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Title: One dimensional time-to-explode (ODTX) in HMX spheres

Abstract

In a series of papers researchers at Lawrence Livermore National Laboratory (LLNL) have reported measurements of the time to explosion in spheres of various high explosives following a rapid, uniform increase in the surface temperature of the sphere. Due to the spherical symmetry, the time-dependent properties of the explosive (temperature, chemical composition, etc.) are functions of the radial spatial coordinate only; thus the name one-dimensional time-to-explosion (ODTX). The LLNL researchers also report an evolving series of computational modeling results for the ODTX experiments, culminating in those obtained using a sophisticated heat transfer code incorporating accurate descriptions of chemical reaction. Although the chemical reaction mechanism used to describe HMX decomposition is quite simple, the computational results agree very well with the experimental data. In addition to reproducing the magnitude and temperature dependence of the measured times to explosion, the computational results also agree with the results of post reaction visual inspection. The ODTX experiments offer a near-ideal example of a transport process (heat transfer in this case) tightly coupled with chemical reaction. The LLNL computational model clearly captures the important features of the ODTX experiments. An obvious question of interest is to what extent the model and/or its individual components (specificallymore » the chemical reaction mechanism) are applicable to other experimental scenarios. Valid exploration of this question requires accurate understanding of (1) the experimental scenario addressed by the LLNL model and (2) details of the application of the model. The author reports here recent work addressing points (1) and (2).« less

Authors:
Publication Date:
Research Org.:
Los Alamos National Lab., NM (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
674675
Report Number(s):
LA-UR-98-1237
ON: DE99000852; TRN: AHC29820%%129
DOE Contract Number:
W-7405-ENG-36
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 2 Jun 1997
Country of Publication:
United States
Language:
English
Subject:
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; CHEMICAL EXPLOSIVES; EXPLOSIONS; TIME MEASUREMENT; SPHERICAL CONFIGURATION; MATHEMATICAL MODELS; CHEMICAL REACTION KINETICS; HEAT TRANSFER

Citation Formats

Breshears, D. One dimensional time-to-explode (ODTX) in HMX spheres. United States: N. p., 1997. Web. doi:10.2172/674675.
Breshears, D. One dimensional time-to-explode (ODTX) in HMX spheres. United States. doi:10.2172/674675.
Breshears, D. Mon . "One dimensional time-to-explode (ODTX) in HMX spheres". United States. doi:10.2172/674675. https://www.osti.gov/servlets/purl/674675.
@article{osti_674675,
title = {One dimensional time-to-explode (ODTX) in HMX spheres},
author = {Breshears, D.},
abstractNote = {In a series of papers researchers at Lawrence Livermore National Laboratory (LLNL) have reported measurements of the time to explosion in spheres of various high explosives following a rapid, uniform increase in the surface temperature of the sphere. Due to the spherical symmetry, the time-dependent properties of the explosive (temperature, chemical composition, etc.) are functions of the radial spatial coordinate only; thus the name one-dimensional time-to-explosion (ODTX). The LLNL researchers also report an evolving series of computational modeling results for the ODTX experiments, culminating in those obtained using a sophisticated heat transfer code incorporating accurate descriptions of chemical reaction. Although the chemical reaction mechanism used to describe HMX decomposition is quite simple, the computational results agree very well with the experimental data. In addition to reproducing the magnitude and temperature dependence of the measured times to explosion, the computational results also agree with the results of post reaction visual inspection. The ODTX experiments offer a near-ideal example of a transport process (heat transfer in this case) tightly coupled with chemical reaction. The LLNL computational model clearly captures the important features of the ODTX experiments. An obvious question of interest is to what extent the model and/or its individual components (specifically the chemical reaction mechanism) are applicable to other experimental scenarios. Valid exploration of this question requires accurate understanding of (1) the experimental scenario addressed by the LLNL model and (2) details of the application of the model. The author reports here recent work addressing points (1) and (2).},
doi = {10.2172/674675},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jun 02 00:00:00 EDT 1997},
month = {Mon Jun 02 00:00:00 EDT 1997}
}

Technical Report:

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  • What will be discussed in this report represents a framework upon which multiphase and other real physical effects can be built. Chemical models of increasing complexity are envisioned and this methodology can provide a tool for evaluating new ideas against known experimental data. The recent work to be reported here addresses the multiphase issue of temperature deviation between phases undergoing chemical and heat transport processes. Modeling of the LLNL ODTX experiment will be performed with FLUENT, a commercially available computational fluid dynamics (CFD) code. FLUENT solves flows in 2D or 3D in Cartesian, cylindrical, or general curvilinear coordinates, with steady-statemore » of fully time-dependent analysis. Multiphase flows in which two or more continuous phases are present can be solved with arbitrary volumetric sources of heat, mass, momentum, and chemical species applied through user-defined FORTRAN subroutines. FLUENT models these of phenomena by solving the conservation equations for mass, momentum, energy, phasic volume fraction, and chemical species for each phase using a control volume based finite difference method. The equations are solved using SIMPLE-like algorithms with an iterative line-by-line matrix solver and multigrid acceleration. Before considering the temperature deviation issue and its dependence upon gaseous bubble diameter in a multiphase system, the author discusses the use of FLUENT for modeling the basic constant and uniform density LLNL ODTX problem. Following the discussion of the temperature deviation in the multiphase treatment, the author discusses possible extensions of this work to include more advanced multiphase effects such as surface reactions within bubbles and gas phase transport out of the HE sample.« less
  • The thermal explosion of trinitrotoluene (TNT) is used as a basis for evaluating the performance of a new One-Dimensional-Time-to-Explosion (ODTX) apparatus. The ODTX experiment involves holding a 12.7 mm-diameter spherical explosive sample under confinement (150 MPa) at a constant elevated temperature until the confining pressure is exceeded by the evolution of gases during chemical decomposition. The resulting time to explosion as a function of temperature provides valuable decomposition kinetic information. A comparative analysis of the measurements obtained from the new unit and an older system is presented. Discussion on selected performance aspects of the new unit will also be presented.more » The thermal explosion of TNT is highly dependent on the material. Analysis of the time to explosion is complicated by historical and experimental factors such as material variability, sample preparation, temperature measurement and system errors. Many of these factors will be addressed. Finally, a kinetic model using a coupled thermal and heat transport code (chemical TOPAZ) was used to match the experimental data.« less
  • MACH1 performs one-dimensional multigroup diffusion solutions and associated calculations, including criticality searches, perturbation, reaction summary, beta effective, group collapsing, and pointwise reaction rates and ratios. Several card dumps of computed data are available on option. A spectral synthesis option is available in the IBM version.CDC6500;IBM360,370/195; FORTRAN IV (CDC6500, IBM360-98%), BAL (IBM360-2%); OS/360 (IBM360) and SCOPE (CDC6500); The IBM360 version uses 5 tape drives and 1645K core storage assuming no overlay organization.
  • HFN solves the homogeneous or inhomogeneous one-dimensional multigroup diffusion equation for its lowest eigenvalue and the corresponding direct and/or adjoint eigenvectors. Inhomogeneous boundary conditions and a flexible scatter-transfer matrix structure are included. Optional calculations include criticality searches, detector activation traverses, and integrals for perturbation theory analysis.UNIVAC1107;CDC6600,CYBER74; FORTRAN IV (99.9%) and SLEUTH-II (0.1%) (UNIVAC1107), FORTRAN IV (CDC6600); CSC EXEC2 Package B (UNIVAC1107), SCOPE 3.4 (CDC6600); 64K UNIVAC1107 with 786,432 word drum (exclusive of system requirements), a tape unit, on-line printer, card reader and clock. The CDC version requires 122K (octal) words of memory.
  • How best to fit chemical decomposition models to experimental data is a very important question. Many experiments are complicated by transport and geometrical effects, and the resulting chemical models have these effects lumped into the kinetic parameter data. This results in kinetic mechanisms without broad applicability to other experimental configurations. In recent years considerable effort has been applied toward understanding the chemistry and transport involved in measuring and modeling the one-dimensional time to explosion (ODTX) in spheres of high explosives (HE). This type of experiment is an example of a system in which transport processes, geometrical effects, and chemical reactionsmore » are highly coupled. It is the intent of this brief communication to demonstrate the need for researchers in this field to consider phase segregation effects in conjunction with developing kinetic mechanisms so that broader applicability might be achieved. In this paper, the results of ODTX calculations are shown for which the effects of spatial phase segregation are considered. The chemical model for the decomposition of cyclotetramethylene-tetranitramine (HMX as LX-10, a bound composite) considered here is widely known. It is quite simple and has been fit to ODTX data without regard to phase segregation effects. It is shown here that if bimolecular gas-phase reactions are constrained to occur in bubbles, then the calculated time to explosion is greatly reduced. What is required of chemical modelers in the future is an approach that explicitly incorporates into the fitting procedure all of the important physical phenomena that affect the observed rate of decomposition.« less