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Multiscale entropy applications for complexity analysis of two-phase flow

100%

Rafałko G. , Mosdorf R. , Grzybowski H. , Dzienis P. , Górski G.

Archives of Thermodynamics

2024

tom Vol. 45, no 2

83--90

Two-phase flow in channels of small dimensions is often a non-stationary process, the nature of such flow is oscillatory. Due to small channel dimensions, high heat flux, parallel channels interactions, pressure and temperature oscillations, the character of the phenomena occurring during boiling is complex. The changes of the measured signals are observed in different time scales. In order to examine in detail two-phase flow parameters changes, many acquisition devices are often installed. This solution becomes challenging concerning mini and microchannel heat-exchangers due to space limitation and modifications of an experimental setup. This paper presents a novel application of multiscale entropies for spatial and temporal analysis of two-phase flow based on only one registered parameter. This analysis is performed based on pixel brightness changes in photo frames registered by a high speed camera during two-phase flow. The spatial changes of pixel brightness are observed on single frames and temporal changes are examined using a set of frames (in time). The Composite Multiscale Sample Entropy is applied to identify two-phase flow patterns and to analyze the complexity of phase distribution. Using Multivariate Multiscale Sample Entropy the most rapid changes of phase distribution in a multichannel heat exchanger are determined.

Preliminary Detonation Study of Dry, Wet and Aluminised ANFO Using High-Speed Video

75%

Araos M. , Onederra I.

Central European Journal of Energetic Materials

2019

tom Vol. 16, no. 2

227--244

ANFO is a well-known, reliable and safe commercial explosive. It has been around since the late 1950’s and its detonation properties are well characterized. In this study, the detonation process of dry, wet and aluminised ANFO, was recorded using two high-speed cameras with recording rates of 1,200 fps and 50,000 fps. The 1,200-fps footage allowed the observation of the post blast fumes (i.e. NOx) produced by ANFOs with different water contents. The 50,000-fps footage allowed the observation of the detonation area, gas expansion phase and the measurement of the velocity of detonation (VOD). The video footage also recorded a bright zone in front of the gases (longer than 50 mm). We assumed that a reaction is taking place in this zone, but it is difficult to be sure if this is the reaction zone or not as it is longer than previously reported reaction zone lengths. Analysis showed that ANFO detonates effectively for water contents of up to 9 wt.%, and more importantly, there is little variation in the VOD. As far as the expansion of gases is concerned, the ANFO-Al expansion rate appears to be different. In this mixture, the absence of NOx fumes could have been due to the expected higher temperatures produced by the burning of the aluminium additive as observed in the images recorded with the high-speed camera.

Kinematic model for yarn movement in turbulent air flows

51%

Jungbecker P. , Seide G. , Gries T.

Autex Research Journal

2008

tom Vol. 8, no. 4

94--99

In the textile industry a tool is needed that can predict fibre and yarn movement in turbulent air streams. The Institut für Textiltechnik of RWTH Aachen University (ITA) has developed a yarn model that can be used to study the movement of single fibres and yarns in turbulent air flows. The kinematic model is described in this article. Special attention is paid to the aerodynamic forces that determine the flight path of fibres and yarns. The coefficient of drag tangential to the fibre axis ct was studied thoroughly using computational fluid dynamics (CFD). It is shown that the diameter has a strong influence on the wall shear stress. Neglecting this effect for thin fibres can lead to errors in the coefficient of drag of a factor of 500. The turbulence intensity also has an important influence on the boundary layer development, which also determines the coefficient of drag. The assumptions made for the yarn model were tested in an experiment in which yarn flight paths were detected with a high-speed video camera. The comparison to the simulation results confirms the usability of the yarn model.