Decomposition Kinetics and Cook-Off Numerical Simulation of Insensitive Energetic Plasticizer Plasticized Propellants

Aiming at the thermal safety issues between the insensitive energetic plasticizer and propellant components, NG/BTTN and insensitive energetic plasticizer BuNENA plasticized propellant was compared by DSC test and cook-off numerical simulation, with the thermal safety property evaluated. The decomposition activation energy Ea and self-ignition temperature Tb of BuNENA plasticized propellant was lower than that of NG/BTTN plasticized propellant. Two kinds of propellant responded in the central area during slow cook-off simulation while in the near shell area during medium cook-off simulation. During fast cook-off simulation, depending on the different thickness of insulator, propellant responded at the area near shell or the area near the caps. The response temperature of two propellants in cook-off simulation agreed with decomposition and self-ignition temperature by DSC, and the decomposition of plasticizer could trigger the response. In cook-off simulation, BuNENA plasticized propellant showed a lower response temperature with a smaller high temperature area before response, resulting a milder response and better thermal safety than NG/BTTN plasticized propellant.

Numerical Simulation and Flame Characteristics Analysis of Non-Premixed Swirling Combustion

Swirling flames are important in practical industrial combustors. The dynamic characteristics of swirling flames form complex velocity and temperature fields, which indicate combustion efficiency and influence pollutant emission. A reliable numerical simulation that can calculate the entire velocity and temperature fields is required to understand and investigate the underlying combustion mechanism. The governing equations of the methane swirling combustion process consist of the mass conservation, Navier-Stokes, and energy equations, all of which are solved by the SIMPLE algorithm based on finite volume method. This study performed a simulation using the realizable k-ε and non-premixed models in conjunction with the GRI Mech 3.0 mechanism. The characteristics of swirling combustion were analyzed on the bases of visualizations of temperature distribution, velocity distribution, and streamlines. In each cross section with varying heights from the nozzle, the high velocity and high temperature areas showed similar closed or semi-closed annular structures. In the central longitudinal section, the V-shaped high temperature and high velocity regions showed the swirling structure of the combustion flow field. The high temperature area did not coincide with the high velocity area but was located relatively downstream. The high velocity area was in the periphery of the high temperature area. Furthermore, the effects of swirl blade position on methane combustion characteristics were discussed. The validity of the numerical simulation results was verified by the simultaneous laser measurement of 3D temperature and velocity fields in the swirling flame.

Flow Field and Temperature Field in a Four-Strand Tundish Heated by Plasma

Tundish plasma heating is an effective method for achieving steady casting with low superheat and constant temperature. In order to study the flow field, temperature field in tundish heated by plasma, a three-dimensional transient mathematical model was established in the present work. A four-strand T-type tundish in a steelmaking plant was used to explore the changes in the flow field and temperature field of molten steel in the tundish under different plasma heating powers. The results showed that plasma heating affected the flow state of molten steel. It could eliminate the short-circuit flow at outlet. When the plasma heating was 500 kW, the molten steel had an obvious upward flow. The turbulence intensity was improved and distributed evenly with an increase in plasma heating power. In the prototype tundish, the temperature of the outlet was dropped by nearly 2–3 K within 300 s. With the increase of plasma heating power, the low temperature area in the tundish gradually was decreased. When the heating power was 1000 kW, the temperature difference of two outlets was 0.5 K and the overall temperature distribution was more uniform. The research results have a certain guiding significance for the selection of the actual plasma heating power on site.

Analysis on rock fracture signals and exploration of infrared advance prediction under true triaxial loading

To predict the fractured rock failure under deep triaxial stress in advance, the true triaxial tests were carried out using thermal infrared monitoring and acoustic emission (AE). This paper proposes “infrared temperature jumping rate (ITJR)” to reflect the “jumpiness” of the temperature field matrix, and establishes an infrared advance prediction method. The results show that the high temperature area will converge and expand gradually, and cracks propagate along a certain direction. In the sudden temperature reduction area, the rock stripping is easy to occur. At the boundary between high-low temperature areas, it is easy to produce breakage cracks and form rock spalling. In the short quiet period, the rock gradually gathers strain energy, which will be released in the fracture period. By comparing the time of AE sudden increase with the time of ITJR mutation, it shows that the method has a good advance prediction effect for rock fracture.

Transmit the heat of rivers to surface seawater

Based on the survey materials of the waters of Jiaozhou Bay in April and August 1981, this article studies the water temperature and horizontal distribution in the surface waters of Jiaozhou Bay. The results have showed that the water temperature ranged within 7.52–30.90°C in April and August, and the length of interval of water temperature was 23.38°C. The water temperature of the ocean was above 7.00°C. It indicated that the water temperature of the entire water body of Jiaozhou Bay was relatively high in April and August, in terms of the changes of water temperature. In April, the water temperature in the water body of Jiaozhou Bay ranged within 7.52–13.70°C, and the length of temperature interval was 6.18°C. In Jiaozhou Bay, from the northeastern coastal waters along the northern coastal waters to the northwestern coastal waters, the range of water temperature changes was 12.82–13.70°C, and the interval length of seawater temperature changes was 0.88°C. From the northern area to the southern area, the range of water temperature changes was 7.52–13.70°C, and the interval length of seawater temperature was 6.18°C. In August, the range of water temperature changes was 24.60–30.90°C, and the interval length of seawater temperature was 6.30°C. In the eastern area of Jiaozhou Bay, the water temperature in the coastal waters of the estuary of Jiaozhou Bay was 30.90°C, forming a high temperature area. In the coastal waters of Jiaozhou Bay from the northwest to the north, the range of water temperature changes was 27.32–27.37°C and the interval length of seawater temperature was 0.05°C. In April and August, the increase of water temperature in the coastal waters from the northeast along the north to the northwest of Jiaozhou Bay was mainly caused by the shortwave radiation from the sun and sky and the longwave radiation from the atmosphere which continuously offered heat to the seawater. In April, it formed a circular water area with low temperature centered with the central water area of Jiaozhou Bay, whose water temperature ranged within 7.52–8.51°C. Thus, there was no heat source to provide heat to the central waters of Jiaozhou Bay, resulting a loop-locked low water temperature area in the center of the bay. In August, in the eastern part of Jiaozhou Bay, that is, the coastal waters in the estuary of Haibo River, the water temperature reached a relatively high value, 30.90°C. The source of the increase in water temperature was the transportation of heat from Haibo River, which transferred the heat of the river to the surface seawater.

Experimental study on the spatial and temporal variations of temperature and indicator gases during coal spontaneous combustion

Coal spontaneous combustion is one of the main potential hazards in the process of mining. To study the spatial and temporal variations of higher-temperature area and indicator gases, an adiabatic oxidation testing system was developed to simulate the whole process of coal spontaneous combustion. The experimental results show that the entire process of coal spontaneous combustion could be divided into three stages: slow-oxidation, accelerated-oxidation and combustion stages. In the slow-oxidation stage, the higher-temperature area shifted slowly from the bottom to the top and then stayed at the top until accelerated-oxidation stage was reached; [Formula: see text] and [Formula: see text] concentration remained more or less constant as well as the oxygen concentration. In accelerated-oxidation stage, the higher-temperature area moved to the bottom rapidly and subsequently stayed approximately in the center of the coal; [Formula: see text], [Formula: see text] concentration and oxygen consumption increased sharply. In addition, the occurrence of higher-temperature area is accompanied by higher oxygen consumption. The obtained results show that higher air supply rate could shorten spontaneous combustion period and there exists a hyperbolic relationship between the temperature and time.

Multifield Coupled Dynamic Simulation of Coal Oxidation and Self-Heating in Longwall Coal Mine Gob

The spontaneous combustion of residual coal in coal mine gob has long been a problem and poses a threat to the safe production of coal. Therefore, it is of great significance to conduct an in-depth study of the oxidation and self-heating progress of residual coal in the gob. Considering that the geometric dimensions and physical characteristics of the gob will change during the advance of the working face, the purpose of the present paper is to determine how the coal self-heating develops during and after coal mining. A fully coupled transient model including gas flow, gas species transport, and heat transfer in the gob and the butt entries, as well as heat transfer in the surrounding strata, is developed to quantify the evolution of coal self-heating in gob during and after mining. The model was solved by COMSOL Multiphysics package and then verified by comparing the field data with the simulated data. On this basis, parametric studies including the influences of the surrounding strata temperature, airflow temperature, coal-rock particle size, and advance rate of the working face on coal oxidation and self-heating in the gob were conducted. The results show that a tailing phenomenon of the high-temperature area is formed on the air inlet side of the gob during mining, and the temperature in the high-temperature zone decreases gradually due to the accumulation and compaction of the gob and heat dissipation to the surrounding strata. Also, although the temperature in gob increases gradually after the stopping of mining, the high-temperature area migrates towards the working face. Moreover, when the temperature of the surrounding strata is consistent, different ventilation temperatures have no obvious effect on the maximum temperature of the gob at the initial mining stage, whereas the higher ventilation temperature results in the higher self-heating temperature after several days of mining. Finally, the smaller average particle size or faster advance rate results in a lower maximum temperature of gob.