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The paper presents a developed 2D mathematical model for a regenerative heat exchanger designed for a ventilation system operating with a periodic change in airflow direction. This kind of ventilation system saves the heat energy required for heating of domestic premises during a winter season. Results for calculations by a two-dimensional model are compared with one-dimensional modeling and with available experimental data. The authors formulated a definition of energy efficiency in terms of reduction in heat losses. Our calculations demonstrate that the efficiency of a regenerative heat exchanger might exceed 90 %. The numerical simulation was applied for parametric study of this problem; we revealed the influence of the heat exchanger operational and design parameters on the energy efficiency. Numerical experiments found a group of parameters most significant for energy efficiency of ventilation system; recommendations on system optimization were formulated.

The influence of the size of water droplets, temperature, and velocity of a streamlining jet of dry air on the rate of evaporation is considered. Due to the systematic studies using a thermal imager, it is shown that the interface temperature changes spontaneously. It is assumed that the temperature nonuniformity on the surface is caused by the release of vapor nanobubbles and can be characterized by the velocity of their outflow. Empirical regularities on the intensity of bubble release from a droplet are obtained both as a function of time and diameter, and in the criterion form.

The gasification of solid urotropine was experimentally studied at filtering a high-temperature flow of carbon dioxide through it. It was shown that with an increase in the temperature of the filtered gas from 650 to 920 K, the time of urotropine gasification decreased and the average gasification rate increased from 0.38 to 1.25 g/s, leading to an increase in the flow of urotropine gasification products. The maximum achieved value of the mass of urotropine gasification products was 0.8 g per 1 g of incoming gas. In the temperature range of 480-530 K, intensive gasification of urotropine occurred, while the temperature of the gaseous products leaving the reactor remained practically unchanged. The amount of noncondensable gaseous gasification products did not exceed 1% of the initial mass of the sample.

The object of an experimental study is a vapor bubble formed in a subcooled liquid as a result of absorption of laser radiation transmitted into the working volume through a thin optical fiber. Evolution of a bubble is characterized by its rapid growth and collapse with generation of a hot submerged jet. Some features of the process under study are considered in relation to the field of medicine. Normal saline is used as the working fluid. It is shown that under the same conditions (radiation power, optical fiber diameter, and initial temperature of liquid), the dimensions reached by a vapor bubble in saline solution are much smaller than those in pure water. A significant influence of the shape of a fiber tip on the nature of the process under study was revealed.

This paper considers the microwave processing for snow-ice mass comprising the heating and melting stages. The search for basic patterns of these processes aimed to optimization, control and design of stages is based on mathematical models and their implementation using analytical or numerical methods. A nonlinear mathematical model of the two-phase Stefan problem for a layered system of dielectrics was constructed. This approach takes into account the dependences of the medium permittivity and other parameters on the medium temperature and the design of a microwave radiation source.

Thin films of polycrystalline silicon are widely used in semiconductor industry. One of the methods for obtaining such structures on cheap and low-melting substrates is metal-induced crystallization, since the use of a metal (for example, Au) as a catalyst during crystallization of an amorphous semiconductor allows a considerable reduction of annealing temperature. However, the typical duration of metal-induced crystallization is several tens of hours, in contrast to the method of laser-induced crystallization. In the present work, for the first time it is proposed to combine the advantages of the laser-induced and Au-induced crystallization methods. The authors have identified laser-processing modes of thin films of non-stoichiometric silicon oxide (a-SiO_0,1) using nanosecond radiation with a wavelength in the infrared range which ensure the formation of polycrystalline silicon.

In this work, the thermal conductivity of refrigerants systems from three different hydrofluoroolefins including R1234yf, R1234ze (E), and R1233zd(E) were studied using artificial neural network. A total of 4395 data points of liquid and vapor thermal conductivity at several temperatures (241.92 to 344.46) K and pressures (0.068 to 21.73) MPa were used to train and test the model. Five neurons were used in the input layer, fifteen neurons at hidden layer and one was used in the output layer. Bayesian Regulation back propagation algorithm, logarithmic sigmoid transfer function, and linear transfer function were used at the hidden and output layer, respectively. Temperature, pressure, applied heating power; acentric factor and dipole moment were considered as input variables of the networks. The optimal parameters were obtained through the weights searching method. The average absolute relative deviations and correlation coefficient were 1.48 and 0.9998, respectively. This study shows therefore that the artificial neural network model represents an excellent alternative to estimate the thermal conductivity of different refrigerant systems with a good accuracy.

A general analysis of heterogeneous sources of waste heat at thermal power plants, taking into account the advanced world and domestic experience in creating high-power steam compression and absorption thermal transformers, has shown the possibility of significantly reducing heat losses by integrating absorption heat pumps and refrigerating machines of various designs and capacities into the thermal circuits of existing and projected thermal power plants. It is proposed to carry out a comprehensive optimization of the plants by creating intra-plant trigeneration systems. Taking into account the specific operating conditions of steam turbine condensers, cheaper multicomponent LiCl salt-based aqueous solutions, which are not inferior in efficiency to imported LiBr solutions with anticorrosive additives, are offered for the use as working bodies.

The paper presents the results of thermodynamic calculations and experimental studies on plasma processing of spent fuels and lubricants, which showed the prospects of using the plasma-chemical technology for processing liquid industrial wastes with the production of fuel gas and inert mineral material. The comparison of experimental and calculation results showed an acceptable agreement.

Results of an experimental study of the influence of argon addition on microwave plasma chemical vapor deposition of diamond from a hydrogen-methane mixture are reported. A specific feature of this method is the use of a high-velocity jet for transporting gases activated in a microwave plasma in the discharge chamber to the substrate located in the deposition chamber. Optical emission spectroscopy is used for systematic investigations of the microwave discharge plasma in the discharge chamber. Diamond coating samples obtained on the molybdenum substrate are studied by methods of scanning electron microscopy and Raman scattering spectrography.