Background: Since the very early documentation of medical treatments, bathing is an essential part of almost all traditional medical systems. In this context the oil-dispersion bath, developed in the 1930s by Werner Junge has been developed from anthroposophic medicine. We aimed at analyzing the apparatus, which chums water and essential oils into an oil-water dispersion, by means of an experimental study. Material and Methods: Using three different oils (rheumatic oil, citrus oil and rosemary oil) oil volumetric flow rate and oil droplet size distribution were examined at three different water volumetric flow rates of 5, 10, and 15 l/min at a constant temperature of 40 degrees C. Additionally, for the rheumatic oil measurements are taken at three different temperatures, 35, 40, and 45 degrees C at a constant volumetric flow rate of 10 l/min. Finally results were compared with a manual oil dispersion process. Results: Oil volumetric flow rate increases with increasing water volumetric flow rates. Oil flow rate increases with increasing water temperature. Droplet-size distribution shows an optimal fit with a log-normal distribution for a volumetric flow rate of 5 l/min in all oils applied with citrus and rosemary oil showing a larger mean diameter compared to the rheumatic oil. Comparing the oil droplet size distribution for a traditional oil bath, distributions behaved completely different in comparison to our distributions. Moreover it seemed not possible to create an oil-dispersion with repeatable droplet size distributions whereas the Jungebad apparatus created similar oil dispersions with predictable results, independent of the user. Discussion: This is the first study to explore the mechanisms of creation of the oil-dispersion bath by means of an experimental set up. Based on these experimental results, a more fundamental theoretical approach should be carried out to complement our findings and to gain deeper insights in the hydrodynamic and droplets forming processes in the Jungebad apparatus.

AbstractThe Jungebad apparatus is used to generate oil‐dispersion baths in medical applications. The oil‐water dispersion is produced by dispersing medically‐effective oil while filling the bathtub. The aim is to produce smaller droplets in comparison to conventionally produced oil‐dispersion baths to generate a high surface‐to‐volume ratio of the oil. Additionally, the oil should be dispersed homogenously in the bath. Due to the greater surface of the oil, a better admission through the skin of the patient is achieved.Experimental investigations with regard to the functionality of the Jungebad apparatus are presented. The analysis of the functionality and the oil‐water dispersion generation is accomplished by observations with a high‐speed camera. Results are discussed with respect to the required characteristics of the dispersion. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

AbstractProcess design of multi‐phase unit operations on the micro‐scale relies on the detailed knowledge of the hydrodynamics and mass transfer of discrete disperse fluid particles. The present work examines gas bubbles in micro‐capillaries. For the case of bubbles rising in vertical capillary, the hydrodynamics and concentration fields are determined over a wide field of parameters (Re, Sc, dbubble/dcapillary) using a combination of level‐set and body‐fitted mesh methods. Drag coefficients and Sherwood numbers are computed from the results and can be used to derive empirical correlations for each parameter and mode of operation. These correlations allow for the individual optimization of the mass transfer process in micro‐capillaries. The results are compared to experimental data and available correlations in literature with generally good agreement. It can be shown that mass transfer can be enhanced by using small geometries like micro‐capillaries. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Process design of multi‐phase unit operations on the micro‐scale relies on the detailed knowledge of the hydrodynamics and mass transfer behavior of discrete disperse fluid particles. The present work examines the hydrodynamics and mass transfer of gas bubbles in vertical capillaries. The hydrodynamic behavior of a single bubble in a capillary including is examined numerically using a modified level‐set method [1]. Additionally, the influence of surface‐active contaminations (‘surfactants’) and the resulting Marangoni effects are taken into account [2]. This enables the differentiation between bubbles with a mobile, i.e. clean, interface and those with a immobile, i.e. contaminated, interface. Based on the hydrodynamics, the mass transfer is examined. In the present work, mass transfer is from the bubble into the bulk fluid. By using a very high mesh resolution, the local concentration field in and around the gas bubble can be resolved, which gives access to the local mass transfer. Results are in good agreement available correlations from literature. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A numerical scheme for the simulation of mass transfer processes at free liquid/liquid interfaces using the interface tracking method is presented. Due to comparable diffusion coefficients in liquid/liquid systems, the mass transfer resistance in both phases is relevant for the entire transient mass transfer process. Exemplary, the extraction process from a free rising spherical droplet of constant shape is used. The presented approach can be used in general for any multiphase steady‐state mass transfer system. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An experimental setup for the examination of single bubbles, rising in a liquid, is presented. Its main part is a rotating chamber, in which the bubble is spatially stabilized by a balance of buoyancy, drag, and lift forces. This allows for long observation periods in time. Experimental results are presented for air bubbles in silicone oil. The experimental results are validated by a comparison with numerical simulations. A modified, mass-conserving level-set method is used for the representation of the free interface, while an immersed-boundary formulation is engaged for the conservation equations. The agreement between experiment and simulation, and to available correlations from literature, is found to be perfect. It is shown that the influence of the liquid shear due to the rotation is negligible. Also, for the presented liquid system, no influence by Marangoni stresses could be found, which makes the system of air and silicone oil a good choice for validation purposes.

The influence of Marangoni stresses, caused by contaminants adsorbed on the surface of small air bubbles, rising in water, is examined by numerical simulations. A modified level set method is used to represent the deformable bubble interface, extended by a model for the contaminant transport on the bubble surface. We show that surface tension variations of less than 2% are sufficient to generate Marangoni stresses that are strong enough to change the rising characteristics of a bubble to that of a corresponding solid particle. In such situations, we find that the bubble surface is fully covered with contaminant and the shear stress profile resembles the shear stress profile around a solid sphere.

Disperse gas bubbles play an important role in many industrial applications. Knowing the rising velocity, the interfacial area, or the critical size for break‐up or coalescence in different systems can be crucial for the process design. Usually the flow experienced by bubbles is not uniform but sheared. Under shear‐flow conditions bubbles develop a lift force perpendicular to the flow direction. In the present work direct numerical simulations are applied to examine the dependency of the lift force on the shear rate for bubbles in pure liquids. A level‐set based volume‐tracking method is implemented into the CFD‐code OpenFOAM, to follow the free interface of the gas bubble. Results show good agreement with available experimental results from single bubbles in a rotating chamber. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

AbstractDisperse gas bubbles play an important role in many industrial applications. Knowing the rising velocity, the interfacial area, or the critical size for break–up or coalescence in different systems can be crucial for the process design. Hence, knowing the fundamental behaviour of a single bubble appears mandatory for the examination of bubble swarms and for the Euler–Lagrange or Euler–Euler modelling of disperse systems. In the present work a level–set–based volume–tracking method is implemented into the CFD–code OpenFOAM to follow the free interface of a single bubble. The volume–tracking method is coupled with a transport model for surfactants on the interface, including adsorption and desorption processes. The dependency of surface tension on the local surfactant concentration on the interface is modelled by a non–linear (Langmuir) equation of state. Marangoni forces, resulting from surface tension gradients, are included. The rise of a single air bubble (i) in pure water and (ii) in the presence of surfactants of different strengths is simulated. The results show good agreement with available correlations from literature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)