Compare NRTL and UNIQUAC activity coefficient models.

NRTL (Non-Random Two-Liquid): uses local composition concept with non-randomness parameter alpha (typically 0.2-0.5). Has three parameters per binary pair, handles highly non-ideal systems including LLE, but alpha is often uncertain. UNIQUAC (Universal Quasi-Chemical): based on lattice theory with surface and volume fractions. Two parameters per binary pair, more theoretically based, foundation for UNIFAC predictive method. Both handle strongly non-ideal systems. NRTL often better for LLE; UNIQUAC better for polymer solutions. Selection depends on available data and system type.