New adiabatic and condensation two-phase flow pattern maps of R14 in a horizontal tube

•Adiabatic and condensation two-phase flow patterns and their transitions of R14 were studied experimentally.•The effects of mass flux, saturation pressure and heat flux were discussed.•The adiabatic flow patterns of R14 were compared with six flow pattern maps.•Two new dimensionless numbers were proposed to develop the new adiabatic and condensation flow pattern maps.•Eight groups of data were compared with the new adiabatic flow pattern map. Heat transfer and pressure drop for two-phase flow are closely related to corresponding flow patterns. In this work, an experimental investigation on adiabatic and condensation two-phase flow patterns and their transitions of tetrafluoromethane (R14) in a horizontal tube with inner diameter of 4 mm was conducted. Experiments were implemented at mass fluxes from 200 to 650 kg/(m2 s), saturation pressures from 1 to 3 MPa and heat fluxes from 8.2 to 28.2 kW/m2. The observed adiabatic flow patterns were compared with six well-known flow pattern maps, none of them can predict all the transition lines accurately. Therefore, a new dimensionless number S1, which takes account of inertia force, gravity force, shear force and surface tension force, was proposed to develop the new adiabatic flow pattern transition criteria. Eight groups of data were compared with the new adiabatic flow pattern map, most of the flow pattern data can be accurately predicted. What’s more, in order to explain the effect of heat flux on condensation flow pattern transitions, another new dimensionless number S2 was proposed by combining the dimensionless number S1 and boiling number together. Finally, a condensation flow pattern map was proposed based on the dimensionless number S2.