How do you calculate pressure drop in two-phase gas-liquid flow?

Two-phase pressure drop is significantly higher than single-phase due to interfacial friction and flow pattern effects. Methods: (1) Homogeneous model: treats mixture as single fluid with averaged properties, reasonable for dispersed bubble/mist flow; ΔP = f(ρ_m)L V_m²/(2D). (2) Separated flow models: Lockhart-Martinelli correlation uses parameter X² = (ΔP_L/ΔP_G) and multiplier φ² where ΔP_TP = φ_L²ΔP_L; accounts for flow patterns through C parameter. (3) Mechanistic models (Beggs-Brill, OLGA): predict flow pattern then apply pattern-specific correlations; most accurate for vertical and inclined pipes. (4) CFD with VOF or Euler-Euler for detailed analysis. Flow pattern maps (Baker, Taitel-Dukler) required for model selection based on superficial velocities and fluid properties.