Publikační činnost Katedry tepelné techniky / Publications of Department of Thermal Engineering (635)

Permanent URI for this collectionhttp://hdl.handle.net/10084/76061

Kolekce obsahuje bibliografické záznamy publikační činnosti (článků) akademických pracovníků Katedry tepelné techniky (635) v časopisech registrovaných ve Web of Science od roku 2003 po současnost.
Do kolekce jsou zařazeny:
a) publikace, u nichž je v originálních dokumentech jako působiště autora (adresa) uvedena Vysoká škola báňská-Technická univerzita Ostrava (VŠB-TUO),
b) publikace, u nichž v originálních dokumentech není v adrese VŠB-TUO uvedena, ale autoři prokazatelně v době jejich zpracování a uveřejnění působili na VŠB-TUO.

Bibliografické záznamy byly původně vytvořeny v kolekci Publikační činnost akademických pracovníků VŠB-TUO, která sleduje publikování akademických pracovníků od roku 1990.

Browse

Now showing 1 - 20 out of 72 results

Analysis of the mathematical models for identifying the thickness of the fouling layer in natural gas coolers
(MDPI, 2024) Čarnogurská, Mária; Příhoda, Miroslav; Andrejiová, Miriam; Tóth, Lukáš
This article presents an analysis of three different approaches to the identification of the thickness of the fouling layer inside the pipes of natural gas (NG) coolers. At present, there is no existing simple analytical procedure for the identification of the fouling layer thickness. The authors of this article describe in detail the balance method, which required the use of a large number of physical parameters, changes in their sizes depending on the output temperature of the gas, the temperature of the cooling air, the air quantity, as well as the physical properties of both media. The computational model was robust, and its disadvantage was the iterative computation. The second analysed method was a dimensional analysis. It was applied using the Buckingham's theorem to express the individual similarity criteria. In this method, 10 simplexes and two complexes were created. The fouling layer thickness, expressed using a derived criterial equation, exhibited real results. The third analysed method was based on analysing selected physical parameters with the use of a multiple regression analysis in MinitabX 18 software. The analysis showed that the fouling layer thickness depended on fewer parameters than the number of parameters assumed in the dimensional analysis or the balance method. The standard deviation that was identified in the multiple linear regression for a double crossflow cooler was 0.0667 and the value of reliability (the coefficient of determination of the multiple linear regression) R2 was 0.9985.
Physical experiments and numerical simulations of the influence of turbulence inhibitors and the position of ladle shroud on the steel flow in an asymmetric five-strand tundish
(MDPI, 2023) Walek, Josef; Tkadlečková, Markéta; Velička, Marek; Machů, Mario; Cupek, Jiří; Huczala, Tomáš; Cibulka, Jiří; Růžička, Jan; Michalek, Karel
The submitted article deals with the use of physical and numerical modelling to study the process of the steel flow in an asymmetric five-strand tundish that continuously casts steel. For the purposes of physical modelling, a 1:4-scale plexiglass model was used as the operating tundish, and for numerical modelling, the geometry of the operating tundish was created on a 1:1 scale. A model liquid (water) was used in the physical modelling of the melt flow process, while liquid steel was used as the standard flowing medium in the numerical modelling. We assessed the relevant operating parameters influencing the characteristics of the flow of the bath in the tundish—the shape of the turbulence inhibitor, the position of the ladle shroud in relation to the turbulence inhibitor and the distance between the ladle shroud orifice and the bottom of the turbulence inhibitor. The preliminary results show that optimal steel flow characteristic results are achieved by using the TI3-C configuration. The results from both modelling methods achieved the same characteristics, therefore verifying the results of each other and demonstrating that when taken together, the results of physical and numerical modelling can be considered sufficiently informative.
A similarity model of specific heat loss determined by dimensional analysis
(MDPI, 2023) Čarnogurská, Mária; Příhoda, Miroslav; Lázár, Marián; Jasminská, Natália; Brestovič, Tomáš; Puškár, Michal
This article describes an innovative method for the determination of heat flow (specific heat loss; linear heat flow density) from a one-metre length of a twin pipe directly-buried heat network. Such heat losses are currently described by applying analytical procedures based on the heat transfer theory. It is rather complicated to accurately express the heat loss using such procedures, due to the necessity to determine the individual values of thermal resistance. A simpler method to express heat loss is the balance method, as it requires measuring a temperature gradient ∆t between the starting point of the heat network and the end point of the heat collection. A suitable measuring device must provide high-accuracy measurements of the temperature. In the case of very well insulated distribution pipelines and short pipes, the temperature measurements must be accurate to the hundredths of a degree Celsius. It is impossible to install such devices as fixed equipment on every heat distribution network, due to such networks measuring many kilometres and the cost of the appropriate measuring technology. For the aforesaid reasons, the authors created a mathematical model for specific heat losses based on dimensional analysis. This method facilitates the identification of dimensionless criteria based on the relevant dimensional quantities. Functional correlations between the identified criteria may be identified on the basis of the results of physical or numerical experiments. In this study, a database of the results obtained from physical experiments conducted on two heat networks was used. The output of the similarity model was a function describing the heat flow from a one-meter pipe length that was applicable to various alternatives in relation to the geometrical, physical and boundary conditions. The standard deviation of a difference in the heat losses identified by applying the balance method and using the proposed criterial equation for a twin pipe directly-buried pre-insulated heat network was 0.515 W·m−1.
The corrosion effect of fly ash from biomass combustion on andalusite refractory materials
(MDPI, 2023) Vlček, Jozef; Ovčačíková, Hana; Velička, Marek; Topinková, Michaela; Burda, Jiří; Matějková, Petra
The main problem affecting the life of refractory linings in furnaces is alkaline corrosion formed during biomass combustion, especially in systems with SiO2–Al2O3 . This corrosion effect is very intensive compared to using conventional technologies designed for burning traditional fuels. This study focuses on the development of a new type of andalusite refractory material with a higher corrosion resistance to K2CO3 and fly ash after biomass combustion. The original andalusite refractory material is labeled A60PT0, with an oxide content of 60 wt.% Al2O3 and 37 wt.% SiO2 , a compressive strength parameter of 64 MPa, and an apparent porosity of 15%. In the experiment, four mixtures (labeled A60PT1–A60PT4) were modified primarily using the raw materials and granulometry. The fly ash was characterized by an X-ray diffraction analysis with the following phases: quartz, calcite, microcline, leucite, portlandite, and hematite. According to the X-ray fluorescence analysis, the samples contained the following oxides: 47 wt.% CaO, 12 wt.% K2O, 4.6 wt.% SiO2 , 3.5 wt.% MgO, and some minority oxides such as P2O5 , MgO, MnO, and Fe2O3 between 2 and 5 %. The tendency for slagging/fouling of the ash was determined with the help of the indexes B/A, TA, Kt , and Fu. The final material was a shaped andalusite refractory material labeled A60PT4 with a content of 65 wt.% Al2O3 and 36 wt.% SiO2. The properties of the andalusite material were a compressive strength of 106.9 MPa, an apparent porosity of 13%, and the recommended temperature of use up to 1300 ◦C. For corrosion testing, a static crucible test was performed according to the norm CSN CEN/TS 15418 and ˇ the company’s internal regulation. The exposure time of the samples was 2 h and 5 h at temperatures of 1100 ◦C and 1400 ◦C for K2CO3 and ash, respectively. For the evaluation of tested samples, an X-ray powder differential analysis, an X-ray fluorescence analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used.
Use of neural networks for lifetime analysis of teeming ladles
(MDPI, 2022) Jančar, Dalibor; Machů, Mario; Velička, Marek; Tvardek, Petr; Kocián, Leoš; Vlček, Jozef
When describing the behaviour and modelling of real systems, which are characterized by considerable complexity, great difficulty, and often the impossibility of their formal mathematical description, and whose operational monitoring and measurement are difficult, conventional analytical-statistical models run into the limits of their use. The application of these models leads to necessary simplifications, which cause insufficient adequacy of the resulting mathematical description. In such cases, it is appropriate for modelling to use the methods brought by a new scientific discipline-artificial intelligence. Artificial intelligence provides very promising tools for describing and controlling complex systems. The method of neural networks was chosen for the analysis of the lifetime of the teeming ladle. Artificial neural networks are mathematical models that approximate non-linear functions of an arbitrary waveform. The advantage of neural networks is their ability to generalize the dependencies between individual quantities by learning the presented patterns. This property of a neural network is referred to as generalization. Their use is suitable for processing complex problems where the dependencies between individual quantities are not exactly known.
Critical evaluation of quantitative determination of minerals in slags by a new MCQMA and QXRD methods
(Springer Nature, 2022) Klika, Zdeněk; Bartoňová, Lucie; Kostura, Bruno; Maierová, Petra; Vlček, Jozef; Dobrovská, Jana; Matýsek, Dalibor; Krčmář, Jiří
A new modified chemical quantitative mineral analysis (MCQMA) method was developed and used for quantitative calculation of crystalline and amorphous phases in ladle and blast furnace slags and their slag blends with 20-100 wt% of the amorphous phase. MCQMA calculation was created by combination of the original chemical quantitative mineral analysis (CQMA) with bulk chemical analysis (XRF) and QXRD-Rietveld method with an internal standard (QXRD*). These X-ray diffraction data were used for a) identification of crystalline minerals and for the support of calculation of average oxide formula of amorphous phase for MCQMA calculation and b) for independent separated quantitative determination of crystalline (C(12)A(7), C(3)A, C2S, C3S, MgO) and amorphous minerals and their comparison with data calculated by MCQMA. The advantage of the MCQMA consists also in the possibility to test separately the quality of determined phase percentages provided by MCQMA and QXRD* methods using their feedback conversion on recalculated chemical analysis and compared them with bulk chemical analysis. For the tested data, the comparison showed that both methods provided comparable results.
Effect of mass ratio and milling on compressive strength and corrosion resistance of blast-furnace slag/fly ash geopolymer activated by solid alkali activator
(Springer Nature, 2022) Ovčačíková, Hana; Tokarský, Jonáš; Maierová, Petra; Matějková, Petra; Velička, Marek; Olšanský, Jiří
Fly ash and granulated blast-furnace slag can be considered "multifunctional waste." This study is focused on properties of a non-cement binder prepared from slag and fly ash activated by solid alkali activator. Fly ash was milled (2.5, 5.0, and 7.5 min) in order to increase its reactivity, and particle size distribution, specific surface area, and grain morphology were determined for all milled FA samples. Two GBFS +FA mixtures (70:30 and 85:15 w/w) were studied. Prepared mixtures were activated by solid alkali activator (Na2SiO3). Optimal weight ratios were calculated for CaO, SiO2, and Al2O3 components. Properties of the mixtures were studied in dependence on the GBFS:FA mass ratio and FA milling time (0-7.5 min). After 2 and 28 days of hydration, compressive strength of all mixtures exceeded 20 and 60 MPa, respectively. The 85:15 ratio led to generally higher compressive strength 108.3 MPa was reached after 90 days using FA milled for 7.5 min. Corrosion resistance was tested by exposing mixtures to distilled water, 0.5% HCl, and 3% Na2SO4 for 65 days, and evaluated by measuring changes in CS. Also the corrosion resistance was found higher (Na2SO4) than and comparable (HCl, water) to the 70:30 ratio. This study aims to show that GBFS +FA mixtures (70:30 and 85:15 w/w) activated by solid Na2SiO3 can achieve high CS and good corrosion resistance.
Alkali-activated metakaolins: Mineral chemistry and quantitative mineral composition
(MDPI, 2022) Valášková, Marta; Klika, Zdeněk; Vlček, Jozef; Matějová, Lenka; Topinková, Michaela; Pálková, Helena; Madejová, Jana
The reaction products resulting from the alkali-activation of metakaolin are impacted by the composition of the initial kaolin, and amount of alkali-activated kaolinite and water. The present study focused on analyzing these parameters on the metakaolins calcined at 800 degrees C from three kaolins, and the metakaolins' alkali activation for 2, 3 and 28 days. The first objective was to evaluate the mineral chemistry and quantitative mineral phase composition from the bulk chemical analysis using the chemical quantitative mineral analysis (CQMA) procedure and conduct a comparison of the chemistry of the metakaolins after alkali activation for 28 days according to the elements Al, Si, Na and K, using the leaching test in distilled water. The second task was to search for possible relationships between the quantitative number of phases in alkali-activated metakaolins and compressive strength. The main methods used for the characterization of material were X-ray fluorescence, X-ray diffraction, thermal TG/DTA and infrared spectroscopy. Metakaolins alkali activated for 28 days contained crystalline quartz, muscovite, orthoclase, and unreacted metakaolinite contained zeolite A (Z-A), hydrosodalite (HS) and thermonatrite (TN) in the amorphous/weakly crystalline phase. The compressive strengths (CS) from 6.42 +/- 0.33 to 9.97 +/- 0.50 MPa are related positively to H2O+ and H2O bound in HS and TN.
Impact of Ni on the thermophysical and thermodynamic properties of Fe–C–Ni based alloys
(Elsevier, 2022) Drozdová, Ľubomíra; Smetana, Bedřich; Machů, Mario; Novák, Vlastimil; Vontorová, Jiřina; Zlá, Simona; Kawuloková, Monika; Řeháčková, Lenka; Sorokina, Světlana
Three model alloys based on Fe-C-Ni were studied containing carbon between 0.338 and 0.382 wt. % and nickel between 1.084 and 4.478 wt. %. Phase transition temperatures, heat capacity, enthalpy change, heat of fusion, coefficient of thermal expansion, and density were experimentally and theoretically determined in the high-temperature area from 1000 degrees C to 1595 degrees C. A number of techniques, namely differential thermal analysis (DTA), differential scanning calorimetry (DSC), and dilatometry, were used in this study, and the heat of fusion was determined by two approaches, that is, from the DSC peak area and from the enthalpy change. The experimental data were compared and discussed with the calculation results obtained using SW IDS, JMatPro, and Thermo-Calc operating with the commercially available TCFE8 thermodynamic database. The obtained experimental results show that the liquidus temperature and the coefficient of thermal expansion decrease with increasing nickel content. On the contrary, the density and heat of fusion values derived from the DSC peak increase with increasing nickel content. Furthermore, an ambiguous influence of nickel on the change in solidus temperature, heat capacity, enthalpy change, and heat of fusion obtained from the enthalpy change was observed.
Utilization of metallurgical slags in Cu-free friction material formulations
(MDPI, 2022) Matějka, Vlastimil; Jayashree, Priyadarshini; Leonardi, Mara; Vlček, Jozef; Sabovčík, Tomáš; Straffelini, Giovanni
The aim of our research was to indicate the suitability of metallurgical slags (two blast furnace slags and one steel furnace slag) as the components of Cu-free friction materials. The base mixture consisted of nine components including phenolic resin, graphite, tin sulphide, steel and aramid fibers, iron powder, a mixture of barite with calcite, and vermiculite. To this base mixture, the slags with a particle size below 0.1 mm were added individually in the amount of 20 wt.%. A base friction mixture with alumina in the amount of 20 wt.% represented the reference. Samples for the friction-wear tests were produced in the form of pins by hot press molding. The prepared pins were tested using a pin-on-disc tester in a drag mode at the pressure of 1 MPa and a constant sliding speed of 1.51 m/s for 90 min. The samples with slags exhibited slightly lower values of steady-state friction coefficient compared to the reference composite with alumina, and at the same time produced lower wear particle emissions. The particle concentration was reduced for the samples with slowly cooled blast furnace and steel furnace slag. The results obtained indicated steel furnace slag as a promising component of Cu-free friction composites.
Corrosive effect of wood ash produced by biomass combustion on refractory materials in a binary Al-Si system
(MDPI, 2022) Ovčačíková, Hana; Velička, Marek; Vlček, Jozef; Topinková, Michaela; Klárová, Miroslava; Burda, Jiří
In terms of its chemical composition, biomass is a very complex type of fuel. Its combustion leads to the formation of materials such as alkaline ash and gases, and there is evidence of the corrosive effect this process has on refractory linings, thus shortening the service life of the combustion unit. This frequently encountered process is known as "alkaline oxidative bursting". Corrosion is very complex, and it has not been completely described yet. Alkaline corrosion is the most common cause of furnace-lining degradation in aggregates that burn biomass. This article deals with an experiment investigating the corrosion resistance of 2 types of refractory materials in the Al2O3-SiO2 binary system, for the following compositions: I. (53 wt.% SiO2/42 wt.% Al2O3) and II. (28 wt.% SiO2/46 wt.% Al2O3/12 wt.% SiC). These were exposed to seven types of ash obtained from one biomass combustion company in the Czech Republic. The chemical composition of the ash is a good indicator of the problematic nature of a type of biomass. The ashes were analyzed by X-ray diffraction and X-ray fluorescence. Analysis confirmed that ash composition varies. The experiment also included the calculation of the so-called "slagging/fouling index" (I/C, TA, Sr, B/A, Fu, etc.), which can be used to estimate the probability of slag formation in combustion units. The corrosive effect on refractory materials was evaluated according to the norm CSN P CEN/TS 15418, and a static corrosion test was used to investigate sample corrosion.
Use of numerical methods for the design of thermal protection of an RFID-based contactless identification system of ladles
(MDPI, 2022) Jančar, Dalibor; Machů, Mario; Velička, Marek; Tvardek, Petr; Vlček, Jozef
A method of contactless identification is proposed for steel ladles to eliminate manual inputs that negatively affect the monitoring system of ladles. It is an RFID (Radio Frequency Identification) method based on the principle of radio data transmission between the sensor and a moving object (in our case, a ladle), which is equipped with a so-called transponder (RFID tag). The RFID tag was part of the ladle; it was placed on its shell, reaching a temperature often exceeding 250 degrees C. The temperature limit for using an RFID transponder is 120 degrees C. For this reason, thermal insulation protection was made for the RFID transponder. Its design was preceded by simulations of temperature fields using numerical methods. The aim was to compare the resulting values obtained from numerical simulations with the actually measured temperatures and, on this basis, to subsequently perform a numerical simulation for conditions that are not operationally measurable.
Alkali activation of ground granulated blast furnace slag and low calcium fly ash using "one-part" approach
(Springer Nature, 2022) Matějková, Petra; Matějka, Vlastimil; Sabovčík, Tomáš; Gryžbon, Luděk; Vlček, Jozef
The utilization of the solid powder activator for the activation of the ground granulated blast furnace slag (GGBFS) and its mixtures with low calcium fly ash (FA) was tested. Utilizing the activator in a powder form enabled to obtain ready-to-use dry mixtures, which, after the addition of mixing water, molding, and hydration, created compact solid samples. The selected procedure known as "one-part" or "just-add water" approach is beneficial with respect to the traditional two parts approach based on the utilization of the liquid alkali activators. The experiments were subdivided into two parts. The first part was focused on the selection of the solid alkali activator for GGBFS activation. In this stage, two solid powder activators: (i) sodium metasilicate (NS) and (ii) disodium silicate pentahydrate in amounts that carry 2.5, 5, and 7 wt% of Na2O, were tested. The second part was focused on the verification of the suitability of selected solid alkali silicate for the activation of the mixtures of GGBFS with low calcium FA (80:20 and 60:40). The evolution of the compressive strength of the prepared alkali-activated materials was studied after 2, 7, 28, and 56 days of hydration. The raw materials and hydrated samples were examined by XRFS, XRD, FTIR, and SEM techniques. The positive effect of the thermal treatment at 400 degrees C on the compressive strength of the prepared samples was observed. The obtained results indicate the "one-part" method as suitable for the activation of low calcium fly ash in combination with GGBFS.
Corrosion resistance of MgO and Cr2O3-based refractory raw materials to PbO-rich Cu slag determined by hot-stage microscopy and pellet corrosion test
(MDPI, 2022) Ludwig, Maciej; Śnieżek, Edyta; Jastrzębska, Ilona; Prorok, Ryszard; Li, Yawei; Liao, Ning; Nath, Mithun; Vlček, Jozef; Szczerba, Jacek
Chemical resistance of commercial refractory raw materials against Cu slag is critical to consider them as candidates for the production of refractories used in Cu metallurgy. In this study, we show the comparative results for the corrosion resistance of four commercial refractory raw materials-magnesia chromite co-clinkers FMC 45 and FMC 57, PAK, and fused spinel SP AM 70-against aggressive, low-melting PbO-rich Cu slag (Z1) determined by hot-stage microscopy (up to 1450 degrees C) and pellet test (1100 and 1400 degrees C). Samples were characterized after the pellet test by XRD, SEM/EDS, and examination of their physicochemical properties to explore the corrosion reactions and then assess comparatively their chemical resistance. Since many works have focused on corrosion resistance of refractory products, the individual refractory raw materials have not been investigated so far. In this work, we show that magnesia chromite co-clinker FMC 45 exhibits the most beneficial properties considering its application in the production of refractories for the Cu industry. Forsterite (Mg2SiO4) and guggenite (Cu2MgO3) solid solutions constitute corrosion products in FMC 45, and its mixture with slag shows moderate dimensional stability at high temperatures. On the other hand, the fused spinel SP AM 70 is the least resistant to PbO-rich Cu slag (Z1); it starts to sinter at 970 degrees C, followed by a fast 8%-shrinkage caused by the formation of guggenite solid solution in significant amounts.
Characterization of waste sludge pigment from production of ZnCl2
(MDPI, 2021) Ovčačíková, Hana; Velička, Marek; Maierová, Petra; Vlček, Jozef; Tokarský, Jonáš; Čegan, Tomáš
This study is focused on the treatment of waste sludge from a zinc chloride production in order to prepare iron-rich pigments usable for a production of glazes. In galvanizing plants, yellow waste sludge containing significant amount of ZnO, Cl, and Fe2O3, is formed. This raw waste sludge cannot be used as a pigment in glaze. Therefore, three methods of treating this material were proposed: (a) washing with H2O, (b) calcination at 180 degrees C and washing by H2O, and (c) calcination at 900 degrees C and washing by H2O. These methods helped to reduce Zn and Cl content up to 97%. According to X-ray fluorescence analysis percentage of Fe2O3 increased from similar to 41% to similar to 98%. X-ray power diffraction analysis confirmed the formation of alpha-Fe2O3 (hematite) in the pigment prepared. Scanning electron microscopy with Energy dispersive X-ray analysis showed clusters of rounded particles, and also the change in size of particles after calcination was observed. Particle size, specific surface area, and density measurements together with thermogravimetric and differential thermal analyses were performed. Pigments prepared from the waste sludge were added to transparent glaze in amounts of 1, 5, 10, and 15 wt.%. Pigment-containing glazes were applied by spraying on fired ceramic tiles and then fired at 1060 degrees C. Color of glazes was determined by (Commission Internationale de l'Eclairage) CIE L*a*b* coordinates as colorless, light brown shades, brown-red, brown-yellow, and deep red-brown. Comparison with colors of glazes prepared using commercial pigments was also performed. Waste sludge can be used to prepare pigments and glazes containing pigments as an alternative to commercial products.
Effects of kaolin additives in fly ash on sintering and properties of mullite ceramics
(MDPI, 2021) Valášková, Marta; Blahůšková, Veronika; Vlček, Jozef
The effective utilization of fly ash (FA) as a raw material for ceramics production is performed on the FA-kaolin mixtures containing kaolins 10% by mass. The mixtures in comparison with FA and three raw kaolins were annealed to mullite ceramics at temperatures of 1000, 1100, 1200 and 1300 degrees C. The main aims were to contribute to the discussion on the effect of impurity of Na,K-feldspars in kaolins and Fe2O3 in FA on sintering procedure, porous ceramics properties and mullite structural properties. The phases were characterized using X-ray diffraction and thermogravimetry DTA/TGA methods. Mercury intrusion porosimetry was used for characterization of porosity of ceramic samples. Results evidenced the influence of feldspars in kaolins and Fe2O3 in FA on the sintering temperatures and properties of mullite ceramics. The fully FA-based ceramic sintered at 1100 degrees C exhibited post-sintering properties of bulk density 2.1 g/cm(3); compressive strength 77.5 MPa; and porosity, 2% in comparison with the FA/kaolin-based ceramics properties of bulk density 2.2 g/cm(3); compressive strength, 60-65 MPa; and porosity from 9.3 to 16.4% influenced by Na,K-feldspars. The best structural and mechanical characteristics were found for the FAK3 sample, supported by the high content of kaolinite and orthoclase in the kaolin K3 additive. The FAK3 annealed at 1100 degrees C exhibited good compressive strength of 87.6 MPa at a porosity of 10.6% and density of 2.24 g/cm(3) and annealed at 1300 degrees C the compressive strength of 41.3 MPa at a porosity of 19.2% and density of 1.93 g/cm(3).
A similarity model of the cooling process of fluids during transportation
(MDPI, 2021) Brestovič, Tomáš; Čarnogurská, Mária; Příhoda, Miroslav; Lázár, Marián; Pyszko, René; Jasminská, Natália
This article presents a description of a novel method for the identification of a decrease in the temperature of a liquid medium transported by railroad tank cars. No exact analytical solution exists for this phenomenon; therefore, the authors of this article have prepared a mathematical expression for the cooling process of the transported fluid by applying a dimensional analysis, which facilitated the identification of the dimensionless criteria using the relevant dimensional parameters. A functional dependence between the criteria can be identified through a physical or numerical experiment. In this case, a database of the results from a detailed numerical model was used; however, its disadvantage is that the calculation takes much longer than in a simpler similarity model. The output of the similarity model was a function of the average temperature of the fluid at a time applicable to various alternatives in the geometrical, physical, and boundary conditions. The standard deviation of the difference between the temperatures predicted by the similarity model and those calculated by the numerical simulation T-mod - T-sim represented 4.8% relative to the simulated fluid temperature.
Characterization of waste sludge pigment from production of ZnCl2
(MDPI, 2021) Ovčačíková, Hana; Velička, Marek; Maierová, Petra; Vlček, Jozef; Tokarský, Jonáš; Čegan, Tomáš
This study is focused on the treatment of waste sludge from a zinc chloride production in order to prepare iron-rich pigments usable for a production of glazes. In galvanizing plants, yellow waste sludge containing significant amount of ZnO, Cl, and Fe2O3, is formed. This raw waste sludge cannot be used as a pigment in glaze. Therefore, three methods of treating this material were proposed: (a) washing with H2O, (b) calcination at 180 degrees C and washing by H2O, and (c) calcination at 900 degrees C and washing by H2O. These methods helped to reduce Zn and Cl content up to 97%. According to X-ray fluorescence analysis percentage of Fe2O3 increased from similar to 41% to similar to 98%. X-ray power diffraction analysis confirmed the formation of alpha-Fe2O3 (hematite) in the pigment prepared. Scanning electron microscopy with Energy dispersive X-ray analysis showed clusters of rounded particles, and also the change in size of particles after calcination was observed. Particle size, specific surface area, and density measurements together with thermogravimetric and differential thermal analyses were performed. Pigments prepared from the waste sludge were added to transparent glaze in amounts of 1, 5, 10, and 15 wt.%. Pigment-containing glazes were applied by spraying on fired ceramic tiles and then fired at 1060 degrees C. Color of glazes was determined by (Commission Internationale de l'Eclairage) CIE L*a*b* coordinates as colorless, light brown shades, brown-red, brown-yellow, and deep red-brown. Comparison with colors of glazes prepared using commercial pigments was also performed. Waste sludge can be used to prepare pigments and glazes containing pigments as an alternative to commercial products.
Alkali-activated metakaolin and fly ash as unfired ceramic bonding systems
(MDPI, 2021) Vlček, Jozef; Topinková, Michaela; Klárová, Miroslava; Maierová, Petra; Ovčačíkova, Hana; Matějka, Vlastimil; Martaus, Alexandr; Blahůšková, Veronika
Metakaolin (MK) prepared by the calcination of kaolin at 550 degrees C and fly ash (FA) from the combustion of black coal in a granulating boiler were used to prepare unfired ceramic bonding systems via the alkali activation process. A long-term stability of the mechanical properties of the prepared samples similar to the unfired ceramic systems was observed. The optimal metakaolin and fly ash ratio, the type of the activator (NaOH or water glass) and its concentration were evaluated after the hydration in: a) laboratory conditions; b) hydration box; and c) under the hydrothermal activation. Raw materials and the samples prepared by alkali activation process were characterized by XRD, XRF, TG/DTA, and FTIR methods. The mechanical properties of the prepared samples were tested using a compressive strength test after 2, 28 and 56 days of hydration. The compressive strengths of 16 and 24 MPa after 28 days of hydration were reached for FA samples activated with water glass. The alkali activation of MK was successful in the NaOH solution of the molar concentration above 5 M. The compressive strength values of metakaolin, activated hydrothermally and hydrated at laboratory conditions, reached 11.2 and 5.5 MPa, respectively, for 5 M activator of NaOH.
Quantitative evaluation of crystalline and amorphous phases in clay-based cordierite ceramic
(MDPI, 2020) Klika, Zdeněk; Valášková, Marta; Bartoňová, Lucie; Maierová, Petra
An innovative chemical quantitative mineral analysis (CQMA) was successfully tested on a cordierite-based clay ceramic sample to quantify crystalline and amorphous components. The accuracy of this method was demonstrated on an added module to the CQMA program that used oxide formulas of amorphous phases obtained by energy dispersive X-ray spectroscopy (EDS) microprobe chemical analysis. This CQMA method was tested for three variants calculated using chemical analysis, i.e., X-ray diffraction (XRD) identification of crystalline (cordierite and enstatite) and amorphous phases by scanning electron microscopy (SEM)/EDS texture and microanalyses. The test results from CQMA suggest their application possibilities as well as the limits of their utilization.

Browse

Recent Submissions