Granular Leidenfrost effect in microgravity
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ORIGINAL PAPER
Granular Leidenfrost effect in microgravity Harol Torres Menéndez1 · Achim Sack1 · Thorsten Pöschel1 Received: 21 January 2020 © The Author(s) 2020
Abstract When a container filled with granular material is subjected to vertical vibration in the presence of gravity, under certain conditions a non-monotonous density profile can be observed. This effect which is characteristic for dissipative granular gases, was termed “floating cluster regime” or “granular Leidenfrost effect”. Here, we study the behavior of vibro-agitated granular matter in the absence of gravity and identify a corresponding stationary state of the granulate, that is, we provide experimental evidence of the granular Leidenfrost effect under conditions of weightlessness. Keywords Granular matter · Floating cluster · Leidenfrost effect · X-ray radiography · Microgravity · Weightlessness · Parabolic flight
1 Introduction When sprinkling a drop of water onto a hot surface, different behavior can be observed, depending on temperature. For T ≳ 100 ◦ C, the drop will evaporate rapidly. For T ≳ 220 ◦ C, however, counterintuitively the drop persists much longer on the hot surface due to a vapor layer formed between the drop and the hot surface, which reduced heat transfer drastically. This phenomenon was first described by Leidenfrost [1–5] and is known as Leidenfrost effect. Although mostly studied with water drops, the Leidenfrost effect can also be observed with stiff sublimable solids, e.g., dry ice [6–9]. Recently, it was found that hydrogel balls, that is, vaporizable soft solids, float above a hot surface similar to a drop of water when gently deposited [10] but bounce persistently when dropped onto the hot surface [11]. Granular materials, can also exhibit a dynamics similar to the Leidenfrost effect when heated from below in the presence of gravity. Here, the term heated refers to the granular temperature [12], that is, the supply of energy from below through mechanical vibration. In a certain range of parameters one observes a density inversion which resembles the Leidenfrost effect [13–18], that is, a dilute region of fast particles (analogous to the vapor layer) supports a denser * Harol Torres Menéndez [email protected] 1
Institute for Multiscale Simulation, Universität ErlangenNürnberg, Cauerstraße 3, 91058 Erlangen, Germany
layer of particles (analogous to the water drop). Because of its phenomenologically similarity to the common Leidenfrost effect, Eshuis et al. called this phenomenon granular Leidenfrost effect [16]. Obviously, gravity is essential to this effect, however, numerical simulations predict a similar effect when granular matter is confined in a vibrating container in the absence of gravity [19–21]. Given a certain filling fraction, independent of the frequency of excitation, for small amplitude, the granular material assumes a gaseous state filling the available volume nearly homogeneously. For larger amplitude, a dense layer forms in the center of the box and the space between this layer and the cont
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