Psychrometric Chart Tool mechanism

Model scope

The supplied formulas cover vapor-pressure conversion, humidity ratio, and enthalpy only. They do not uniquely specify the saturation correlation, wet-bulb equation, dew-point inversion, specific volume, valid ranges, or convergence behavior. The four vectors therefore use an explicit Magnus correlation and conventional moist-air equations; implementation should not be marked complete until those conventions are made part of the instrument specification.

• The saturation-pressure correlation is underspecified: Magnus has multiple coefficient sets and valid temperature ranges, while ASHRAE correlations are not interchangeable with Magnus.
• The wet-bulb algorithm is underspecified. A wet-bulb calculation requires an explicit psychrometric relation, such as W=Ws(Twb)−0.622·0.00066·(1+0.00115·Twb)·(Tdb−Twb), plus a stated pressure convention and convergence tolerance.
• Specific volume is claimed as an output but no formula is supplied. A standard ideal-gas moist-air formula is v=0.287042·(T+273.15)·(1+1.607858W)/P when T is in °C and P is in kPa.
• The claim that any two listed properties always determine a full state is too broad: pairs can be redundant, physically inconsistent, outside the correlation range, or insufficient without pressure and a defined thermodynamic model.
• The listed enthalpy formula is a conventional approximation for moist air with T in °C, h in kJ/kg dry air, and W in kg water/kg dry air; this basis and reference state must be displayed.
• Dew-point inversion and wet-bulb solving need explicit domain constraints, especially for supersaturated inputs, RH=0, negative absolute pressure, and temperatures outside the saturation-correlation range.

Units and conventions

• Worked vectors use pws(T)=0.61094·exp(17.625T/(T+243.04)) kPa, with T in °C; this particular Magnus coefficient set must be fixed in the implementation.
• Pressure P is absolute pressure in kPa.
• Humidity ratio W is kg water/kg dry air; enthalpy h is kJ/kg dry air; specific volume v is m³/kg dry air.
• RH is a fraction in [0,1] in calculations; displayed percentages must be converted by dividing by 100.
• Wet-bulb calculations use W=Ws(Twb)−0.622·0.00066·(1+0.00115Twb)·(Tdb−Twb), solved by Newton iteration to |delta T|<0.000001 °C.
• The specific-volume checks use v=0.287042·(T+273.15)·(1+1.607858W)/P.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "dry_bulb_C": 25,
    "relative_humidity": 0.5,
    "pressure_kPa": 101.325,
    "saturation_correlation": "Magnus: 0.61094 exp(17.625T/(T+243.04))"
  },
  "expected_outputs": {
    "saturation_pressure_kPa": 3.16176,
    "vapor_pressure_kPa": 1.58088,
    "humidity_ratio_kg_per_kg_da": 0.0098595,
    "dew_point_C": 13.86,
    "wet_bulb_C": 17.9,
    "enthalpy_kJ_per_kg_da": 50.267,
    "specific_volume_m3_per_kg_da": 0.85707
  },
  "working": "pws(25)=0.61094·exp(17.625·25/(25+243.04))=3.16176 kPa. pv=0.5·3.16176=1.58088 kPa. W=0.622·1.58088/(101.325−1.58088)=0.983308/99.74412=0.00985950. Dew point: L=ln(1.58088/0.61094)=0.95070; Td=243.04L/(17.625−L)=13.8600 °C. Wet bulb uses Newton's method on f(Twb)=Ws(Twb)−0.622·0.00066·(1+0.00115Twb)(25−Twb)−0.00985950, tolerance 1e−6 °C: Twb(0)=15.0000 °C; Twb(1)=18.0200 °C; Twb(2)=17.9011 °C; Twb(3)=17.9000 °C; converged Twb=17.9000 °C. h=1.006·25+0.00985950·(2501+1.86·25)=25.1500+0.00985950·2547.50=50.2670 kJ/kg_da. v=0.287042·298.15·(1+1.607858·0.00985950)/101.325=0.857070 m³/kg_da."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The tool has a real undefined-result failure at P-p_v=0, and exactly zero relative humidity produces a non-finite dew point. The supplied specification also does not state the water/ice saturation branch or the unit conventions for temperature and humidity ratio, so different plausible interpretations produce different states.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche6/tranche6-results.json
• BOUNDARY_HAZARD_CATALOG.json