Modeling of thermal radiation of polymer coating containing hollow microspheres

The paper deals with the effect of hollow microspheres added to paint or another polymer coating for open surfaces of a building on the heat loss due to thermal radiation. An approximate theoretical model is suggested, which is based on the spectral calculation of the radiative characteristics of a disperse system and determination of the integral flux of thermal radiation. Calculations are performed for a layer of paint with hollow glass microspheres. It is demonstrated that the microsphere shell thickness has the strongest effect on the reduction of heat loss.__________Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 2, 2005, pp. 256–266.Original Russian Text Copyright © 2005 by L. A. Dombrovsky.     

Conjugate problem of thermal explosion

The problem of thermal explosion of a reagent in the form a plane layer placed between two plane-parallel inert walls is solved analytically under boundary conditions of the third kind. Critical conditions for thermal explosion for the general case and particular cases are investigated. Results of calculations are compared with previously published data. An engineering method for evaluation of the critical conditions for thermal explosion is proposed.     

Determination of the effect of a thermal explosion of organic peroxides (homogeneous explosion test)

In this paper an instrument for investigating the pressure effects caused by thermal explosions of such unstable substances as organic peroxides is desThe design of the instrument makes it possible to simulate situations with a moderate degree of confinement. A number of intermediate scale experiments     

The effect of thermal explosion in a supercritical water

The conversion of hydrocarbons (eicosane, naphthalene, and synthetic bitumen) dissolved in super-critical water (SCW) was studied in a batch reactor at a pressure of P=30 MPa and a range of temperatures from 450 to 75°C. It was established that water participates in the conversion process on a chemical level: in particular, oxygen from water molecules is involved in the formation of carbon oxides. Even in the absence of added molecular oxygen, the process of naphthalene and bitumen conversion in a certain temperature interval exhibited an exothermal character. Upon adding O₂ into SCW, the oxidation reaction may proceed in a burning regime with self-heating of the mixture. Under certain conditions, the self-heating process may lead to the thermal explosion effect accompanied by ejection of the substance from the reactor, which is explained by the high rate of hydrocarbon burning in SCW.     

Modeling environmental effects in the simulation of explosion events

Explosion events from malicious activities produce tremendous losses. The magnitude of these losses is directly tied to the overpressure field generated during the event. This field is dependent on both the explosive charge and the environment in which the event occurs. Environmental factors, such as blast focusing and channeling, greatly alter the damage patterns. A useful tool in investigating and preparing for such events is computational fluid dynamics (CFD) modeling. Here, a CFD tool, Computational Explosion and Blast Assessment Model (CEBAM), is tested to determine the accuracy to which environmental effects can be represented. Configurations ranging from long single streets to barricaded buildings are simulated to determine the utility of CFD modeling in predicting the overpressure fields. The CEBAM simulations are found to compare well with the available test data supporting the use of CFD modeling to investigate potential events.     

A conjugate problem of thermal explosion of a hollow cylinder

A conjugated problem of heat conduction for two hollow cylinders that are in close contact, with one consisting of a reagent, has been solved analytically. The problem has been solved by the backward method under boundary conditions of the first kind. The critical conditions of thermal explosion were investigated as functions of the parameters of a reagent and of an inert body. An engineering method for determining the critical conditions of a thermal explosion is suggested. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 110–113, July–August, 2006.     

Natural thermal radiation of heat-absorbing thermal vacuum chamber shields

A simplified method for computing the natural thermal radiation of heat-absorbing shields of vacuum chambers is elucidated; computational dependences are presented for shields of herringbone outlines and the influence of the geometric profile characteristics on the magnitude of the natural radiation is shown.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 2, pp. 317–321, February, 1976.     

Growth of aluminum nitride single crystals under thermal explosion conditions

The process of aluminum nanopowder combustion in air under thermal explosion conditions has been studied. It is established that the presence of a constant magnetic field with an induction of 0.4 T favors the formation of aluminum nitride single crystals under non-steady-state combustion conditions.     

Towards a predictive thermal explosion model for energetic materials

We present an overview of models and computational strategies for simulating the thermal response of high explosives using a multi-physics hydrodynamics code, ALE3D. Recent improvements to the code have aided our computational capability in modeling the behavior of energetic materials systems exposed to strong thermal environments such as fires. We apply these models and computational techniques to a thermal explosion experiment involving the slow heating of a confined explosive. The model includes the transition from slow heating to rapid deflagration in which the time scale decreases from days to hundreds of microseconds. Thermal, mechanical, and chemical effects are modeled during all phases of this process. The heating stage involves thermal expansion and decomposition according to an Arrhenius kinetics model while a pressure-dependent burn model is employed during the explosive phase. We describe and demonstrate the numerical strategies employed to make the transition from slow to fast dynamics. In addition, we investigate the sensitivity of wall expansion rates to numerical strategies and parameters. Results from a one-dimensional model show that violence is influenced by the presence of a gap between the explosive and container. In addition, a comparison is made between 2D model and measured results for the explosion temperature and tube wall expansion profiles.Approved for public release; distribution is unlimited. The work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.     

Modeling the delay in mixing to the molecular level in calculating the thermal radiation of turbulent flows

An appropriate method is proposed for taking account of the delay in mixing to the molecular level in turbulent flows of jet type; the method is intended for the calculation of the thermal radiation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 46, No. 2, pp. 225–233, February, 1984.     

Evaluation on thermal explosion induced by slightly exothermic interface reaction

An asphalt-salt mixture (ASM), which once caused a fire and explosion in a reprocessing plant, was prepared by imitating the real bituminization process of waste on a lab scale to evaluate its actual thermal hazards. Heat flux reaction calorimeters were used to measure the release of heat for the simulated ASM at a constant heating rate and at a constant temperature, respectively. Experimental results show that the reaction in the ASM below about 250 degrees C is a slightly exothermic interface reaction between the asphalt and the salt particles contained in the asphalt, and that the heat release rate increases sharply above about 250 degrees C due to melting of the salt particles. The reaction rates were formulated on the basis of an assumed reaction model, and the kinetic parameters were determined. Using the model with the kinetic parameters, temperature changes with time and drum-radius axes for the ASM-filled drum were numerically simulated assuming a one-dimensional infinite cylinder system, where the drum was being cooled at an ambient temperature of 50 degrees C. The minimum filling temperature, at which the runaway reaction (MFTRR) can occur for the simulated ASM in the drum is about 194 degrees C. Furthermore, a very good linear correlation exists between this MFTRR and the initial radius of salt particles formed in the bituminization product. The critical filling temperature to the runaway reaction is about 162 degrees C for the asphalt-salt mixture, containing zero-size salt particles, filled in the same drum at an ambient temperature of 50 degrees C. Thus, the runaway reaction will never occur in the drum filled with the asphalt-salt mixture under the conditions of the filling temperature below 162 degrees C and a constant ambient temperature of 50 degrees C. As a consequence, the ASM explosion occurred in the reprocessing plant likely was due to a slightly exothermically reaction and self heating.     

Temperature fields in thermal radiation detectors

Results of analysis of thermal processes in a superconducting thermal radiation detector, formulated as a boundary-value problem of complicated heat transfer in a three-dimensional region of complex geometry, are reported. Variants of the problem for simplification are given; the limitations of these assumptions are pointed out.Khar'kov Aviation Institute. Translated from Inzhenerno-Fizicheskii zhurnal, Vol. 64, No. 2, pp. 228–232, February, 1993.     

Characteristics of thermal radiation in axisymmetric cavities

Radiation heat transfer in axisymmetric cavities with a lateral surface formed by a truncated cone and plane ends is investigated. A numerical example is considered for a range of cavities. The calculated results are universal and can be used for rapid estimates of radiation heat transfer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 27, No. 2, pp. 208–214, August, 1974.     

Effect of heating rate on porous TiAl-based intermetallics synthesized by thermal explosion

TiAl-based porous materials were synthesized by a novel process of thermal explosion (TE) reaction. The effects of heating rate on the expansion behavior of powder assemblies, phase compositions, and pore structures were investigated. Results showed that the actual temperature of specimen increased rapidly from 655 to 661°C (furnace temperature) to 1018–1136°C (combustion temperature) in a short time interval of 25–55?s, indicating that an obvious TE reaction occurred at different heating rates (1, 2, 5, and 10°C min^?1). TE reaction in Ti/Al powder assemblies resulted in the formation of open-celled TiAl-based intermetallics. When the heating rate was set at 5°C min^?1, the maximum open porosity of 59% was obtained in Ti-Al bodies, which experienced the highest combustion temperature (1136°C) and underwent maximum volume expansion (48%). The pore size distribution was uniform and pores were interconnected in TE products.     

冲击载荷作用下火工分离保护装置的建模与分析

为了模拟空间火工分离保护装置冲击载荷下的动力学特性,首先,建立了该保护装置的简化模型,计算得到火工分离体的初速度,推导了装置的冲击变形和变形能公式;保护装置分别采用2A12、TC4、蜂窝夹层材料,建立三种材料的多线性本构模型,采用显式动力学求解步分析其冲击响应特性,分析可知,蜂窝夹层材料具有最佳的能量吸收特性,2A12的能量吸收特性介于蜂窝夹层材料和TC4之间,其塑性变形量适中;应变能释放和冲击碰撞的耦合分析可知,应变能占比小,体现为振荡衰减的过程,结构的冲击响应特性主要由碰撞冲击导致;试验表明,该火工分离保护装置的瞬态动力学过程与分析一致,局部最大应力为302MPa,冲击响应谱最大值为3242g,满足有效载荷的可靠解锁分离要求。     

An apparatus for noncontact measurement of thermal conductivity by thermal radiation heating

Thermal radiation calorimetry was applied to measure the thermal conductivity of insulating solid specimens. We consider the system in which a disk-shaped specimen and a flat heater are mounted in a vacuum chamber with the specimen heated on one face by irradiation. A temperature difference between two faces was observed at elevated temperatures under steady-state conditions. An apparatus was developed using a thin graphite sheet as the heater element. Disk-shaped Pyrex glass and Pyroceram specimens, whose surfaces were blackened with colloidal graphite, were used in the measurements. Noncontact temperature measurement was performed using pyrometers and a thermocouple set in the gap between the heater and the specimen. Deviations of the estimated thermal conductivities from the recommended values were about 5% in the temperature range 250 to 800°C. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Characteristics of the thermal radiation of nonisothermal regions

Analytical equations are derived which describe a distortion of heat radiation characteristics for gray diffuse and black surfaces, bounded by straight lines or circumferences, with linear and parabolic temperature profiles.All-Union Scientific Center S. I. Vavilov State Institute for Optics, St. Petersburg. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 6, pp. 866–872.