Том 65, № 7 (2018)

The purpose of this research is to estimate the energy potential of the Barents Sea based on numerical modeling of the wave energy over a long period of time from 1979 to 2010. Using the WaveWatchIII wave model, the wave energy flux in the open part and in the coastal zone of the Barents Sea has been calculated. The calculations are based on the data of the NCEP/CFSR reanalysis with spatial resolution of 0.3°. The calculations were performed on a unstructured grid, which has high spatial resolution at the shore (200–500 m). The long-term average annual significant wave height¹ varies from 1.5–2.0 m for the open part of the Barents Sea to 1.0–1.5 m in the coastal zone of Murmansk oblast. The long-term average annual wave energy flux varies from 15–20 kW/m for the open part of the Barents Sea to 5–10 kW/m in the coastal zone of Murmansk region. The probability of exceedance of wave energy of more than 1 kW/m is 80–90% for the open part of the sea and 70–75% at the northeastern coast of the Rybachy Peninsula. To the east and west of the peninsula, this figure decreases significantly. Near the village of Teriberka, the probability of exceedance of the wave energy is 65–70%. The probability of exceedance of energy of more than 5 kW/m is 50–60% in the open sea and it does not exceed 35% in the coastal zone. The average probability of exceedance of the wave energy is subject to seasonal fluctuations. Thus, in the coastal zone, the probability of exceedance of energy of 1 kW/m is approximately 90% in the winter months and it does not exceed 50% in summer. The obtained results can be applied to designing a wave power station in the Barents Sea.

Chemical looping combustion and gasification of fuels with using metal oxides as oxygen carriers is a rapidly developing technology for capturing carbon dioxide. This technology is based on the use of interconnected reactors with a fluidized bed and circulating fluidized bed. Crucial in the technology is the reliable security of a high solid circulation rate between the reactors to maintain the desired temperature. When burning solid fuels, ash particles inevitably enter the metal oxide stream. This can lead to a change in the hydrodynamic parameters of an interconnected reactor system. In this paper, we present the results of an experimental study of fluidization conditions and hydrodynamics of a reactor with a circulating fluidized bed under motion conditions of binary mixtures of particles with different density. We also justified the conditions for simulating the particle sizes of heavy and light fractions as well as their mass in the reactor and a portion of a light fraction. We showed that, at a small addition of a light fraction, the minimum fluidization rate decreases markedly. Particle segregation was observed for large metal oxide particles, while light particles were found to be near the layer surface. The addition of a light fraction with a mass fraction of 3–12% does not significantly affect the mass flow profile of particles in a circulating fluidized bed reactor. The fractional composition of the particles in both the upward flow in the center and the downward stream near the walls of reactor is approximately the same. In the central part of the riser, the concentration of the light fraction was found to be slightly higher than its average value. The obtained results support the possibility of using the previously developed dependences for the calculation of hydrodynamics under motion conditions of binary mixtures of particles of different densities in the presence of a light fraction of 3–12%.

Organizational models of the heat energy market on a Single Heat Supplier basis (SHS) operating in free (liberalized) and regulated tariff environments are considered. An equilibrium mathematical model is proposed for the liberalized tariff setting conditions based on a microeconomic monopolistic market model. This mathematical model allows for taking into account energy production and transportation costs as part of a single economic criterion and to determine the supply-and-demand equilibrium for heat energy. A regulated heat energy market model on the SHS basis considers an option of a tariff setting for consumers of the housing and utility sector at the level of average total costs and on the demand basis for industrial consumers. Hydraulic circuit theory models and methods, as well as basic microeconomic provisions, are adopted as a scientific and methodological basis describing the proposed mathematical models. To solve the energy supply and demand equilibrium problem, an algorithm is developed for both energy tariff options based on univariate relaxation using redundant design schemes and simple iteration. The developed mathematical models fully reflect the current “rules of the game” between heat energy producers and consumers and allow a maximum consideration for the interests of all participants of the heat supply process under physical and engineering constraints on heat energy sources and heat networks. By means of the developed mathematical models, practical studies are carried out on the effect of the adopted heat energy price calculation method on both the market supply-and-demand equilibrium and on the main technical and economic characteristics of the real heat supply system of the city of Angarsk. Technical and economic assessments performed according to the indicated tariffs make it possible to conclude that the lack of regulation will lead to an uncontrolled rise in prices for heat energy for consumers and gaining of abnormal profits by energy suppliers.

Hypotheses about the mechanisms governing fragmentation of superheated liquid metal droplets falling into cold water are analyzed. It is shown that a physical model based on the cavitation–acoustic mechanism governing fine fragmentation of melt under steam explosion conditions is likely the most suitable one for consistently describing the fragmentation of both low-melting and refractory metals. For checking this conjecture, special experiments for studying the processes triggered when cold (20°С) water comes into contact with a heated surface and for measuring the pressure impulses (arising both in coolant and in the hot body) accompanying the coolant flashing were carried out using liquid metal (tin and steel) droplets and superheated solid steel bodies. The working substance temperatures were varied in the range from 200 to 1600°С. The results obtained from the performed experiments are not in contradiction with the melt fine fragmentation process represented by the cavitation–acoustic model. It is shown that the acoustic waves generated during explosive growth of bubbles on a hot surface propagate in the solid body and are alternating in nature. Their intensity (including that at negative pressure values) differs only slightly in the modulus from the pressure impulses measured in the coolant and is sufficient for finely fragmenting the droplets. It is experimentally found—with the use of a conductance measuring technique—that the transition from the coolant film to bubble boiling mode is preceded by a short-term (lasting a few milliseconds) process involving intense interaction of waves at the steam–liquid boundary with the heated surface. The signal from the conductance measuring transducer was subjected to a wavelet analysis for different values of the heated surface temperature. The study results testify that high-frequency (several tens of kilohertz) pulsations of electric current are generated in the preburnout region with their characteristics varying (toward increasing the amplitude and intensity) with time as the heating and heated media come closer into contact with each other. A probabilistic process development scenario is suggested.

Heat exchangers used in the composition of large-capacity energy conversion systems for space applications must be able to operate at high temperatures (above 1000 K) and at high (several MPa) values of pressure difference between the “hot” and “cold” heat carrier/coolant channels. This is why especially demanding strength and stiffness requirements are posed to the heat-transfer matrix of these devices, a circumstance that precludes almost completely the use of well-known compact and light plate-and-fin devices with 50–100-μm-thick foil fins. The article presents the results from experimental investigations into the thermal and hydraulic characteristics of alternative versions of heat-transfer elements involving the use of different heat transfer enhancement methods. Experimental investigations of heat transfer and hydrodynamics were carried out for three types of heat-transfer surfaces: a tubular one composed of small-diameter (3 mm) thin-walled tubes deformed over the cross-section perimeter and length (twisted tubes), a plate one finned with pins having a diamond-shaped cross section (2 × 2 mm in cross section and 4 mm in height), and a plate one composed of thin-walled 0.2-mm-thick plates with the surface formed by oppositely directed truncated cones with saddle-like bridges (a biconvex stamped plate). After processing and analyzing the experimental data obtained for these heat-transfer surfaces, dimensionless dependences for the Nusselt number and the pressure-drop coefficient on the Reynolds number were constructed. The dimensionless formulas obtained for twisted tubes and for the pin-finned surface are compared with the well-known correlations. It is shown that the use of twisted tubes instead of round ones results in improving the heat transfer intensity by more than 20% with the hydrodynamic indicators worsened by 50%. The use of the pin-finned plate surface improves the heat transfer intensity by more than a factor of two as compared with using a staggered tube bundle.

Two different nozzle cascades designed for an LP aircraft turbine have been investigated. The cascade had large convergence, a moderate curvature of the airfoils, and it flowed over so that the outlet subsonic velocity was high. It was designed for a flow inlet angle of α₀ = 63.5°, an outlet angle of α₁ = 28.6°, and a reduced isoentropic outlet velocity of λ₁ = 0.93. Having the same width of 41 mm, the first cascade was made up of 5.9 mm thick profiles, while the second one from 4 mm thick profiles. To improve the efficiency of the second cascade, the suction side curvature near the trailing edge decreased more sharply, which yielded a smoother velocity distribution over the suction side according to the design calculation. However, calculations of a viscous flow in the second cascade revealed no tendency towards a decrease in the profile losses. The experiments demonstrated that both cascades featured a high efficiency on the ranges of λ₁ = 0.80–0.98 and α₀ = 52°–69°. It is important that the design mode with respect to λ₁ coincided with the mode giving the lowest energy losses. The first cascade from thicker profiles was more efficient than the second cascade where, with the same overexpansion of the flow on the suction side, the critical velocity was attained just downstream of the throat while it was shifted to the trailing edge in the first cascade. A slight flow deceleration on the suction side did not result in a local velocity equal to the velocity downstream of the cascade, and a flow separation occurred near the trailing edge at λ₁ ≥ 0.93. It is these features of the flow in the second cascade that are responsible for an increase in the profile loss coefficient by 0.26% under the design operating condition.

Technologies for utilizing the wastewater of the reverse-osmosis plants (ROPs) to prepare the make-up water for power-generating plants of combined heat and power plants and nuclear power plants are proposed and substantiated using mathematical models and full-scale experiments. The ROPs use natural feedwater with a wide range of quality characteristics. For the first time, variants of the treatment of the concentrate formed in the ROP cycle have been proposed for the reuse of the latter by acidifying it in H-type cation- exchange filters charged with a weakly acidic cation-exchange resin. By admixing part of the filtrate processed in the H-type cation-exchange filters to the feedwater, the latter is acidified thus reducing the probability of formation of carbonaceous sediments and water consumption. The rest of the filtrate subjected to a conversion process is used as a constituent of the make-up feedwater of the heating system or potable water, which eliminates the discharge of the reverse-osmosis plant wastewater into the environment. Another feature of the proposed technology is that the H-type cation-exchange filters are integrated into a regenerant solution reuse circuit (RSRC). As a result, the consumption rate of sulfuric acid for regeneration equals the stoichiometric rate and the regeneration yields gypsum used to produce a binding agent for construction. The kinetics of separation of gypsum from the spent regenerant solutions with different chemical compositions was studied experimentally as applied to the RSRC conditions. The procedure of operating filters charged with the Lewatit CNP-LF cation-exchange resin was trialed under production conditions. It was established that the height of the filtering cation-exchange resin layer should be 1.0–1.5 m and the concentration of the regenerant solution should not exceed 0.8% at a rate of 10–15 m/h. The basic components of the technological scheme were trialed under production conditions on a water treatment plant in service.