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1、中原工学院毕业设计（论文）译文Mathematical Modeling of Chemical Conversionin Thin-Layer Exothermic Mixtures underPeriodic Electric-Spark Discharges B. S. Seplyarskii,1 T. P. Ivleva, and E. A. Levashov2Translated from Fizika Goreniya i Vzryva, Vol. 40, No. 3, pp. 5968, MayJune, 2004.Original article submitted April
2、 23, 2003.Abstract:The dynamics of coating production using a reaction mixture with thermoreactive electric-spark strengthening is studied numerically. It is shown that the main parameter that determines the thermal regime of coating is the initial thickness of the mixture layer. The parameter range
3、s for the process in a combustion regime and in a quasivolume conversion regime are determined. The effect of discharge frequency and the thermal characteristics of the reaction mixture and the substrate being strengthened on coating time is investigated. It is established that for a particular reac
4、tion mixture, the characteristic conversion temperature can be controlled by varying the electric discharge power and, hence, the heat flux at the active stage of the process,and for coating formation at this characteristic temperature, it is necessary that the thickness of the active layer be lower
5、 than a certain critical value.Key words: mathematical modeling, chemical conversion, mixtures, action, charge.One of the widely used methods for the surface strengthening of dies, rolls, and cutting tools is electric-spark alloying 1. To apply functional coatings,Podlesov et al. 2, 3 used electrode
6、s produced by self-propagating high-temperature synthesis (SHS) 4. In this case, for each particular problem of surface strengthening, it was necessary to develop a technology to produce electrodes of the required composition. Levashov et al. 57 were the first to propose to combine the processes of
7、electric-spark alloying and SHS in the interelectrode gap. This method was called thermoreactive electric-spark strengthening (RESS). The idea of the TRESS method is that an electric discharge of a definite power not only produces transport of the alloying agent to the substrate but also initiates a
8、 chemical exothermic reaction between the components of the reactive mixture, which is placed in a tubular electrode (cathode). Unlike in the coating method proposed in 2, 3, in the TRESS method, the production of a coating of the required composition is achieved by varying the composition of the mi
9、xture placed in the tubular electrode and by varying the energy parameters of plant operation. For successful implementation of the method, it is necessary that the chemical reaction between the mixture components stop after detachment of the electrode from the surface being alloyed, which leads to
10、current-circuit break. Experiments 5 7 showed that the efficiency of the process increases markedly only when the heat effect of the chemical reaction is comparable to the pulsed-discharge energy. In the present study, the thermal regimes of a new version of the TRESS process were first studied usin
11、g mathematical modeling. The essence of the method is as follows: a layer of a reactive mixture of the required composition 60300 m thick is applied to the surface to be strengthened. The electric discharge resulting from periodic contact of the electrode with the strengthened product through the mi
12、xture layer ensures heating of the mixture in the contact area and initiates a chemical exothermic reaction between the mixture components. The chemical conversion leads to formation of a protective layer on the sample surface. In this version of the method, the electrode material is virtually not c
13、onsumed and the required technical characteristics of the coating are attained by varying the composition of the mixture, the thickness of the applied layer, and the power and duration of the spark discharge. The goal of the theoretical part of this investigation was to study how the time characteri
14、stics of the chemical conversion and the thermal regime of coat application are affected by the main parameters of the process: the time th of contact of the electrode with the surface during which a current flows in the circuit and the mixture and substrate are heated; the time tad between the cont
15、acts of the electrode with the surface when there is no current flow in the circuit and adiabatic conditions are specified on the surface of the mixture; discharge power, which determines the heat-flux magnitude; the thickness of the mixture layer, which determines the thermal regimes of the reactio
16、n of the mixture and substrate preheating.The following model of the process (Fig. 1) is considered. At the time t = 0, the electrode (cathode) is brought into contact with the mixture layer on the surface of the substrate (anode), thus completing the circuit. The electric current flowing in the circuit heats the reactive layer. The heating of the material abruptly increases the reaction rate in the surface layers of the mixture, which can
