Correlations
- Last UpdatedAug 14, 2026
- 3 minute read
Process Model Manager Reference Manual offers you the powerful ability to enter correlations between properties, to be used when measurements are not available for particular properties. These correlations are specified in terms of:
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Input properties Calculation steps
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The Correlation Manager offers you the necessary functionality to enter these correlations (Correlation Manager).
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The possible mathematical operations which may be used in the correlation functions is indicated in a further appendix (Write Formulae).
The following correlations are industry standard, and may be included in your version of Process Model Manager Reference Manual.
Note: Your version of Process Model Manager Reference Manual may have additional correlations defined.
|
Correlation |
Unit Category |
Properties involved |
Calculation Steps |
|
Carbon/Hydrogen ratio |
Proportion |
CH — Carbon/Hydrogen ratio C — Carbon by weight % H — Hydrogen by weight % |
CH = C / H |
|
Cetane index (ASTM-D976) SI |
None |
CI — Cetane index (ASTM- D976) SI den — Density at 15°C t50 — TBP in °C at yield by volume of 50% measured using D86 and converted to standard barometric pressure. |
CI = 454.74 - 1641.416*den + 774.74*den^2 - 0.554*t50 + 97.803* (log t50)^2 |
|
Cetane index (D4737-90) |
None |
CI — Cetane index (D4737-90) T10 — D86 in °C at yield by volume of 10% T50 — D86 in °C at yield by volume of 50% T90 — D86 in °C at yield by volume of 90% T10N — Intermediate variable T50N — Intermediate variable T90N — Intermediate variable DN — Density number B — Intermediate variable DEN — Density at 15°C in kg/m³ |
DN = DEN - 0.85 B = exp(-3.5 * DN) - 1 T10N = T10 - 215 T50N = T50 - 260 T90N = T90 - 310 CI = 45.2 + 0.0892 * T10N + 0.131 * T50N + 0.0523 * T90N + 0.901 * B * T50N - 0.420 * B * T90N + 4.9E-4 * (T10N^2 - T90N^2) + 107 * B + 60 * B^2 |
|
Cetane index (IP218) |
None |
CI — Cetane index (IP218) API — API gravity TBP50 — TBP in °F at yield by volume of 50% T50 — Intermediate variable X — Intermediate variable |
T50 = (TBP / 0.8718)^ (1/1.0258) X = 97.833 * (log10 (T50))^2 + 2.2088 * API * log10(T50) + 0.01247 * API^2 - 423.51 * log10(50) - 4.7808 * API + 419.59 CI = 0.49083 + 1.06577 * X - 0.0010552 * X^2 |
|
Flash point |
Temperature (°C) |
FP — Flash point (°F) ASTM10 - D86(vol) boiling point (°C) of 10% ASTMIBP - D86(vol) boiling point (°C) of 1% |
FP = (1.32 - 0.006* (ASTM10 - ASTMIBP))*ASTM10 - 103 + 0.64*(ASTM10 - ASTMIBP) |
|
Isoparaffins to n-paraffins |
Proportion (%) |
ITON — Isoparaffins to n-paraffins ISOPAR — isoparaffins by weight % NPAR — n-paraffins by weight % |
ITON = ISOPAR / NPAR |
|
Luminometer Number |
Dimensionless |
LN — Luminometer number S — Smoke point in mm |
LN = -12.03 + 3.009 * S - 0.0104 * S^2 |
|
Molecular Weight |
mole |
MW — methane + ethane DEN — Density in g/cc at 15°C E — Mean boiling point by weight in Rankines X1 — Intermediate variable X2 — Intermediate variable X3 — Intermediate variable X4 — Intermediate variable X5 — Intermediate variable |
X1 = 4.6523 - 3.3287 * DEN X2 = 1 + DEN * (-0.77074 - DEN * 0.02058) X3 = 1.3437e7 - 720.97e7 / MBP X4 = 1 + DEN * (-0.80882 + DEN * 0.2226) X5 = 1.8828e12 - 181.98e12 / MBP MW = max(60, - 12272.6 + 9486.4 * DEN + X1 * MBP + X2 * X3 / MBP + X4 * X5 / MBP^3) |
|
N+2A |
Proportion (%) |
N2A — N+2A N — Naphthenes by weight % A — Aromatics by weight % |
N2A = N + 2 * A |
|
Saturates |
Proportion (%) |
S — Saturates PAR — Paraffins by weight % NAP — Naphthenes by weight % |
S = PAR + NAP |
|
UOPK |
Dimensionless |
K — UOPK (Watson K) VABP — Volume averaged mean boiling point SG — Specific gravity at 60°F |
K = VABP^(1/3)/SG |