Coal and gas outburst is an extremely destructive gas dynamic disaster in mines. Since such dynamic disasters are usually difficult to observe directly, physical similarity simulation of coal and gas ...outburst has become an important method for collecting observational data on outburst and studying outburst mechanisms. However, the energy principles of outburst similarity simulation experiments still lack systematic research. A review of outburst simulation experiments over the past 70 years revealed that experimental coals generally have a higher porosity (10%–40%, median 21.2%), which significantly increases the expansion energy of the initial free gas stored in the coal pores (by several times to several tens of times). To further elucidate the energy release characteristics of outburst simulation experiments, a series of outburst simulation experiments were conducted using a true triaxial coal and gas outburst simulation system, based on similarity criteria. Combined with observational data and energy anal
The normal infrared (IR) spectral emissivity of pure titanium TA1 is experimentally investigated using a self-designed emissivity measurement apparatus. The apparatus and the measurement method are ...described in detail. Seven samples are treated with abrasive paper to obtain the roughness needed. The emissivity of one sample is obtained between 473 and 1035 K with wavelength range of 3–27 µm in an argon environment. The other six samples are oxidized at a high temperature (873 K) for various times. The surface roughness and composition of the samples are analyzed using roughness tester and X-ray diffraction before and after the emissivity measurement. The results show that the spectral emissivity of titanium sample increases with the increase of temperature and decreases with the increase of wavelength from 3 to 27 µm. For the oxidized samples, the spectral emissivity increases with increasing oxidization time, and after being heated for 12 h, the emissivity values increase slightly. The influence of the oxide film thickness on the spectral emissivity is discussed based on interference theory, and the thickness of oxide film with different oxidation time is accurately measured using scanning electron microscope.
A review on hot tearing of magnesium alloys Song, Jiangfeng; Pan, Fusheng; Jiang, Bin ...
Journal of magnesium and alloys,
September 2016, 2016-09-00, 2016-09-01, Letnik:
4, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Hot tearing is often a major casting defect in magnesium alloys and has a significant impact on the quality of their casting products. Hot tearing of magnesium alloys is a complex solidification ...phenomenon which is still not fully understood, it is of great importance to investigate the hot tearing behaviour of magnesium alloys. This review attempts to summarize the investigations on hot tearing of magnesium alloys over the past decades. The hot tearing criteria including recently developed Kou's criterion are summarized and compared. The numeric simulation and assessing methods of hot tearing, factors influencing hot tearing, and hot tearing susceptibility (HTS) of magnesium alloys are discussed.
Long-runout rockslides at high altitude could cause disaster chain in river basins and destroy towns and major infrasturctures. This paper firstly explores the initiation mechanism of high-altitude ...and long-runout rockslides. Two types of sliding-prone geostructure models, i.e. the fault control type in orogenic belt and the fold control type in platform area, are proposed. Then, large-scale experimental apparatus and associated numerical simulations are conducted to understanding the chain-style dynamics of rockslide-debris avalanche-debris flow. The results reveal the fragmentation effects, the rheological behaviors and the boundary layer effect of long-runout avalanche-debris flow. The dynamic characteristics of quasi-static-transition-inertia state and solid-liquid coupling in rapid movement of rockslide-debris avalanche-debris flow are investigated. Finally, the risk mitigation strategy of the non-structure and structure for resilient energy dissipation are illustrated for initiation, transition and deposition zones. The structural prevention and mitigation methods have been successfully applied to the high-altitude and long-runout rockslides in Zhouqu and Maoxian of the Wenchuan earthquake zone, as well as the other major geohazards in Qinghai-Tibet Plateau and its adjacent areas.
This paper describes experimental performance data for MnFeP1−xAsx multilayer active magnetic regenerators. Five different matrices are tested: (i) one with three layers; (ii) one with six layers; ...and (iii) three, eight-layer regenerators where the layer thickness is varied. The tests are performed using a dual regenerator bespoke test apparatus based on nested Halbach permanent magnets. (PM II test apparatus at the University of Victoria.) Operating variables include displaced volume (3.8-12.65 cm3), operating frequency (0.5-0.8 Hz) and hot-side rejection temperature (293-313 K). The results are mainly reported in terms of zero net load temperature span as a function of rejection temperature; a few tests with non-zero applied load are also presented. A maximum temperature span of 32 K is found for an eight-layer regenerator, which is similar to a previous work performed with gadolinium in the same experimental apparatus.
Carbon capture, utilization and storage (CCUS) is considered as a very important technology for mitigating global climate change. Carbon dioxide (CO2) injected into an underground reservoir will ...induce changes in its physical properties and the migration of CO2 will be affected by many factors. Accurately understanding these changes and migration characteristics of CO2 is crucial for selecting a CCUS project site, estimating storage capacity and ensuring storage security. In this paper, the basic principles of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) technologies are briefly introduced in the context of laboratory experiments related to CCUS. The types of NMR apparatus, experimental samples and testing approaches applied worldwide are discussed and analyzed. Then two typical NMR core analysis systems used in CCUS field and a self-developed high-pressure, low-field NMR rock core flooding experimental system are compared. Finally, a summary of the current deficiencies related to NMR applied to CCUS field is given and future research plans are proposed.
Collapsible soils are one of the moisture sensitive soils that experience sudden and significant settlements due to wetting. These soils are widely distributed and constitute about 10% of the total ...land area of the world, which are typically located in arid and semi-arid areas. In foundation engineering, the most important issue in dealing with these soils is to measure their collapse potential with different water infiltration patterns. The effect of parameters such as initial soil conditions, loading conditions and gradation quality on the behavior of these soils has been investigated. The amount of clay in the soil is considered as an important factor in the behavior of the collapsible soils. Water enters the soil from different sources, but the existing devices and tests to measure the collapse potential are not capable of modeling water infiltration patterns. In this study, an apparatus was used that simulates different water infiltration patterns based on the direction of water movement (from top or bottom) and type of water distribution (point or wide). The results show that in oedometer tests and tests with the ability to simulate the water infiltration patterns, with the increase in the amount of clay in the sample, the collapse potential increases, but the amount of increase is not the same in different tests. The amount of increase in collapse potential due to the increase of clay in the sample is greater in single and double oedometer tests than in tests with the ability to simulate the water infiltration patterns, and for a more accurate prediction of the collapse potential, tests with the ability to simulate the water infiltration patterns should be used. Among the different water infiltration patterns in the soil, for the sample with clay compared to the sample without clay, the highest increase in collapse potential is related to the top-point water infiltration pattern ) and the lowest increase is related to the bottom-wide water infiltration pattern( ). But for the sample with 23% clay compared to the sample without clay, the highest increase in collapse potential is related to the top-wide water infiltration pattern( ) and the lowest increase is related to the bottom-wide water infiltration pattern.
•The performance of an active magnetic regenerator (AMR) test apparatus is discussed.•Tests with 195.5 g of Gd gave a maximum cooling capacity of 53.7 W at 1 Hz.•Maximum system temperature spans of ...the order of 30 K were obtained.•Peak values of COP and η2nd were found in terms of utilization and frequency.
In this first part of a two-part paper, a new active magnetic regenerator (AMR) laboratory apparatus is presented and evaluated. The setup is composed of a nested Halbach cylinder magnetic circuit (maximum magnetic flux density of 1.69 T) assembled in phase with a double effect displacer that provides the cold and hot blows to the regenerator. A single packed-bed regenerator with 195.5 g of gadolinium spheres is used in a discontinuous (i.e., reciprocating) cycle. The system performance is evaluated in terms of characteristic curves (i.e., cooling capacity as a function of temperature span), coefficient of performance and second-law efficiency as a function of the utilization factor and operating frequency. Maximum values of COP have been identified for a given temperature span. The maximum values of second-law efficiency were obtained at system temperature spans between 15 and 20 K.
Background
To evaluate the stability of jointed rock masses subjected to dynamic disturbance, laboratory dynamic shear test on rock joint is necessary. Developing dynamic shear test equipment for ...rock joint is currently a pressing issue.
Objective
To address this issue, a new apparatus is developed to reproduce the shear-slip process of rock joint subjected to dynamic disturbance under various initial stress state.
Methods
The disturbance load, which has a dominant frequency close to that of seismic waves, is generated by an electromagnetic-driven disturbance generator, and its amplitude and duration can be accurately controlled in a stable manner. The initial normal and shear stresses can be applied in the shear test under dynamic disturbance using servo-controlled loading unit, which facilitates the simulation of the real stress state of rock joint.
Results
The shear tests under dynamic disturbance show that when an initial shear stress is applied to rock joint, an additional deformation stage of stress recovering can also trigger a slip displacement, which contributes to the destabilization of jointed rock masses. With increasing initial shear stress, the dynamic slip displacement, stress drop and post-disturbing deformation increase. The feasibility of the apparatus to conduct quasi-static direct shear tests with both the constant normal loading (CNL) and constant normal stiffness (CNS) boundaries is also verified.
Conclusions
Test results demonstrate that using the new apparatus, shear-slip properties of rock joint subjected to dynamic disturbance can be tested in various initial stress states.
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