A spray generator was constructed for the production of monodisperse liquid sprays at industrially relevant liquid flow rates. The operation of the generator is based on the Rayleigh-type breakup of ...multiple liquid jets. Laser drilled nozzle holes (diameters 41 or 76 μm) in the nozzle plate (diameter 105 mm) produce 613 individual laminar liquid jets; liquid mass flow rates of up to 170 kg/h are thus obtained. The breakup of these liquid jets is controlled by a piezoceramic oscillator which is driven by a square wave excitation signal. The operation of the spray generator was characterized using video imaging. The spray generator provides a well controlled monodisperse spray with a fairly wide operation envelope with respect to nozzle Reynolds number and wave number (
Re = 600–1200,
k = 0.3–1.0). The liquid jet velocities at different positions of the nozzle plate were found to be equal. Furthermore, the excitation proved to affect all the liquid jets emerging from the nozzle properly. The relative standard deviation of drop diameters in the spray was typically 2–4%. With increasing downstream distance from the nozzle plate, the interaction between the spray and the surrounding gas leads to the loss of monodispersity through collisions and subsequent coalescence of neighbouring droplets in the jets. Some preliminary investigations about the influence of an amplitude modulated excitation signal on the operation of the spray generator were also conducted.
A method of elongational rheometry suitable for characterizing the behavior of viscoelastic polymer solutions in elongational flows is presented. The rheometer optically measures the temporal ...evolution of the diameter of a liquid thread. From measurements with viscoelastic fluids, the relaxation time and the steady terminal elongational viscosity of the liquid are deduced. The mutual dependence of the two quantities is different for nonionic (flexible) and for ionic (rigid) polymers, so that the molecular flexibility or rigidity of the solute in elongational flows can be estimated from the measurement results.
The morphology of particles produced by spray drying is of significant importance for many technical applications of powders. The morphological properties of the particles are influenced by the ...initial properties of droplets produced by atomization of a solution or suspension, as well as by drying conditions. A theoretical model is developed which describes the mass transfer process inside the droplet during the drying process.
In the continuing search for highly efficient technical cooling devices, the nucleate flow boiling regime is becoming increasingly appreciated for providing the highest possible heat transfer rates. ...Regarding the case of liquid cooling systems of combustion engines, it is known that subcooled boiling occurs in thermally highly loaded regions. Therefore, reliable thermal management requires sufficient knowledge on how specific operation conditions and system parameters typically found in engine cooling jackets can affect the subcooled boiling heat transfer. In particular, the present work investigates experimentally the effects of varying volume fractions of the two main components of the coolant, of varying roughness and orientation of the hot wall surface with respect to the vector of gravitational acceleration, and of vibrations of the hot surface. The obtained comprehensive data set is highly valuable to elucidate and quantify the impact of the investigated effects. The data are also used to evaluate the performance of a wall heat flux model, which was specially developed for use in subcooled boiling flow in automotive applications. The model is proven to provide good overall accuracy for the considered experimental conditions.
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