Three-field mechanistic modelling of annular-regime water boiling in rectangular mini/micro-channels based on analysis of dispersed droplet clusters

The development of predictive models for water boiling in mini and micro-channels is becoming increasingly important due to the micro/miniaturization of modern electronics and the growing use of water as a coolant. This paper introduces a novel three-field mechanistic model for annular-regime water boiling in rectangular mini/micro-channels, based on a comprehensive analysis of dispersed droplet clusters. The magnitudes of momentum transfer intensities caused by the droplet surface forces, interfacial shear forces, and liquid film evaporation range from 10^-1 to 1, 10^-2 to 10^-1, and 10^-4 to 10^-3, respectively. The discrepancy in film thickness calculated by the mechanistic model that accounts for dispersed droplet clusters versus those that do not can exceed threefold. This discrepancy arises from varying criteria for the onset of annular-regime boiling. Compared to existing empirical, universal empirical and mechanistic models, the new model demonstrates superior performance with notably lower mean relative errors (MREs) of 22.2 % for the annular-regime heat transfer coefficient and 24.1 % for pressure drop. The model's extrapolation is validated for thermal–hydraulic characteristics at low pressures (p ≤ 0.101 MPa). However, its applicability is compromised at higher pressures (p > 0.2 MPa) due to the invalidity of the uniform droplet assumption.