Modelling of flow pattern transitions in small diameter horizontal and inclined tubes

•Mechanisms responsible for flow pattern transitions in mini tubes are elucidated.•Dimensionless groups governing each of the flow pattern transitions are identified.•The system EoD = ΔρgD2/σ determines the characteristic length scales in the models.•The tube inclination significantly affects the flow pattern map when EoD > 1.•Models' predictions favorably compare with experimental flow pattern maps.