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Dynamics and thermodynamics of a nickel uptake from a water system onto the blast furnace sludg
Get PDFThis study describes the use of blast furnace sludge (BFS) for the removal of toxic Ni(II) ions from a water system.Blast furnace sludge is a by-product and a waste material of the steelmaking industry. Chemical and mineralogical characteristics of BFS are determined by Proton Induced X-ray Emission and X-ray Diffraction methods.The surface area properties are determined by the Brunauer-Emmett-Teller method. The adsorption is investigated in a batch adsorption system in view of its kinetics and thermodynamics. The kinetic experiments show that the adsorption process follows a pseudo-second order model. The adsorption mechanism is investigated by intra-particle diffusion and Boyd-Reichenberg kinetic models. Thermodynamic parameters (activation free energy change, activation enthalpy change, and activation entropy change) reveal that the adsorption of Ni(II) on BFS is spontaneous, exothermic, and chemical in nature. The results suggest that BFS is an inexpensive and efficient adsorbent for the removal of Ni(II) ions from aqueous solutions
Application of thermography in the optimization of high-pressure die casting
No full textU ovom radu dan je pregled metoda proizvodnje lijevanjem, s posebnim osvrtom na tehnologiju visokotlačnog lijevanja Al legura u trajne kalupe. Opisani su postupci proizvodnje visokotlačnim lijevom, te poteškoće koje mogu nastati u procesu proizvodnje. Nadalje su pobliže opisane karakteristične greške koje se javljaju na odljevcima od visokotlačnog lijeva, s naglaskom na nedolivenost. Kao glavni razlog nedolivenosti uzima se pothlađenost dijelova kalupa, odnosno loša temperaturna raspodjela po kalupu. Za dobivanje mogućih informacija o temperaturnoj raspodjeli dan je osvrt na metode mjerenja temperature, točnije na termografsku metodu. Opisani su principi termografske metode i načini mjerenja. Također su dani primjeri iz prakse iz kojih se vide pouzdanost i prednosti primjene termografske metode pri istraživanju temperaturne raspodjele i otkrivanju mogućih zona u kojima može dolaziti do pothlađenja i toplinskih naprezanja.In this paper, an overview is givenon production methods by casting, with special reference to the technology of high-pressure die casting of Al alloys into permanent molds. High-pressure die casting production processes are described, as well as difficulties that may arise in the production process. The characteristic defects that occur during high-pressure castings are described, with an emphasis on misruns. The main reason for misruns is the low temperature of the mold parts, and poor temperature distribution on the mold.
In order to receive information on the temperature distribution, a review is given on the temperature measuring methods, in particular on the thermographic method. The principles of the thermography and measuring methods are described. Practical examples are also given, which show the reliability and advantages of using thermographic methods in the study of temperature distribution in order to detect zones in which there is possibility of low temperature zones and occurrence of heat stresses
Numerical analysis of ammonia combustion as a non-carbon alternative fuel in an experimental premixed burner
No full textAmonijak predstavlja bezugljično alternativno gorivo i moguće rješenje u tranziciji prema niskougljičnoj ekonomiji, ali kinetika izgaranja je i dalje aktualan istraživački problem. U ovom radu provedena je simulacija izgaranja amonijaka u eksperimentalnom predmiješanom gorioniku. Analizirani su utjecaji različitih modela turbulencije na polja fizikalnih svojstava te koncentracije produkata na izlazu simulacijske domene. Za izradu rada korišten je programski paket za računalnu dinamiku fluida baziran na metodi kontrolnih volumena.
Cilj ovoga rada je unaprijediti razumijevanje procesa izgaranja amonijaka za industrijske radne uvjete variranjem modela turbulencije te omjera gorivo/zrak. Primjena različitih modela turbulencije je pokazala zadovoljavajuća podudaranja s eksperimentalnim mjerenjima. Simulacije predviđaju razine CO2 niže od eksperimentalnih, ali pokazuju isti trend variranjem omjera gorivo/zrak. Predviđanja koncentracija NO pokazuju zadovoljavajuću točnost u usporedbi s eksperimentalnim vrijednostima za slučaj blizu stehiometrijskog omjera. Ovaj rad doprinosi širenju trenutnog znanja o izgaranju amonijaka pri radnim uvjetima usko nalik onima u industrijskim postrojenjima. Očekuje se da saznanja iz ovog rada pomognu pri budućim analizama prilikom konstruiranja stvarnih industrijskih sustava za izgaranje amonijaka.Ammonia represents an alternative carbon-free fuel and a possible solution towards transition to a low carbon economy, although combustion kinetics is currently still a major problem. In this work, simulation of ammonia combustion in an experimental premixed burner has been conducted. The effect of different turbulence models on physical value fields, as well as species concentrations at the domain outlet was analysed. For this work, a computational fluid dynamics software based on the finite volume method was used.
The object of this work is to enhance the current understanding of the ammonia combustion process for industrial operating conditions by varying turbulence models and fuel/air ratio. Application of various turbulence models has shown satisfactory agreement to experimental measurements. Predictions of CO2 concentrations were lower than experimental measurements, although a similar trend by varying fuel/air ratio was achieved. Predicted NO concentrations were matched with experimental data for the case nearest to stoichiometric conditions. This work contributes to the extension of current knowledge of ammonia combustion at operating conditions closely resembling those in industrial plants. It is expected that obtained findings from this work will help in future analysis while designing real industrial systems for ammonia combustion
Energy equilibrium analysis in the effervescent atomization
No full textAbstract In this paper, the flow characteristics and energy equilibrium analysis of the effervescent atomization had been investigated theoretically and experimentally. The effect of the gas–liquid rate (GLR from 0.04 to 0.15) on the atomization stability was revealed. When the GLR was small, the atomization was unstable. The atomization was gradually stable with an increase in the GLR. The optimal atomization region can be obtained. The Sauter mean diameter (SMD) of the droplets was measured by the phase Doppler analyzer. The SMD decreases with an increase in the GLR. The energy equilibrium analysis was investigated for the swirl atomizer theoretically and experimentally. The results show that the energy dissipation terms are mainly compressed gas expansion, liquid viscosity dissipation, and resistance losses. However, the ratio of the spray kinetic energy and the surface tension energy to the total energy is small
The influence of the processing parameters on the porosity and microhardness of sintered Ti-20Nb biomedical alloy
No full textTitanium based alloys are increasingly used in biomedicine due to their favourable properties. However, because of their high cost, new methods are being developed to produce more economical alloys. Therefore, in the framework of this work, Ti-20Nb alloy was produced by powder metallurgy. Namely, experimental alloy was prepared by mechanical alloying in a ball mill. The samples were singled out from the powder mixture and pressed on a hydraulic press. Sintering was carried out in a tube furnace in an argon atmosphere. Different processing parameters regarding the time and temperature of sintering were applied. Chemical homogeneity was analysed using the energy-dispersive spectrometry. Porosity was observed using the light microscope and microhardness was determined by Vickers method. The obtained results show that with a small correction of the applied technological parameters, in terms of time extension of mixing/mechanical alloying, it is possible to produce economically Ti-20Nb alloy having the properties suitable for biomedical application by using powder metallurgy technology
Influence of graphene oxide on photocatalytic properties of titan (IV) oxide
No full textPorastom broja stanovništva dolazi do razvoja industrije što uzrokuje veću potrebu za proizvodnjom i uporabom različitih pesticida, farmaceutika i drugih proizvoda, klasificiranih kao mikro onečišćivači koji imaju velik negativan utjecaj na vodeni okoliš. Porast koncentracije mikroonečišćivača u prirodi dovodi do potrebe pronalaska načina u kojem bi iste uklonili ili preveli u bezopasan oblik. Jedna od modernih metoda uklanjanja farmaceutika iz vode dolazi korištenjem naprednih oksidacijskih tehnika, to jest fotokataliza.
U ovome radu pripravljeni su fotokatalizatorinanašanjem titan (IV) oksida sa i bez grafen oksida na staklene mrežice sol-gel postupkom te su uspoređena njihova fotokatalitička svojstva. Fotokataliza se provodila u reaktoru s UV lampom te se reakcija pratila kroz degradaciju salicilne kiseline UV/VIS spektrofotometrom.Najbolji rezultati dobiveni su korištenjem čistog titan (IV) oksida bez prisustva grafen oksida. Uspješno nanašenje fotokatalizatora je potvrđeno vizualno i SEM analizom.The increase in population leads to the development of industry, which causes a greater need for the production and use of various pesticides, pharmaceuticals and other products, classified as micro-pollutants than have negative side effects on water ecosystem. The increase in the concentration of micro-pollutants in nature leads to the need for a way in which they would be removed or converted into a harmless form. One of the modern methods of removing pharmaceuticals from water comes by using advanced oxidation techniques, i.e. photocatalysis.
In this work photocatalysts were prepared by applying titanium (IV) oxide with and without graphene oxide onto glass fibres with sol-gel process and their photocatalytic properties were compared. Photocatalysis was performed in a reactor with a UV lamp and the reaction was monitored through the degradation of salicylic acid by UV / VIS spectrophotometer. The best results were obtained using pure titanium (IV) oxide without the presence of graphene oxide. Successful photocatalyst application was confirmed visually and by SEM analysis
Experimental and numerical investigation of cyclic creep and recovery behavior of bovine cortical bone
No full textAn experimental and numerical study of the creep behavior of the bovine metatarsal cortical bone is presented. The experimental procedure included the multiple cycle tensile creep-recovery tests at eleven creep stress levels between 20 and 120 MPa. The threshold values of stress above which viscoplastic strain and damage start to accumulate are determined. Furthermore, based on the experimental data, a one-dimensional constitutive model has been developed. We demonstrate that Abdel-Tawab's viscoelasticity/damage model combined with the viscoplastic model proposed by Zapas and Crissman can predict the nonlinear behavior of cortical bone tissue subjected to creep-recovery loading conditions. Within the framework of numerical investigations, an efficient algorithm for the integration of the proposed constitutive model at the material point level is derived and implemented into the finite element software ABAQUS using user subroutines. The computational algorithm shows a good capability to describe the tensile behavior of bovine cortical bone for the specific mechanical conditions analyzed
Greenhouses gases from the process of aluminium production and the possibilities of their reduction
Get PDFU ovom radu prikazan je pregled emisija stakleničkih plinova koji nastaju proizvodnjom
primarnog aluminija te potencijalne mogućnosti za njihovo smanjenje. Staklenički plinovi
imaju veliki utjecaj na zdravlje ljudi i cjelokupni okoliš te im se iz tog razloga posvećuje velika
pažnja. Uz emisije stakleničkih plinova ugljikovog (IV) oksida (CO2) i perfluorougljika, PFC
(CF4, C2F6) za vrijeme proizvodnje primarnog aluminija nastaju druge onečišćujuće tvari poput
crvenog mulja, prašine te plinova, kao što su fluoridi, sumporovi, dušikovi oksidi i mnogi drugi.
Najveće količine emisija stakleničkih plinova nastaju prilikom elektrolitičke redukcije glinice
što uvelike ovisi o vrsti tehnologije koja se upotrebljava. Tehnologije se dijele s obzirom na
vrstu anode koja se upotrebljava kao i prema načinu na koji se glinica dodaje u ćeliju. Primarna
emisija koja nastaje prilikom elektrolitičke redukcije je CO2, nakon čega slijede emisije PFC.
Emisije CO2 nastaju kao posljedica potrošnje ugljičnih anoda te kao posljedica reakcije između
ugljičnih anoda, glinice i taline kriolita za vrijeme elektrolitičke redukcije. Emisije PFC nastaju
kao posljedica poremećaja u radu elektrolitičke ćelije (tzv. anodni efekt). Prilikom rada
elektrolitičke ćelije u normalnim uvjetima emisije, PFC se emitiraju u nemjerljivim količinama.
Kako bi se količine spomenutih emisija mogle smanjiti upotrebljavaju se neke od mogućnosti
smanjenja stakleničkih plinova, kao i kontrola njihovog ispuštanja.This paper gives an overview of green-house emissions created during the production of
primary aluminium and different possibilities of their reduction. Greenhouses gasses have a
major impact on human health and the environment and therefore deserve great attention. In
addition to the greenhouse gas emissions of carbon (IV) oxide (CO2) and perfluorocarbon ,PFC
(CF4, C2F6), other pollutants such as red mud, dust and gases, such as fluorides, sulfur, nitrogen
oxides and many others, are produced during the production of primary aluminum. During the
process of electrolytic reduction of alumina largest amount of greenhouse gases are released,
which depends on the technology being used. The technologies available can be divided based
on the type of anode used in the process, as well as the method of adding alumina to the reaction
cell. The primary emission during electrolytic reduction is CO2, after which perfluorocarbons
follow. CO2 emissions are a product of carbon anodes consumption and a consequence of
reactions between the anodes, alumina and cryolite melt during the electrolytic reduction. PFC
emissions are a product of disturbances in the operation of electrolytic cell, the so-called anode
effect. During normal workflow amount of perfluorocarbon are released in non-traceable
amounts. In order to reduce the amounts of the aforementioned emissions, some of the
possibilities of reducing greenhouse gases, as well as the control of their discharge, are used
Characterization of microstructure of sintered titanium-niobium alloy for biomedical application
Get PDFLegure titana, zbog svojih povoljnih svojstava, pronalaze sve veću primjenu u
biomedicini. Međutim, zbog njihove visoke cijene, danas se sve više razvijaju i koriste nove
metode s ciljem proizvodnje ekonomičnijih legura. Stoga je u okivru ovog rada za
proizvodnju legure Ti80Nb20 korištena tehnologija metalurgije praha.
Istraživana titan-niobij legura pripravljena je iz elementarnih prahova miješanjem
odnosno mehaničkim legiranjem u kugličnom mlinu. Nakon toga je iz smjese izdvojeno 8
uzoraka koji su prešani na hidrauličnoj preši, te sinterirani u cijevnoj peći u zaštitnoj atomsferi
argona. Mikrostruktura sinteriranih uzoraka je karakterizirana različitim metodama kako bi se
utvrdili optimalni tehnološki parametri za postizanje mikrostrukture sa zadovoljavajućim
karakteristikama za primjenu u biomedicini.
Dobiveni rezultati pokazuju da je uz malu korekciju primijenjenih tehnoloških
parametara, u smislu produžavanja vremena miješanja/mehaničkog legiranja, primijenjenom
tehnologijom metalurgije praha moguće ekonomično proizvesti Ti80Nb20 leguru sa svojstvima
povoljnim za biomedicinsku primjenu.Due to their favourably properties, titanium alloys are increasingly used in
biomedicine. However, because of their high cost, new methods are being developed and used
today to produce more economical alloys. Therefore, in the frame of this work, powder
metallurgy was used to produce Ti80Nb20 alloy.
The investigated titanium-niobium alloy was prepared from elemental powders by
mixing i.e. mechanical alloying in a ball mill. After that, 8 samples singled out from the
mixture were pressed on a hydraulic press and sintered in a tube furnace in a protective
atmosphere of argon. For the characterization of the microstructure of sintered samples
various methods were applied to determine the optimal technological parameters for
achieving microstructure with satisfactory characteristics for biomedical applications.
The obtained results show that with a small correction of the applied technological
parameters, in terms of time extension of mixing/mechanical alloying, it is possible to
economically produce Ti80Nb20 alloy with properties suitable for biomedical application by
using powder metallurgy technology
The effect of annealing time on microstructure and impact energy of stainless steel AISI 316L
Get PDFIn this work the results of microstructural analysis and impact energy testing of austenitic stainless steel AISI 316L were carried out. Investigations were performed before and after annealing at 850 °C. Annealing time in this investigation varied from 30 to 90 minutes. After annealing, the samples were cooled in room temperature air. Microstructural analysis of initial rolled and different annealed states was performed by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with device for energy dispersive spectroscopy (EDS). Impact tests were performed on Charpy V-notch specimens at room temperature. Initial rolled state of investigated steel showed the presence of typical elongated polygonal grains austenite and delta ferrite while annealed states showed the presence and evolution of sigma phase in microstructure. Impact energy value of initial rolled state was 260 J and by increasing annealing time it decreases