Experimentelle Untersuchungen der Strömunscharakteristik und des Wärmeübergangs bei welligen Rieselfilmen

Abstract

In the present work experimental investigations of the flow characteristic and heat transport of wavy silicone oil films were accomplished with different angles of inclination and Kapitza numbers, which allow a deeper view into the structure and the heat transport phenomena. From the experimental results of laminar-wavy and turbulent films dimensionless approximation equations for different parameters were determined for the description of the film flow like the film thickness, wave frequency and the wave velocity. Furthermore new boundaries for the different film regimes could be discriminated from the results.
A substantial part of the work was the development of more suitable temporally and locally high resolving measurement techniques. Thus a measurement technique on the basis of the fluorescence intensity method was developed, which is able to determine simultaneously the film thickness and the wave velocity.
A further component of the work was the measurement of the film velocity of periodically excited two-dimensional-wavy films with the Particle Image Velocimetry PIV. The velocity field of a complete length of a two-dimensional wave could be reconstructed by simultaneous film thickness measurements.
By measurements of the wall temperature distribution with a developed measuring system on the basis of the infrared thermography the influence of the wavy surface on the heat transfer within the laminar-wavy flow range could be examined.
The results of the flow characteristic investigations of wavy film flow are valuable contributions to understand the influence of the waves on hydrodynamics and heat-transport.