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Number of results: 13
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Abstract

In summer 1998 detailed measurements of ablation were carried out on the Waldemar Glacier in order to determine its spatial and time variation. Five-days' average ablation was equal to 14.7 cm water equivalent (w.e.), with maximum total ablation of 160-180 cm w.e. at 200 m a.s.l., and the lowest ablation of 106 cm w.e. at 350 m a.s.l. Total ablation for the whole glacier was estimated at 120.5 cm w.e. Simplified scheme of changes of summer ablation with altitude was exampled by this glacier. Relation between discharge from individual fragments of the Waldemar Glacier and their ablation was examined. Discharge of the Waldemar River was analysed: from about 4,800,000 m3 of water in the stream, 67% came from surface ablation of the Waldemar Glacier.
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Abstract

The ductility of High Performance Concrete (HPC) can develop both in tension and compression.This aspect is evidenced in the present paper by measuring the mechanical response of normalvibrated concrete (NC), self-compacting concrete (SC) and some HPCs cylindrical specimensunder uniaxial and triaxial compression. The post-peak behaviour of these specimens is definedby a non-dimensional function that relates the inelastic displacement and the relative stress duringsoftening. Both for NC and SC, the increase of the fracture toughness with the confinement stressis observed. Conversely, all the tested HPCs, even in absence of confinement, show practically thesame ductility measured in normal and self-compacting concretes with a confining pressure. Thus,the presence of HPC in compressed columns is itself sufficient to create a sort of active distributedconfinement.
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Abstract

This study is concerned with liquid flow induced by a disk which rotates steadily around its axis and touches the free surface of liquid contained in a cylindrical vessel. It is a simplified model of the flow in the inlet part of a vertical cooling crystallizer where a rotary distributor of inflowing solution is situated above the free surface of solution contained in the crystalliser. Numerical simulations of flow phenomena were conducted and the simulation results were interpreted assuming an analogy with Kármán’s theoretical equations. In a cylindrical coordinate system, the components of flow velocity were identified as functions of distance from the surface of the rotating disk. The experimental setup was developed to measure velocity fields, using digital particle velocimetry and optical flow. Conclusions concerning the influence of disc rotation on liquid velocity fields were presented and the experimental results were found to confirm the results of numerical simulation. On the basis of simulation data, an approximation function was determined to describe the relationship between the circumferential component of flow velocity and the distance from the disk.
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Abstract

Analysis of the state of-the-art in research of refrigerant condensation in miniature heat exchangers, so-called multiports, was made. Results of refrigerant R407C condensation in a mini condenser made in the form of two bundles of tubular minichannels from stainless steel with an inside diameter 0.64 mm and length 100 mm have been presented. Two exchangers consisted of four minichannels and 8 minichannels have been investigated. The values of average heat transfer coefficient and frictional pressure drops throughout the condensation process were designated. The impact of the vapor quality of refrigerant and the mass flux density on the intensity of heat transfer and flow resistance were illustrated. A comparative analysis of test results for various refrigerants in both mini heat exchangers were made.
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Abstract

This paper presents the analysis of the influence of works related to the dynamic replacement column formation on the bridge pillar and the highway embankment located nearby. Thanks to DR columns, it is possible to strengthen the soil under road embankment in a very efficient way. However, the construction of such support carries risk to buildings and engineering structures located in the neighbourhood. Therefore modelling and monitoring of the influence of the conducted works should be an indispensable element of each investment in which dynamic replacement method is applied. The presented issue is illustrated by the example of soil strengthening with DR columns constructed under road embankment of DTŚ highway located in Gliwice. During the inspection, the influence of vibrations on the nearby bridge pillar and road embankment was examined. The acceleration values obtained during these tests were used to verify the elaborated numerical model.
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Abstract

In Poland, it often happens that construction objects are subject to demolition work for different reasons. Demolition, according the Construction Law, is defined as a type of construction works and, as such, represents a particular type of construction project. As in other construction projects, a very important phase, in addition to execution of the works, is to prepare, design and plan demolition works. Some demolition activities are covered by appropriate regulations and can be described as typical. On the other hand the technical side of demolition works depends on many factors such as: the type of building, its age, technical condition, type of construction, etc. This article covers the analysis of the stages and tasks in the preparatory phase of the building demolition. This work will also present a description of the tasks carried out during the demolition works based on the example of a historic tenement house located in Krakow. This analysis aims to identify implementation problems and sources of risk that may occur during this type of construction work.
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Abstract

Numerical analysis of the tensioning cables anchorage zone of a bridge superstructure is presented in this paper. It aims to identify why severe concrete cracking occurs during the tensioning process in the vicinity of anchor heads. In order to simulate the tensioning, among others, a so-called local numerical model of a section of the bridge superstructure was created in the Abaqus Finite Element Method (FEM) environment. The model contains all the important elements of the analyzed section of the concrete bridge superstructure, namely concrete, reinforcement and the anchoring system. FEM analyses are performed with the inclusion of both material and geometric nonlinearities. Concrete Damage Plasticity (CDP) constitutive relation from Abaqus is used to describe nonlinear concrete behaviour, which enables analysis of concrete damage and crack propagation. These numerical FEM results are then compared with actual crack patterns, which have been spotted and inventoried at the bridge construction site.
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Abstract

In this paper, effect of Hall currents on the thermal instability of couple-stress fluid permeated with dust particles has been considered. Following the linearized stability theory and normal mode analysis, the dispersion relation is obtained. For the case of stationary convection, dust particles and Hall currents are found to have destabilizing effect while couple stresses have stabilizing effect on the system. Magnetic field induced by Hall currents has stabilizing/destabilizing effect under certain conditions. It is found that due to the presence of Hall currents (hence magnetic field), oscillatory modes are produced which were non-existent in their absence.
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Abstract

Thermal analysis of a heat and power plant with a high temperature gas cooled nuclear reactor is presented. The main aim of the considered system is to supply a technological process with the heat at suitably high temperature level. The considered unit is also used to produce electricity. The high temperature helium cooled nuclear reactor is the primary heat source in the system, which consists of: the reactor cooling cycle, the steam cycle and the gas heat pump cycle. Helium used as a carrier in the first cycle (classic Brayton cycle), which includes the reactor, delivers heat in a steam generator to produce superheated steam with required parameters of the intermediate cycle. The intermediate cycle is provided to transport energy from the reactor installation to the process installation requiring a high temperature heat. The distance between reactor and the process installation is assumed short and negligable, or alternatively equal to 1 km in the analysis. The system is also equipped with a high temperature argon heat pump to obtain the temperature level of a heat carrier required by a high temperature process. Thus, the steam of the intermediate cycle supplies a lower heat exchanger of the heat pump, a process heat exchanger at the medium temperature level and a classical steam turbine system (Rankine cycle). The main purpose of the research was to evaluate the effectiveness of the system considered and to assess whether such a three cycle cogeneration system is reasonable. Multivariant calculations have been carried out employing the developed mathematical model. The results have been presented in a form of the energy efficiency and exergy efficiency of the system as a function of the temperature drop in the high temperature process heat exchanger and the reactor pressure.
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Abstract

According to a fuel flexibility, fluidized bed boilers are considered as appropriate for biomass combustion as cofiring. But the burning of fuels such as forest and agricultural biomass raises a number of operational problems. Most important of these problems are bed agglomeration and deposition. Deposition appears when biomass contains significant amounts of alkali elements, such as sodium and potassium. The purpose of the work is to select a fuel additive to overcome these operational problems. Investigations were conducted in two stages at a pilot scale 0.1 MWth laboratory circulating fluidized bed reactor. As the fuel, the mixture of biomass contained forest residues, sunflower husks, straw and wood pellets from mixed woods was selected. In the first stage biomass was burnt without any additives, while in the second one the fuel was enriched with some additive. The additive (liquid mixture of chemicals) was added to the fuel in amounts of 1 dm3 per 5-10 Mg of fuel. The following operational parameters were examined: temperature profiles along the height of the circulating fluidised bed column, pressure profiles, emissions. After the tests, the laboratory reactor was inspected inside. Its results enables expression of the following conclusions: there was no agglomeration during fuel additive testing, and the deposition was reduced as well. Moreover, the parts (heating surfaces, separator) of the laboratory reactor were coated with a protective layer. The layer covered microcracks and protected the parts from deposition for a long period after the operation.
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Abstract

Self-curing concrete SC is a concrete type that can be cured without using any external curing regimes. It can perform by several methods such as using lightweight aggregate or chemical agents. In this research chemical curing agent is used to produce SC. This paper reports the results of a research study conducted to evaluate the effect of sulfates on the performance of self-curing concrete compared to ordinary concrete. Samples are immersed in sodium sulfate Na2S04 solution of 4% concentration. Results are measured in terms of compressive strength, tensile strength, flexural strength and mass loss. It was found that the rate of strength loss is noticed at ordinary concrete compared to SC concrete. Sulfate resistance is improved when using self-curing concrete. This improvement appears to be dependent on using a chemical curing agent.
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Abstract

The paper presents the solution to a problem of determining the heat flux density and the heat transfer coefficient, on the basis of temperature measurement at three locations in the flat sensor, with the assumption that the heat conductivity of the sensor material is temperature dependent. Three different methods for determining the heat flux and heat transfer coefficient, with their practical applications, are presented. The uncertainties in the determined values are also estimated.
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Abstract

Production of sanitary safe water of high quality with membrane technology is an alternative for conventional disinfection methods, as UF and MF membranes are found to be an effective barrier for pathogenic protozoa cysts, bacteria, and partially, viruses. The application of membranes in water treatment enables the reduction of chlorine consumption during final disinfection, what is especially recommended for long water distribution systems, in which microbiological quality of water needs to be effectively maintained. Membrane filtration, especially ultrafiltration and microfiltration, can be applied to enhance and improve disinfection of water and biologically treated wastewater, as ultrafiltration act as a barrier for viruses, bacteria and protozoa, but microfiltration does not remove viruses. As an example of direct application of UF/MF to wastewater treatment, including disinfection, membrane bioreactors can be mentioned. Additionally, membrane techniques are used in removal of disinfection byproducts from water. For this purpose, high pressure driven membrane processes, i.e. reverse osmosis and nanofiltration are mainly applied, however, in the case of inorganic DBPs, electrodialysis or Donnan dialysis can also be considered.
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