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Abstract

In the paper presented is an idea of organic Rankine cycle (ORC) operating with supercritical parameters and so called dry fluids. Discussed is one of the methods of improving the effectiveness of operation of supercritical cycle by application of internal regeneration of heat through the use of additional heat exchanger. The main objective of internal regenerator is to recover heat from the vapour leaving the turbine and its transfer to the liquid phase of working fluid after the circulation pump. In effect of application of the regenerative heat exchanger it is possible to obtain improved effectiveness of operation of the power plant, however, only in the case when the ORC plant is supplied from the so called sealed heat source. In the present paper presented is the discussion of heat sources and on the base of the case study of two heat sources, namely the rate of heat of thermal oil from the boiler and the rate of heat of hot air from the cooler of the clinkier from the cement production line having the same initial temperature of 260 oC, presented is the influence of the heat source on the justification of application of internal regeneration. In the paper presented are the calculations for the supercritical ORC power plant with R365mfc as a working fluid, accomplished has been exergy changes and exergy efficiency analysis with the view to select the most appropriate parameters of operation of the power plant for given parameters of the heat source.
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Authors and Affiliations

Aleksandra Borsukiewicz-Gozdur
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Abstract

The paper presents thermodynamic analysis of the gas-steam unit of the 65 MWe combined heat and power station. Numerical analyses of the station was performed for the nominal operation conditions determining the Brayton and combined cycle. Furthermore, steam utilization for the gas turbine propulsion in the Cheng cycle was analysed. In the considered modernization, steam generated in the heat recovery steam generator unit is directed into the gas turbine combustion chamber, resulting in the Brayton cycle power increase. Computational flow mechanics codes were used in the analysis of the thermodynamic and operational parameters of the unit.
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Authors and Affiliations

Andrzej Chrzczonowski
Paweł Ziółkowski
Janusz Badur
Krzysztof Jesionek
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Abstract

This paper presents a numerical method for determining heat transfer coefficients in cross-flow heat exchangers with extended heat exchange surfaces. Coefficients in the correlations defining heat transfer on the liquid- and air-side were determined using a nonlinear regression method. Correlation coefficients were determined from the condition that the sum of squared liquid and air temperature differences at the heat exchanger outlet, obtained by measurements and those calculated, achieved minimum. Minimum of the sum of the squares was found using the Levenberg-Marquardt method. The uncertainty in estimated parameters was determined using the error propagation rule by Gauss. The outlet temperature of the liquid and air leaving the heat exchanger was calculated using the analytical model of the heat exchanger.
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Authors and Affiliations

Dawid Taler
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Abstract

In the paper a research on cost-effective optimum design boiling temperature for Organic Rankine Cycle utilizing low-temperature heat sources is presented. The ratio of the heat exchanger area of the boiler to the power output is used as the objective function. Analytical relations for heat transfer area as well power of the cycle are formulated. Evaporation temperature and inlet temperature of the heat source medium as well its mass flow rate are varied in the optimization method. The optimization is carried out for three working fluids, i.e. R 134a, water and ethanol. The objective function (economics profitability, thermodynamic efficiency) leads to different optimal working conditions in terms of evaporating temperature. Maximum power generation in the near-critical conditions of subcritical ORC is the highest. The choice of the working fluid can greatly affect the objective function which is a measure of power plant cost. Ethanol exhibits a minimum objective function but not necessarily the maximum cycle efficiency.
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Authors and Affiliations

Dariusz Mikielewicz
Jarosław Mikielewicz
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Abstract

In the paper presented are definitions of specific indicators of power which characterize the operation of the organic Rankine cycle (ORC) plant. These quantities have been presented as function of evaporation temperature for selected working fluids of ORC installation. In the paper presented also is the procedure for selection of working fluid with the view of obtaining maximum power. In the procedure of selection of working fluid the mentioned above indicators are of primary importance. In order to obtain maximum power there ought to be selected such working fluids which evaporate close to critical conditions. The value of this indicator increases when evaporation enthalpy decreases and it is known that the latent heat of evaporation decreases with temperature and reaches a value of zero at the critical point.
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Authors and Affiliations

Władysław Nowak
Aleksandra Borsukiewicz-Gozdur
Sławomir Wiśniewski
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Abstract

In this paper the results of the thermodynamic analysis of the oxy-combustion type pulverized bed boiler integrated with a hybrid, membrane- cryogenic oxygen separation installation are presented. For the calculations a 600 MW boiler with live steam parameters at 31.1 MPa /654.9 oC and reheated steam at 6.15 MPa/672.4 oC was chosen. In this paper the hybrid membrane-cryogenic technology as oxygen production unit for pulverized bed boiler was proposed. Such an installation consists of a membrane module and two cryogenic distillation columns. Models of these installations were built in the Aspen software. The energy intensity of the oxygen production process in the hybrid system was compared with the cryogenic technology. The analysis of the influence of membrane surface area on the energy intensity of the process of air separation as well as the influence of oxygen concentration at the inlet to the cryogenic installation on the energy intensity of a hybrid unit was performed.
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Authors and Affiliations

Sylwia Berdowska
Anna Skorek-Osikowska
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Abstract

The paper presents a thermodynamic optimization of supercritical coal fired power plant. The aim of the study was to optimize part of the thermal cycle consisted of high-pressure turbine and two chosen highpressure feed water heaters. Calculations were carried out using IPSEpro software combined with MATLAB, where thermal efficiency and gross power generation efficiency were chosen as objective functions. It was shown that the optimization with newly developed framework is sufficiently precise and its main advantage is the reduction of computation time on comparison to the classical method. The calculations have shown the tendency of the increase in efficiency, with the rise of a number of function variables.
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Authors and Affiliations

Witold Elsner
Łukasz Kowalczyk
Maciej Marek
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Abstract

During heat transport through the walls of a hollow sphere, the heat stream can achieve extreme values. The same processes occur in regular polyhedrons. We can calculate the maximum heat transfer rate, the so-called critical heat transfer rate. We must assume here identical conditions of heat exchange on all internal and external walls of a regular polyhedron. The transfer rate of heat penetrating through the regular polyhedron with different heat transfer coefficients on the walls is called the heat transfer rate with asymmetric boundary conditions. We show that the heat transfer rate in this case will grow up if we replace those coefficients with their average values.
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Authors and Affiliations

Ewa Pelińska-Olko
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Abstract

One of the major concerns of the power energy industries is a proper operation of steam power blocks. Pressurized working medium and high temperature cause very high stresses in the construction elements such as collectors, separators or steam valves. They are exposed to sudden temperature and pressure changes that cause high stresses at certain points. Additionally, the cyclic character of loading causes material fatigue, known as low-cyclic fatigue, which may lead to the formation of fracture. Thus, methodologies offered by many companies should ensure reliable and safe operation of steam power blocks. The advanced numerical solutions for determining time-optimum medium temperature changes are presented. They are based on Levenberg-Marquardt and nonlinear programming by quadratic Lagrangian methods. The methods allow us to find parameters for start-up and shut-down operation that can reduce total stresses to limits governed by European regulations. Furthermore, the heating and cooling operations are conducted in a shortest time possible.
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Authors and Affiliations

Dariusz Rząsa
Piotr Duda
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Abstract

A method for determining time-optimum medium temperature changes is presented. The heating of the pressure elements will be conducted so that the circumferential stress caused by pressure and fluid temperature variations at the edge of the opening at the point of stress concentration, do not exceed the allowable value. In contrast to present standards, two points at the edge of the opening are taken into consideration. The first point, P1, is located at the cross section and the second, P2, at the longitudinal section of the vessel. It will be shown that the optimum temperature courses should be determined with respect to the total circumferential stress at the point P2, and not, as in the existing standards due to the stress at the point P1. Optimum fluid temperature changes are assumed in the form of simple time functions. For practical reasons the optimum temperature in the ramp form is preferred. It is possible to increase the fluid temperature stepwise at the beginning of the heating process and then increase the fluid temperature with the constant rate. Allowing stepwise fluid temperature increase at the beginning of heating ensures that the heating time of a thick-walled component is shorter than heating time resulting from the calculations according to EN 12952-3 European Standard.
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Authors and Affiliations

Piotr Dzierwa
Jan Taler
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Abstract

The paper describes tests intended to examine the occurrence of natural convection within the space occupied by 40×20 mm rectangular steel sections. Within these tests the bed of four layers of section was heated by the electric palate heater. Depending on the manner in which the heater was positioned, the tests were divided into two series. In the case of heating from above, the heat flowing through the bed is transferred only by conduction and radiation. When heating the bed from below, in addition to conduction and radiation, also a convective heat transfer will occur. Should this be the case, it will result in the intensification of the heat exchange. The results of measurements carried out have not demonstrated that the occurrence of any possible natural convection would influence the development of a temperature field in this type of charge.
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Authors and Affiliations

Rafał Wyczółkowski
Dorota Musiał
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Abstract

Some studies show that cells are able to penetrate through pores that are smaller than cell size. It concerns especially Red Blood Cells but it also may concern different types of biological cells. Such penetration of small pores is a very significant problem in the filtration process, for example in micro- or ultrafiltration. Deformability of cells allows them to go through the porous membrane and contaminate permeate. This paper shows how cells can penetrate small cylindrical holes and tries to assess mechanical stress in a cell during this process. A new mathematical approach to this phenomenon was presented, based on assumptions that were made during the microscopic observation of Red Blood Cell aspiration into a small capillary. The computational model concerns Red Blood Cell geometry. The mathematical model allows to obtain geometrical relation as well as mechanical stress relations.

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Authors and Affiliations

Maciej Szwast
Teresa Suchecka
Wojciech Piątkiewicz
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Abstract

The article presents tests carried out on three selected samples of limestone originating from three commercially exploited deposits. The tests of sorbents included desulphurisation in different atmospheres and a physicochemical analysis of desulphurisation products. The aim of the tests was to determine desulphurisation efficiency and conversion degree as dependent on the concentration of O2 and CO2.

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Authors and Affiliations

Angelika Kochel
Aleksandra Cieplińska
Arkadiusz Szymanek
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Abstract

The pressure drop in microreactors for the gas - liquid Taylor flow was measured for 4 different microreactor geometries and 3 different gas - liquid systems. The results have been compared with the existing literature correlations. A selection of the best correlations has been made.

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Authors and Affiliations

Paweł Cygański
Paweł Sobieszuk
Ryszard Pohorecki
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Abstract

Based on hydrodynamic data, Kato-Wen and Kunii-Levenspiel bubbling-bed model parameters, supplemented with assumptions characteristic for tested confined fluidised bed, were analysed. The calculated bubble diameters and the bed composition proved essential influence of inter-particle space of packed compacted component onto fluidisation character. The usability of the conducted model analysis was also confirmed. Finally, it can be concluded that Kunii-Levenspiel and Kato- Wen models with characteristic assumptions (for the tested bed) can be applied for calculation of the confined fluidised bed layer porosity. Discrepancies of ε f value, determined on the basis of the above mentioned bubbling-bed models do not exceed 8% of the error. The model parameters obtained from the matching the model relations to experimental data εf = f(u0) allow an analysis of the fluidisation character as well as gas velocity regime and the fluidised bed structural composition identification. A description of the regime of the process in which confined fluidised bed is characterised with an increase of mass and heat transfer rate is also possible using relation (17) derived in the present study.

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Authors and Affiliations

Piotr Zabierowski
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Abstract

The homogeneous stirred reactor designed for kinetic studies of the combustion of hydrocarbons with intensive internal recirculation in high temperature combustion chamber is described. The originality of our reactor lies in its construction which allows to intensively mix fuel and flue gases, measure gas temperature as well as obtain samples which can be used to investigate diffusion flames. The cylindrical construction enables to use the reactor in laboratory cylindrical electrically heated ovens. The CFD analysis of the reactors, the mixing parameters (turbulent Peclet number and mixing level) and the volume average temperature in the reactors were elaborated on the basis of the typical dimensions of classical reactors to kinetics research as well as the own reactor design. The results of the analysis allow to reveal advantages of our construction.

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Authors and Affiliations

Iwona Gil
Piotr Mocek
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Abstract

The application of aqueous two-phase systems (ATPS) is a cost-effective and simple method of protein separation (including enzymes) from complex systems. The first stage of designing the protein purification process in an ATPS involves the identification of the conditions for the formation of a given extraction system. For this purpose, the conditions for the formation of ATPSs in a thermoseparating EO50PO50 polymer/potassium phosphates system have been studied. Factors determining the ATPS formation comprised: separation temperature (4ºC or 20ºC), phosphate solution pH (6, 7.5 or 9) as well as the concentration of NaCl introduced into the systems (0.085 M, 0.475 M and 0.85 M). ATPS without NaCl were prepared as well. The conditions for the formation of the primary EO50PO50/potassium phosphate ATPS were determined with their phase diagrams. It was observed that with an increase of phosphate pH and NaCl concentration in the system, there was a decrease of the EO50PO50 and phosphate concentrations necessary to form a primary ATPS. After the primary two-phase separation, the top phase (rich in the EO50PO50 polymer) was partitioned from the bottom phase (rich in phosphates). Next, by means of polymer phase thermoseparation, a secondary two-phase system was formed. In the secondary EO50PO50/phosphate ATPS, the bottom phase was formed by the concentrated EO50PO50 polymer (30-80% concentration), while the top phase by a solution composed mainly of water, containing phosphate ions and remains of EO50PO50 polymer (3-7%).

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Authors and Affiliations

Radosław Dembczyński
Wojciech Białas
Tomasz Jankowski
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Abstract

The paper presents results of experimental studies on removal of NOx from flue gas via NO ozonation and wet scrubbing of products of NO oxidation in NaOH solutions. The experiment was conducted in a pilot plant installation supplied with flue gas from a coal-fired boiler at the flow rate 200 m3/h. The initial mole fraction of NOx,ref in flue gas was approx. 220 ppm, the molar ratio X = O3/NOref varied between 0 and 2.5. Ozone (O3 content 1÷5% in oxygen) was injected into the flue gas channel before the wet scrubber. The effect of the mole ratio X, the NaOH concentration in the absorbent, the liquid-to-gas ratio (L/G) and the initial NOx concentration on the efficiency of NOx removal was examined. Two domains of the molar ratio X were distinguished in which denitrification was governed by different mechanisms: for X ≤ 1.0 oxidation of NO to NO2 predominates with slow absorption of NO2, for X >> 1.0 NO2 undergoes further oxidation to higher oxides being efficiently absorbed in the scrubber. At the stoichiometric conditions (X = 1) the effectiveness of NO oxidation was better than 90%. However, the effectiveness of NOx removal reached only 25%. When ozonation was intensified (X ≥ 2.25) about 95% of NOx was removed from flue gas. The concentration of sodium hydroxide in the aqueous solution and the liquid-to-gas ratio in the absorber had little effect on the effectiveness of NOx removal for X > 2.

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Authors and Affiliations

Maciej P. Jakubiak
Włodzimierz K. Kordylewski
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Abstract

The possibility of scaling viscoelastic properties of starch solutions in relation to biopolymer concentration was presented in this study. An application of this empirical method enabled to widen the observation horizon of viscoelastic properties. It was also determined that the scope of its applicability is limited by amylose content in the solution. In high amylose solutions, for which up to 40% (w/w) concentration was the highest one obtained, calibration caused the formation of master curve in the widest frequency range. Determined values of scaling coefficients aC changed exponentially in starch concentration function in the solution. For waxy starch solutions of maximum concentration equal to 20% (w/w), scaling did not significantly widen the observation window. Based on master curves constructed in such way, continuous relaxation spectra H(λ) were determined using Tikhonov regularisation method. Their structure indicates advantageous of viscous elements in the process of viscoelastic phenomena formation.

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Authors and Affiliations

Marcin Łukasiewicz
Paweł Ptaszek
Anna Ptaszek
Mirosław Grzesik
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Abstract

The porous structure of cylindrical and ring-shaped char material was developed by partial steam gasification. Micropore and mesopore structures of active carbons with various forms of burn-off were evaluated by nitrogen adsorption/desorption isotherms. Parameters of the Dubinin- Radushkevich equation were calculated as well as the micropore size distribution by the Horvath- Kawazoe method. The results of textural investigations showed that more uniform micropore structure and better mechanical properties were found for ring-shaped active carbons.

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Authors and Affiliations

Bronisław Buczek
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Abstract

A method of parameters fitting to the experimental vapour - liquid - liquid equilibrium (VLLE) data is presented for the NRTL and the Uniquac equations for six quaternary mixtures. The same equations but with coefficients taken from the simulator Chemcad database were also used for calculation of the VLLE for the same mixtures. The calculated equilibrium temperatures and compositions for all the three phases were compared with the experimental data for these four cases. The investigated models were also applied for calculation of the compositions and temperatures of ternary azeotropes occurring in the considered quaternary mixtures. The computed values were compared with the experimental ones to appreciate the model's accuracy and to confirm whether the model correctly predicts the presence of homo- or heteroazeotrope. The NRTL equation with coefficients fitted to the VLLE data proved to be the most accurate model. For the mixtures containing water, ethanol and two different hydrocarbons this model shows particularly high accuracy. In three cases the mean deviations between the calculated and measured temperatures do not exceed 0.25 K, and for the fourth mixture the difference equals 0.33. Besides, the mean deviations between the calculated and the measured concentrations in the gas and liquid phases, with one exception do not exceed 1 mole %.

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Authors and Affiliations

Andrzej Wyczesany
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Abstract

Based on mathematical modelling and numerical simulations, a control strategy for a Molten Carbonate Fuel Cell Hybrid System (MCFC-HS) is presented. Adequate maps of performances with three independent parameters are shown. The independent parameters are as follows: stack current, fuel mass flow and compressor outlet pressure. Those parameters can be controlled by external load, fuel valve and turbine-compressor shaft speed, respectively. The control system is purposed to meet many constraints: e.g. stack temperature, steam-to-carbon ratio, compressor surge limitation, etc. The aim is to achieve maximum efficiency of power generated within these constraints. Governing equations of MCFC-HS modelling are given. An operational line of the MCFC-GT system is presented which fulfils several constraints (temperature difference, cell temperature, etc.) The system is able to achieve efficiency of more than 62% even in part-load operation.

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Authors and Affiliations

Jarosław Milewski
Andrzej Miller
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Abstract

One of the methods of obtaining energy from renewable sources is the technology of indirect cofiring of biomass. It consists in the gasification of secondary fuel and combustion of the generated gas in the boiler together with its primary fuel. The paper presents a thermodynamic analysis of the use of the boiler flue gases as the converting medium in the process of indirect co-firing - a technology which is being developed at the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology. The basis of the analysis are the data resulting from variant calculations conducted with the use of the Gaseq program. The calculations were made for various compositions of gasified fuel and the converting medium, variable fuel/oxidiser ratios and variable gasification temperatures. As a result, the equilibrium composition and the calorific value of the generated gas were obtained. The main optimisation objective adopted here was the nondimensional efficiency coefficient, which is the ratio of the chemical energy of products to the chemical energy of the process reactants.

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Authors and Affiliations

Rafał Litka
Sylwester Kalisz
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Abstract

The paper presents the properties of surface oxide layers with an increased content of carbon for tribological applications. The composite surface oxide layers were produced using a two-step technology through hard anodising of the surface of an aluminium alloy, followed by thermochemical treatment of anodic oxide coatings. The surface oxide layers were subjected to tribological tests in an oil-less sliding couple with T5W plastic. The presented test results confirm the usefulness of the proposed modifications of surface oxide layers for the purpose of enhancing the operational durability of oil-less sliding couples in a reciprocating motion.

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Authors and Affiliations

Tomasz Kmita
Marek Bara

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