Changes in the Distribution of Temperature in a Coal Deposit and the Composition of Gases Emitted during Its Heating and Cooling

This article presents the results of tests conducted on a measuring system for monitoring changes in the distribution of temperature in a coal deposit during the heating and cooling phases, and their correlation with the analysis of the concentration of gases. The tests were conducted on five samples of hard coal collected in deposits mined in Poland. Measurements of the changes in temperature and changes in gas concentration were conducted from the temperature of 35 to 300 C, for the heating phase, and from 300 to 35 C, for the cooling phase. The percentage share of coal of given temperatures was calculated. When comparing the percentage share for the same temperature in the hot spot, for the heating and cooling phase, significant differences in the distribution of the given percentages were observed. Changes in gas concentrations during heating and cooling were analyzed and the dynamics of changes in gas concentrations were determined for the coals tested. Changes in the values of fire hazard indices were analyzed. There were significant differences in the concentration of gases and the values of fire hazard indices between the heating and the coolin

A laboratory-numerical approach for modelling scale effects in dry granular slides

Granular slides are omnipresent in both natural and industrial contexts. Scale effects are changes in physical behaviour of a phenomenon at different geometric scales, such as between a laboratory experiment and a corresponding larger event observed in nature. These scale effects can be significant and can render models of small size inaccurate by underpredicting key characteristics such as ow velocity or runout distance. Although scale effects are highly relevant to granular slides due to the multiplicity of length and time scales in the flow, they are currently not well understood. A laboratory setup under Froude similarity has been developed, allowing dry granular slides to be investigated at a variety of scales, with a channel width configurable between 0.25-1.00 m. Maximum estimated grain Reynolds numbers, which quantify whether the drag force between a particle and the surrounding air act in a turbulent or viscous manner, are found in the range 102-103. A discrete element method (DEM) simulation has also been developed, validated against an axisymmetric column collapse and a granular slide experiment of Hutter and Koch (1995), before being used to model the present laboratory experiments and to examine a granular slide of significantly larger scale. This article discusses the details of this laboratory-numerical approach, with the main aim of examining scale effects related to the grain Reynolds number. Increasing dust formation with increasing scale may also exert influence on laboratory experiments. Overall, significant scale effects have been identified for characteristics such as ow velocity and runout distance in the physical experiments. While the numerical modelling shows good general agreement at the medium scale, it does not capture differences in behaviour seen at the smaller scale, highlighting the importance of physical models in capturing these scale effects

EPR Study of Ammonium Nitrate Doped with Copper(II) Ions

This work is devoted to a study of the structural changes in a single crystal of ammonium nitrate, NH$\text{}_{4}$NO$\text{}_{3}$, doped with copper(II) cations by electron paramagnetic resonance. Ammonium nitrate crystallizes at atmospheric pressure in several polymorphic forms, phase VII → V → IV → III → II → I → melt, with transition temperatures of 103 K, 255 K, 305 K, 357 K, 398 K, and 443 K, respectively. The aim of our work was to study the temperature phase transition V → IV at about 255 K using electron paramagnetic resonance technique. The electron paramagnetic resonance spectra were performed using an X-band spectrometer with microwave frequency of 9.4 GHz and magnetic modulation of 100 kHz in the temperature range of 153-296 K. For a single crystal the angular dependence of the copper(II) electron paramagnetic resonance spectra was measured at 293 K and 168 K. The anisotropic behaviour measured at 293 K points to the existence of one kind of two equivalent copper(II) complexes with inverse g and A tensors. A second pair of equivalent complexes also with inverse g and A tensors was observed. The minimal values of g-factors correspond to the maximum values of A. The angular dependence taken at 168 K shows the existence of two types of non-equivalent copper complexes which differ in comparison with the complexes observed at room temperature. The temperature dependence of the intensities of hyperfine structure lines for all copper(II) complexes observed shows a phase transition V → IV occurring in the temperature range of 237-246 K with a hysteresis. One of the hyperfine structure lines of a copper(II) complex measured at low temperatures shows a superhyperfine structure with line intensities 1:2:3:2:1 originating from the interaction of the copper $\text{}^{63,65}$Cu (I=3/2) nucleus with two $\text{}^{14}$N (I = 1) nuclei of two ammonia, NH$\text{}_{3}$, ligand molecules

Determination of the fraction of paramagnetic centers not-fulfilling the Curie law in coal macerals by the two-temperature EPR measurement method

Two-temperature electron paramagnetic resonance (EPR) measurements, applied to determine the relative contributions of paramagnetic centers – fulfilling and not-fulfilling the Curie law, were carried out. The measurements were made on the macerals – exinite and vitrinite, separated from clarain of the Polish medium-rank coal (85.6 wt% C). The two-temperature EPR measurements, presented in this work, were performed respectively, at temperatures: T1 = 293 K and T2 = 173 K for exinite, and T1 = 293 K and T2 = 153 K for vitrinite. The relative contributions X of spins not-fulfilling the Curie law present in the studied macerals were calculated. A comparison of different methods of calculating the relative contributions of paramagnetic centers – fulfilling and not-fulfilling the Curie law, present in exinite and vitrinite studied by EPR was made

Determination of the fraction of paramagnetic centers not-fulfilling the Curie law in coal macerals by the two-temperature EPR measurement method

Two-temperature electron paramagnetic resonance (EPR) measurements, applied to determine the relative contributions of paramagnetic centers – fulfilling and not-fulfilling the Curie law, were carried out. The measurements were made on the macerals – exinite and vitrinite, separated from clarain of the Polish medium- -rank coal (85.6 wt% C). The two-temperature EPR measurements, presented in this work, were performed respectively, at temperatures: T1 = 293 K and T2 = 173 K for exinite, and T1 = 293 K and T2 = 153 K for vitrinite. The relative contributions X of spins not-fulfilling the Curie law present in the studied macerals were calculated. A comparison of different methods of calculating the relative contributions of paramagnetic centers – fulfilling and not-fulfilling the Curie law, present in exinite and vitrinite studied by EPR was made