Experiments in free falling and downward cocurrent annular flows – Characterization of liquid films and interfacial waves

•Experimental measurements of gas-liquid interfacial wave properties in vertical downward cocurrent annular flows.•Development and custom manufacturing of conductance probes.•Effects of gas and liquid flow rates in the liquid film thickness and interfacial wave properties.•Correlation of experimental data in terms of dimensionless numbers.•Comparison of the new correlations against experimental data and other widely used expressions.