D.
• Link the page from the unit model documentation index.
• Document the model purpose, configuration options, degrees of freedom, model structure, added constraints, and class references.

Validation

• python -c "from watertap.unit_models.steam_heater_0D import SteamHeater0D, Mode"
• git diff --check
• sphinx-build -M html docs docs/_build -W --keep-going completed HTML generation and did not emit warnings for the new steam_heater_0D.rst page. The local command exited nonzero because existing/global docs warnings were treated as errors, including unreachable intersphinx inventories and existing unresolved references outside this change.

Legal Acknowledgement

By contributing to this software project, I agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the license terms described in the LICENSE.txt file at the top level of this directory.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[MarcusHolly]

Thanks for putting this together, just a few improvements to be made. I'd be fine with merging this as is and refining at a later date if we just want to get some level of documentation in before the release.

[adam-a-a]

The PR description is missing the required Legal Acknowledgment section to contribute code.

[adam-a-a]

We would need to ensure the documentation aligns with the latest revisions to the steamheater model, which may have removed the heater and condenser modes. We'll need to double-check to be sure.

[aryanputta]

Thanks @adam-a-a. I double-checked against the current main (model last touched in #1717, commit e50196e) and both modes are still present in watertap/unit_models/steam_heater_0D.py:

• class Mode(Enum): HEATER = auto(); CONDENSER = auto()
• CONFIG.declare("mode", ... default=Mode.HEATER, domain=Mode)
• CONFIG.declare("estimate_cooling_water", ... default=False), used only in condenser mode

So nothing was removed. The reference page documents exactly those two config options, the two added hot-side constraints (outlet_liquid_mass_balance, outlet_pressure_sat), and the default heat-exchanger costing method, all matching the model. I also tightened the mode row to mirror the model's own config description ("Mode of operation: heater or condenser") instead of "Initialization mode." Let me know if you'd like the condenser-mode initialization paths spelled out further.

[kurbansitterley]

Thanks @adam-a-a. I double-checked against the current main (model last touched in #1717, commit e50196e) and both modes are still present in watertap/unit_models/steam_heater_0D.py:

• class Mode(Enum): HEATER = auto(); CONDENSER = auto()
• CONFIG.declare("mode", ... default=Mode.HEATER, domain=Mode)
• CONFIG.declare("estimate_cooling_water", ... default=False), used only in condenser mode

So nothing was removed. The reference page documents exactly those two config options, the two added hot-side constraints (outlet_liquid_mass_balance, outlet_pressure_sat), and the default heat-exchanger costing method, all matching the model. I also tightened the mode row to mirror the model's own config description ("Mode of operation: heater or condenser") instead of "Initialization mode." Let me know if you'd like the condenser-mode initialization paths spelled out further.

#1760 would go in first so this doc should align with the model there.

[aryanputta]

@kurbansitterley #1760 has merged, so I rebased this doc onto latest main and confirmed it matches the updated SteamHeater0D model:

• Documents the new pressure_deltaP margin variable and the set_subcooling_margin / release_subcooling_margin helpers.
• outlet_pressure_sat is now documented as the equality P = P_sat + ΔP (no longer the old inequality).
• Total condensation is documented as the hot-side vapor flow being fixed to its lower bound, replacing the removed outlet_liquid_mass_balance constraint.

Every model object referenced in the page exists in the merged model. Ready for another look.

[aryanputta]

will work on this tdy.

[aryanputta]

Thanks @MarcusHolly. I have addressed all three points:

1. Variables and Sets sections are now included, following the pattern in the other unit model reference pages.
2. The added hot-side relationships are written out under Equations and Relationships: total condensation (hot-side vapor flow fixed to its lower bound) and the outlet pressure relation P = P_sat + deltaP.
3. The mode row is no longer present. Fixes redundunt constraint in SteamHeater0D #1760 removed the heater/condenser Mode config, so the page instead documents the current model: the pressure_deltaP margin variable and the set_subcooling_margin / release_subcooling_margin helpers.

The branch is rebased onto latest main (post #1760) and I verified the page against the current steam_heater_0D.py. The Read the Docs build passes. Please let me know if you would like anything else refined.

[MarcusHolly]

LGTM