저탄장 자연발화 현상의 수치해석적 연구

Екологічна небезпека шахтних породних відвалів в умовах урбанізованого середовища є високою. Для її оцінювання у кожному конкретному випадку потрібно проводити екологічний моніторинг для розроблення природоохоронних заходів з мінімізації негативних їх чинників. Наголошено на чинниках, які призводять до самозаймання вугільних відвалів, та на підставі наукових джерел детально описано хімізм досліджуваних процесів. Окиснення і горіння породних відвалів супроводжується значним виділенням водяної пари, яка є мінералоутворюючим середовищем для більшої частини мінералів: сульфатів, гідрокарбонатів, карбонатів, фосфатів, арсенатів. Окрім цього, внаслідок окиснення виділяється вуглекислота, нітроген оксид (IV), який з водою утворює нітратну кислоту. У разі нестачі кисню в осередках горіння в парогазових викидах міститися сірководень, вуглеводні, амоніак, оксид карбону (II). Акцентовано увагу на тому, що важливе значення в процесах окиснення належить сірці. Окиснення вугілля посилюється на дрібних частинках, через збільшення площі поверхні, що доступна для окиснення. Висвітлено, що найнадійнішим способом захисту від самозаймання вугільних відвалів є створення на їх поверхні рослинного покриву. Процес формування рослинного покриву є дуже важливим, адже при цьому відбувається як накопичення важких металів у рослинах, так і зв'язування субстрату їхніми коренями й кореневищами, що зменшує процес вивітрювання та вимивання породи, яка містить велику кількість важких металів. Встановлено показники температури займання та самозаймання зразків деревних порід відвалів вугільних шахт згідно з ДСТУ8829:2019. Дослідження показників займання та самозаймання твердих речовин і матеріалів здійснювали у весняний та літній періоди. Досліджуваними об'єктами були проби листя та деревина з терикону шахти Нововолинського гірничопромислового району (Волинська область, м. Нововолинськ). Встановлено, що для сосни звичайної температура займання становить: +225 °C, а самозаймання +475 °C. Температура займання берези повислої +260 °C, дуба звичайного +275 °C, козячої верби +280 °C, температура самозаймання – берези повислої +470 °C, дуба звичайного +475 °C, верби козячої +473 °C. Температура займання берези повислої, дуба звичайного, верби козячої ніж сосни звичайної робить їх перспективними породами дерев для запобігання самозайманню вугільних відвалів.

A review on spontaneous ignition mechanism of pressurized hydrogen released through tubes

Very recently the tuned liquid column damper (TLCD) is receiving an increasing interest from researchers concerned with vibration control, to be considered an alternative device with respect to the tuned mass damper (TMD), since the former has low cost, easy adjustment, flexible installation. However, in recent studies the authors [1] have pointed out that for TMD the analytical formulation provides results that are in good agreement with the experimental ones, while for TLCD it has been deducted that the analytical formulation needs further investigation. In fact using the classical formulation of the problem, numerical results are very different from the experimental results obtained by the authors using the facilities at the experimental dynamic laboratory of University of Palermo. In particular it has been shown that the total liquid length should be corrected in an effective one, but in a different way from what has been done in literature, where only the variation of section of the vessel has been taken into account. On the other hand, from experimental investigations it is seen that the liquid moves more in the central area of the tube and less in the area in contact with the side walls. This aspect plays a fundamental role for capturing the real performance of TLCD. In fact, being the TLCD a special type of auxiliary damping device which relies on the inertia of liquid column in a U-tube to counteract the forces acting on the structure, then it is necessary to identify the effective moving liquid mass. To aim at this, in this paper the authors differentiate the total liquid mass into a liquid dead mass and a liquid dynamic mass, then introducing these values into a properly modified mathematical formulation numerical results match the experimental ones for all tests.

The rate of temperature rise of a subbituminous coal during spontaneous combustion in an adiabatic device: The effect of moisture content and drying methods

The flow structuration of silicon oil (Prandtl number of 10.3) in a open cylindrical pool heated from the center of the surface is investigated numerically. Our purpose is to perform the numerical simulation of experimental results obtained by Favre [Phys. Fluids 9, 1473 (1997)] who observed transitions between steady and axisymmetric flows at sufficiently low values of the Marangoni number (Ma) and various types of instability depending on the height of the fluid. The hydrothermal wave regime has been obtained at critical values of Ma which depend on the Bond number and on the aspect ratio. The numerical results are in good agreement with the experimental ones.

The authors consider the radiation problem of an aperture on a dielectric-coated perfectly conducting cylinder. The aperture is modeled by an infinite line source. The modeling follows the approach of R. Paknys (1985). In the experimental study, a longitudinal X-band slot (8-12 GHz) was set on the conducting surface of the cylinder. Theoretical results are in good agreement with the experimental ones except for the oscillations present in the numerical results. >

Simultaneous thermal analysis was used to study the influence of Vitamin C as possible chemical additive inhibiting coal oxidation process at low temperature. Some oxidation characteristics of Vitamin C affecting the coal oxidation were investigated at different heating rates. The TG-DSC data show that the impact of Vitamin C on coal oxidation process can be directly evaluated using ignition temperature and critical temperature. Comparison with the effect of water on coal oxidation shows that Vitamin C is more efficient than water. However, the blank experiment conducted with inert α-Al2O3 also suggests that Vitamin C can decompose at about 200 °C, which limits the usage of Vitamin C on inhibiting coal oxidation.

An experimental apparatus consisting of a heating unit and a wind duct capable of flexibly adjusting radiation power and forced airflow velocity was used in this work to examine the heat transfer and thermal decomposition in condensed phase, mass diffusion of pyrolyzate in boundary layer in gas and the consequent ignition behaviors of PMMA (polymethyl methacrylate) in forced airflow condition. Constant heat flux (HF) was employed and spontaneous ignition was studied. Finite thick, 3, 6 and 10 mm, 5 cm squared samples and six sets of airflow velocities 0 to 1.2 m/s were selected in the tests. Surface temperature and ignition time under the designed conditions were collected and compared with corresponding numerical simulation results, performed by ANSYS fluid dynamics simulator, which consider thermal decomposition in solid and thermal insulation layer. The results shown that the ignition temperature of PMMA is positively correlated with increasing airflow velocity, indicating the critical temperature is not a reliable ignition criterion in these scenarios. The airflow velocity has little effect on surface temperature. For airflow velocities larger than 0.4 m/s, the ignition time increases significantly with the increase of airflow velocity and sample thickness. While for 0.4 m/s airflow velocity, the ignition temperature is lowered and the ignition time is shortened.

Experiments and numerical results on non-linear vibrations of an impacting Hertzian contact. Part 2: random excitation

The damage caused by spontaneous combustion of coal stockpiles is proportional to the increase in the use of low carbon in coal-fired power plants. The spontaneous ignition of the coal stockpile causes not only serious economic loss but also environmental impact. In order to prevent spontaneous ignition, a cooling ball device is used and a prediction is made using HMM (Hidden Markov Model) algorithm. To prevent the occurrence of spontaneous ignition in advance.

In this paper, a numerical analysis to study thermal radiation effect on magnetohydrodynamic (MHD) unsteady mixed‐convection flow over a moving vertical cylinder with constant heat flux through a porous medium in the presence of transversal uniform magnetic field has been performed. The boundary layer equations are transformed into a linear algebraic system by a Crank–Nicolson type of implicit finite‐difference method. The stability condition of the scheme was studied. Numerical results are presented with various sets of parameters for both air and water. The results show many interesting effects on velocity, temperature and concentration profiles on local as well as average shear stress, rate of heat and mass transfer. Also, the velocity and temperature profiles are compared with the available results in the literature and it is found to be in good agreement. Copyright © 2007 John Wiley & Sons, Ltd.

Characteristics of low-temperature oxidative heating and gas production in coal storage under forced convection: Influencing factors and mechanisms.

A few studies have been reported on the transient vibration of clamped beams impulsed by a spherical impactor. The governing equation of the transient vibration becomes a nonlinear equation due to the contact force between the beam and impactor, and due to the axial force caused by bending of the beam. Although effects of contact force and axial force on the transient vibration of the beam have been studied independently in some reports, one can find no reports discussing both effects. In the present study, it is assumed that the contact force can be estimated by the Hertzian force-deformation relationship. A numerical approach has been proposed for taking into account effects of both contact force and axial force. With the comparison of numerical results and experimental ones, it follows that one can estimate accurately the deflection of the beam and the axial force caused by bending using the proposed approach. From numerical results, furthermore, it has been made clear that one cannot neglect the effect of the axial force caused by bending on the deflection in the case of the clamped thin beam.

This research work aims to investigate the effect of fabrication techniques on the physico‐mechanical properties of pistachio shell (PS) filled glass‐epoxy composites and to compare the experimental findings with numerical simulation results using finite element analysis (FEM). These hybrid composites are fabricated by vacuum‐assisted resin transfer molding (VARTM) and hand layup (HL) techniques with fixed glass fiber fraction (20 wt. %) but different PS powder loadings of 0–30 wt. %. The composites are then characterized for physical, compositional, micro‐structural and mechanical properties. The micro‐structural analysis of the filler and composites is performed using electron microscopy and stereo‐microscopy. To identify the phases present in both the raw filler and the composite, an x‐ray diffraction test is performed. The presence of functional groups is identified with the help of Fourier transform infrared spectroscopy (FTIR). It is observed that there is a reasonable improvement in the mechanical properties of the composites with increase in PS powder content, irrespective of the fabrication process used. The density and void fraction are also greatly affected by the amount of filler particles present in the composites and also on the composite fabrication technique. The FEM analysis is also carried out using ANSYS 22.0 workbench to determine the characteristic properties numerically. The comparison of experimental and numerical results yields that the properties obtained by using VARTM results are close to experimental ones with errors lying in the range of 1%–4%. These composites can possibly find potential applications in light duty structures and wear resistant applications.Highlights Development of hybrid composites using HL and VARTM techniques. Physical and mechanical properties alter with filler loading. Evaluation of mechanical properties using finite element analysis. Validating the model by comparing experimental and numerical results.

Transient analysis of the DSIFs and dynamic T-stress for particulate composite materials—Numerical vs. experimental results