This paper reports on an experimental study of the impact of water droplets on a solid substrate, with a droplet radius between 18 and 42 μm. We optically measured the interface shape during impact. The measured impact sequences show the impact phenomenology, droplet radius as a function of time, and oscillation behavior in the later stages of impact. The measured radius during impact is compared with existing models, and some of the deficiencies of common models are shown. The measured oscillation frequency in the later stage of impact compares well with an available analytical model. In addition, we measured the volume of the small bubble, which forms in the initial impact stage, as a function of impact velocity. The measured volume compares reasonably well with an approximate model based on air entrapment.

This article presents a numerical model that was developed for the drying of ink-jet-printed polymer solutions after filling the pixels in a polymer LED display. The model extends earlier work presented in the literature while still maintaining a practical approach in limiting the number of input parameters needed. Despite some rigorous assumptions, the model is in fair agreement with experimental data from a pre-pilot ink-jet printing line. Comparison inside a single pixel is shown, as well as a general trend in which the amount of polymer that is transported out of the central part of the pixel decreases with the rate of viscosity increase as a function of polymer concentration. Moreover, the effect of a varying solute diffusion coefficient is studied.

We carry out small‐scale hydraulic fracture experiments to investigate the physics of hydraulic fracturing. The laboratory experiments are combined with time‐lapse ultrasonic measurements with active sources using both compressional and shear‐wave transducers. For the time‐lapse measurements we focus on ultrasonic measurement changes during fracture growth. As a consequence we can detect the hydraulic fracture and characterize its shape and geometry during growth. Hence, this paper deals with fracture characterization using time‐lapse acoustic data. During fracture growth the acoustic waves generate diffractions at the tip of the fracture. The direct compressional and shear diffractions are used to locate the position of the tip of the fracture. More detailed analysis of these diffractions can be used to obtain information on the geometry and configuration of the fracture tip, including the creation of a zone that is not penetrated by fluid. Furthermore, it appears that the acoustic diffraction is generated mainly at the fluid front and only weakly at the dry tip. In addition, the wavefield that has been transmitted through the hydraulic fracture is measured. Shear‐wave transmissions are shadowed because the shear modulus vanishes inside the fluid‐filled fracture. From this observation we conclude that the fracture is mechanically open. In other words, no friction occurs related to the movement of fracture faces that are in mechanical contact. Compressional transmissions show a distinctive dispersion relative to the measurement in the unfractured medium. This dispersion can be used to determine the width (or aperture) of the fracture by fitting the measured dispersion with the theoretical prediction as a function of the unknown fracture width. We show that the width profile of the fracture can be reconstructed by using a set of transmission records with different source and receiver locations. By performing a validation experiment, we show that the width determination method is reliable, although the estimated fracture width is only a few percent of the incident wavelength. The strength of the method relies on time‐lapse measurements combined with fitting the changes in the measured waveforms during the experiment. The combination of diffractions and transmissions helps us visualize the dynamic process of hydraulic fracture growth. Hence, acoustic measurements with active sources prove their usefulness for fracture characterization.

We performed scaled laboratory experiments of hydraulic fracture propagation and closure in soft artificial rock and outcrop rock samples. We also performed numerical simulations of the fracture behavior in plastic rocks with independently measured rock properties. The simulations aided in interpreting the measurements and extrapolating the results to field scale.Compared with elastic rock, plasticity induces a larger width for a given net pressure. However, the pressure to propagate fractures is only marginally increased and, in the case of the laboratory tests, was actually lower than expected from elastic behavior. The most dramatic effect of plasticity is that closure is much lower than the confining stress because of strong stress redistribution along the fracture.