NMR Imaging of Falling Water Drops

Abstract

The falling water drop is a simple model for studying phenomena related to chemical extraction, where two immiscible phases are dynamically blended to promote the transport of solute molecules from one phase to the other. Convective motion inside the drop significantly influences the extraction efficiency. Whereas optical and tracer methods are model bound or invasive, NMR imaging is noninvasive, direct, and applicable to nontransparent media. The first NMR measurements of a water drop falling through air are reported. It is shown that, in drops from pure water, large-scale convection rolls are observed in contrast to drops with the surface tension lowered by surfactants.

A model for absorption of solar radiation by mineral dust within liquid cloud drops

“…During the peer-review process it was brought to our attention that a toroidal circulation of fluid within falling droplets is known to exist (Wang, 2013). Such a flow pattern in falling drops is discussed and imaged within Han et al (2001). It is difficult to definitively state whether such fluid flow patterns within a falling cloud droplet will be sufficient to mix/disperse mineral dust inclusions for several reasons.…”

“…It is difficult to definitively state whether such fluid flow patterns within a falling cloud droplet will be sufficient to mix/disperse mineral dust inclusions for several reasons. First, the water drops considered in Han et al (2001) had a diameter and falling velocity approx. two orders of magnitude greater than terminal falling velocities that typical cloud droplets would experience.…”

Practical shape optimization of a levitation device for single droplets

“…The sedimentation of droplets in unbounded and bounded media is studied in (Han et al 2001;Han 2001;Tomiyama et al 2002;Clift et al 1978;Henschke 2004). The forces acting on the droplet in the vertical direction are the buoyancy F B , gravity F G , and drag forces F D .…”

“…We are particularly interested in solvent extraction (Kumar and Hartland 1994;Henschke and Pfennig 1996) where droplets of different sizes are sedimenting while simultaneously undergoing mass transfer. Although theoretical, numerical, and experimental investigations on single droplets were conducted in the past (Han et al 2001;Han 2001;Tomiyama et al 2002;Clift et al 1978;Henschke 2004), the distinct influence of the behavior of the interfacial region is still an open problem. Since interfacial stress and velocity distribution cannot be directly measured, the effect of the interfacial region on the adjoining phases must be examined instead (Slattery 1990).…”

Rapid Multiphase Flow Dynamics Mapped by Single‐Shot MRI Velocimetry

“…[18] So far, dynamic NMR imaging is the only method capable of measuring the velocity patterns within falling and levitated drops completely noninvasively. [19][20][21] However, of all known imaging techniques, only time-consuming sequences based on the generation of single Hahn echoes could be used to monitor the rapid internal flow dynamics of these systems. Different NMR methods have been implemented in the past with great success to map flow fields in nontransparent systems, such as arteries and blood vessels, plant stems, and even porous rocks, thus covering a wide dynamic range that extends from the ultraslow laminar regime up to the very rapid regime that includes turbulence.…”