Multicomponent Nonisothermal Diffusion in Thermal Decomposition of Dispersed Ammonium Nitrate

Theoretical Foundations of Chemical Engineering - An analysis of a particular case of the heterogeneous chemical process accompanied by multicomponent nonisothermal diffusion and the thermal...     

Effect of Heat Treatment of Molten Bi2O3 Containing 22 mol % SiO2 on the State of the Metastable δ*-Phase Forming during Solidification

Inorganic Materials - We have studied the effect of isothermal holding of a melt containing 78 mol % Bi2O3 and 22 mol % SiO2 and various melt cooling schedules on the morphology, microstructure,...     

Investigation and optimization of the depth of flue gas heat recovery in surface heat exchangers

Economic issues associated with designing deep flue gas heat recovery units for natural gas-fired boilers are examined. The governing parameter affecting the performance and cost of surface-type condensing heat recovery heat exchangers is the heat transfer surface area. When firing natural gas, the heat recovery depth depends on the flue gas temperature at the condenser outlet and determines the amount of condensed water vapor. The effect of the outlet flue gas temperature in a heat recovery heat exchanger on the additionally recovered heat power is studied. A correlation has been derived enabling one to determine the best heat recovery depth (or the final cooling temperature) maximizing the anticipated reduced annual profit of a power enterprise from implementation of energy-saving measures. Results of optimization are presented for a surface-type condensing gas–air plate heat recovery heat exchanger for the climatic conditions and the economic situation in Tomsk. The predictions demonstrate that it is economically feasible to design similar heat recovery heat exchangers for a flue gas outlet temperature of 10°С. In this case, the payback period for the investment in the heat recovery heat exchanger will be 1.5 years. The effect of various factors on the optimal outlet flue gas temperature was analyzed. Most climatic, economical, or technological factors have a minor effect on the best outlet temperature, which remains between 5 and 20°С when varying the affecting factors. The derived correlation enables us to preliminary estimate the outlet (final) flue gas temperature that should be used in designing the heat transfer surface of a heat recovery heat exchanger for a gas-fired boiler as applied to the specific climatic conditions.     

Selection of power semiconductor devices for parallel connection

The method of selecting power semiconductor devices for group parallel connection on the basis of models developed on the basis of the measured electrical and thermal parameters and characteristics of certain devices are considered. Experimental data are obtained using the ADIP-6 test equipment. The electrical part of the model is constructed on the basis of the electrical parameters of the volt–ampere characteristic in a high-conductivity condition, and the thermal part is developed on the basis of the electrothermalanalogy method. The parameters of the thermal model are determined on the basis of the measured value of the thermal junction-to-case resistance in the steady-state thermal mode. The electrical and thermal parts of the model are connected through the temperature dependences of the volt–ampere characteristic parameters. A sample of ten power diodes is considered as an example, parallel connections consisting of two diodes are constructed of them, and the electrical and thermal processes are analyzed in this group using the simulation method for all possible combination of the diodes. The potentially reliable and unreliable diode combinations were specified on the basis of the simulation results. The temperature of the semiconductor structure is used as a criterion for determining reliability. A connection in which the temperature of the semiconductor structures of the devices included in the connection did not exceed the admissible limit value was considered as potentially reliable. Two connections, referred to as “potentially reliable” and “potentially unreliable” connections, are considered as an example.     

Influence of Heat Treatment on the Properties of Nickel–Chromium–Silicon Bronze Wire

The selection of optimal heat-treat conditions for nickel–chromium–silicon bronze wire used in the production of helical compression springs is considered. In experiments, the microstructure of samples after aging at 440–480°C is investigated. Tensile tests are conducted.     

Nonpositional analog-digital conversion methods

This paper describes the analysis of analog-digital converters operating in positional and nonpositional number systems. A new method for analog-digital conversion on the basis of the features of a modular number system is proposed.     

Computational-and-experimental evaluation of the implementation condition of combined rolling–pressing using the power balance method

The results of solving the problem of determining the implementation of combined rolling–pressing (CRP) are presented. Components of the total power for the process under study are written in the analytical form, they are calculated with the help of the computer program, and the influence of separate factors on the CRP implementation is analyzed. The possibility of implementing the process for CRP conditions of aluminum alloys with the use of a pilot installation of the combined treatment is evaluated quantitatively using the capacity reserve coefficient as the main criterion.     

Substrates for spintronic structures based on epitaxial gallium nitride films

The possibility of obtaining semiconductors that do not contain surface-growth defects using postgrowth processing based on the multiple ion beam sputter deposition of a submicron-thick aluminum oxide layer was demonstrated by the example of gallium nitride films on leucosapphire and silicon nitride. The obtained films are promising as substrates for the formation of spintronic structures.