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285 results on '"Medved', Igor"'

7. Modeling of a heat capacity peak and an enthalpy jump for a paraffin-based phase-change material

Author

Medved', Igor, Trnik, Anton, and Vozar, Libor

Subjects
Condensed Matter - Materials Science
Abstract

Rubitherm RT 27 is a paraffin-based phase-change material (PCM) in which a change between a solid and liquid phase is used to store/release thermal energy. Its enthalpy and heat capacity, as measured in a quasistatic regime by adiabatic scanning calorimetry, has a single distinct jump and peak, respectively, at about 27.3 C. We present a microscopic development from which the jump and peak can be accurately fitted and that could be analogously applied even to other PCMs. It enables us to determine the baseline and excess part of the heat capacity and thus the latent heat associated with the phase change. It is shown to be about 84 % of the total enthalpy change that occurs within 5 C from the peak maximum position. The development is based on the observation that PCMs often have polycrystalline structure, being composed of many single-crystalline grains. The enthalpy and heat capacity measured in experiments are therefore interpreted as superpositions of many contributions that come from the individual grains., Comment: 10 figures

Published
2016

8. Use of Secondary Aggregates for Concrete Production

Author

Chystiakov, Artem, Kroviakov, Sergii, Ihnatenko, Andrii, Medved, Igor, Chystiakov, Artem, Kroviakov, Sergii, Ihnatenko, Andrii, and Medved, Igor

Abstract

The properties of concretes based on different types of secondary coarse and fine aggregates were studied experimentally with a view to their potential for the construction of pavement layers. Namely, the prototypes were tested for compressive and flexural strengths, water absorption, and frost resistance. The results show that these concretes are characterized by fairly high tensile strength and frost resistance, which is an important requirement for road pavements. Thus, the use of secondary coarse and fine aggregates in pavement concretes could be a plausible solution from the viewpoint of both construction and environmental sustainability.

Published
2024

9. Sustainable Energy Solutions: Utilising UGS for Hydrogen Production by Electrolysis.

Author

Zelenika, Ivan, Novak Mavar, Karolina, Medved, Igor, and Pavlović, Darko

Subjects
RENEWABLE energy sources, CLEAN energy, GREEN fuels, HYDROGEN as fuel, NATURAL gas storage
Abstract

Increasing the share of renewable energy sources (RESs) in the energy mix of countries is one of the main objectives of the energy transition in national economies, which must be established on circular economy principles. In the natural gas storage in geological structures (UGSs), natural gas is stored in a gas reservoir at high reservoir pressure. During a withdrawal cycle, the energy of the stored pressurised gas is irreversibly lost at the reduction station chokes. At the same time, there is a huge amount of produced reservoir water, which is waste and requires energy for underground disposal. The manuscript explores harnessing the exergy of the conventional UGS reduction process to generate electricity and produce hydrogen via electrolysis using reservoir-produced water. Such a model, which utilises sustainable energy sources within a circular economy framework, is the optimal approach to achieve a clean energy transition. Using an innovative integrated mathematical model based on real UGS production data, the study evaluated the application of a turboexpander (TE) for electricity generation and hydrogen production during a single gas withdrawal cycle. The simulation results showed potential to produce 70 tonnes of hydrogen per UGS withdrawal cycle utilising 700 m3 of produced field water. The analysis showed that hydrogen production was sensitive to gas flow changes through the pressure reduction station, underscoring the need for process optimisation to maximise hydrogen production. Furthermore, the paper considered the categorisation of this hydrogen as "green" as it was produced from the energy of pressurised gas, a carbon-free process. [ABSTRACT FROM AUTHOR]

Published
2024
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10. Reducing Torque and Drag in Extended-Reach Wells Using Thermoplastic Polymers for Protective Sliding Rings.

Author

El Sabeh, Karim, Pašić, Borivoje, Mijić, Petar, and Medved, Igor

Subjects
MECHANICAL wear testing, MECHANICAL wear, LUBRICANT additives, FRICTION, MUD
Abstract

Extended-reach drilling represents an advanced way of drilling and accessing reservoirs that were previously economically not feasible to drain, impossible to reach or in an environmentally sensitive area. One of the main issues that appears while drilling such wells is caused by the high values of friction factor which cause high values of torque and drag. One of the suggested solutions is to use a protective sliding ring made from materials such as POM, Teflon and PA6 in combination with lubricants added to a polymer mud system. First, measurements were conducted on a lubricity tester to choose the best material and, after finishing, a mechanical wear test was conducted on a specially designed device to measure mechanical wear. Results showed that Teflon showed lower values of friction factor in comparison to steel and the mechanical wear was minimal. The lowest value of friction force was recorded for blocks made from Teflon in tested mud systems. It is also noticeable that, in polymer mud with weighting additives and lubricant, the value of the friction force is higher than in polymer mud with lubricant only. [ABSTRACT FROM AUTHOR]

Published
2024
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11. Evaluation of Moisture Diffusivity from Pore Distribution Curves for a Ceramic Brick.

Author

Medved', Igor and Černý, Robert

Subjects
*MOISTURE, *PORE size distribution, *PLASTER, *POROUS materials, *THERMAL diffusivity, *WATER distribution, *ABSORPTION coefficients, *CERAMICS
Abstract

The 1D moisture diffusivity of porous materials may strongly depend on the content of moisture in the materials, varying over an order of magnitude or more. In this paper we present a new model from which the diffusivity can be evaluated, using the pore size distribution and water absorption coefficient. We point out that this is a more efficient approach than the standard Boltzmann–Matano (BM) method, because measurements of pore curves and water absorption are much shorter and rather accurate compared to moisture profile experiments needed in the BM method. As an example, we apply our model to two samples of a ceramic brick for which experimental data on both pore curves and moisture profiles had been measured. A very good quantitative agreement in the diffusivity is obtained for early stage profiles. For later stages, however, the model predicts three to four times higher diffusivity than the BM method. The reasons for this discrepancy are discussed and further tasks to validate the effectiveness of the new model are proposed. We also compare our model with the pore models of Burdine and Mualem. [ABSTRACT FROM AUTHOR]

Published
2024
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13. Competing effects of interactions in the adsorbed and activated states on surface diffusion at low temperatures

Author

Medved', Igor, Trnik, Anton, and Cerny, Robert

Subjects
Condensed Matter - Statistical Mechanics
Abstract

The competing influence of two types of interactions on surface diffusion is investigated: one of them, epsilon, acts between adsorbed particles, while the other one, eta, between activated and adsorbed particles. To this end, a specific lattice-gas model on a triangular, square, and hexagonal lattice is considered with an attractive epsilon and an attractive or repulsive eta, both restricted to nearest neighbors. For all three lattices the influence is qualitatively the same. Namely, when eta is neglected, then epsilon is shown to decelerate diffusion with a rate exponential in epsilon and inverse temperature. Moreover, when eta is present and epsilon is fixed, then a sufficiently attractive eta (relative to epsilon) accelerates diffusion exponentially fast in eta and inverse temperature. However, quite surprisingly, a repulsive or slightly attractive eta has practically no effect on diffusion. Finally, when eta is set proportional to epsilon via a parameter $a$, surface diffusion is exponentially accelerated (decelerated) for $a$ above (below) a threshold value equal to 4, 5/4, and 7/8 for the three lattices. Thus, an eta of strength comparable to epsilon is enough to boost diffusion on the square and hexagonal lattices, while an eta of a rather large strength is needed for the boost on the triangular lattice., Comment: 19 pages, 9 figures

Published
2013

14. Surface diffusion coefficient near first-order phase transitions at low temperatures

Author

Medved', Igor and Trnik, Anton

Subjects
Condensed Matter - Statistical Mechanics
Abstract

We analyze the collective surface diffusion coefficient, $D_c$, near a first-order phase transition at which two phases coexist and the surface coverage, $\te$, drops from one single-phase value, $\te_+$, to the other one, $\te_-$. Contrary to other studies, we consider the temperatures that are sufficiently sub-critical. Using the local equilibrium approximation, we obtain, both numerically and analytically, the dependence of $D_c$ on the coverage and system size, $N$, near such a transition. In the two-phase regime, when $\te$ ranges between $\te_-$ and $\te_+$, the diffusion coefficient behaves as a sum of two hyperbolas, $D_c \approx A/N|\te - \te_-| + B/N|\te - \te_+|$. The steep hyperbolic increase in $D_c$ near $\te_\pm$ rapidly slows down when the system gets from the two-phase regime to either of the single-phase regimes (when $\te$ gets below $\te_-$ or above $\te_+$), where it approaches a finite value. The crossover behavior of $D_c$ between the two-phase and single-phase regimes is described by a rather complex formula involving the Lambert function. We consider a lattice-gas model on a triangular lattice to illustrate these general results, applying them to four specific examples of transitions exhibited by the model., Comment: 17 pages, 3 figures

Published
2012
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15. Collective surface diffusion near a first-order phase transition

Author

Medved', Igor and Trník, Anton

Subjects
Condensed Matter - Statistical Mechanics
Abstract

For a large class of lattice models we study the thermodynamic factor, $\Phi$, of the collective surface diffusion coefficient near a first-order phase transition between two phases at low temperatures. In a two-phase regime its dependence on the coverage, $\te$, is $\Phi \approx \te/[(\te-\te_-)(\te_+ - \te)N]$, where $N$ is the number of adsorption sites and $\te_\pm$ are the single-phase coverages at the transition. In the crossover between the two-phase and single-phase regimes $\Phi(\te)$ is shown to have a more complex behavior. The results are applied to a simple 2D lattice model., Comment: 9 pages, 4 figures

Published
2011
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18. THE INFLUENCE OF MANDARIN PEEL POWDER ON FILTRATION PROPERTIES AND TEMPERATURE STABILITY OF WATER-BASED DRILLING MUD

Author

Medved, Igor, Pašić, Borivoje, Mijić, Petar, Medved, Igor, Pašić, Borivoje, and Mijić, Petar

Abstract

The growing energy demand in the world, as well as the current geopolitical situation, require countries to additional investments in the exploration and production of hydrocarbons from their own sources. This means that companies must develop new fields which have remained undeveloped until now mostly because extremely harsh environment where they are located (deep sea, high temperature, high pressure, heavy oils, etc.). The development of these new fields requires the development and adoption of new technology, among other things, and the development of a temperature-stable drilling fluid system able to fulfil all tasks according to the new technical challenges. Except for the technological challenges, there are also growing concerns related to the influence of the drilling operation on the environment. All of the above encourage the industry to develop new, inexpensive, and environmentally friendly additives which will be able to satisfy all technical and technological requirements and challenges of modern drilling. In the last few years, there has been a growing trend of laboratory research that includes different types of biodegradable waste as a potential additive that can achieve useful properties in mud. In this paper, the influence of mandarin peel powder on the filtration properties of mud after the aging process at elevated temperatures is examined. This eco-friendly additive was added to water-based muds in concentrations of 1% and 2% by volume of water. Laboratory research have shown stable filtration properties of the water-based mud containing mandarin peel powder even after exposing the mud to temperatures higher than 130 °C., Sve veća potražnja za energijom u svijetu, kao i trenutna geopolitička situacija, zahtijevaju od zemalja dodatna ulaganja u istraživanje i proizvodnju ugljikovodika iz vlastitih izvora. To znači da tvrtke moraju razviti nova polja koja su do sada ostala nerazrađena uglavnom zbog izuzetno zahtjevnih uvjeta u podzemlju gdje se ona nalaze (duboko more, visoka temperatura, visoki tlak, teška nafta, itd.). Razvoj ovih novih polja zahtijeva razvoj i usvajanje novih tehnologija, između ostalog, i razvoj temperaturno stabilnog bušotinskih fluida koji mogu ispuniti sve zadatke sukladno tehničkim izazovima koji se pred njih stavljaju. Osim tehnoloških izazova, raste i zabrinutost vezana uz utjecaj bušaćih operacija na okoliš. Sve navedeno potiče industriju na razvoj novih, cjenovno povoljnijih i ekološki prihvatljivih aditiva koji će moći zadovoljiti sve tehničko-tehnološke zahtjeve i izazove suvremenog bušenja. Posljednjih nekoliko godina sve je veći trend laboratorijskih istraživanja koja uključuju različite vrste biorazgradivog otpada kao potencijalnih aditiva kojima se u isplaci mogu postići korisna svojstva. U ovom radu ispituje se utjecaj praha kore mandarine na filtracijska svojstva isplake nakon procesa starenja pri povišenim temperaturama. Ovaj ekološki prihvatljivi aditiva dodavan je u isplake na bazi vode u koncentracijama od 1% i 2% na volumen vode. Ispitivanja su pokazala stabilna filtracijska svojstva isplake na bazi vode koja sadrži prah kore mandarine i nakon izlaganja isplake temperaturama višim od 130 °C.

Published
2023

22. Utjecaj kore mandarine na svojstva isplake na bazi vode i stabilnost kanala bušotine

Author

Medved, Igor, Pašić, Borivoje, Simon, Katarina, Gaurina-Međimurec, Nediljka, and Tomašić, Vesna

Abstract

In recent period, researchers have started conducting laboratory research to determine whether different types of biodegradable food waste can be used as additives in water-based muds (drilling fluids). Correctly designed composition of the mud is extremely important for the successful construction of the wellbore, since mud is complex fluid whose composition and properties affect the efficiency of drilling process. Therefore, any new type of additive must be researched in detail in relation to all the necessary properties that must be obtained during drilling operations. Wasted drilling mud and associated waste generated during drilling operations represents one of largest waste volumes accumulated during exploration and production projects in oil and gas industry, so this kind of research can have considerably positive results for the environment. Among the analyzed types of biodegradable waste, there is some data on the use of mandarin peel for these purposes, and due to the considerable annual production of this type of fruit in Croatia, it was decided that detailed laboratory research will be carried out on this type of biodegradable waste. By adding dried, grinded and sieved mandarin peel powder, in the water-based drilling mud, it was tested how this additive affects the mud filtration properties, rheological properties and the wellbore stability. Drilling muds that have a certain concentration of mandarin peel powder in their composition were compared with base mud which consists of water, bentonite and sodium hydroxide (NaOH). In addition to studying the influence of the concentration of mandarin peel powder, the influence of different particle sizes divided into two groups, particles smaller than 0.1 mm and particles between 0.10 mm and 0.16 mm in size, was also researched. The selected concentrations in the mud samples varied from 0.5% to 2% by the volume of water, since it was concluded during preliminary laboratory test phase that a concentration higher than 2% leads to a significant increase in plastic viscosity of the tested muds. On the basis of the conducted laboratory tests and the analysis of the results, useful insights were obtained on the effect of mandarin peel on the observed mud properties. Results show that mandarin peel have positive effect on mud filtration, since every mud sample with added mandarin peel powder showed decrease of filtrate volume. An exceptionally positive influence of mandarin peel powder was also observed in data obtained after swelling of pellets that have a clay component in their composition, when pellet is in contact with mud to which this eco-friendly additive is added. Laboratory tests showed significant swelling reduction, and this correlates well with results of filtration measurements which is essential to II prove the improvement of the wellbore stability. The rheological properties of mud samples that are containing mandarin peel were not decreased but also did not significantly increase observed properties. Rheological parameters show increase and remain within acceptable limits up to concentration of 1.5% of mandarin peel powder by volume of water. Because of this data set, the recommended concentration of this additive should be kept in the range of 1.0% to 1.5%, and at those concentrations observed additive has a significant positive effect on the filtration properties and wellbore stability as well as maintaining stable rheological properties at the same time. Considering the particle size used for laboratory research of mentioned mud properties, it can be concluded that slightly better results were obtained with larger particles between 0.10 mm and 0.16 mm but both sizes provide satisfactory water-based drilling mud properties. Also, by conducting laboratory tests of temperature stability, it can be concluded that water-based drilling mud with added mandarin peel powder is stable even after exposing the water-based drilling mud to temperatures up to 133 °C., Mnogi komercijalno dostupni aditivi spadaju u kategoriju nerazgradivih i ekološki opasnih materijala te postoji potreba za pronalaženjem i stvaranjem novih ekološki prihvatljivih aditiva koji osiguravaju postizanje svih potrebnih svojstava isplake kao i komercijalno dostupni aditivi, ali uz minimalan utjecaj na okoliš. Stoga se posljednjih nekoliko godina aktivno provode mnoga istraživanja o mogućnostima primjene otpada od hrane i drugih vrsta biorazgradivog otpada u pripremi isplaka na bazi vode. Budući da su preliminarna ispitivanja pokazala pozitivan utjecaj praha kore mandarine na različita svojstva isplake na bazi vode, te uzevši u obzir razinu godišnje proizvodnje mandarina u Republici Hrvatskoj (40.580 tona u 2021. godini), korisno je detaljnije istražiti može li se otpad koji nastaje konzumacijom ovog voća iskoristiti u naftnoj industriji, odnosno za pripremu bušotinskih fluida. Ciljevi i hipoteze Ciljevi ovog rada su utvrditi primjenjivost koncepta kružne ekonomije u tehnologiji bušenja korištenjem otpadnog materijala (kore mandarine) u pripremi isplake te odabrati koncentraciju i veličinu čestica praha kore mandarine čija će primjena poboljšati reološka i filtacijska svojstva isplake, smanjiti bubrenje glinovitih stijena i posljedično povećati stabilnost kanala bušotine. Ciljevi su bazirani na tri hipoteze: (i) dodavanjem praha kore mandarine u isplaku na bazi vode poboljšat će se njena filtracijska i reološka svojstva, (ii) dodavanjem praha kore mandarine smanjit će se bubrenje glinovitih stijena i poboljšati stabilnost kanala bušotine i (iii) prah kore mandarine smanjit će toksičnost isplake. Znanstveni doprinos Rezultati ovog istraživanja donose uvid u odabir koncentracije i veličine čestica praha kore mandarine s ciljem optimiranja svojstava isplake i povećanja stabilnosti kanala bušotine u različitim bušotinskim uvjetima. Na temelju provedenih ispitivanja moguće je pojasniti mehanizam temeljem kojeg čestice praha kore mandarine djeluju na svojstva isplake i povećanje stabilnosti kanala bušotine te potvrditi primjenjivosti koncepta kružne ekonomije u području istraživanja ugljikovodika. Metode i postupci U svrhu definiranja utjecaja praha kore mandarine na odabrana fizikalna svojstva isplake na bazi vode provedena su detaljna laboratorijska ispitivanja prema standardima API 13A i 13B-1. Sukladno navedenim standardima za istraživanje utjecaja ovog biorazgradivog aditiva na bubrenje stijene korišteni su umjetno stvoreni uzorci stijene (peleti), a njihovo bubrenje ispitano je uređajem za mjerenje bubrenja (engl. Dynamic Linear Swell Meter). Laboratorijsko ispitivanje filtracije kroz keramičke diskove različite propusnosti u uvjetima povišenog tlaka i temperature provedeno je na uređaju za određivanje sposobnosti isplake da stvori premoštenje na licu formacije (propusnom mediju) (engl. Permeability Plugging Tester (PPT)). Primjenom skenirajućeg elektronskog mikroskopa (SEM) dobivene su SEM snimke površine isplačnog obloga kako bi se utvrdio mehanizam temeljem kojeg čestice praha kore mandarine čepe pore i tako smanjuju vrijednosti filtracije. Reološka svojstva (plastična viskoznost, naprezanje pri pokretanju i čvrstoća gelova) određena su Fann viskozimetrom model 35A. Rezultati i zaključci Kako bi se što bolje istražio utjecaj praha kore mandarine na filtracijska i reološka svojstva te smanjenje bubrenja umjetnih uzoraka glinovitih stijena (peleta), za usporedbu je odabrana isplaka na bazi bentonita (osnovna isplaka). Rezultati dobiveni laboratorijskim ispitivanjima osnovne isplake uspoređeni su s rezultatima ispitivanja osam isplaka na bazi vode u čijem se sastavu nalazila različita koncentracija praha kore mandarine različitih veličina čestica. Od toga su četiri isplake (oznake A1, A2, A3 i A4) sadržavale prah kore mandarine s česticama manjim od 0,10 mm, dok su preostale četiri isplake (oznake B1, B2, B3 i B4) sadržavale prah kore mandarine s veličinama čestica između 0,10 i 0,16 mm. Prah kore mandarine dodan je u sastav isplake u četiri različite koncentracije: 0,5% (oznake A1 i B1), 1% (oznake A2 i B2), 1,5% (oznake A3 i B3) i 2% (oznake A4 i B4) na volumen vode korištene za pripremu isplake. Laboratorijskim ispitivanjima utvrđeno je da prah kore mandarine značajno smanjuje API filtraciju isplake već pri koncentraciji praha kore mandarine od 0,5%, ali je dodatkom 2% praha kore mandarine volumen filtrata smanjen čak za 44% u odnosu na osnovnu isplaku. U uvjetima povišenog tlaka i temperature (34,5 bar i 88 °C) dobiveni su još bolji rezultati, odnosno zabilježeno je smanjenje volumena filtrata za čak 61,5% (isplaka B4) u odnosu na osnovnu isplaku. Vrijedno saznanje vezano za filtracijska svojstva je da prah kore mandarine uspijeva dodatno smanjiti filtraciju isplake na bazi vode koja sadrži PAC R (komercijalni aditiv za smanjenje filtracije) do čak 46,2%. Metodom 16- V satnog starenja isplake na povišenim temperaturama (75 °C, 100 °C, 125 °C, 133 °C, 142 °C i 150 °C) ispitivana je i temperaturna stabilnost isplake na bazi vode u koje je dodan prah kore mandarine te je dokazano da ovaj materijal ima pozitivan utjecaj na filtracijska svojstva isplake i nakon njenog dugotrajnog izlaganja temperaturama do 133 °C. Vrijednosti reoloških svojstava isplaka na bazi vode koje, u različitim koncentracijama i veličinama čestica, sadrže prah kore mandarine nisu smanjene, ali nisu niti značajno povećane što znači da dodavanje ovog materijala ne narušava navedena svojstva isplake. Općenito, dodavanjem praha kore mandarine (obje ispitivane skupine veličina čestica) vrijednosti reoloških svojstava ispitivanih isplaka se povećavaju, ali ostaju u prihvatljivim granicama do koncentracije od 1,5% praha kore mandarine na volumen vode. Pri koncentraciji od 2% praha kore mandarine (veličine čestica između 0,10 i 0,16 mm) značajno se povećavaju vrijednosti reoloških parametara. Korištenje isplake na bazi vode s 2% praha kore mandarine u bušotinskim uvjetima rezultiralo bi povećanim gubitkom tlaka pa se može zaključiti da je prihvatljiva koncentracija praha kore mandarine do maksimalno 1,5% na volumen vode za testirane veličine čestica. Iznimno pozitivan utjecaj praha kore mandarine uočen je i kod ispitivanja bubrenja umjetnih uzoraka stijene (peleta) koje u svom sastavu imaju glinovitu komponentu. Smanjenje bubrenja peleta u isplakama koje sadrže prah kore mandarine, u usporedbi s bubrenjem u osnovnoj isplaci, bilo je vidljivo već nakon dodavanja 0,5% ovog aditiva na volumen vode za pripremu isplake. Međutim, najbolji rezultati, odnosno najmanje bubrenje peleta, zabilježeno je u isplakama na bazi vode koje su sadržavale 2% praha kore mandarine. Smanjenje bubrenja peleta nakon 24-satnog ispitivanja bilo je do 45% u sobnim uvjetima, a do 48,6% na temperaturi od 90 °C. Jednako kao i za provedena ispitivanja filtracijskih svojstava, još bolji rezultati zabilježeni su u uvjetima povišene temperature u odnosu na sobne uvjete, a čestice veličine između 0,10 mm i 0,16 mm imaju nešto bolji učinak na smanjenje bubrenja, tako da ovi rezultati dobro koreliraju s rezultatima mjerenja filtracije što je bitno za procjenu poboljšanja stabilnosti kanala bušotine. Usporedbom zbirnih rezultata ispitivanja utjecaja praha kore mandarine na sva promatrana svojstva isplake na bazi vode, može se zaključiti da su nešto bolji rezultati dobiveni s većim česticama praha kore mandarine (između 0,10 mm i 0,16 mm), iako se s obje veličine dobivaju zadovoljavajuća svojstva ispitivanih isplaka. Dodavanjem praha kore mandarine u koncentraciji od 1,0% do 1,5% na volumen vode za pripremu isplake, bez obzira na veličinu čestica, dobiveni su iznimno pozitivni rezultati vezani uz filtracijska svojstva i stabilnost kanala bušotine. Navedena koncentracija može se smatrati optimalnom za pripremu VI isplake na bazi vode koja će se koristiti za izradu kvalitetnog kanala bušotine. Međutim, osim očitog pozitivnog utjecaja na filtracijska i reološka svojstva isplake te povećanje stabilnosti kanala bušotine, primjenom praha kore mandarine u isplakama na bazi vode doprinosi se i konceptu kružne ekonomije u tehnologiji bušenja obzirom da iz otpadnog materijala nastaje koristan aditiv za dizajn isplake.

Published
2023

24. Transport of gadolinium in a cement composite

Author

Medved’ Igor, Kalvoda Ladislav, Vejmelková Eva, Vratislav Stanislav, and Černý Robert

Subjects
Engineering (General). Civil engineering (General), TA1-2040
Abstract

Development of cement based composites suitable for radionuclide immobilization is of great interest for secure containment of nuclear waste. This requires, in particular, detailed knowledge of how radionuclides are transported in such composites. In this paper we investigate the transport of gadolinium in a dry cement composite. Experimental data are obtained in a non-destructive way by neutron imaging. Their theoretical interpretation is based on a diffusion-advection model in which sorption is included.

Published
2019
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26. Extended-Reach Drilling (ERD)—The Main Problems and Current Achievements.

Author

El Sabeh, Karim, Gaurina-Međimurec, Nediljka, Mijić, Petar, Medved, Igor, and Pašić, Borivoje

Subjects
CASING drilling, NATURAL gas reserves, PETROLEUM reserves, ENERGY industries, PETROLEUM sales & prices
Abstract

With the development of different segments within the drilling technology in the last three decades, well drilling has become possible in harsh downhole conditions. The vertical well provides access to oil and gas reserves located at a certain depth directly below the wellsite, and a large number of vertical wells are required for the exploitation of hydrocarbons from spatially expanded deposits. However, the borehole can deviate from the vertical well, which means that the target zone can be reached by a horizontal directional well. With this type of well, especially in the case of drilling an extended-reach well (ERW), the length of the wellbore in contact with the reservoir and/or several separate reservoirs is significantly increased, therefore, it is a much better option for the later production phase. Unfortunately, the application of extended-reach drilling (ERD technology), with all of its advantages, can cause different drilling problems mostly related to the increased torque, drag, hole cleaning and equivalent circulation density (ECD), as well as to an increase in the well price. Overcoming these problems requires continuous operational change to enable operators to address downhole challenges. Today, the longest well reaches 15,240 m (50,000 ft), which raises the question of the technological and economic feasibility of this type of drilling project, especially with the lower oil price on the energy market. This paper provides a comprehensive overview of extended-reach drilling technology, discusses the main problems and analyzes current achievements. [ABSTRACT FROM AUTHOR]

Published
2023
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32. Elaborat o zaštiti okoliša za ocjenu o potrebi procjene utjecaja na okoliš za zahvat 'Istražna bušotina Veliki Rastovac-1 (VRa-1) s radnim prostorom za smještaj bušaćeg postrojenja na istražnom prostoru Drava-03'

Author

Gaurina-Međimurec, Nediljka, Pašić, Borivoje, Mijić, Petar, Medved, Igor, Novak-Mavar, Karolina, Hrgarek, Marija, Rak Zarić, Ivana, Rak, Mihaela, Mađerić, Antonija, and Dubovečak, Vinka

Subjects
zaštita okoliša, istražni prostor ugljikovodika DR-03, istražna bušotina Veliki Rastovac-1 (VRa-1)
Abstract

Planirani zahvat obuhvaća bušotinski radni prostor (plato veličine 88 m x 88 m), građevinske objekte na bušotinskom radnom prostoru koji su u funkciji izrade bušotine, te izradu istražne bušotine Veliki Rastovac-1 (VRa-1) do dubine 1 000 m bušaćim postrojenjem R-69. Do radnog prostora istražne bušotine, koja se nalazi u šumskom području, pristupit će se s lokalne ceste koja se spaja na državnu cestu D5 (Terezino Polje – Virovitica – Veliki Zdenci – Donji Daruvar –Lipik – Stara Gradiška) kod mjesta Lončarica. Unutar površine zahvata, od postojećeg šumskog puta do budućeg bušotinskog radnog prostora izgradit će se pristupni put, duljine oko 1 550 m, širine kolnika oko 5 m. Primarni cilj istražne bušotine VRa-1 je pretpostavljeno plinsko ležište u panonskim pješčenjacima. Lokacija zahvata nalazi se unutar granica istražnog prostora ugljikovodika DR-03 (Drava-03), u Bjelovarsko-bilogorskoj županiji, na području Općine Grubišno Polje. Elaborat o zaštiti okoliša za ocjenu o potrebi procjene utjecaja zahvata na okoliš obuhvaća detaljan opis zahvata i lokacije zahvata, opis mogućih značajnih utjecaja zahvata na okoliš (klimatske promjene, zrak, vodu, tlo, krajobraz, bioekološke značajke, ekosustave i staništa, zaštićena područja, ekološku mrežu, povećanje buke, nastanak otpada, gospodarske djelatnosti i itd.), prijedlog mjera zaštite okoliša i program praćenja stanja okoliša.

Published
2022

33. Prolonged activation of cardiomyocytes calpain 2 in sudden cardiac death caused by early myocardial ischemia and acute myocardial infarction contributes to activation of myocytes apoptosis in the area of myocardial ischemia and infarction

Author

Kunišek, Leon, Medved, Igor, Ferenčić, Antun, Arbanas, Silvia, Matušan Ilijaš, Koviljka, Leniček, Tanja, Ulamec, Monika, and Stephany Kirigin, Monica

Subjects
apoptoza, imunohistokemija, ishemija, kalpain, miokard
Abstract

Objectives The aim of the study was to analyze the expression of calpain 2 and the degree of apoptosis of the cardiomyocytes and to compare them between the examined groups of people who died of sudden cardiac death (SCD) caused by early myocardial ischemia (EMI)/acute myocardial infarction (AMI) and control groups. Patients and Methods Respondents were divided into three groups. Group 1 consisted of 50 persons who died of SCD caused by EMI in the period from January 2013 to August 2019. The tissue samples were taken from the zone of ischemia/infarction and the opposite left ventricular wall during the forensic autopsy at the Department of Forensic Medicine and Criminalistics, Faculty of Medicine, University of Rijeka. Group 2 consisted of 51 persons who died of SCD caused by AMI. The control group included myocardial samples obtained from 50 persons who died of instant death by head gunshot. The expression of calpain 2 in the studied heart cells was analyzed immunohistochemically, while the degree of apoptosis was determined by the TUNEL method. Statistical data processing was performed using the computer program MedCalcStatistical Software version 20.011. Results Calpain 2 in myocytes showed greater expression in the zone of EMI (and even greater in AMI zone) compared to the opposite wall and control group (P

Published
2022

41. Determination of phase change temperature of materials from adiabatic scanning calorimetry data.

Author

Medved', Igor, Jurči, Milan, and Trník, Anton

Subjects
*PHASE transitions, *HEAT capacity, *CALORIMETRY, *PHASE change materials
Abstract

Melting and other first-order phase changes usually occur in phase change materials (PCMs) within a noticeable temperature range rather than at a unique phase change temperature ( T pc ). Then the enthalpy and heat capacity have rather wide jumps and peaks, respectively, spread over such ranges of temperatures. Surprisingly, wide jumps and peaks are observed even in plain and simple cases when PCMs are pure substances with negligible hysteresis and/or supercooling and the measurements are quasi-equilibrium using very slow heating/cooling rates, as in adiabatic scanning calorimetry (ASC). We show that in such cases a unique T pc can be identified and calculated from the measured heat capacity peaks. It suffices to take into account that PCM samples do not have an ideal microstructure but are rather composed of many micro- to nano-sized domains. The heat capacity peak is then an average of individual peaks that (a) come from all domains and (b) have different shifts from T pc for different domain sizes. Interpreting a heat capacity peak measured by ASC in this way, we present a procedure from which T pc can be evaluated. We apply the procedure to three examples of materials using available ASC data and point out the importance of the size distribution of domains. [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
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44. Elaborat o zaštiti okoliša za ocjenu o potrebi procjene utjecaja na okoliš za zahvat 'Istražna bušotina Mikleuš-1 (Mik-1) s radnim prostorom za smještaj bušaćeg postrojenja na istražnom prostoru Drava-03'

Author

Gaurina-Međimurec, Nediljka, Pašić, Borivoje, Mijić, Petar, Medved, Igor, Novak-Mavar, Karolina, Hrgarek, Marija, Rak Zarić, Ivana, Rak, Mihaela, Mađerić, Antonija, and Dubovečak, Vinka

Subjects
zaštita okoliša, istražni prostor ugljikovodika DR-03, istražna bušotina Mikleuš-1
Abstract

Planirani zahvat obuhvaća bušotinski radni prostor (plato veličine 103 m x 98 m), građevinske objekte na bušotinskom radnom prostoru koji su u funkciji izrade bušotine, te izradu istražne bušotine Mikleuš-1 (Mik-1) do dubine 1 550 m bušaćim postrojenjem R-69. Do radnog prostora istražne bušotine pristupit će se izravno s županijske ceste 4069 (Slatinski Drenovac – Humljani – D2) koja se veže na državnu cestu D2. Primarni cilj istražne bušotine Mik-1 je pretpostavljeno naftno ležište u srednje miocenskim konglomeratičnim pješčenjacima i pretpostavljeno plinsko ležište u panonskim pješčenjacima. Lokacija zahvata nalazi se unutar granica istražnog prostora ugljikovodika DR-03 (Drava-03), u Virovitičko-podravskoj županiji, na području Općine Čačinci. Elaborat o zaštiti okoliša za ocjenu o potrebi procjene utjecaja zahvata na okoliš obuhvaća detaljan opis zahvata i lokacije zahvata, opis mogućih značajnih utjecaja zahvata na okoliš (klimatske promjene, zrak, vodu, tlo, krajobraz, bioekološke značajke, ekosustave i staništa, zaštićena područja, ekološku mrežu, povećanje buke, nastanak otpada, gospodarske djelatnosti i itd.), prijedlog mjera zaštite okoliša i program praćenja stanja okoliša.

Published
2021

45. STUDIJA O UTJECAJU NA OKOLIŠ EKSPLOATACIJE UGLJIKOVODIKA NA BUDUĆEM EKSPLOATACIJSKOM POLJU SEVEROVCI

Author

Gaurina-Međimurec, Nediljka, Simon, Katarina, Pašić, Borivoje, Novak-Mavar, Karolina, Mijić, Petar, Hrnčević, Lidia, Medved, Igor, Hrgarek, Marija, Rak Zarić, Ivana, Rak, Mihaela, Mađerić, Antonija, Dubovečak, Vinka, Glavica Hrgarek, Petra, Hrgarek, Petar, Kisić, Ivica, and Vidič, Sonja

Subjects
studija o utjecaju na okoliš, pridobivanje ugljikovodika, eksploatacijsko polje ugljikovodika Severovci
Abstract

Buduće eksploatacijsko polje ugljikovodika (EPU) Severovci nalazi se na sjevernom dijelu Republike Hrvatske, u Koprivničko-križevačkoj županiji, te se većim dijelom prostire na području Općine Novo Virje, Općine Ferdinandovac i Grada Đurđevca, a manjim dijelom na području Općine Molve i Općine Kalinovac. Na budućem eksploatacijskom polju ugljikovodika Severovci planirani su sljedeći zahvati: opremanje bušotine Sev-1 površinskom i dubinskom opremom za pridobivanje plina, smanjenje bušotinskog radnog prostora Sev-1 na optimalnu veličinu za pridobivanje plina (80 m x 70 m) i izgradnja površinskog sustava za eksploataciju na BRP-u Severovci-1, izgradnju priključnog plinovoda DN 100 (4“) od bušotine Sev-1 do plinske stanice (PS) Molve istok te polaganje elektro i signalnog kabela u zajednički rov od BRP Mol-31R do BRP Sev- 1. S ciljem održavanja kontinuiteta proizvodnje ugljikovodika, u budućnosti se može pojaviti i potreba za rekonstrukcijom postojećih, odnosno izgradnjom novih rudarskih i drugih objekata u funkciji tehnoloških procesa. Izrađena studija o utjecaju na okoliš eksploatacije nafte i plina obuhvaća detaljan opis zahvata i lokacije zahvata, opis mogućih značajnih utjecaja zahvata na okoliš (klimatske promjene, zrak, vodu, tlo, krajobraz, bioekološke značajke, ekosustave i staništa, zaštićena područja, ekološku mrežu, povećanje buke, nastanak otpada, gospodarske djelatnosti i itd.), prijedlog mjera zaštite okoliša i praćenja stanja okoliša.

Published
2021

46. Elaborat o zaštiti okoliša za ocjenu o potrebi procjene utjecaja na okoliš za zahvat 'Istražna bušotina Obradovci-1Jug (Obr-1J) s radnim prostorom za smještaj bušaćeg postrojenja na istražnom prostoru Drava-03'

Author

Gaurina-Međimurec, Nediljka, Pašić, Borivoje, Mijić, Petar, Medved, Igor, Novak-Mavar, Karolina, Hrgarek, Marija, Rak Zarić, Ivana, Rak, Mihaela, Mađerić, Antonija, and Dubovečak, Vinka

Subjects
zaštita okoliša, istražni prostor ugljikovodika DR-03, istražna bušotina Obradovci-1Jug (Obr-1J)
Abstract

Planirani zahvat obuhvaća bušotinski radni prostor (plato veličine 88 m x 87 m), građevinske objekte na bušotinskom radnom prostoru koji su u funkciji izrade bušotine, te izradu istražne bušotine Obradovci-1Jug (Obr-1J) do dubine 1 850 m bušaćim postrojenjem R-69. Do radnog prostora istražne bušotine pristupit će se s županijske ceste ŽC4063 (Čačinci – Zdenci) koja se veže na državnu cestu D2. U tu svrhu izgradit će se pristupni put, korištenjem kamenog materijala, od postojeće županijske ceste ŽC4063 (Čačinci – Zdenci) do bušotinskog radnog prostora. Primarni cilj istražne bušotine Obr-1J je pretpostavljeno plinsko ležište (prognozirana su dva nivoa u zasićenju plinom) u gornje panonskim pješčenjacima i pretpostavljeno naftno ležište u srednje miocenskim andenzitnim brečama. Lokacija zahvata nalazi se unutar granica istražnog prostora ugljikovodika DR-03 (Drava-03), u Virovitičko- podravskoj županiji, na području Općine Zdenci. Elaborat o zaštiti okoliša za ocjenu o potrebi procjene utjecaja zahvata na okoliš obuhvaća detaljan opis zahvata i lokacije zahvata, opis mogućih značajnih utjecaja zahvata na okoliš (klimatske promjene, zrak, vodu, tlo, krajobraz, bioekološke značajke, ekosustave i staništa, zaštićena područja, ekološku mrežu, povećanje buke, nastanak otpada, gospodarske djelatnosti i itd.), prijedlog mjera zaštite okoliša i program praćenja stanja okoliša.

Published
2021

49. Utjecaj indeksa tjelesne mase na pojavu komplikacija nakon operacija na srcu

Author

Mrkonjić, Ružica and Medved, Igor

Subjects
BIOMEDICINA I ZDRAVSTVO. Kliničke medicinske znanosti. Kirurgija, indeks tjelesne mase, komplikacije, kardijalna kirurgija, BIOMEDICINE AND HEALTHCARE. Clinical Medical Sciences. Surgery
Abstract

Uvod: Sve boljim rezultatima kliničkih ishoda i manjoj pojavnosti komplikacija u kardijalnoj kirurgiji doprinijela su i saznanja o čimbenicima koji mogu utjecati na klinički ishod, a na koje se može utjecati eliminacijom ili modifikacijom. Cilj rada: Epidemiološka analiza pojavnosti ukupnoga broja komplikacija u ranom poslijeoperacijskom razdoblju uz analizu prediktivne vrijednosti indeksa tjelesne mase, kao alata u procjeni rizika za nastanak komplikacija nakon operacija srca. Metode: Retrospektivno su analizirani podaci 143 bolesnika kod kojih je izvedena miokardijalna revaskularizacija. Bolesnici su podijeljeni u 5 kategorija obzirom na vrijednosti ITM: pothranjeni (ITM manji od 18, 5kg/m2), bolesnici idealne tjelesne mase (ITM 18, 5-24, 9 kg/m2), bolesnici prekomjerne tjelesne mase (ITM 25-29, 9 kg/m2), blago pretili (ITM 30-34, 9 kg/m2) i teško pretili bolesnici (ITM > 35 kg/m2). U analizi pojave komplikacija razmatrana je pojava smrtnosti unutar 30 dana od operacije, pojava novonastale fibrilacije atrija, infarkta miokarda, infekcije mjesta kirurške incizije, pojava novonastalog bubrežnog zatajenja, te neuroloških komplikacija. Rezultati: Bolesnici prekomjerne tjelesne mase češće su imali hipertenziju, hiperlipidemiju, šećernu bolest, te fibrilaciju atrija u prijeoperacijskom razdoblju. Učestalost stanja rasla je s porastom vrijednosti tjelesne mase. Od komplikacija u poslijeoperacijskom razdoblju najčešća je bila fibrilacija atrija za koju je evidentno da je učestalost ovisila o indeksu tjelesne mase. Zaključak: Analiza podataka 143 bolesnika kod kojih je učinjena miokardijalna revaskularizacija nije pokazala statistički relevantnu vrijednost indeksa tjelesne mase kao prediktora nastanka komplikacija u ranom poslijeoperacijskom tijeku, osim u pojavi fibrilacije atrija.

Published
2020

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