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Radial capillary transport occurs, for example, when wine spreads in the tablecloth, ink in paper, rain drops in textiles, or dye into yarn. It is of technical relevance for propellant and other liquid transport in space. We present a theoretical and experimental study on the more basic situation when liquid spreads radially from an infinite reservoir. Our theoretical model predicts both outward and inward radial transport in a porous screen. While the outward wicking is fed by a circular wick in the center, the inward wicking is fed by a ring-like wick from the outside. For both cases, an analytical solution is obtained in terms of time versus radius as well as radius versus time aided by the Lambert W function. In the experiments, we use four different filter papers combined with three cylindrical wicks for outward wicking and one ring wick for inward wicking, respectively. The wicking process is recorded by a digital camera. Afterward, the resulting image series are evaluated with Matlab routines to detect the wicking front line. From the wetted area, we derive the mean radius versus time. Beside radially outward and inward wicking, we consider also experimental reference data from horizontal and vertical wicking in a strip.

The dynamic behavior of liquid metal drops submitted to a high-frequency magnetic field is investigated experimentally. The motivation for this study comes from the coating industry. In this industry, liquid metals showing a free surface held in a dome-type shape are evaporated by applying electromagnetic pressure. The Galinstan drops are placed on a curved glass plate. A ringlike inductor fed by an alternating electrical current generates the magnetic field. The surface contour of the drop is observed using a high-speed camera system. The data are analyzed by utilizing image processing methods. In the experiment, we vary the inductor current I and the drop volume V while the frequency is fixed at 20 kHz . Upon increasing the inductor current within the range 0I(C), these symmetric states become unstable to capillary waves. The critical current (critical electromagnetic Bond number) as well as the critical mode number, the critical frequency, and the amplitudes of the waves depend strongly on the volume (Bond number).

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