Two-phase Frictional Pressure Gradient Correlation for Saturated Flow Boiling in Single Circular and Non-Circular Mini/ Micro-Channels

Accurate prediction of two-phase frictional pressure gradients is crucial for operating two-phase flow systems within safe limits. However, existing correlations predict with high mean absolute errors (MAEs) especially for new low-GWP refrigerants, for instance, 53% for R1234yf and 41% for R32. To overcome this challenge, the present study developed a new correlation for frictional pressure gradient for mini/micro-channels applicable to both conventional and low-GWP working fluids. The correlation incorporates the effects of channel geometry, heat flux, inertial forces, and viscous forces through several dimensionless parameters including aspect ratio, heated-to-wetted perimeter ratio, boiling number, liquid-only Weber number, liquid-only Reynolds number, liquid-to-vapor density ratio, and two-phase Prandtl number. The amassed database consists of 3473 data points, of which 2882 are for circular and 591 are for non-circular cross-sectional geometries. The database encompasses flow boiling of 17 different fluids in single circular and non-circular mini/micro-channels of 0.529-8 mm hydraulic diameters with a mass velocity range of 33-2738 kg/(m2.s). This database is used to evaluate the predictive performance of 18 existing correlations. Following this assessment, a new universal correlation is developed using nonlinear optimization on the consolidated database. The new correlation accurately predicts both circular and non-circular channels with respective MAEs of 19.22% and 23.13%, and using the entire combined database yields an MAE of 19.88%.