Since the inception of 3D printing, an evolutionary process has taken place in which specific user and customer needs have crossed paths with the capabilities of a growing number of machines to create value-added businesses. Even today, over 30 years later, the growth of 3D printing and its utilization for the good of society is often limited by the various users' understanding of the technology for their specific needs. This article presents an overview of current 3D printing technologies and shows numerous examples from a multitude of fields from manufacturing to education.
Large droplets and puddles jump spontaneously from sufficiently hydrophobic surfaces during routine drop tower tests. The simple low-cost passive mechanism can in turn be used as an experimental device to investigate dynamic droplet phenomena for drops up to 104 times larger than their normal terrestrial counterparts. We provide and/or confirm quick and qualitative design guides for such “drop shooters” as employed in drop tower tests including relationships to predict droplet ejection durations and velocities as functions of drop volume, surface texture, surface contour, wettability pattern, and fluid properties including contact angle. The latter is determined via profile image comparisons with numerical equilibrium interface computations. Water drop volumes of 0.04–400 ml at ejection speeds of −0.007–0.12 m/s are demonstrated herein. A sample application of the drop jump method is made to the classic problem of low-gravity phase change heat transfer for large impinging drops. Many other candidate problems might be identified by the reader.
The ability to separate liquid and gas phases in the absence of a gravitational acceleration has proven a challenge to engineers since the inception of space exploration. Due to our singular experience with terrestrial systems, artificial body forces are often imparted in multiphase fluid systems aboard spacecraft to reproduce the buoyancy effect. This approach tends to be inefficient, adding complexity, resources, and failure modes. Ever present in multiphase phenomena, the forces of surface tension can be exploited to aid passive phase separations where performance characteristics are determined solely by geometric design and system wettability. Said systems may be readily designed as demonstrated herein where a regulated bubbly flow is drawn through an open triangular sectioned duct. The bubbles passively migrate toward the free surface where they coalesce and leave the flow. The tests clearly show container aspect ratios required for passive phase separations for various liquid and gas flow rates. Preliminary data are presented as regime maps demarking complete phase separation. Long duration microgravity experiments are performed aboard the International Space Station. Supplementary experiments are conducted using a drop tower.
In many ways, plumbing is essential to life support. In fact, the advance of humankind on Earth is directly linked to the advance of clean, healthy, reliable plumbing solutions. Shouldn’t this also be true for the advancement of humankind in space? Unfortunately, the reliability of even the simplest plumbing element aboard spacecraft is rarely that of its terrestrial counterpart. This state of affairs is due entirely to the near-weightless “low-g” state of orbiting and coast spacecraft. But the combined passive capillary effects of surface tension, wetting, and system geometry in space can be exploited to replace the passive role of gravity on earth, and thus achieve similar outcomes there. In this paper, we review a selection of experiments conducted in low-g environments (i.e., ISS and drop towers) that focus on capillary fluidic phenomena. The results of each experiment are highly applicable to subsequent advances in spacecraft plumbing. With examples ranging from spurious droplet ejections to passive bubble coalescence, to droplet bouncing, to complex container wicking, we show how simple low-g demonstrations can lead to significant reliability improvements in practical passive plumbing processes from pipetting to liquid-gas separations, to wastewater transport, to drinking in space.
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