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A model of a rivulet formed on the coils of a tubular heat exchanger has been developed. The cross-sectional shape of the rivulet is determined taking into account the forces of gravity of liquid, the forces of surface tension, and centrifugal forces. The equations for the coordinates of the free boundary points of the rivulet are presented in the integral form based on the analytical solution of the problem. The cross-sectional areas of rivulet and liquid bridge are compared, as well as the areas of their contacts with the working tubes.

The results of experimental studies on the properties of a capillary liquid bridge in the gap between two glass spheres of an equal diameter are presented. It is shown that for the case when the diameter of the spheres is much larger than the capillary scale of liquid, the shape of the capillary liquid bridge can be described as a figure formed by two “drops”, touching the spheres, and the central catenoid. The contact angle between the “drop” and the sphere depends on the effective mass of the “drop”, and the relative position of the catenoid and the “drops” is set by the condition that the contact angle between them is equal to zero. In the field of gravity, the position of the minimum cross section of the catenoid does not coincide with the middle of the gap between the spheres and is determined by the magnitude of the surface energy and the way how the mass of liquid in the bridge is distributed over the “drops” and the catenoid.

The paper presents the experimental study on the influence of parameters of a multi-jet impingement spray on the cooling efficiency for a large flat surface. The study is based on common principes for engineering systems with high-rate heat and mass transfer using the impinging jets; this enables the draining of hogh heat loads with a low flow rate of the coolant. These results, along with using the Nusselt and Reynolds criteria, give the approach for estimating the aggregated efficiency of heat transfer coefficient while cooling with a multi-jet impingement spray.

In industry, there is a whole class of heat exchangers with low values of specific heat fluxes: evaporators of refrigerating machines, steam generators of binary freon stations, steam generators of heat pumps, etc. Such heat exchange modes are realized when boiling in the film is just beginning, and the intensity of heat exchange during evaporation is commensurate with the heat exchange during boiling. The article presents the results of an experimental study of heat transfer during boiling on copper finned pipes, the entire surface of which is subjected to special treatment in an air stream containing corundum particles with the size below 500 microns. The result of such treatment is a significant decrease in the temperature head, at which boiling and a noticeable intensification of heat transfer, compared to a finned pipe without treatment with corundum particles, begin.

The paper presents an experimental study of the processes of ignition and combustion for a stoichiometrical propane-oxygen mixture in a closed volume (a single cylinder of internal combustion engine). The object of study was the dynamics of gas ignition and combustion in a cylinder of diameter D = 72 mm and height h = 4 mm as a function of location of N spark points for ignition ( N = 1÷9) under the condition of simultaneous ignitions. The big number of ignition points reduces the interval for generating the force impact on the engine’s piston and increases the maximum amplitude of the force.

A Raman spectrometer with the full use of energy of the probing laser radiation, repeatedly passing through the object of study to increase the scattering, is described. In a flame of a propane and air mixture, the local values of temperature and composition of gases were measured simultaneously with broadband registration of Raman spectra. The results of their processing using the original software are presented.

The paper presents the study of oxidation of benzene, pyridine, and pyrrole in a dense steam at uniform heating of the reactor. The time dependencies for temperature and pressure of reaction mixtures suggest that the fuel oxidation is enhanced by catalytic action of the Pt-Rh/Pt thermocouple inserted into the center of the reaction volume. It was shown that the fuel ignition temperature T _in^* increases within the fuel molecular series C₆H₆ < C₅H₅N < C₄H₄NH. The higher fuel equivalence ratio and steam density create a lower T _in^*. The benzene oxidation is a dual-stage process and it is described by low carbon burning. For a lean fuel mixture, combustion of pyridine occurs with detonation due to shock waves generation in the vicinity of the Pt-Rh/Pt thermocouple. The higher density of steam prevents the complete burnout of fuel. These features of fuel combustion are explained by differences in molecular structure and reactants adsorption on the platinum surface.

Studies of nonstationary conductive heat transfer on a cylindrical surface are presented in the approximation when the thickness of the thermal boundary layer is less than the surface diameter. The temperature profiles at the cylindrical surface and the specific heat flux on this surface are obtained. Using the experimentally established law for the stationary mode of thermal conduction of a cylindrical surface (Nu = 0.5), the value of the Fourier number at which the stationary mode occurs (Fo = 1.27) is determined. For mantle plumes having conduit diameters d = (7.4 _¸ 85)×10³ m, the time of plume ascent to the surface t _a and the time of establishment of the stationary conductive heat transfer t _s are estimated depending on the dimensionless value Ka = N / N_H , where N is the thermal power at the base of the plume, and N_H is the thermal power transferred from the plume conduit to the surrounding mantle in stationary mode. For Ka = 0.97 _¸ 1.58 ( t _a / t _s = ¥ _¸ 1) and Ka = 1.58 _¸ 129 ( t _a / t _s = 1 _¸ 0.005), the effect of unsteady heat transfer to the sur-rounding mantle on the plume ascent to the surface is shown and it is established that for Ka > 4 ( t _a / t _s < 0.19, d > 15 km), the effect of unsteadiness during the plume rise may be neglected.

A mathematical model of dissolution of a titanium carbide particle in a titanium melt containing nano-sized refractory particles is developed. The model allows one to study the influence of the parameters of the medium with nanoparticles on the stability of dissolution of refractory compounds under the conditions of laser cladding of a nano-modified coating with a hardening phase (titanium carbide). The time needed for the carbon-containing chemical compound to dissolve is determined as a function of the concentration of the nano-modifying additive, inclusion size, and melt temperature. It is found that the presence of nanoparticles in the fluid reduces the mass transfer intensity, resulting in a longer time of solid inclusion dissolution.

The results of studies of solid tungsten rod-type cathodes in different gases are presented. The thermal states of the electrodes under the action of cathode plasma, radiation and joule heat release are determined. The thermal nature of the rate of destruction (erosion) of the thermocathode is shown depending on the main determining parameters of the arc discharge and the design features of the cathode node. The obtained experimental data indicate the possibility of a long service life of W-cathodes in technological plasma torches.