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The technology of obtaining coatings consisting of alumina nanoparticles and their agglomerates is presented. The transport properties of coatings and the change of these properties with time are investigated. The dependence of the height of capillary ascent on the quantity of deposited nanofluid on substrates has been established. An estimate of the change in the height of liquid rise and of the permeability of a coating with the change in the size of particles has been made. Deterioration of the transport properties of porous coatings consisting of alumina nanoparticles with time is investigated, and the possibility of restoring these properties is shown.

Boiling curves of distilled water and isopropanol in 12.5x3x0.2 mm microchannel with rigid inlet and outlet lines are obtained. Critical heat flux is calculated for isopropanol by using the previously obtained correlation for water.

In this work, coatings of nanoparticles of aluminum oxide are investigated. Photos were obtained using an electron and optical microscope. A method is proposed for the formation of a coating of nanoparticles with and without agglomerates. The transport properties of nanoparticles of aluminum oxide, silicon carbide, titanium oxide and diamond have been investigated. The effect of agglomerates of nanoparticles on the rise of liquid has been determined.

The reflooding investigations of large-scale model fuel assemblies and sphere beds under Design Basis Accident and Beyond Design Accident of Light Water Reactors WWER and PWR are presented. The generalizing correlation on the quench front velocity for model fuel rod assemblies and sphere beds was developed on the base of heat balance and Leidenfrost temperature correlation. It is shown that reflooding duration calculation results of model fuel assemblies and sphere beds are in good agreement with the experimental data.

Results are presented of an investigation into water boiling in a single microchannel 0.2 mm high, 3 mm wide, and 13.7 mm long with a smooth heating surface or with a coating from aluminum oxide nanoparticles. The experimental procedure and the test setup are described. The top wall of the microchannel is made of glass so that video recording in the reflected light of the process can be made. A coating of Al2O3 particles is applied onto the heating surface before the experiments using a method developed by the authors of the paper. The experiments yielded data on heat transfer and void fraction and its fluctuations for the bubble and transient boiling in the microchannel. The dependence was established of the heat flux on the temperature of the microchannel wall with a smooth surface or a surface with Al2O3 nanoparticle coating for various mass flows in the microchannel. The boiling crisis has been found to occur in the microchannel with a nanoparticle coating at a considerably higher heat flux than that in the channel without coating. The experimental data also suggest that the nanoparticle coating improves heat transfer in the transition boiling region. Processing of the data obtained using a high-speed video revealed void fraction fluctuations enabling us to describe two-phase flow regimes with the flow boiling in a microchannel. It has been found that a return flow occurs in the microchannel under certain conditions. A hypothesis for its causes is proposed. The dependence of the void fraction on the steam quality in the microchannel with or without a nanoparticle coating was determined from the video records. The experimental data on void fraction for boiling in the microchannel without coating are approximated by an empirical correlation. The experiments demonstrate that the void fraction during boiling in the microchannel with a nanoparticle coating is higher than during boiling in the channel without coating (where φ and х are the void fraction and the steam quality, respectively) in the region of a sharp increase in the φ(х) curve.

This article discusses well-known models and equations for calculating the heat transfer gain during film and drop condensation on a pipe, which need to be improved. Film condensation heat transfer on horizontal pipe made from brass with knurling is analyzed. The heat transfer data for investigated steam mixture condensation on horizontal tube with spikes heat intensifiers is analyzed. It is noted that the functions of drop growth for various conditions and their distribution must be known for calculating heat transfer during drop condensation. The maximum droplet radius, droplet size distribution, and then condensation heat transfer performance could be adjusted with special condensing surfaces, such as gradient, superhydrophobic, grooved, hydrophobic-hydrophilic patterned and hybrid surfaces. Now the nanoscale structures can by nanotechnologies.

The objective of this paper is to select a coating on the surface of zirconium hydride (ZH) in order to reduce hydrogen losses under the operating conditions of an irradiation device of FN-reactors. Tests were carried out on the samples of the moderator units made of zirconium hydride. Oxide, phosphide-oxide and oxide-enamel coatings were considered as a protective layer. Hydrogen yield out of the ZH was studied using a calorimeter and a mass spectrometer by thermal heating of the samples according to the test program (heating rate of 10 °C/min, maximum temperature of 1000 °C, isothermal exposure of 40 min, cooling with a furnace). The hydrogen content in the samples was determined by high temperature vacuum extraction. It is shown the oxide coating is the most technologically advanced and effective. A thermogravimetric analysis of the ZH sample with the protective oxide coating was carried out, and the temperature-time dependence of a stoichiometric coefficient (H / Zr) was determined. The amount of the hydrogen released was determined in a temperature range of 20–1100 °C. The temperature increase in up to 1100 °C leads to almost total loss of hydrogen (98–99 %). In this case, the sample retained its integrity, and the coating exfoliated and fragmented.

Heat transfer crisis was investigated during water boiling in a microchannel without coating and with coating of aluminum oxide nanoparticles. Experiments were performed on an advanced setup with a horizontally located microchannel with dimensions of 12.5x3x0.2 mm. Calculation of the critical heat flux in the microchannel without coating and with a coating from nanoparticles, carried out by formulas for heat transfer crisis in a horizontal pipe with microporous coating and one-sided heating. For the microchannel coated with nanoparticles the critical heat flux was calculated for the conditions of no influence of liquid subcooling and initial section. The satisfactory agreement between the experimental and calculated data was obtained. dependences of the critical heat flux from the coating thickness and characteristic size of particles were also shown. However, the data array is limited and needs to be expanded what will improve the equations for critical heat flux in a microchannel with nanoparticles coating.

In the work, porous coatings of alumina nanoparticles are investigated. The coatings were formed by various methods. The dependence of the lift height of the nanofluid on its volume was established. The properties of the coating are compared with and without microtrenches.

Film and drop condensation are important processes in technics. This article includes the features of macroscale heat transfer intensifiers under film condensation, microscale and nanoscale heat transfer intensifiers under drop condensation. It is noted that condensation heat transfer may be influenced by the wall material. The mechanism underlying this influence is the nonuniform distribution of the wall temperature in the case of a low heat conduction coefficient. Based on the research results, a dependence of the wetting angle from the combined coating consisting of 7 alumina oxide and water repellent is obtained.

The results of high temperature steam oxidation tests of cladding specimens made of VCPM at nominal test temperature of 1200 °C and exposure duration of up to 8.5 hours at GASPAR facility are presented. The experimental data were obtained by the steam-molybdenum reaction rate constant in the range of steam mass rates from 10 to 120 mg/s and compared with the calculation results of oxidation process taking into consideration the kinetic and diffusion mechanism.

The results of a reflood investigation of model VVER and PWR fuel assemblies for maximum design-basis and beyond design-basis accidents performed on the RBHT, SVD, and PARAMETR stands are presented. The variation ranges of the regime parameters are: initial temperature of fuel element 460–600°C; mass velocity of water 47–160 kg/(m2·sec), underheating at the entry into the model fuel assembly 11–108°C; pressure 0.14–0.42 MPa; and, linear heat flux density simulating the residual heat release 0–2.3 kW/m. A colligating relation describing the experimental data to within 30% is obtained for the wetting front of model fuel assemblies, which makes it possible to calculate the cool-down time of model fuel assemblies with different designs and evaluate the reflooding time of VVER and PWR.

Results of investigation of the phase interface fluctuations at film and bubble boiling and sea surface agitation are presented. The vapor film thickness and vapor bubble growing on the wall were determined with the aid of laser diagnostics. Oscillations of a growing vapor bubble and simultaneous pressure oscillations in liquid were detected using optical (laser) and acoustic diagnostics. For the very first time volume and shape oscillations of a vapor bubble growing on a wall were determined. An approached model of volume oscillations of a vapor bubble, growing on a heat transfer surface is presented basing on experimental data. The system of model equations and bubble dynamics were presented considered, accounting simultaneous evaporation and condensation at the interface. It has been found that the growth of a vapor bubble is accompanied by its volume oscillations, which become chaotic under certain circumstances.

Boiling of water was investigated in a flat rectangular microchannel with dimensions 13.5x3x0.2 mm. Boiling curves are constructed by processing thermograms obtained by a thermal imager. Data on heat transfer are compared with known results, and the effect of the output section length has been investigated on the critical heat flux in the microchannel.

The work presents the results of a study of corrosion resistance of chrome-coated fragments of zirconium cladding of VVER-1000 reactor fuel elements. The coatings had been deposited by electrochemical deposition on the standard cladding fragments with pre-treated surfaces. Gas-dynamic treatment of the surface with chrome powder proved to have a positive effect on the surface-to-cladding adhesion. Annealing at a temperature of 400 °C contributes to relieving of the residual stresses resulting from the gas-dynamic treatment. Investigation of the durability of the coatings was performed under exposure to overheated steam at a temperature of 1200 °C and exposure period of up to 1500 s. As it has been demonstrated, the produced coatings hinder formation of ZrO2 oxide layer at the outer surface and reduce the depth of penetration of oxygen into the metallic sublayer, in comparison with the specimens in the original condition. All this contributes to retention of the residual ductility of the tested specimens at the level of no less than 2%.

The thermal resistance of the composite thermal stabilizer and methods for its reduction are investigated. The thermal resistance of thermal stabilizer decreases due to the heat exchange intensification in evaporator by a layer of aluminum oxide nanoparticles. A method of producing aluminum oxide nanoparticles has been developed. The liquid capillary rise height is measured in the layer of nanoparticles. Estimate of the properties stability is obtained in the coating from aluminum oxide nanoparticles. The thermal resistance dependences are obtained on the transferred heat flux for models of thermal stabilizers from steel and aluminum

We present the results from a study of heat transfer enhancement for bulk water boiling at atmospheric pressure on a surface with micro- and nanorelief, including a relief formed from silicon carbide and aluminum oxide nanoparticles. Horizontally oriented steel tube 1.2 mm in diameter and copper plate 15 × 3 mm in size were selected as test sections. The process was recorded by means of a video camera, and the values of heat transfer, critical heat fluxes, and contact angles were measured. The use of surface with micro- and nanorelief makes it possible to obtain a significantly higher critical heat flux and boiling heat transfer coefficient owing to a change of surface wettability. The results of investigations can find use in compact heat exchangers, refrigerating plants, heat pipes, in the mirrors of high-capacity lasers, in the targets and resonators of charged particle accelerators and for external cooling of reactor vessels under emergency conditions.

A balance procedure is proposed for estimating the main parameters characterizing the process of model fuel assemblies reflooding of a VVER reactor made on different scales under the conditions of a design basis accident by subjecting them to bottom reflooding1. The proposed procedure satisfactorily describes the experimental data obtained on PARAMETER test facility in the temperature range up to 1200°C. The times of fuel assemblies quenching by bottom reflooding calculated using the proposed procedure are in satisfactory agreement with the experimental data obtained on model fuel assemblies of VVER- and PWR-type reactors and can be used in developing measures aimed at enhancing the safety of nuclear power stations.

A balance method is proposed for calculating the main characteristics of the cooling of the heat-releasing assemblies of light-water nuclear reactors in the case of repeated flooding of them at the bottom under the conditions of a maximum projected accident. The calculation data obtained by this method agree well with the corresponding results of experiments in the temperature range of up to 1200°C. The method proposed allows one not only to calculate the parameters of the flooding of a heat-releasing assembly under the conditions of an accident, but also to estimate the flow rate of the water and the time, necessary for flooding of the fuel core of a power unit in the case of its damage that is not due to the breakage of a pipe-line.

The available data on critical heat fluxes for boiling of subcooled and saturated liquid in tubes with twisted tape inserts are considered. Experimental data obtained by different researchers are generalized, and an equation for calculating critical heat fluxes for both smooth tubes and tubes with flow swirling by means of a tape is proposed.

This publication concerns the analysis of an interaction between steam bubbles in highly mineralized aqueous solutions flowing in the natural-circulation loop of a flash evaporator. Data are given on the distribution of steam bubbles with respect to their diameters and their floating velocities; an expression is also given for the interaction factor making it possible to improve the technique of hydrodynamics calculations for the apparatuses under discussion.

The dependences are obtained of the pressure drop in a vertical pipe under conditions of boiling aqueous solution of sodium sulfate on the flow velocity, steam quality, and concentration of the solution.

Results obtained from field and laboratory studies of the thermohydraulic operating conditions of natural-circulation evaporators are presented.

Results from investigating the enhancement of heat transfer during condensation of water vapor from flue stack gases produced by boilers when firing natural gas. It is shown that enhancement of heat transfer results in a larger quantity of the condensate obtained.

An empirical dependence for computing the heat-transfer factor in a boil-type evaporator obtained on the basis of data of start and make-ready work and thermochemical tests of multistage evaporating installations at various thermal plants is presented. Results of computation of the heat-transfer factor and of the capacity of an evaporating installation by known methods are compared with the results obtained with the help of the suggested dependence. A dependence for evaluating the change in the heat-transfer factor with the operating time is suggested.

The high-temperature oxidation tests were carried out for the regular fuel rod claddings specimens made of sponge-based zirconium alloy (E110G) and for the accident tolerant fuel (ATF) ones – pure vacuum melted molybdenum (VCPM) and niobium alloy (Nb-1%Zr). The tests were carried out under the ambient pressure p ~ 0.1 MPa in pure water steam. The experimental data on the oxidation characteristics were obtained for E110G specimens in the temperature range T = 1100 − 1500 °C, that for VCPM and Nb-1%Zr are investigated under extended temperature-duration range (more than 1 hour). The thermal effects of molybdenum (Q SMR) and niobium (Q SNR) interactions with steam were defined and the derived oxidation rate constants for refractory metals were compared with the known ones. Based on the computations performed with PARAM-TG code the high-temperature oxidation characteristics of model fuel assemblies of large-scale facilities under LOCA conditions with regular and ATF claddings were compared. It was shown that Zr-steam interaction of fuel rod cladding (Q SZR) is more intensive compared with VCPM and Nb-1%Zr ones under investigated conditions.

Interface oscillations during boiling are studied experimentally and theoretically. The output-signal spectra of light and acoustic sensors indicate that the liquid-pressure and interface oscillations are interrelated. A model is suggested for the oscillations of a bubble growing on a heating surface, and the existence of an attractor is deduced for the first time from the solution of model equations. The data obtained enable one to determine the ranges of interface oscillation amplitude and frequency and can be used in the modeling of boiling.

A pulsation model is suggested for the detachment of a vapor bubble that is growing on a solid wall according to a prescribed law.

Experiments were carried out on the characteristics of the transition area for water solutions of sodium sulphate under low mass velocities and pressures. Calculations were made on a two-zone evaporator whose production is increased and recommendations of the optimum design are given. The effect of porous coating on heat transfer was studied on the “I” evaporator type in TPS-8 MOSENERGO.

Investigation of the dryout in upward water flow within the ranges of mass velocities 10–150 kg/m2.s, pressures 0.1–1.6 MPa, and heat flux 50–420 kW/m2 is reported. The distributions of wall temperature and wall temperature fluctuations on the length of the tube, the time variations of flow temperature are obtained. The dependences of the boundary vapor quality and the critical heat flux from mass velocity are discovered. The mechanism of the heat transfer crisis at low mass velocities is also analyzed.

The experimental setup, methods, and results of a study of the heat transfer mechanism in film boiling on a horizontal cylinder are described.

Burnout is investigated in tubes under nonuniform heating on the perimeter. Data on heat transfer and critical heat flux (qcht) in the case of water were obtained for ranges of mass velocity pw = 200-3000 kg/m2 s, pressure p = 0.1-1 MPa, and inlet water temperature T = 25-98°C. The test section was a horizontal copper tube of 21 mm outer diameter, 8 mm inner diameter with a technically smooth surface and heat transfer-intensifying twisted tape and porous sintered coating. The test section was heated by bombardment with electrons. It is established that a redistribution of heat fluxes and an increase of wall temperature fluctuations occur at burnout. The range of regime parameters to prevent burnout of a heat transfer surface is determined.

The water and Na2 SO4 water solution boiling investigation had been carried in pool on the surfaces with artificial and natural nucleons sites under different pressures using high speed digital camera. The boiling of water was investigated at atmosphere pressure on a surface with a artificial nucleons site, which had a micro scale (cavity’s diameters – 100 and 200 μm and depth – 80 μm), in the Fridrich-Alexander University Erlangen-Nurnberg, Germany in the Institute of Fluid Mechanics. The boiling of water and Na2 SO4 water solution with concentration 20 g/l was investigated on a surface with natural nucleons sites in the pressure range 0.1 – 1 MPa in the Moscow Power-Engineering Institute (Technical University) on department of Thermal Physics. The “hand” video processing was used for the study’s results in case of the pool boiling on a surface with a artificial nucleon site. The data processing was realized for the study’s results using with a program “Bubble Detector”, which was specially developed for case of the pool boiling on a surface with the natural nucleon sites, and the “hand” processing was carried for video, which showed the reliability of the program “Bubble Detector”. First the distributions and dependences of basic boiling characteristics (frequency, departure diameter) were obtained at water pool boiling on a surface with a artificial cavity in the range of heat flux from 20 to 128 kW/m2 and the time dependence of vapor bubble’s grow. It was obtained, that departure diameters of vapor bubbles do not depend in case of boiling on a surface with a single cavity practically on heat flux. First the distributions and dependences of swimming velocities and equivalent diameters were obtained at water and Na2 SO4 water solution with concentration 20 g/l pool boiling on a surface with natural nucleon sites in range of pressures from 0.1 to 1 MPa. The comparison of diameters’ and swimming velocities’ distributions of vapor bubbles was carried for under consideration conditions.Copyright © 2008 by ASME

A method is given for recording the onset of water boiling in a tube; a formula is given for the onset at a porous-coated surface, which applies for free or forced convection.