Solid-Fuel Combustion in the Sintering of Siderite Ore

Two technologies are considered for the preparation of solid fuel used in sintering: crushing with portions of roasted siderite ore whose strength is less than that of the fuel; or crushing of the fuel alone and subsequent mixing with the ore portions. On the basis of derivatographic data, kinetic equations are written for the high-temperature combustion of coke fines in a fuel–ore mixture obtained by the two methods. The most flammable fuel fraction in sintering is established. The results indicate that crushing of the fuel mixed with weaker additives is more effective in terms of decreasing the content of fines in the fuel and hence intensifying the combustion of large pieces.     

Cyclic Tests of Stress-corrosion Cracks in Steel Gas Pipelines with No Corrosive Fluid

Stress-corrosion defects in the output pipeline of a compressor station are subjected to metallographic analysis and mechanical tests. The pipeline consists of pipe imported in the 1980s. Diagnostic data obtained in nondestructive monitoring of such pipelines are analyzed, and the effectiveness of various diagnostic methods in detecting stress-corrosion defects in large-diameter pipe is assessed. The grade of steel in the pipeline is identified. The cracks are identified by type and morphology, and their development is determined. Nonmetallic sulfide inclusions have no influence on pipeline failure in the stress-corrosion conditions considered. The sulfur content in the corrosion products is no more than the sulfur content in the metallic sample. In some samples, the sulfur content may be decreased except for local sections with nonmetallic sulfide inclusions. Electron-microscope images show that such nonmetallic inclusions do not promote failure. The results of cyclic tests of cracked samples cut from the pipeline are presented. The test conditions are selected in accordance with recent operating conditions of the compressor station. According to the results, pipe with defects at the initial stage of development exhibits considerable durability in the tests. In fact, the cracked samples withstand (1.6–7.5) × 10⁶ cycles under transverse cyclic flexure in a single plane, in the absence of corrosive fluid. In practice, the number of such cycles is no more than 120–200 per year, in normal pipeline operation. Hence, a pipeline with stress-corrosion defects in their initial stage of development will last a long time if its metal wall is protected from the action of corrosive fluid.     

Optimizing Estimation of a Statistically Undefined System

Consideration was given to the optimal choice of the parameters for the best estimation of the phase state of a linear system fallible to the action of the Gaussian perturbation with undefined covariances of increments. The matrices at system perturbation and those in the measurement equation are the parameters to be selected for the choice of the observer player. The undefined increment matrices are selected by the opponent player. Both parameters are limited by compact sets. The problem comes to a differential game for the Riccati equation with a performance criterion in the form of a matrix trace. In a special case, consideration was given to the problem with constant matrices. Used were the methods of minimax optimization, optimal control theory, and the theory of differential games. Examples were considered.     

On diffusion theory in inhomogeneous media: Thin-film source of diffusant

Using asymptotic methods in the theory of differential equations, the original solution of the atomic diffusion problem in the semi-infinite inhomogeneous medium has been obtained for the thin-film (instantaneous) source of diffusant and arbitrary coordinate dependence of the diffusion coefficient. We have mathematically estimated the applicability of this solution and compared it numerically with the known exact solution for a particular case of the exponential coordinate dependence of the diffusion coefficient and a trivial case of the constant diffusion coefficient. Based on our analysis, the ranges of annealing times and depths of diffusant penetration for which the suggested approach proves to be correct have been established.     

Influence of Tool Design on the Cutting Force in the Machining of Noninvolute Gears

The cutting forces in the machining of gears with noninvolute teeth are considered, for the example of a triangular tooth profile, by means of robust experiment design and analysis of variance. The rounding radius of the cutter tip has the greatest influence on the cutting force.     

Experiments on a Low-Emission Two-Stage Model Combustor for a Medium-Power Gas Turbine

This paper is the last in the series on the reasearch into the sequential combustion process in a combustor with an outlet gas temperature of 1600 –     

Calculation of the Surface Energy of Metals: Agreement of the Thermodynamic Vacancy Model with the First-Principles Theory

Protection of Metals and Physical Chemistry of Surfaces - The thermodynamic vacancy model (TVM) of surface energy (SE) leads to the formula of the linear dependence of the minimum SE value of the...