Transitional regimes of wave propagation in metastable systems

Results of a theoretical study of deflagration-to-detonation transition processes in hydrogen-air mixtures are presented. The dependence of the deflagration-to-detonation transition scenario on the governing parameters (initial temperature of the mixture, ignition energy, ignition time, geometric characteristics of cavities, and distances between cavities in the ignition zone) is considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 25–37, September–October, 2008.     

Nonclassical regimes of wave diffraction in combustible mixtures

Experimental and numerical results of investigating the diffraction of combustion and detonation waves, including the diffraction in unsteady deflagration-to-detonation transition regimes, are presented. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 137–143, November–December, 2006.     

An empirical correlation for polymer self-diffusion data in the dilute and semidilute concentration regimes

An expression is presented which can be used to correlate and predict, in an empirical fashion, polymer self-diffusion coefficients in solution over a wide range of concentrations and molecular weights, and whose parameters can be established with a minimal amount of data. Predictions thus made have been found to agree well with the limited amount of available experimental data over the entire concentration-molecular weight spectrum studied to date. This is in marked contrast to other available expressions, whose validity is confined to a narrow range of concentrations and/or molecular weights.     

Split rate fatigue propagation in polymer blends

Summary The long-term properties of PSAN/PMMA blends have been examined by conducting fatigue tests on a fracture mechanics-type specimen. Initial testing on the individual constituents showed that the crack initiation threshold was higher in the PMMA polymer than in the PSAN system. Alloying these polymers resulted in the crack initiation thresholds between those of the two base polymers. A scanning electron microscopy study of the fracture surfaces indicated that fatigue loading resulted in the formation of well defined striations, the spacing of which depended on the crack velocity and morphology. The fatigue striations in a fine-structured blend remained straight and did not appear to be modified by the presence of the secondary phase. Crack extension in a coarser structure depended upon the characteristics of the particular phase in which the crack was extending. It was observed that the striations in the less ductile PSAN phase were more closely spaced as well as being curved. It is believed that the crack propagated more rapidly in this phase resulting in a split rate crack velocity within the polymer blend.     

Thermal heating regimes during first-order homogeneous reactions

Qualitative features of self-heating regimes for first-order homogeneous reactions are considered by analyzing the structure of the phase trajectories. Consideration of the temperature dependence of the heating rate makes it possible to extend the main results of Semenov’s theory of thermal explosion and pass to a two-dimensional parameter diagram, which allows the determination of the critical ignition conditions taking into account kinetic inhibition. It is found that the diagram of the Todes criterion versus the reciprocal of the Semenov criterion has four characteristic regions with different kinetics, two of which are limiting and two transitional ones. The boundaries of the regions are calculated, and the classical theory of thermal explosion is shown to be a special case of the projections of these boundaries on the range of the Semenov criterion.     

Thermal strategy for the separation of a polymer mixture

We propose a separation technique for a mixture of polymer materials that involves unsteady heat conduction and thermal adhesion. Since the softening temperature is related to the melt or glass transition temperature of these materials, each material has its own adhesion temperature. Further, the adhesion temperature of each material was typically between its glass transition temperature and melt temperature. In the present study, we used these characteristics to separate particular components from a mixture of polymer materials. Five types of virgin polymer pellets were used as test materials in the experiment and two experimental designs were used to investigate the capabilities and characteristics of this separation technique. The first experiment simply consisted of heating and pushing plates. Using this apparatus, the adhesion temperature of each material was determined experimentally and the effect of the surface condition of the test material was investigated. The contaminants on the material surface behaved as a thermally resistant medium, and coloring paint present on the surface significantly affected the adhesion behavior. In order to improve the separation efficiency, we examined another separation system, which consisted of counter‐rotating twin rollers. Continuous material separation was achieved using the roller system. POLYM. ENG. SCI., 45:1419–1425, 2005. © 2005 Society of Plastics Engineers     

On regimes I and II during polymer crystallization

Summary The temperature of the transition from Regimes I and II has been analyzed for several systems for which data is available for both overall crystallization rates and the direct growth rate of supermolecular structures. The same transition temperature is observed irrespective of the experimental method. In addition it is found that the Regimes do not serve as boundaries between distinct morphological forms.     

Effect of radiative heat transfer on the combustion wave propagation in a model of a heterogeneous system

The subject of investigation was the behavior of integral curves of the problem of combustion-wave propagation in a model of a heterogeneous system. The influence of radiative heat transfer on steady combustion regimes was considered. It was shown that for sufficiently large gaps between the plates in the system (when a quasihomogeneous temperature distribution still exists) in the regime of weak retardation by the growing product layer, the radiation can result in a notable acceleration of the combustion wave. In the regime of strong retardation with the remaining conditions being the same, the radiation can be neglected. Translated fromFiz. Goreniya i Vzryva, Vol. 34, No. 3, pp. 69–76, May–June 1998.     

Combustion wave propagation through deformed solids

A one-dimensional model for combustion wave propagation in deformed media is proposed taking into account the coherence of the deformation and temperature fields. It is shown that stresses and deformations change temperature profiles in the steady-state combustion wave and the conditions of steady-state combustion wave stability loss. The concept of the thermomechanical loss of combustion wave stability is introduced, which can occur before the thermal loss of combustion stability. It is shown that the coherence of deformation and temperature fields can be the reason for the exponential stability loss.Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 48–53, May–June, 1993.     

Investigation of the thermal structure of a combustion wave by the microthermocouple method in the system titanium-carbon-chlorine-containing polymer

Erevan. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 6, pp. 43–45, November–December, 1992.     

Characterization of wave propagation in nonsymmetric laminated plates

This article presents a theoretical approach to predict the characterization of wave propagating in nonsymmetric laminated plates based on first‐order shear deformation theory. It was developed as an extension of Mindlin theory including the effects of shear and rotary inertia. We formulated the equations of motion by substituting the deformations including three displacement functions and two rotary functions, and in any case of laminated plates, more precise wave velocities were calculated. We also described velocity–frequency curves of waves in five modes from the numerical results and investigated the influence of the laminate angle, number of layers, and stacking sequence in detail. POLYM. COMPOS., 31:1914–1921, 2010. © 2010 Society of Plastics Engineers.     

Thermal regimes of exothermic processes in continuous stirred tank reactors

Thermal regimes of a CSTR are analysed from the standpoint of the thermal explosion theory. Critical phenomena and time characteristics of the process are considered. It is shown that for appropriately chosen dimensionless parameters the critical conditions of the thermal explosion and induction period in a CSTR slightly differ from those for non-flow (batch) systems. These corrections may be performed by using an additional parameter which is characteristic for flow systems. In the region of multiplicity of steady states, the critical condition of thermal explosion is characterized by a jump of self-heating, while in the non-flow systems such phenomenon occurs only for a zero order reaction. For a unique steady state the transition through the critical condition is continuous.     

Determination of the propagation velocity of a polymerization wave

We consider the propagation of a plane polymerization wave in an infinite mass assuming that the temperature dependence of the reaction rate is a function of the type of exp Θ−1. Existence conditions for a steady regime are determined. It was found that, for a continuous heat-release function, the minimum possible velocity of the wave is given by two different analytic dependences that transform into one another continuously for some critical value of the dimensionless adiabatic temperature. An approximate analytic expression for the temperature profile of the wave is obtained. Russian Research Center “Applied Chemistry,” St. Petersburg 197198. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 5, pp. 62–75, September–October, 1997.     

Thermal conductivity of polymer melts

Thermal conductivities were measured for melts of a series of polypropylene and a series of polyethylene samples that had been characterized by GPC. Results indicate that thermal conductivity depends upon the molecular weight distribution and degree of branching of the polymers. The results of this work can probably be used to predict the thermal conductivity of a commercially available polypropylene or polyethylene to within 25%.