Wolfgang Samenfink

Droplet interaction with shear-driven liquid films : analysis of deposition and secondary droplet characteristics

Abstract The paper describes the results of a detailed investigation of droplet interaction with shear-driven liquid films. Particularly the mechanism of droplet splashing and the characteristics of the deposited mass fraction had been studied experimentally. A new integral method based on conductivity and volume flux measurements was used. The deposited mass fraction and the composition ratio of the secondary droplets are given as a function of the impact angle and the film height. Comprehensive measurements of the primary and secondary droplets had been performed by means of a Phase-Doppler-Anemometer (PDA). The resulting distributions for droplet diameter, velocity and angle had been used to evaluate correlations for the interaction between single droplets and a shear-driven wall film. Together with the results on droplet deposition they can serve as basis for a complete 2D model simulation in CFD codes.

Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gases

In this paper detailed measurements of wavy liquid films driven by the shear stress of turbulent air flow are described for different air temperatures, air velocities, and flow rates of the liquid. The experimental conditions are chosen from characteristic data of liquid film flow in prefilming airblast atomizers and film vaporization employing combustors. For the measurement of the local film thickness and film velocity a new optical instrument-based on the light absorption of the liquid-has been developed, which can be used at high temperatures with evaporation. The measured data of the gas phase and the liquid film are compared with the results of a numerical code using a laminar as well as a turbulent model for the film flow and a standard numerical finite volume code for the gas phase. The results utilizing the two models for the liquid film show that the film exhibits laminar rather than turbulent characteristics under a wide range of flow conditions. This is of considerable interest when heat is transferred across the film by heating or cooling of the wall. With this information the optical instrument can also be used to determine the local shear stress of the gas phase at the phase interface.

Velocity Profiles in Shear-Driven Liquid Films: LDV-Measurements

In design and layout of fuel preparation systems for SI-engines or gas turbines as well as other technical systems working with shear-driven liquid films accurate information on the velocity distribution within the film as a function of film height is necessary for numerical modeling. To meet this requirements an improved LDV system was built which allows for the first time accurate velocity measurements in thin and wavy liquid films down to an average thickness of about 100 µm. Layout and the optical arrangement of the new system is presented in details together with some examplary applications.

Effect of Variable Liquid Properties on the Flow Structure within Shear-Driven Wall Films

Liquid wall films driven by air flow occur in fuel preparation processes of advanced prefilming gas turbine combustor nozzles or in intake manifolds of SI-engines. There is a need to develop new and more accurate models to describe the heat transfer from the wall to the film. To obtain data necessary for the modeling a new measurement device in combination with an enhanced data processing technique has been developed. The device combines two novel measurement systems. It consists of a film structure measurement system and a specially adapted LDV-system with a miniaturized probe volume. This combination allows simultaneous measurements of film thickness and flow velocity within the film. For the first time detailed information of the internal flow structure are provided under consideration of the effect of variable liquid properties on the film hydrodynamics.