Vol 52, No 2 (2018)

The kinetics of the heterogeneous process of the thermal decomposition of condensed substance particles with the formation of gaseous reaction products is considered using an example of the process of obtaining nitrous oxide via the thermal decomposition of the ammonium nitrate melt. A mathematical model has been obtained based on the methods of the thermodynamics of irreversible processes taking into account the thermal phenomena and the multicomponent composition of the reaction products. Using the methods of multicomponent hydrodynamics, expressions of crossed kinetic coefficients determined from the measured physical quantities have been obtained. An analysis was carried out for some particular cases of the process using the developed mathematical model.

The results of studying the effect of solid-surface vibrations on the kinetics of mass transfer in the frequency range of 24–200 Hz and at displacement amplitudes of up to 1.5 mm have been presented. The direct dependence of the mass-transfer coefficient on the cosine of the angle between the normal line to a vibrating surface and the direction of vibrations has been found. The mathematical modeling of the process has shown that there is no significant effect of molecular diffusion on the rate of mass transfer.

Adsorption (chemical) heat transformation (AHT) is a new energy conservation and environmentally friendly technology that allows efficient use of heat sources with low temperature potential. Recently, a new cycle, called “Heat from Cold” (or HeCol) has been proposed to upgrade the temperature potential of the ambient heat. In the HeCol cycle, a natural reservoir of water with a temperature above 0°C is used as a heat source, and ambient air at T = (–20)–(–50)°C as a heat sink. The cycle is designed to produce heat at a temperature of 30–50°C, which can be used for heating of dwellings. The aim of this work is to select the adsorbent for the HeCol cycle and to test the laboratory prototype with the selected adsorbent. The work consists of three parts: (a) formulation of requirements to adsorbent, specialized for the HeCol cycles under various conditions; (b) analysis of data on adsorption equilibrium of commercial activated carbons and selection among them the materials suitable for the new cycle; and c) study of the laboratory prototype HeCol with the chosen adsorbent to analyze the feasibility of the new cycle. The main findings of this study are (i) the experimental demonstration of the HeCol cycle feasibility and (ii) the achievement of the specific heat generation power 8 kW/kg, which is of practical interest.

Heat-resistant Ni/MgO block catalysts have been developed on porous nickel carriers for the air conversion of natural gas to synthesis gas. The catalysts were tested under normal pressure, which allowed one to select of a number of samples that demonstrate relatively the low temperature of the frontal layer of the catalytic block of 880–940°C at the inlet temperature of the mixture of 20°C and excess air factor of 0.3. The composition of the mixture at the outlet remained close to thermodynamic equilibrium at a volumetric flow rate of up to 49 000 h^–1. It was experimentally established that the temperature of the frontal layer decreases with increasing pressure (2–6 atm), an increase in the frontal layer temperature with an increasing coefficient of excess air (0.31–0.42) and the rate of the inlet mixture (0.30–0.74 m/s). This made it possible to obtain approximate estimates of the areas of exothermic and endothermic reaction stages taking into account external diffusion inhibition based on the analysis of the heat balance equation for the frontal layer of the catalyst.

Methods for calculating and modeling individual processes that occur during the thermal treatment of solid waste in reactors with constant and variable temperatures of the medium have been considered. Studies of the influence of various mathematical models of the heating of dispersed material on the results of kinetic analysis of the pyrolysis of wood waste have been carried out. The influence of the type of the mathematical model and its parameters on process characteristics have been shown. For the model of material heating that takes into account the change in the local temperature both with time and with coordinate, the dependences of the average nondimensional temperature of material of spherical and cylindrical form on nondimensional time have been proposed for different values of the Biot number.

The process of the sulfuric-acid alkylation of isoparaffins with olefins in a new-generation reaction apparatus, namely, the energy-efficient tubular contactor with diffuser–confuser design, which operates in the mode of jet agitation of raw material flows and a catalyst with the arrangement of internal cooling due to partial evaporation of isobutane, has made it possible to obtain high-octane hydrocarbon fractions with a content of 3-methylpentanes of up to 47 wt % and an octane number of up to 92. Energy efficiency has been achieved by eliminating the external cooling of the reaction mass, mechanical agitation, and additional pump-forced circulation equipment. The results of the industrial trials of the new contactor have been described.

The present work deals with the effect of thermal feed quality on the performance of a divided wall distillation column (DWC). The thermal condition of the feed alters the pressure profile across the two sides of the dividing wall, thereby affecting not only the mass transfer characteristics but also the hydrodynamics of a DWC. It was observed that the natural (feasible) vapor split ratio does not depend on the liquid split ratio and the reflux flow rate when the feed is saturated liquid or sub-cooled liquid (q ≥ 1). However, for q < 1, that is, for two phase (vapor-liquid), saturated vapor, or superheated vapor feed, the liquid split ratio and the reflux flow rate have profound effect on the feasible vapor split ratio, and the pressure profiles are altered significantly. For the stable operation of a DWC, the feed should be either saturated liquid or sub-cooled liquid or the feed quality may be manipulated to adjust the vapor split ratio.

This paper reports a two-dimensional numerical investigation of mixed convection inside a liddriven square enclosure, completely filled with a non-Newtonian fluid obeying the Bingham model, having two rectangular adiabatic partitions mounted in different dispositions. Due to the problem’ complexity, the latter is solved using finite volume method when the SIMPLER algorithm is adopted for the pressure-velocity coupling. In order to investigate the yield stress effects on flow field and heat transport, we maintain the Richardson number (Gr/Re²) as 0.01, 1 and 10, respectively, which generates a good simulation of forced, mixed and natural convection dominated flow. The Prandtl and Grashof numbers are fixed at 50 and 10⁴, respectively, while the Bingham number covers the range from 0 to 30. The validity of the computing code was ascertained by comparing our results with the numerical ones already available in the literature and that for both cases: Newtonian and non-Newtonian fluid. The phenomenon is analyzed through the streamlines, the isotherms and the Nusselt numbers with special attention to the partitions’ arrangement and its size. It is found that all parameters related to the geometrical dimensions of the partitions play a crucial role on the temperature distribution, flow field and heat transfer enhancement. For all values of the Bingham number, the mean Nusselt number is found as an increasing function of the decrease Richardson number. Thus, the heat transfer improves.