Vol 66, No 12 (2019)

The rather high distributed generation (DG) ramp-up observed in the world is largely associated with the progress in low-power generation technologies and the measure of state support for renewable energy sources. Distributed generation delivers sustainable development of low electricity demand areas where centralized power supply is too expensive. In Russia, the installed electrical capacity of DG has reached 37 GW and its contribution to the country’s electric power industry turns out to be very significant: approximately 13.7%. Moreover, more than half of the available facilities are used as stand-by, peak-load, and seasonal sources of electricity. The technological basis of the DG in the country is thermal power plants. The article considers in detail the possible options for operating DG plants. It is shown that the priority areas for the DG application are areas with low density of electrical loads, including rural and low population areas. The presence of infrastructural restrictions for connecting new consumers to the electrical network favors the use of DG in the centralized power supply zone as well. Prospects for the further DG application in the world are associated with the development of renewable energy and the improvement of electrochemical technologies, primarily electricity storage devices. In Russia, apparently, DG technologies based on fossil fuels will prevail for a long time. The country’s great demand for thermal energy will contribute to the widespread use of cogeneration plants. A significant reserve for DG development is the reconstruction of the country’s numerous gas boilers in small CHP plants with a potential of 41 GW of electrical capacity.

The main results obtained for the last decade in studying the possibilities of enhancing boiling heat transfer and increasing critical heat fluxes are reviewed. Heat transfer enhancement methods involving the use of a modified/structured boiling surface obtained by means of mechanized processing, electrochemical technologies, plasma and ion deposition, laser emission, and subcooled liquid boiling are considered.

In this paper, the results from calculations of heat and mass transfer in a variable-cross-section channel with a bundle of smooth horizontal tubes, on the surface of which steam from a moving steam-gas mixture (SGM) condenses, are presented. The decrease in the channel’s cross section and, accordingly, the number of tubes in the vertical rows along the SGM movement provides the mixture with approximately constant velocity as the steam condenses. The mathematical model used in this study is described in detail in our previous publications. The two-dimensional equations of single-phase hydrodynamics, energy, and diffusion are solved for the external SGM flow. The condensation process is modeled at the level of the boundary conditions on the tube surface, taking into account a moving laminar condensate film. The heat transfer through the tube wall from the film to the cooling water is described using a one-dimensional model of the wall. To account for the irrigation of the bundle’s lower tubes with condensate formed on the upper tubes (inundation effect), a simplified model is used. The data on the velocity fields and impurity concentration in the condenser and the heat transfer characteristics are presented. The calculation results of the heat transfer coefficients on the tubes of the first vertical row of the bundle and the heat transfer coefficients for individual sections of the simulated condenser containing several tube rows at a 0–8.5% volume fraction of air in the SGM at the inlet to the apparatus are compared with experimental data. A quite satisfactory agreement between the calculated and experimental data is obtained, which confirms the efficiency of the used model. The calculated data on the local velocity fields and the composition of the steam-air mixture indicate a significant heterogeneity of these characteristics. This complicates the development of relatively simple engineering methods for calculating the heat load of condensers at high air concentrations. The calculations were performed using in-house CFD-code ANES.

The issues of developing small-scale and microhydropower generation under present-day conditions as one of the renewable energy sources that do not aggravate environmental problems are considered. Some of the most effective approaches to designing microhydropower plants and small-scale and microhydroturbines that meet the environmental friendliness and high-energy efficiency requirements are outlined. The results of a computational study of a microturbine prototype with a blade system modified according to a principle of biomimetics (nature-imitation technologies) have been validated experimentally. Two modified configurations of the blade system are considered and compared with the original version under identical conditions. To increase the reliability of the findings, the experiment with the original and modified impellers of the microhydroturbine was repeatedly conducted. The energy characteristics of a microhydroturbine based on experimental data that demonstrate the best repeatability with an error not exceeding 10% are presented. Based on the calculated and experimental data, a comparative assessment of the turbine’s energy characteristics with the original and modified impellers is made. It has been established that the use of the so-called “growths” on the entrance edge of the impeller blades contributes to streamlining the flow pattern in the interblade channel. This, in turn, leads to a decrease in hydraulic drag and, consequently, to a decrease in hydraulic losses when flowing around the blade system. As shown by quantitative assessment of the energy characteristics, the energy efficiency of a microhydroturbine is increased by 20%, which proves the viability of the chosen direction for developing smallscale and microhydropower generation as well as the effectiveness of the approaches used in the design of the working bodies of microhydroturbines. Further ways of improving the approaches under study and obtaining new developments in this field of hydropower generation are scheduled and set forth.

The KORSAR/CFD code results from the development of the KORSAR/GP system code certified in 2009 by the Rostekhnadzor (Federal Service for Ecological, Technological, and Nuclear Supervision) as applied to the calculated justification of the safety for VVER reactors. One of the important aspects of the development consists in the introduction of the CFD-module code into functional content for the simulation of spatial turbulent flows in the mixing chambers of reactors using a nested boundary method in the RANS-approximation. The CFD module is combined with a 1D model according to a semi-implicit scheme as a standard code element. Based on the calculations performed for three modes with an asymmetrical equipment operation in the heat-transfer loops of the VVER-1000 reactor, cross-verification has been performed for a 3D model in the CFD approximation, and a quasi-3D-multichannel model of the KORSAR/CFD computation code for the reactor pressure chamber. For cross-verification, the following modes have been chosen: breaking steam pipeline in a steam generator, connecting the main circulation pump while initially operating three pumps at the reactor power of 71% with respect to the nominal value, connecting a pump while initially operating two opposite pumps at the reactor power of 52% with respect to the nominal value. The scenario of the chosen modes is characterized by a decrease in the heat-carrier temperature at the entry into the pressure chamber from a single loop, which leads to an asymmetric increase in the reactor power with respect to the fuel assemblies owing to a negative reactivity effect. It is shown that, because of the artificial increase in the resistance to the downward heat-carrier flow along the channels that represent a pressure chamber in the multichannel calculation scheme, the reproduction of a spatial in-chamber flow pattern obtained using the 3D model of the chamber and its effect exerted on temperature change in the course of the heat-carrier stirring have been gained. The results of calculation using this scheme are in good agreement with data obtained by means of the 3D simulation of the pressure chamber in the CFD approximation in all the considered modes. A sensitivity of the calculation results with respect to changes in the calculation scheme under using the quasi-3D multichannel model of the reactor chamber is demonstrated.