Rankine Cycle Efficiency Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Thermodynamics, Fluids & Aero

Tranche

tranche-7

Evidence ID

t7-013

Ledger rows

1

No ledger note is attached.

Review findings

The simple-cycle equation is standard only under explicit state definitions and consistent units. The advertised reheat option makes the current formula and input specification insufficient, so the instrument cannot honestly be labeled as a general Rankine efficiency calculator. The honest label should state either simple ideal/nonideal Rankine cycle with specified isentropic efficiencies, or provide a separate fully defined reheat-cycle algorithm using additional enthalpy states and heat-input terms.

Formula and scope findings

• The stated formula is valid only for a simple Rankine cycle with states defined as 1=turbine inlet, 2=turbine exit, 3=pump inlet, and 4=pump exit. Those state definitions are not specified.
• The formula is incorrect for the claimed reheat option. A reheat cycle requires Wt=(h1-h2)+(h3-h4), Qin=(h1-h6)+(h3-h2), and Wnet=Wt-Wp, with additional states and a separate reheat heat input.
• Turbine and pump efficiencies are listed as inputs, but the specification does not state how they modify isentropic enthalpy changes. The standard relations are eta_t=(h_in-h_out)/(h_in-h_out,s) and eta_p=(h_out,s-h_in)/(h_out-h_in).
• The specification does not identify whether supplied enthalpies are table-looked-up actual states or whether outlet states are calculated from isentropic reference states.
• Steam rate is not defined; the usual mass-specific result is steam rate=3600/Wnet in kg/kWh when Wnet is in kJ/kg.
• A complete lookup implementation must specify the state-property inversion procedure, including pressure-temperature, pressure-entropy, pressure-enthalpy, and two-phase quality handling.

Unit assumptions

• Pressure is in kPa absolute, not gauge pressure.
• Temperature is in degrees C.
• Specific enthalpy is in kJ/kg, specific volume is in m^3/kg, heat and work are in kJ/kg, efficiency is dimensionless, and steam rate is kg/kWh.
• Pump work uses wp,s=v3(P4-P3), because 1 kPa*m^3/kg=1 kJ/kg.
• The test vectors use rounded steam-table values identified in reference_data; production calculations should use a consistent IAPWS-IF97 implementation rather than mixing rounded table entries.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The calculator can encounter a zero heat-input denominator, producing an undefined efficiency and requiring explicit rejection or an undefined result. The optional-reheat branch and the pump-work sign convention also require explicit handling to prevent materially different outputs.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "cycle": "simple Rankine",
    "boiler_pressure_kPa": 8000,
    "boiler_temperature_C": 480,
    "condenser_pressure_kPa": 10,
    "turbine_efficiency": 0.85,
    "pump_efficiency": 0.8,
    "h1_kJ_per_kg": 3349.5,
    "h2s_kJ_per_kg": 2145,
    "h3_kJ_per_kg": 191.81,
    "v3_m3_per_kg": 0.00101
  },
  "expected_outputs": {
    "eta": 0.322067,
    "net_work_kJ_per_kg": 1013.737625,
    "steam_rate_kg_per_kWh": 3.5512,
    "heat_rejected_kJ_per_kg": 2133.865
  },
  "reference_data": {
    "h1_kJ_per_kg": {
      "value": 3349.5,
      "source_convention": "widely tabulated standard value; superheated-steam tables consistent with IAPWS-IF97"
    },
    "h2s_kJ_per_kg": {
      "value": 2145,
      "source_convention": "widely tabulated standard value; pressure-entropy steam-table state"
    },
    "h3_kJ_per_kg": {
      "value": 191.81,
      "source_convention": "widely tabulated standard value; saturated-liquid water at 10 kPa"
    },
    "v3_m3_per_kg": {
      "value": 0.00101,
      "source_convention": "widely tabulated standard value; saturated-liquid water at 10 kPa"
    }
  },
  "working": "Isentropic turbine enthalpy drop = h1-h2s = 3349.5-2145.0 = 1204.5 kJ/kg. Actual turbine drop = 0.85*1204.5 = 1023.825 kJ/kg, so h2 = 3349.5-1023.825 = 2325.675 kJ/kg. Isentropic pump work = v3(P4-P3) = 0.00101*(8000-10) = 0.00101*7990 = 8.0699 kJ/kg. Actual pump work = 8.0699/0.8 = 10.087375 kJ/kg, so h4 = 191.81+10.087375 = 201.897375 kJ/kg. Wnet = (h1-h2)-(h4-h3) = 1023.825-10.087375 = 1013.737625 kJ/kg. Qin = h1-h4 = 3349.5-201.897375 = 3147.602625 kJ/kg. eta = 1013.737625/3147.602625 = 0.322067. qout = h2-h3 = 2325.675-191.81 = 2133.865 kJ/kg. Steam rate = 3600/1013.737625 = 3.5512 kg/kWh."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

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

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche7/tranche7-results.json
• BOUNDARY_HAZARD_CATALOG.json