Sedimentation analysis of columnar ice crystals in viscous flow regimes

The sedimentation process of columnar ice crystals was evaluated using data obtained by the lattice Boltzmann method. The data used correspond to columnar ice crystals with maximum dimension less than 100 μm and aspect ratios between 1 and 3. The terminal velocity was computed for different ice-crystal bulk densities and for three falling orientations. The analysis corresponds to ice crystals falling in viscous flow regimes, where theoretical formulations overestimate the terminal velocity. Different characteristic lengths of columnar ice crystals and different theoretical proposals for the sedimentation process were tested in order to find the best representation of the data. Characteristic lengths reported in the literature do not represent the sedimentation process for all the falling orientations used in this study. Thus, it was not possible to obtain a unique relation between the Best and Reynolds numbers. In particular, columnar ice crystals falling with their longer dimension parallel to the vertical direction show a large dispersion that it does not seem possible to reduce. The theoretical and semi-empirical formulations of the terminal velocity evaluated show large deviations in the computed velocity, with a strong dependence on ice-crystal aspect ratio. The dispersion observed seems to be intrinsically related to the dimensionless variables used to parametrize the terminal velocity. To derive a unique scale law that could represent the sedimentation process of ice crystals, geometric, kinematic, and dynamic similarities are required. However, these conditions are not fulfilled in the sedimentation process.Fil: Burgesser, Rodrigo Exequiel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Giovacchini, Juan Pablo. Ministerio de Defensa. Instituto Universitario Aeronautico de la Faa; ArgentinaFil: Castellano, Nesvit Edit. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Single-shot velocity mapping by rewinding of velocity encoding with Echo-Planar Imaging

The ability of single-shot NMR imaging methods to follow the time evolution of a velocity distribution within an object is strongly limited by the phase errors accumulated as velocity maps are acquired. In the particular case of Carr-Purcell based sequences combined with Echo Planar Imaging acquisition, phase accumulates through subsequent images, hampering the possibility to acquire several velocity maps, which would be useful to determine transient behavior. In this work, we propose the use of a rewinding velocity encoding module applied after the acquisition of each image during the CPMG echo train. In this way, the first velocity module imparts a velocity dependent phase prior to the image acquisition and the second pair cancels this phase out before the next refocusing radiofrequency pulse is applied. The performance and limits of this method are studied by acquiring 100 images of a co-rotating Couette cell over a period of 1.6 s as a function of the rotation speed. The method is applied to determine the kinematic viscosity of a water/alcohol mixture, which is a relevant topic in many physical, chemical and biological processes.Fil: Serial, María Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Silletta, Emilia Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Perlo, Josefina. Magritek GmbH; AlemaniaFil: Giovacchini, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Velasco, Manuel Isaac. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Blümich, Bernhard. RWTH Aachen University. Institut für Technische und Makromolekulare Chemie; AlemaniaFil: Danieli, Ernesto Pablo. Magritek GmbH; AlemaniaFil: Casanova, Federico Martin. Magritek GmbH; AlemaniaFil: Acosta, Rodolfo Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin