The primary objective of the present study is to clarify the droplet disintegration mechanism and the film properties of liquid oil films driven by shear stress, which is induced by a co-current gas flow. This work focuses on the flow behavior within the starting length of the complex two-phase flow and the effect of inclination on the entrainment rate. Many investigations have been performed in the past to determine the droplet entrainment in the gas core for fully-developed flow conditions with respect to their relevance in pipes of power plants and various chemical engineering systems (Hewitt and Taylor, van Rossum, Ishii and Grolmes [1, 2, 3]). In more recent work the effect of inclination has been studied in detail (Lee and Mjani, Azzopardi, Azzopardi et al. [4, 5, 6]). Nevertheless, a lack of knowledge can be realized for droplet entrainment within the starting length of this complex flow type.

Thus, fundamental experiments have been carried out to provide a data base for droplet entrainment of liquid disintegrated from an oil film within its starting length at several inclination angles of the flow. The experimental results have been compared with correlations from literature. Additionally, the wall film thickness has been measured to allow a fully-coupled modelling of entrainment and liquid film properties depending on global flow parameters. Based on film Reynolds number, Weber number, a dimensionless film flow length and a modified Froude number, taking into account the angle of inclination, correlations have been developed, where those from literature are not applicable.

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