อัปเดต 2026-09-07

Fluid Properties

FDB lookup + ideal-mixing rules

Fetches single-fluid density/viscosity/Cp/k/vapor-pressure from the fluid database (FDB) at a given temperature, derives kinematic viscosity and Prandtl number, and — for user-defined blends — combines per-component properties with textbook ideal-mixing rules (mass↔mole fraction conversion done internally).

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Direct property fetch for single fluids; for mixtures, normalises component fractions then applies Amagat's law (density), Grunberg-Nissan G_ij=0 (viscosity), mass-weighted means (Cp, k) and Raoult's law (vapor pressure), each flagged as an ideal-mixing approximation. Phase is classified by comparing system P to P_vap(T) and T_c; vapor-phase density falls back to the ideal-gas law.

สมการ

Kinematic viscosity & Prandtl number

ν = \frac{μ}{ρ} P r = \frac{μ c _{p}}{k}

Derived from the FDB base properties (μ in Pa·s, ρ in kg/m³, c_p in J/(kg·K), k in W/(m·K)); ν in m²/s, Pr dimensionless.

Ideal-mixing rules — density & viscosity

\frac{1}{ρ _{mi x}} = i \sum \frac{w _{i}}{ρ _{i}} ln μ_{mi x} = i \sum x_{i} ln μ_{i}

Amagat's law (additive liquid volumes) for density; Grunberg-Nissan with G_ij=0 (log-mole-fraction average) for viscosity — Reid, Prausnitz & Poling, 'Properties of Gases and Liquids' 5th ed. §4-9 / §11-2. Cp mixes mass-weighted; vapor pressure mixes mole-weighted (Raoult's law).

Ideal-gas density (vapor phase)

ρ = \frac{P \cdot M W}{R T}

R = 8.314462618 J/(mol·K); used when system pressure falls below P_vap(T) (superheated vapor) or T exceeds T_c (gas-above-T_c) — the liquid-phase FDB correlations no longer apply.

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