Том 55, № 7-8 (2019)

A method for intensifying the process of condensation of a steam–air mixture on the surface of a pipe is studied, consisting in the removal of non-condensed gas from the interphase surface by circulation vortices forming behind the protrusions of a helix installed at the heat exchange surface. With the use of the Comsol Multiphysics program, numerical simulations of the hydrodynamics of the steam–air flow were carried out and velocities in the axial and transverse directions of the moving flow were calculated. It is concluded that the flow of non-condensed gas from the interphase surface is diverted by vortices that move in the transverse direction to the moving vapor in the pipe. The results of heat transfer during condensation are presented, according to which the presence of a spiral in the cavity of the tube intensifies the process of condensation of the steam–air mixture by a factor of 2.3. The geometric parameters of the spiral are established, which ensure the greatest intensification of heat transfer during condensation.

Designs and principles of operation of new rotary-pulsation apparatuses are described. The essential technical feature of the developed designs consists in installation of additional dispersing elements in the apparatus chambers. Turbulent pulsations with randomly directed velocity vectors occur when the components of the treated medium interact with such elements. This causes increase of relative velocity of the flow around the particles of a heterogeneous medium, which ensures intensification of emulsification, dispersion, and mass transfer processes.

The results of simulation of a system for removing asphalt-resin-paraffin deposits from casing of well with high-viscosity oil, based on local noncontact induction heating, are presented. It is shown that gradual removal of deposit fragments by melting them at the point of adhesion bonding with the casing is possible with a heating power of 3 kW and an inductor moving speed of 2–3 cm/min.

The paper presents formulas for determining the torsional compliance of flat disks with a central hole and a torque measuring system, which are part of the planetary gears of drilling rigs.

Spraying processes for composite pseudo-alloy coatings by plasma and electric-arc methods are analyzed. During performance of the work the effect of interaction of components of mechanical mixtures of powders in a plasma jet and materials of dissimilar wires in the electric-arc method on properties of the coatings obtained is considered. The possibility of preparing pseudo-alloy coatings by plasma and electric-arc spraying is demonstrated. Plasma spraying of mixtures of powders of aluminum oxide and nickel is conducted with a PP-25 plasma torch. Electric-arc spraying is carried out using EM-14M equipment with a combination of copper wire and steel and aluminum wires.

In the process of discrete dosing, a zone of plastic flow appears in the gravity feeder at the moment of release, and this zone extends a very small distance into the mass of the powder material forming a dynamic arch. This dynamic arch can become a static one when the size of the outlet is insufficient. After solving the equation of the energy balance with the help of the Mohr–Coulomb yield criterion the formulae were obtained to calculate the sizes of slit and round arch-forming openings.

Experiment tests have shown that the suggested calculation method is in very good agreement with the experimental results for finely dispersed cohesive bulk powder materials. Based on the analysis of experimental data, a dimensionless criterion has been suggested to evaluate the applicability of the method depending on the physical and mechanical properties of the powder material.

Thermal distillation is one of the most common and reliable methods of water treatment, but its use is constrained by high energy-intensity. There are processes where thermal distillation is one of the main methods of liquid purification, for example for getting water for medical purposes. The most effective way of reducing distillate production cost is use of thermal transformers that allow recovery and regeneration of heat of liquid phase transformations. The results of mathematical-experimental investigations of high-temperature vapor-compression heat pump distiller using the natural working substance n-heptane are presented. The possibility of using standard leakproof small-capacity refrigeration compressor as the main means of pressure elevation and transfer of vapors of the working substance as a component of the heat pump distiller is shown. The efficiency and energy consumption data for the proposed equipment are obtained.

An analysis of the processes involved in heating of the liquid present above a piston in the working cavity of the compressor section of a positive-displacement hybrid power machine is given. On the basis of the general fundamental laws of conservation of energy and mass a thermodynamic calculation of the parameters of a two-phase, two-component open thermodynamic system with deformation and thermal interaction of phases is carried out. The influence of deformation work, external heat exchange, and direct-contact heat transfer on the variation of the temperature of the liquid is determined.

An adaptive method of control of a system with single degree of freedom along a given trajectory of displacement under the conditions of unpredictable variation of a surmountable external load is set forth. Simulation of the load with the use of a special force vector that reflects the nature of its variation is proposed. The components of the force vector (averaged values of partial derivatives of the load with respect to time and spatial coordinate) are calculated from the working information which the control system receives at previous moments of displacement of the control object. The order of the model is the maximumorder of the derivatives included in the model. The general structure and derivation of formulas for models of zero, first and second order are given. The practical case of measurement of the angular displacement of a shaft using incremental encoders is given separately. Initially, direct load models are considered in which time is the independent variable. Then, for a drive with incremental encoders, inverse models are presented separately in which the angle of rotation of the output shaft is the independent coordinate. Conditions under which the adequacy of the parameters of the power vector and the redundancy and insufficiency of the order of the control model is estimated are considered separately. Based on these conditions, a general algorithm for the functioning of the control system by means of which both the parameters and the structure of the control system may be dynamically changed is given.

Corrosion breakdown of the surface layer of components made of steel 45 subjected to combined strengthening (electromechanical treatment (EMT) + surface plastic deformation (SPD)) and operating under the influence of corrosive media is investigated. It is established that hardness and corrosion resistance of a hardened surface layer is influenced by the amount of tool feeding during EMT, which determines the distribution of structural components (white layer, original material), as well as the degree of medium corrosivity and interaction time with this medium.

A classification of tube-in-tube heat-transfer devices is proposed. The most typical constructions of this type of heat-transfer device developed by domestic and foreign designers and inventors along with the advantages and drawbacks of the constructions are considered.

Composite polytetrafluoroethylene – cellulose acetate membranes containing 8 to 19% of the latter by weight, depending on the number of composite layers, were obtained by spraying cellulose acetate suspended in acetone on the surface of a polytetrafluoroethylene substrate. It was found that the wettability of the surface layer of the membrane with a drop of distilled water increased as a result of the deposition of cellulose acetate on the surface of the initial membrane. A decrease in the specific flux of membranes from 4613 to 96 dm³ /(m²· hr) depending on the number of layers after the deposition of cellulose acetate was observed. It is shown that membrane modification leads to an increase in retention capacity of oil products from an oil-in-water emulsion from 84.0 to 99.9 %, while the size of the smallest particles separated by the membrane decreases after modification from 450 nm to 207 nm. A decrease in the absolute value of the ζ -potential with a decrease in the concentration of petroleum products in the emulsion was also detected.

One of the most effective ways of excluding heat treatment during the manufacture if tube bundles is replacement of arc welding by rotary friction welding. The corrosion resistance of welded joints of 12Cr18Ni10Ti steel, prepared by friction welding and not subjected to heat treatment is evaluated. The corrosion properties of such welded joints, including those not subjected to heat treatment, are evaluated. Measurements of the electrode potential of welded samples are performed to determine zones prone to brittle fracture. It is established that the spread of electrode potential values is small that makes it possible to propose that there is uniform corrosion in a welded joint. Tests for welded joint specimen resistance to intergranular corrosion show that there is no grain boundary breakdown to a depth of more than 30 μm in 12Cr18Ni10Ti steel specimens, which indicates joint intergranular corrosion resistance.