Experimental studies into the process of mixing two different-temperature flows of sodium coolant in a T-shaped connection of cylindrical channels (tee) have been carried out. The measurements were carried out for two combinations of flow rates and temperatures of hot and cold sodium. The main result of the experiments is the characteristics of temperature fluctuations both in the sodium flow and on the outer surface of the tee pipes. Spectral analysis of signals from thermocouples located on the axis of the pipe in the mixing zone showed that the flow is turbulent in all cases. The average temperature of the pipe surface in regime 1 (the flow rate of cold sodium is approximately half the flow rate of hot sodium) in the observation zone increases monotonically with distance from the side (cold) branch pipe downstream as does the intensity of temperature fluctuations. In regime 2 (cold sodium flow rate is comparable to hot sodium flow rate), there is a small temperature dip in the middle of the observation region, which indicates the presence of a stationary reverse vortex in this region. In regime 2, the level of pulsations is lower than in regime 1 and is maintained over the entire measurement area. The amplitude of temperature fluctuations on the surface of the tee is significantly lower than in the flow, but the structure of the Fourier spectra is similar. With the help of a infrared camera (IR camera), variations in the temperature field on the surface of the tee are visualized, which manifest themselves in the form of emerging and migrating with the flow areas with an increased amplitude of temperature pulsations. The process is not regular and does not indicate the presence of periodic temperature fluctuations on the wall. The spatio-temporal structure of the temperature pulsation field is analyzed by wavelet analysis methods, which make it possible to identify nonstationary quasi-periodic pulsations in a certain region of the channel and in a certain frequency range.

Russia’s energy sector that uses coal for heat and electricity generation is a large source of ash and slags, the dumps of which occupy large areas and at the same time pose problems for the environment. These dumps contain, among other components, alumina and other valuable products. In the ash dumps from coal-fired power plants in the Ural region, approximately 350 million t of ash has been accumulated by now, and the amount continues to grow by 7–8 million t per annum. Given the conditions emerging on the world market, the obtaining of alumina from the ash and slag dumps at their own enterprises is a problem of Russia’s metallurgical industry that is of utmost importance. Thus, the ashes from large, coal-fired thermal power plants in the Ural region of Russia, including the Troitsk, Reftinsk, Verkhnii Tagil, and other power plants, contain 28–32% of alumina and could become a man-made raw material for producing aluminum, thereby partially substituting the import of bauxites in Russia from foreign countries. The article presents the results of experimental studies aimed at elaborating a technology for extracting high-quality alumina from the alumina-rich ash of coal-fired power plants. The influence of various technological parameters on the target product’s obtainment process is studied. At the first stage of this process, which involves partial desiliconization of ash by treating it with alkali solution, enriched alumina concentrate is extracted, which is close to low-grade bauxite raw material in its physicochemical properties. At the technology’s second stage, a product with a 97–98% content of Al2O3 is obtained using the method of sintering the alumina concentrate with sodium and calcium carbonates; as a result, the alumina extraction ratio from ash is 88–90%.

The article describes a new method and device for automatically controlling the charge of a storage battery (SB) for an autonomous power supply source with the function of the photovoltaic array (PVA) maximum power point tracking control (an MPPT controller). The controller is intended for charging Li-ion batteries and can be used to operate with both lithium iron phosphate (LiPePO4, 3.2 V) and lithium-ion (NiCoMnO, 3.7 V) batteries. The controller is constructed on the basis of a high-frequency synchronous buck converter. The controller’s distinctive features are that it equalizes the voltages across the storage battery sections and controls its heater prior to perform the battery charging. Owing to the SB preheating, it becomes possible to discard the use of lead storage batteries, which are heavy-weight devices with a rather short service life, and make a shift to the use of reliable, compact, and durable Li-ion batteries, also under low temperature conditions, in which the use of such batteries is difficult or even impossible in view of a drop of their energy-storage capacity. An important feature of the developed controller is that its auxiliaries take power supply from a photovoltaic array and not only from the storage battery, as is the case in the absolute majority of the commercially available controllers, due to which it has a broader field of practical applications. The controller is equipped with the necessary set of protections, including those from photovoltaic array connection in inverse polarity, from SB overcharging and deep discharge, overcooling or overheating, and load overcurrent. The operating range of voltage across the photovoltaic array varies from 15 to 45 V. The storage battery maximal charging, as well as load current, is 20 A. The entire set of controller functions has been implemented on a single-sided printed-circuit board. A set of experimental studies of the device operation modes was carried out, which has confirmed the efficiency of built-in control algorithms. The proposed controller can be used in various fields of activity, in particular, for supplying power to remote telecommunication equipment, offence recording cameras, in agriculture (primarily in livestock farming), in tourism industry, etc.

Results of experimental and numerical studies are presented on the steam distribution among the main bundles and the built-in bundle of condensers in cogeneration turbines using a specific steam load defined as the ratio of the amount of steam condensed in the bundle to the bundle surface area. The experiments agree well with the standard characteristics of the condenser. To calculate the specific steam loads in the condenser tube bundles, the manufacturing plant calculation procedure was updated. It allows for determining a steam flow rate in each tube bundle based on the condition of the same steam pressure in all the zones (tube bundles) of the condenser. It has been demonstrated that the specific steam loads of tube bundles can differ from each other by a factor of 20 or more and depend on the flow rates of steam and cooling water to the condenser, the water temperature at the bundle inlet, the number of water passes in the built-in bundle, and other factors. The effect of specific steam loads in tube bundles on the steam pressure in the condenser has been established to be considerable at steam flow rates close to the nominal values. One of the methods for improving the thermal performance of the built-in tube bundle for additional heating of make-up water, the application of profiled tubes, is examined. The obtained results are important from the standpoint of increasing the heat load of the built-in tube bundle (BB) when make-up water for the heating network is supplied through it and circulation water is fed through the main bundles (MBs) and of rising the oxygen content in the main condensate at the condenser outlet owing to condensate overcooling caused by nonuniform distribution of steam among tube bundles.

Radiative heat transfer in a gaseous medium of furnaces and ovens is the most important heat-transfer process controlling the efficiency of industrial installations. This explains the great interest of thermal engineers in modern methods of numerical simulation of radiative heat transfer. Heat transfer in high-temperature gases is mathematically described by the differential equation of radiative heat transfer together with the transport equations of thermal convection. The main problem is that triatomic gases, such as water vapor and carbon dioxide, selectively emit and absorb radiation energy, as a result of which their absorption coefficients become variable in spatial coordinates. The advances of recent decades in infrared spectroscopy have brought about favorable conditions for the development of well-substantiated models suitable for the calculation of absorption coefficients of the most important triatomic gases. The polylinear calculation of radiative transfer in a million spectral lines gave way to a narrow band model with a correlated absorption coefficient and then to global full spectrum models. Along with models of the absorption coefficient, methods for the numerical solution of the differential equation of radiative transfer are being improved. As a result, more than a dozen different models and methods can be used at present to calculate radiative heat transfer in industrial units. The proposed review partially eliminates the lack of publications that compare different approaches to the numerical study of radiation problems. It traces, up to up to the present time, more than 20 years of successive development of mathematical models of radiative heat transfer in selective gases. The main methods for the iterative solution of the differential equation of radiative heat transfer are also included in the review. At the same time, to eliminate complication of the model analysis, the review does not include excess information on boundary conditions and beam scattering. To ensure the unambiguity of the concepts used, the review is preceded by a short theoretical note.

The concentration of thermal stresses is one of the main factors leading to a decrease in thermal strength under cyclic loading conditions. It is characterized by the stress concentration factor Kt, the value of which can be determined by analytical or numerical methods as well as experimentally. In modern regulatory documents, various values of the thermal stress concentration coefficient are indicated. The results of studies carried out as part of the work on the justification of thermal and cyclic strength are presented. Their comparison with the data of current regulatory documents is given on the example of typical outlet headers of superheaters for heat recovery steam generators of modern combined cycle gas turbines (CCGT). Formulas have been obtained that make it possible to calculate the concentration coefficient in a tee connection according to the known size ratios and parameters of the operating mode and to substantiate the operation modes of heat recovery steam generators. It is shown that taking into account a number of factors that determine the intensity of heat transfer in tee joints leads to a decrease in the concentration coefficients relative to the value of 2.0 currently accepted in some regulatory documents for all heat-transfer modes and ratios of the tee joints' dimensions. Reducing the values of the concentration factor included in the calculation when designing a part makes it possible to reduce metal consumption, lighten the design, and save money on its manufacture.

To experimentally determine the coefficient of friction resistance on a large-scale bench, tests of collapsible plate heat exchangers (HE) of two standard sizes with plate packs of three types (five configurations in total) were carried out, differing in the angle of inclination of the chevron surface of the plates. Water was used as the heat carrier during the tests. The dependence of the friction drag coefficient on the Reynolds number and the value of the critical Reynolds number corresponding to the transition from laminar to turbulent flow are obtained. A difference of up to several times in the experimental values of the friction drag coefficient for the same tested HE model at close Reynolds numbers was found. The obtained data were divided into two groups, which included similar values of the coefficient of friction resistance. It is concluded that a significant scatter of the experimental data is due to the elastic deformation of the plates caused by the pressure drop between the heat-exchanger circuits. Due to the introduction of the deformation coefficient, the dependence of the friction resistance coefficient on the Reynolds number was refined, which showed good convergence of the results obtained, combined into one group. The refined algorithm for processing experimental data made it possible to determine the coefficients and exponents included in the criterion formulas for calculating the friction resistance in the transitional and turbulent flow regimes. For each HE configuration, the values of the critical Reynolds number have been refined. The dependence of elastic deformation on the size and type of corrugation of the chevron surface has not been established. The alleged cause of the deformation, identified after disassembling the tested models, is the different depths of stamping of the chevron surface and the mechanical deformation limiter.

To mitigate the consequence of severe accident involving core meltdown, many advanced reactors employ ex-vessel core catchers which stabilize and cool the corium for prolonged period by strategically flooding it. The cooling system for the core catcher is one of the key components in designing the core catcher. To understand the coolability of melt pool including the effects of decay heat, a simulated experiment was performed in a scaled down ex-vessel core catcher model (CCM) employing electrical heaters to simulate decay heat of 1 MW/m3. The experiment was carried out by melting about 25 liters of sodium borosilicate glass, as a mixture of corium and sacrificial material simulant, using cold crucible induction furnace at about 1200°C. The electrical heaters were turned on as the molten corium was poured in the CCM test vessel. K-type thermocouples were used to monitor melt pool temperature as well as the bulk water temperature at different locations with time. The results show that in presence of water outside of the CCM test vessel for the present geometry, coolability of melt pool including removal of decay heat is achievable with outside vessel temperatures not exceeding 100°C. A stable crust was observed at the top surface of the melt pool, which prevented water ingression into the molten corium.

The purpose of the study presented in this paper is to assess the engineering and environmental performance during the long-term operation of four BKZ-160-1.4-5 boilers on off-design fuel, consisting of 50% of Grade 2BR brown Borodino coal (with a lower heating value of Qr = 11.3–16.3 MJ/kg) and 50% of Grade 3BR brown Bol’shesyrsk coal (Qr = 19.3–20.1 MJ/kg) from the Kansk-Achinsk basin. The fuel-handling system operated normally with this mixture. The application of water washing eliminated any problems with slagging of the furnace water walls. Increasing the heating values of the coal mixture and the gross efficiency of the boilers reduced the total fuel consumption at the CHPPs. As a result of a decrease in heat losses with flue gases, the efficiency of boilers when operating on the mixture, according to the reported data on the CHPP performance, increased by 0.4%. These data also demonstrate that decreasing the heat losses with the flue gases increased the boiler efficiency by 0.4% when firing the above-mentioned mixture. The gross emission of nitrogen oxides remained at the same level, while the emission of sulfur dioxide increased by 40.6 t/month (14.4%) due to the elevated sulfur content in the fuel mixture. A lower ash content in the fuel mixture decreased the gross atmospheric emissions of solid particles by 15.1 t/month (25.2%), while the amount ash and slag wastes reduced by 1166 t/month (25.3%).

The quality of the coolant at combined heat and power plants (CHPPs) can be improved by upgrading the water chemistry and its support systems. In the context of this problem, we should analyze the experience gained in operating the equipment, determine the advantages and disadvantages of the employed technologies and apparatuses, and propose promising solutions with the maximum use of reliable and environmentally friendly materials and process developments. A new water chemistry based on amine-containing reagents has been mastered at Russian CHPPs. The paper presents examples of the use of domestic complex reagents under the VTIAMIN brand, which differ from imported equivalents in composition and have been tested in actual applications at CHPPs, in implementing the proper water chemistry in the main and auxiliary coolant circuits. Membrane-based water treatment plants (WTPs) are used at CHPPs together with conventional WTPs. The results of the inspection of several WTPs at CHPPs are presented, and schemes combining ion-exchange and membrane processes are proposed to decrease the consumption of reagents and reduce the amount of effluents with a high process reliability of the equipment. Promising information technologies are widely applied at CHPPs. The potential is demonstrated for developing digital systems for chemical-process monitoring of the water chemistry based on the new generation of Russian-made analyzers.