Direct numerical simulation of the process of filtration of nanofluids through a porous medium has been performed. The phenomenon of pore clogging due to the adsorption of nanoparticles on the ...channel walls is studied. The theoretical study is motivated by the need to improve the technological process of impregnation of media with powdered substances with desired properties. To describe such a filtration process, Darcy’s law taking into account the variables of porosity and permeability of the medium—which are related by the Kozeny–Carman formula—is used. The model takes into account the nonlinear effect of the reverse reaction to clogging, which consists in the fact that the filtration rate decreases even to a larger extent and, therefore, the adsorption of the impurity in the pores increases. An algorithm for solving the problem was developed on the basis of the finite difference method, and a computer program code for the process of suspension penetration into a rectangular sample is compiled. The calculated fields of velocity, pressure, porosity, permeability, and concentrations of mobile and immobile impurities are constructed, which makes it possible to fully trace the dynamics of the filtration process. The calculation results confirm that the nonlinear interaction between the nanofluid flow and the porous material is a major factor that has an effect on the flow shape and clogging. It is shown that the change in the distribution of an immobile impurity in a porous medium is determined by the dynamics of the concentration front, whose steepness and propagation velocity depend on the ratio of the problem parameters (characteristics of adsorption–desorption processes and the permeability and diffusion coefficient values) and on the pressure drops at the inlet and outlet. Based on the results of solving the problem from the initial point in time to the time of complete filling of the pores, i.e., clogging, the duration of the technological process is estimated for different saturated layer thicknesses obtained within the framework of the model under consideration, which is in good agreement, as it turned out, with experimental data on the impregnation of artificial porous materials.
Abstract
The results of direct numerical simulation are intended to describe the saturation process of a nanofluid through artificial porous medium. The calculations were fulfilled using the ...hypothesis, which presumed the adsorptive nature of nanoparticles adhesion to the solid boundaries of pores. Mathematical statement of the problem was based on the modified MIM-model and Darcy – Boussinesq equations. The dependence of the desorption intensity on the value of filtration velocity was taken into account in the course of theoretical investigation. It was shown that this factor for concentration redistribution of the immobile impurity led to the steepening of the wave front as a function of time. Phenomenological realization of novel physical assumptions made the results of numerical modeling closer to the experimental data.
At the Joint Institute for High Temperature, Russian Academy of Sciences, a power plant scheme has been developed and implemented in the form of an operating test bed, which includes several energy ...sources (solar battery, electrochemical generator), a storing device (accumulator battery), a base load, and an additional consumer (an electrolyzer, a heat/cold generator, or redox-flow battery). All devices are connected to a common DC bus through individual matching converters that have the same hardware and software implementation. The created test bed with a data acquisition and processing system can be used to study various schemes for control of hybrid power plants, including not only renewable energy sources, but also selected groups of consumers for excessive production of hydrogen, heat, cold, and purified water. In the course of field tests, the possibilities of controlling energy flows due to the DC bus voltage control are demonstrated: the introduction of a guaranteeing source at night and the operation into an electrolyzer simulator during peak solar generation.
Annotation An active drive of the wheels of the chassis is necessary on the take-off and run with reduced coupling characteristics of the airplane on an unpaved or icy runway in crosswind conditions ...to reduce lateral drift from the axis of the strip. The hydraulic transmission has been developed for the active drive of the wheels by aircraft chassis. At using a control system, that regulates the moment wheels characteristics and includes an adaptive circuit with neural network, it is possible to reduce the lateral drift of the aircraft about 30-40 %. The output parameters of the hydraulic motors intended for the landing gear wheels of aircraft weighting 21 tons are determined.
The paper presents the principle of providing uninterrupted power supply to low-voltage dc consumers, as well as a technical device that implements this principle—a bidirectional step-up step-down ...voltage converter. The proposed principle and the converter make it possible to provide backup power to low-voltage consumers with minimal losses due to direct conversion of the backup battery dc voltage into the target device dc supply voltage. The converter is designed to provide uninterrupted power supply to low-voltage devices operating at a supply voltage of 12- to 48-V dc. One side of the converter is connected to the power–supply line of the protected device, and the other side is connected to the backup battery. In normal mode, part of the current from the power line of the target device is taken by the converter and transferred to the backup battery for its charging. When the mains power fails, the converter transfers power from the battery back to the power line of the target device. Switching to battery operation is instantaneous, with no voltage dips. The uninterrupted power-supply system constructed on the basis of the presented converter is easy to connect and configure and has low cost and high efficiency. The converter allows one to add redundant power at no extra cost, including to dc power systems in which it was not originally provided.
Special features of the process of resistance flash welding of ring-shaped components made of large-section pressed aluminium profiles are investigated. The effect of different parameters on the ...process of plastic deformation of metal during upsetting is studied. Recommendations are given for decreasing the number of defects in welded joints and increasing the wear resistance of the tooling.
The paper considers the influence of the insolation level on the electric power quality indicators and efficiency of a grid-tie inverter operating as part of a grid-connected photovoltaic power ...plant. Over the course of a year, data were recorded for Moscow on incoming solar radiation and the grid-tie inverter input and output capacity provided by a 1 kW grid-connected photovoltaic power plant. The insolation threshold values for a Solar River 1100 TL inverter are experimentally established, corresponding to both the beginning and end of stable inverter operation, as well as the required phase angle value for the electric energy supplied to the grid.
In this book, space systems are situated in the global processes of the 21st centurys information society and the role that space information systems could play in risk management is determined; ...methods of detecting and forecasting of both natural disasters and technogenic catastrophes and existing global and regional monitoring systems are described; and the IGMASS is introduced with its architecture and design concept and social and economic aspects and estimates of its creation, development, and utilization. Finally, results of the international symposium held in Limassol, Cyprus, in November 2009 in preparation of the IGMASS projects submission to the United Nations are discussed.
The research has been devoted to benefits for heterojunction silicon PV panels application evaluation. Evaluation has been conducted through numerical simulation and field tests in Moscow conditions. ...During simulation PV array year energy yields for HJT monocrystalline Si panels have been derived for 2013–2018 years using NASA Power initial satellite data on solar radiation daily sums. Experimental investigation has been realized through multicrystalline and HJT panel comparative test using test bed, simulating small off-grid power unit. Specific energy yield of panel (ratio of energy yield for given period of time to the panel peak power) has been chosen as a criterion for panels operation comparison in both cases. The research novelty is concerned with attempt to estimate additional energy, produced due to amorphous silicon layer presence by means of field tests in different weather conditions. Calculation showed no benefits for HJT PV panels. Experimental research showed that up to 5–6 kWh/m
2
/day solar radiation sum value HJT panel provides 1–20% power output gain relatively multicrystalline panel with maximum gain of 14–16% in range of 2–2.5 kWh/m
2
/day solar radiation sum values.
The analysis of the results on the study of erosion products of tungsten-containing elements of a thermonuclear reactor first wall by spectroscopic and other methods is carried out, combined with a ...brief comparison of studies of carbon erosion products in the form of carbon-deuterium films CD
x
(
x
~ 0.5) from the T-10 tokamak with graphite walls and mixed films CH
x
–Me (with impurities Me = W, Fe, etc.) from a high-current plasma accelerator QSPA-T with hydrogen plasma, performed using similar methods. Examples of other unique modern experiments with tungsten and carbon in Russia and abroad are also considered, including in situ diagnostic methods of erosion products, and additionally are presented three new spectra of CD
x
and CH
x
–Me films. The relevance and interconnection of research on the topic “the first wall carbon–metal materials” is dictated by the construction of the JT-60SA fusion reactor in support of the ITER and DEMO project, which will operate for the first ten years with the first wall and divertor made of carbon fiber composites, followed by a transition to metal walls. It is shown that the technique for studying CD
x
films has a universal character, and a number of presented new methods for erosion research of tungsten-containing materials complement and enhance it. As shown, spectroscopic methods for the comparative research of tungsten and carbon erosion products on the surface and in the bulk of the material, including new methods and physical results, make it possible to identify associated problems and prepare practical recommendations for the safe operation of thermonuclear devices.
PDF
