Scholarly Works, Mechanical Engineering

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https://hdl.handle.net/10919/23262
Research articles, presentations, and other scholarship

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Browsing Scholarly Works, Mechanical Engineering by Author "Ahmadi, S. Farzad"

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    How soap bubbles freeze
    Ahmadi, S. Farzad; Nath, Saurabh; Kingett, Christian M.; Yue, Pengtao; Boreyko, Jonathan B. (Springer Nature, 2019-06-18)
    Droplets or puddles tend to freeze from the propagation of a single freeze front. In contrast, videographers have shown that as soap bubbles freeze, a plethora of growing ice crystals can swirl around in a beautiful effect visually reminiscent of a snow globe. However, the underlying physics of how bubbles freeze has not been studied. Here, we characterize the physics of soap bubbles freezing on an icy substrate and reveal two distinct modes of freezing. The first mode, occurring for isothermally supercooled bubbles, generates a strong Marangoni flow that entrains ice crystals to produce the aforementioned snow globe effect. The second mode occurs when using a cold stage in a warm ambient, resulting in a bottom-up freeze front that eventually halts due to poor conduction along the bubble. Blending experiments, scaling analysis, and numerical methods, the dynamics of the freeze fronts and Marangoni flows are characterized.
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    Latent heat of traffic moving from rest
    Ahmadi, S. Farzad; Berrier, Austin S.; Doty, William M.; Greer, Pat G.; Habibi, Mohammad; Morgan, Hunter A.; Waterman, Josam H.C.; Abaid, Nicole; Boreyko, Jonathan B. (IOP Publishing, 2017-11-22)
    Contrary to traditional thinking and driver intuition, here we show that there is no benefit to ground vehicles increasing their packing density at stoppages. By systematically controlling the packing density of vehicles queued at a traffic light on a Smart Road, drone footage revealed that the benefit of an initial increase in displacement for close-packed vehicles is completely offset by the lag time inherent to changing back into a ‘liquid phase’ when flowresumes. This lag is analogous to the thermodynamic concept of the latent heat of fusion, as the ‘temperature’ (kinetic energy) of the vehicles cannot increase until the traffic ‘melts’ into the liquid phase.These findings suggest that in situations where gridlock is not an issue, drivers should not decrease their spacing during stoppages in order to lessen the likelihood of collisions with no loss in flowefficiency. In contrast, motion capture experiments of a line of people walking from rest showed higher flow efficiency with increased packing densities, indicating that the importance of latent heat becomes trivial for slower moving systems.