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Performance analysis of a plate heat exchanger using various nanofluids
No full textIn this paper, a corrugated plate heat exchanger in solar energy systems is used to investigate heat transfer and fluid flow characteristics of various nanofluids. By adding various nanoparticles (Al2O3-30 nm, SiC-40 nm, CuO-30 nm and Fe3O4-25 nm) into the base fluid, effects of nanofluid types and particle concentrations (0.05 wt.%, 0.1 wt.%, 0.5 wt.% and 1.0 wt.%) on the thermal performance of the plate heat exchanger are analyzed at flow rates in the range of 3–9 L/min. Results indicate that both heat transfer enhancement and pressure drop for nanofluids show significant increases compared to the base fluid. The Fe3O4-water and CuO-water nanofluids show the best and the worst thermal performances of the plate heat exchanger, respectively. When 1.0 wt.% Fe3O4-water nanofluid is used as the working fluid, compared to DI-water, the convective heat transfer coefficient is increased by 21.9%. However, an increase of 10.1% in pressure drop is obtained for the 1.0 wt.% Fe3O4-water nanofluid. Finally, empirical formulas of experimental Nusselt number are obtained based on the experimental data. A new way to predict the thermal performance for various nanofluids in heat transfer systems is provided. © 2020 Elsevier Lt
Disposal and utilization of red mud
No full textZbog sve većeg porasta potražnje aluminijskih proizvoda javlja se globalni problem zbrinjavanja velikih količina crvenog mulja, koji nastaje kao nusprodukt pri proizvodnji glinice Bayerovim postupkom. Ekološki problemi vezani uz odlaganje crvenog mulja su njegov visoki pH, mogućnost prodiranja lužine, teških metala i radionuklida u tlo i podzemne vode; emisije čestica crvenog mulja u zrak te potreba velikih površina za odlaganje, što ga svrstava u kategoriju opasnog otpada. Iz tih razloga njegovo sigurno odlaganje, obrada i skladištenje zasigurno predstavlja velike izazove u gospodarenju otpadom.
Crveni mulj se može odlagati suhim (slojevito odlaganje i odlaganje „kolača“) ili mokrim (odlaganje u rijeke / mora i odlaganje u zemljane bazene / lagune) postupcima. U prošlosti je najzastupljenije bilo odlaganje mokrim postupcima, dok su danas najčešće zastupljeni suhi načini odlaganja crvenog mulja. Da bi se smanjila potreba za velikim površinama za odlaganje crvenog mulja (godišnje se generira više od 120 mil. t crvenog mulja u cijelom svijetu), otvaraju se različite mogućnosti njegove upotrebe, kao što su izdvajanje metala (npr. željeza), primjena u građevinskim materijalima, za sanaciju tla, za boje i pigmente, kao pročišćivač vode, koagulant, adsorbens itd.Due to increaseofdemand for aluminiumproductsthereis a global problem ofdisposallargequantitiesof red mud. Red mudisgenerated as a nusproductofaluminaproductionbyBayer'sprocess. Environmentalproblemsrelatedwith red muddisposal are high pH; alkali, heavy metalsandradionuclidesleakageintosolidandundergroundwaters, alkalineairbornedustemissions, vastareaoflandrequired for disposal, whichputs red mudinthecategoryofhazardouswaste. For thisreasonsit'ssafedisposal, processing andstorageis for sure a major challengeinwaste management.
Red mudcouldbedisposedbydry (drystackingmethodanddry cake disposalmethod) orwet (marine disposalandlagooning) methods. In the past most commonwaswetdisposal, but todaywe use drydisposalmethods. To decreasethenecessity for largespaces for disposal (thereis 120 mil. t of red mudgenerated on a yearlybasicsinthewholeworld) differentposibilitiesofit'susage are opening, for example, metal recovery (for exampleiron), applicationinconstructionmaterials, for soilremediation, paintsandpigments, applicationinwastewatertreatment, coagulant, adsorbents, etc
Steel scrap as a secondary raw material for steel production
No full textČelik je materijal koji se najviše koristi od svih metala i to u svim granama industrije (npr. metaloprerada, transport, poljoprivreda, rudarstvoitd.) zbog svojih dobrih svojstava kao što su čvrstoća, žilavost, rastezljivost i sl. Proizvodnja čelika se može podijeliti na dva osnovna načina: proizvodnja u integralnim željezarama i pretaljivanje čeličnog otpada. Suvremena proizvodnja čelika sastoji se od tri vrste metalnog uloška koji može biti u obliku sirovog željeza, čeličnog otpada i direktno reduciranog željeza. U grupu primarnih sirovina za proizvodnju čelika ubrajaju se sirovo željezo i produkti direktne redukcije, dok čelični otpad predstavlja sekundarnu sirovinu. Cilj ovog rada bio je ukazati na važnost primjene čeličnog otpada kao sekundarne sirovine te koliko se takvim načinom proizvodnje čelika pridonosi uštedi energije odnosno zaštiti okoliša. Pregledom dostupne literature, dan je poseban osvrt na kvalitetu i klasifikaciju čeličnog otpada, pripremu čeličnog otpada za proizvodnju čelika kao i osnovni postupci proizvodnje čelika koji kao sekundarnu sirovinu koriste čelični otpad.Steel is the material which from all metals in all branches of industry is mostly used (eg. metal processing, transport, agriculture, mining, etc.) due to it's good properties such as strength, toughness, elongation, etc. Steel production can be divided into two basic processes: production in integral steelworks and remelting of steel scrap. Modern steel production consists of three types of metal charge which can be in the form of pig iron, steel scrap and directly reduced iron. The group of primary raw materials for steel production includes pig iron and direct reduction products, while steel scrap is a secondary raw material. The aim of this paper was to point out the importance of steel scrap use as a secondary raw material and the extent to which such a method of steel production contributes to energy savings and environmental protection. By the review of available literature, a specific overview was given to the quality and classification of steel scrap, the preparation of steel scrap for steel production as well as the basic processes of steel production that use steel scrap as a secondary raw material
Influence of Strip Cooling Rate on Lüders Bands Appearance During Subsequent Cold Deformation
No full textThis paper presents the results of study of Lüders bands appearance on hot rolled strip during cold deformation. The research was carried out on niobium microalloyed steel. After the thermomechanical treatment the strip was cooled at different rates. Samples taken from hot rolled strip were tested by stretching to fracture with simultaneous application of the methods thermography and digital image correlation. The analysis of measurement results was performed with the software packages IRBIS 3 professional and MatchID. Significant differences were found in the samples tested at different cooling rates. In the samples cooled at a lower cooling rate, the appearance of Lüders bands in the elastoplastic area was determined. The appearance of Lüders bands was not observed in the samples cooled at a higher rates
Aging of photocatalysis based on titanium(IV) oxide and carbon nanotubes
No full textOnečišćenje vode postaje sve veći globalni problem.Jedan od problema predstavljaju mikroonečišćivačikoji zahtijevaju posebne uvjete pročišćavanja, a u tu skupinu onečišćivača spadaju farmaceutici. Jedan od učinkovitijih načina njihova uklanjanja su napredni oksidacijski procesi, u koje spada i fotokataliza. Za proces fotokatalize potreban je fotokatalizator koji će prilikom djelovanja UV zračenja stvoriti hidroksilne radikale. Jedan od najkorištenijih fotokatalizatora je TiO2, koji se radi poboljšavanja svojstava može kombinirati s ugljikovim nanocijevima.
U ovom radu su pripremljene dvije vrste fotokatalizatora, TiO2 i TiO2/MWCNT čije je uspješno vezanje na staklenu mrežicu potvrđeno SEM i EDS analizom. Fotokatalitička svojstva ispitana su prije i nakon starenja fotokatalizatora u vodi i zraku. Iz dobivenih rezultata je utvrđeno da starenjemfotokatalizatora njihova svojstva opadaju te se kao najbolji fotokatalizatoru ovome radu pokazao TiO2.Water pollution is becoming an increasing global problem. One of the problems is posed by micro-pollutants that require special purification conditions. This group of contaminants includes pharmaceuticals. One of the most effective ways to remove them are advanced oxidation processes, which include photocatalysis. The process of photocatalysis requires a photocatalyst that will create hydroxyl radicals under the action of UV radiation. One of the most widely used photocatalysts is TiO2, which can be combined with carbon nanotubes to improve properties.
In this paper, two types of photocatalysts were prepared, TiO2 and TiO2 / MWCNT, whose successful binding to the glass mesh was confirmed by SEM and EDX analysis. Photocatalytic properties were investigated before and after aging of photocatalysts in water and air. From the obtained results, it was determined that with the aging of photocatalysts, their properties decrease, and TiO2 proved to be the best photocatalyst in this work
Povijesni pregled metalurških aktivnosti na tlu Republike Hrvatske
No full textMetalurške aktivnosti vezane za bakreno i brončano doba na tlu Republike Hrvatske prisutne su u periodu od 6000 godina, a i proizvodnja željeza pojavila se gotovo u isto vrijeme s početkom željeznog doba na tlu Europe. U uvodu rada istaknuta je važnost proizvodnje metala iz ruda u povijesti razvoja ljudskog roda. U nastavku je prikazan povijesni razvoj metalurških aktivnosti na tlu Republike Hrvatske u razdobljima Starog doba, Srednjeg vijeka, Novog vijeka te nakon Prvog svjetskog rata do današnjih dana. Iz razloga što je nemoguće izdvojiti razvitak metalurgije na ovom prostoru bez za nju vezanog rudarstva daje se i kratki prikaz rudarenja na rude metala. Posebice je dan naglasak na povijesni pregled rudarstva i metalurgije na području Trgovske gore. Naime, metalurgija se na području Siska i Banovine razvila od vučedolske kulture te Ilira, Kelta i Rimljana koji su rudarili na području Trgovske gore na rude bakra, željeza i srebronosne rude olova te ih prerađivali u gotove proizvode
Numerical analysis of sulfur dioxide absorption in water droplets
No full textAbstract Mass transfer between the phases is a cornerstone of many technological processes and presents a topic whose understanding and modelling is of high importance. For instance, absorption of gases in liquid droplets is an underlying phenomenon for the desulfurization of flue gases in wet scrubbers. Wet scrubbing is an efficient cleaning method where the liquid is sprayed in a stream of rising gases, removing pollutants due to the concentration difference between the gas phase and droplets. A model for absorption in water droplets has been developed to describe the complex physical and chemical interactions during the exposure to flue gases. The main factors affecting the absorption are the mass transfer of pollutants through the gas–droplet interface and the aqueous phase chemistry in a droplet. The mass transfer coefficient, which has been modeled with several approaches, is the most significant parameter regulating the absorption dynamic into the droplet, while the in-droplet chemistry controls the maximum quantity of dissolved pollutants. Dissociation of sulfur dioxide and the chemical reactions in seawater have been described by the equilibrium reactions. Afterward, the influence of the mass transfer coefficient has been investigated, and the model has been validated against the literature data on a single droplet scale. Obtained results are comparable with the experimental measurements and indicate the applicability of the model for the design and development of industrial scrubbers
Anisotropic behavior of hot rolled strip during cold deformation
No full textČelik je danas najrasprostranjeniji materijal u svijetu. U svjetskoj proizvodnji čelika valjanje je najčešći proces deformacije. Posljednjih godina razvijaju se novi materijali i nove tehnologije oblikovanja deformacijom. Iz tog razloga nameće se potreba detaljnijeg poznavanja anizotropnih svojstava metalnih materijala, posebno čelika. U ovom radu istražena je anizotropija toplovaljane trake iz niskougljičnog čelika statičkim vlačnim pokusom, metalografskom analizom mikrostrukture, metodama termografije i digitalne korelacije slike, te numerički. Utvrđena je niska anizotropija toplovaljane trake, prihvatljiva za tehnologije dubokog izvlačenja. Posebno je istražen utjecaj stupnja deformacije na anizotropno ponašanje toplovaljane trake pri hladnoj deformaciji. Utvrđeno je da do ukupne deformacije od 30% ne postoji anizotropno ponašanje toplovaljane trake tijekom hladne deformacije. Nakon ukupne redukcije od 30% utvrđena je određena anizotropija tijekom hladne deformacije toplovaljane trake. Pokazalo se da su metode termografije i digitalne korelacije slike vrlo pogodne za istraživanje anizotropnog ponašanja toplovaljane trake kod hladne deformacije.Steel is today the most widely used material in the world. In world steel production, rolling is the most common deformation process. In recent years, new materials and new deformation forming technologies have been developed. For this reason, there is need for more detailed knowledge of the anisotropic properties of metallic materials, especially steel.In this paper, anisotropy of hot rolled low carbon steel strip was investigated by static tensile test, metallographic analysis, thermography. digital image correlation and numerical.Low and acceptable anisotropy of hot rolled strip was determined for deep drawing technologies. In particular, the influence of the degree of deformation on the anisotropic behavior of hot rolled strip at cold deformation was investigated. It was found that up to a total deformation of 30% there is no anisotropic behavior of the hot rolled strip during cold deformation. After a total reduction of 30%, certain anisotropy was determined during the cold deformation of the hot-rolled strip. The methods of thermography and digital image correlation have been shown to be very suitable for investigating the anisotropic behavior of the hot spot strip in cold deformatio
Effect of boron and tungsten carbides on the properties of TiC-reinforced tool steel matrix composite produced by powder metallurgy
No full textThe influence of boron carbide and tungsten carbide on the apparent porosity, density, coercive force, hardness and microstructure of metal matrix composite of the Ferro-TiC type, is presented in this paper. The samples of investigated steel/titanium carbide composite were produced by powder metallurgy process, i.e. by powders mixing and compacting followed by sintering in the vacuum furnace. According to the results, steel/titanium carbide composite materials with addition up to 11.9 vol.% of boron carbide are interesting to detailed investigation as well as materials having more than 17.2 vol.% of tungsten carbide because these compositions show significant changes in hardness and coercive force values
Vježbe iz korozije i zaštite metala
No full textKorozija je proces koji dovodi do propadanja materijala uslijed mehaničkog, biološkog ili
kemijskog djelovanja. Osim što zbog korozije nepovratno propada velik broj konstrukcija,
proizvoda i sl., uzrokujući materijalne gubitke i zastoje proizvodnje, korozija negativno
djeluje i na radni okoliš i zdravlje ljudi na radu. Stoga se u praksi primjenjuju mnogobrojni
načini zaštite od korozije, a najčešće upotrebljavani su zaštita metalnim prevlakama,
elektrokemijska zaštita i zaštita primjenom inhibitora.
Ova skripta obuhvaća upute za izvođenje laboratorijskih vježbi iz područja korozije i zaštite
metala te je koncipirana na način da su na početku svake laboratorijske vježbe dane kratke
teorijske osnove, zatim je detaljno objašnjen sami eksperiment s prikazom odgovarajuće
aparature te je dana obrada rezultata.
Kroz jedanaest laboratorijskih vježbi obrađena su sljedeća područja:
- visokotemperaturna plinska korozija,
- elektrokemijska korozija,
- određivanje brzine korozije metodom prirasta i gubitka mase,
- određivanje korozijskih parametara na osnovu primjene različitih elektrokemijskih
metoda,
- zaštita metala kemijskim dobivanjem metalnih i nemetalnih prevlaka,
- zaštita metala dobivanjem prevlaka primjenom električne energije (galvanizacija),
- elektrokemijska zaštita metala,
- zaštita metala obradom korozivne sredine (dodatak inhibitora korozije s naglaskom na
primjenu ekološki prihvatljivih inhibitora),
- napetosna korozija i utjecaj statičkog naprezanja na brzinu korozije metala
napregnutog u otopini elektrolita,
- difuzija vodika i vodikova krhkost kao specijalni oblik napetosne korozije i kao
fenomen prisutan u različitim industrijama.
Nastavni materijal Vježbe iz Korozije i zaštite metala izrađen je u skladu s nastavnim
programom kolegija Korozija i zaštita metala. Namijenjen je studentima prve godine
diplomskog sveučilišnog studija Metalurgija, a sve u svrhu njihovog razumijevanja različitih
vrsta korozijskih procesa i primjene određenih metoda zaštite metala od korozije u
metalurškom inženjerstvu i ostalim proizvodnim procesima