Using primary instability analysis for determination of apparent liquid viscosity at jet breakup atomizing non-Newtonian Fluids

An internal mixing twin-fluid atomizer used for the application of cavity wax in automotive engineering is investigated. At typical pressures of 100 bars the wax material is atomized into a chamber and mixed with air at elevated pressures between 4 and 6 bars. The formed two-phase flow is further flowing along a straight tube and finally discharging through a number of radially arranged orifices undergoing a secondary atomization process. The original aim of these investigations is to provide inlet and boundary conditions for numerical simulations of the unsteady film formation on the substrate. Applying a number of optical measuring techniques, the initial secondary disintegration process, initial droplet velocities and droplet size distributions could be determined. In general, it was found that at typical distances between 10 and 20 mm between nozzle and target surface the disintegration process is not yet completely finished. Due to high initial velocities of more than 100 m/s in the spray centre, the wax material deposits to a large extent in the form of ligaments. Therefore, the measured droplet size distributions can only be taken as a rough indication for the length scales of the droplets and ligaments.