A Droplet-Scale Analytical Model of Gas–Liquid Two-Phase Heat-Transfer Attenuation by a Water-Mist Curtain in a High-Temperature Confined Flow

Water-mist curtains act as thermal barriers to longitudinal smoke propagation in confined-space fires, but their downstream cooling remains difficult to predict with reduced-order models. This study develops a calibrated semi-analytical model that uses the incident temperature at the curtain’s upstream face and combines a one-dimensional droplet residence-time solution with a Stefan-flow heat-transfer reduction. A lumped closure coefficient, k = Aeq/A0, collectively accounts for the simplified initial velocity and trajectory, spray nonuniformity, ensemble shielding, representative properties, and boundary inputs. The coefficient is inferred from 5 MW FDS cases with D32 = 400–700 μm and is not interpreted as breakup or coalescence, which were absent from the monodisperse simulations. Cases at 2, 4, and 6 MW provide within-domain blind tests, whereas 1, 3, and 7 MW provide supplementary assessment; the maximum reconstructed relative deviation in exit temperature is 13.4%. A 1:5 experiment supplies a cross-scale trend comparison, but its geometry differs from the full-scale FDS domain, and only the 3 MW-equivalent fire has an archived mass-loss calibration. The model is therefore limited to the present calibration domain and should not be transferred directly across geometries, nozzles, or ventilation conditions.