Unified correlation for heat transfer during boiling in plain mini/micro and conventional channels

•Presents a new correlation applicable to both macro and mini/micro channels•Correlation verified with 4852 data points from 137 data sets from 81sources•Data include 30 fluids, diameter 0.38 to 27.1 mm, and reduced pressure 0.0046 to 0.787.•Mean absolute deviation 18.6 %, much lower than other correlations A correlation is presented for predicting heat transfer coefficients during saturated boiling prior to critical heat flux in mini/micro channels as well as channels of conventional sizes in horizontal and vertical upward flow. The correlation is verified with a database that includes channels of various shapes (round, rectangle, triangle), fully or partially heated, horizontal and vertical downflow, diameters 0.38 to 27.1 mm, 30 fluids (water, CO2, ammonia, halocarbon refrigerants, organics, cryogens), reduced pressure 0.0046 to 0.787, and mass flux 15 to 2437 kg m−2s−1. The new correlation predicts the 4852 data points from 137 data sets from 81 sources with a mean absolute deviation of 18.6 %. Several other correlations were also compared with the same database; all had significantly higher deviations.