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1

Kształtowanie wybranych właściwości cieplnych geopolimerów poprzez ich modyfikację metalami

Ciemnicka Justyna, Brych-Dobrowolska Małgorzata, Prałat Karol, Koper Artur, Buczkowska Katarzyna Ewa

Przegląd Budowlany

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2025

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R. 96, nr 3

98--101

PL

Przeprowadzono badania współczynnika przewodzenia ciepła oraz dyfuzyjności cieplnej kompozytów geopolimerowych modyfikowanych rodzajem kruszywa oraz dodatkiem proszku metalicznego. Stwierdzono znaczący wpływ dodatku kruszywa szamotowego na zmniejszenie współczynnika przewodzenia ciepła badanych geopolimerów. Zastosowanie odpowiedniego proszku metalicznego oraz dobranie odpowiedniej jego ilości również wpływa pozytywnie na parametry cieplne kompozytów geopolimerowych.

EN

Thermal conductivity coefficient and thermal diffusivity of geopolymer composites modified with the type of aggregate and the addition of metal powder were tested. A significant effect of the addition of fireclay aggregate was found on reducing the thermal conductivity coefficient of the tested geopolymers. The use of appropriate metal powder and the selection of its appropriate amount also have a positive effect on the thermal parameters of geopolymer composites.

2

Characterisation of the microstructure, thermophysical, and mechanical properties of the ti3alc2-tic composite

Łęczycki Krzysztof, Starczewski Maciej, Panas Andrzej, Sałaciński Michał, Krupińska Anna

Journal of KONBiN

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2025

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Vol. 55, iss.2

97--109

EN

This study focuses on a complex complementary investigation of the properties of the composite structure with a Ti3AlC2 MAX phase matrix and dispersive titanium carbide particle filling. The paper presents the results of microstructure studies, thermophysical and mechanical properties of the Ti3AlC2-TiC composite obtained by the SPS (spark plasma sintering) method.. Microstructural observations, including the distribution of both phases of the composite, were carried out using Scanning Electron Microscopy (SEM) combined with Energy-Dispersive X-ray Spectroscopy (EDS). As part of the thermophysical properties analysis, the temperature-dependent thermal diffusivity was determined using the Laser Flash Analysis (LFA) method, along with specific heat capacity measured by LFA using a reference sample, and linear thermal expansion. Based on the parameters and density of the composite (determined from geometric and weight measurements), its thermal conductivity was calculated, accounting for its temperature dependence. The presented material characterisation was supplemented with the results of Dynamic Mechanical Analysis (DMA), performed in a three-point bending mode instrument operation on a free-standing sample, as well as hardness measurements using the Vickers method. The obtained data were analysed, and the results were used both for ongoing calculations of interdependent parameters and to verify the correctness of the acquired data.

PL

Praca dotyczy kompleksowych komplementarnych badań właściwości struktury kompozytu z osnową fazy MAX Ti3AlC2 i dyspersyjnym wypełnieniem cząstkami węglika tytanu. W referacie przedstawiono wyniki badań mikrostruktury, właściwości cieplnofizycznych oraz mechanicznych kompozytu Ti3AlC2-TiC uzyskanego metodą SPS (spark plasma sintering). Obserwacje mikrostruktury z uwzględnieniem rozmieszczenia obydwu faz kompozytu przeprowadzono z wykorzystaniem metod skaningowej mikroskopii elektronowej (SEM) z zastosowaniem spektroskopii dyspersji energii (EDS). W ramach badań właściwości cieplnofizycznych określono zależności temperaturowe dyfuzyjności cieplnej metodą wymuszenia laserowego (LFA), ciepła właściwego metodą LFA z wykorzystaniem pomiarów wzorca oraz liniowej rozszerzalności cieplnej. Na podstawie uzyskanych parametrów oraz gęstości kompozytu wyznaczonej metodą wypornościową obliczono jego przewodność cieplną z uwzględnieniem jej zależności od temperatury. Przedstawioną charakterystykę materiału rozszerzono o wyniki pomiarów dynamicznej analizy (termo)mechanicznej (DMA), które zrealizowano w trybie trójpunktowego zginania próbki swobodnej oraz o pomiary twardości metodą Vickersa. Uzyskane dane były poddane analizie, której wyniki wykorzystano zarówno do bieżącego przeliczania wartości zależnych od siebie parametrów, jak i do sprawdzenia poprawności uzyskiwanych danych.

3

Effect of the addition of microencapsulated phase change material to epoxy resin on the thermal diffusivity of the resulting structure

Omen Łukasz, Panas Andrzej J., Wajdzik Przemysław, Szczepaniak Robert

Advances in Science and Technology. Research Journal

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2025

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Vol. 19, no. 2

445--452

EN

This work concerns the study of the effect of adding microgranules containing a phase change material (PCM) on the thermal diffusivity value of the resulting composite structure. Two commercially available epoxy resins were applied as the composite matrix material: pure epoxy resin and epoxy resin with a filler in the form of metal powder. The dispersed phase was the BASF Micronal DS5038 X microgranulate, i.e. a bed of polymer spherical shells containing PCM filling. The tests were carried out using the modified Ångström method in a symmetrical bilateral harmonic excitation of the temperature of outer sides of assembled two tested disc-shaped samples. The temperature range of measurements covered the interval from 0°C to 35°C, i.e. most of the typical working range of microgranules. In selected measurement cases, the tests were extended to temperatures from ‒10°C to 75°C. The results obtained for the four structures studied were compared and analyzed to illustrate the quantitative effects of structure modification and to document the qualitative effects of the observed phase changes that occurred both on heating and cooling.

4

Thermal Diffusivity Prediction from P-Wave Velocity and Porosity Assessment for Sandstone Reservoirs

El Sayed Abdel Moktader A., El Sayed Nahla A.

Inżynieria Mineralna

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2024

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Vol. 1, no. 1

115--123

EN

Petrophysical heterogeneities of sandstone reservoirs which are generated by rock internal variability resounded to the magnitude of the rock thermal diffusivity. This is expected mostly to variation of rock density, porosity, reservoir temperature and its thermal conductivity. New methodology for calculating thermal diffusivity in a sandstone rock formation is intended and effectively employed some laboratory thermophysical measurements for sandstone reservoirs. The proposed petrophysical model establishes thermal diffusivity if both the effective porosity and acoustic (compressional) wave velocity of the rock are known. Some reliable petrophysical models (El Sayed, 2011 and Ahmed, 2019) concerned to both the Baharyia (Egypt) and Szolnok (Hungary) sandstone formations are used with only some modifications to build an innovative nomography. It permitted precise quantification and determination of the thermal diffusivity for both dry and saturated sandstone samples normalized to reservoir temperature (300K-1060 K). Verification of the proposed model is achieved with applying study cases of laboratory measured thermophysical properties (i.e., porosity, thermal diffusivity/or conductivity and longitudinal wave velocity) for different sandstone types, geological ages and geographic locations. A regression analysis of thermal diffusivity between laboratory measured and predicted data for dry (Ҡ-dry) rock samples yield a plausible coefficient of correlations as (R =0.73; 0.86 and 0.98) for three different sandstones obtained from Permo-Carboniferous in Germany (Aretz, 2016) and of dissimilar geologic age in Switzerland (Pimienta, 2018) respectively while, the average standard error equals 0.011. Then again, the laboratory measured and predicted thermal diffusivity (Ҡ-sat) of saturated samples display an appropriate coefficient of correlation (R = 0.76) and average standard error (0.0089).

5

Stabilization of Sewage Sludge from North Moroccan Wastewater Treatment Plants Using Convective Indirect Solar Drying

Bougayr El Houssayne, Bahammou Younes, Fantasse Azeddine, Lakhal El Khadir, Berroug Fatiha, Bouziane Abdelkhalek, Idlimam Ali

Ecological Engineering & Environmental Technology

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2024

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Vol. 25, iss. 10

1--16

EN

The significant production of sewage sludge by wastewater treatment plants on a global scale and the lack of correspondence between housing development and the expansion of sanitation infrastructure indicate a genuine concern regarding environmental preservation. This study addresses the crucial issue of effective sewage sludge management and its environmental impact. In the context of searching for new drying methods that optimize energy use and effectively stabilize sewage sludge, this work investigated the drying behavior of sewage sludge from treatment plants in two northern Moroccan cities using a prototype of an indirect forced convection solar dryer. The drying experiments enabled the determination of drying kinetics as well as highlighted the influence of temperature and humidity on the drying rate. The characteristic drying curve (CDC) and its mathematical expression were determined using Van Meel’s formalism. Thermal diffusivity of wastewater sludge during drying was also investigated. Using Fick’s diffusion model, diffusion coefficients ranged between 0.59 × 10-9 m2/s and 1.43 × 10-9 m2/s, demonstrating an increase in effective diffusivity with rising temperature. The Arrhenius equation provided activation energy values of 16.80 kJ/mol for Oujda samples and 19.72 kJ/mol for Nador samples, indicating the effect of temperature on effective diffusivity. A new equation based on the Midilli-Kucuk model was proposed to predict the drying behavior under untested aerothermal conditions, considering drying temperature and the initial dryness. This study offers a comprehensive analysis of the drying kinetics and effective diffusivity of sewage sludge, providing valuable insights for designing large dryers for sludge management in WWTPs. This approach presents an optimal solution for drying and stabilizing sludge, contributing to environmental preservation efforts.

6

Thermophysical properties and microstructure of 32CrMoV12-28 hot-work tool steel

Koniorczyk Piotr, Zieliński Mateusz, Sienkiewicz Judyta, Zmywaczyk Janusz

Archives of Thermodynamics

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2024

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Vol. 45, no. 2

269--277

EN

Measurements of thermal diffusivity, heat capacity and thermal expansion of hot work tool steel 32CrMoV12-28 have been carried out in the temperature range from room temperature (RT) to 1000℃. 32CrMoV12-28 steel has been tested for military applications as steel for gun barrels. The thermophysical properties of this steel can be used as input data for numerical simulations of heat transfer in gun barrels. Both the LFA 427 laser flash apparatus in the RT 1000℃ temperature range and the LFA 467 light flash apparatus in the RT 500℃ temperature range were used for thermal diffusivity tests. Specific heat capacity was investigated in the range RT 1000℃. The specific heat was determined by two methods, i.e. the classical method, the so-called continuous-scanning method and the stepwise-scanning method according to EN ISO 11357-4. The paper compares both methods and assesses their suitability for testing the specific heat capacity of barrel steels. Thermal expansion was investigated in the range RT 1000℃. Inconel 600 was selected as the reference material during the thermal diffusivity test using LFA 467. Light microscopy (LM), scanning electron microscopy (SEM), and Vickers microhardness measurements were performed to detect changes in the microstructure before and after thermophysical measurements. We compared the results of measurements of the thermophysical properties of 32CrMoV12-28 steel with the results of our tests for other barrel steels with medium carbon content, i.e. X37CrMoV5-1 (1.2343), 38HMJ (1.8509) and 30HN2MFA. The comparison was made in terms of shifting the effect of material shrinkage towards higher temperatures.

7

The influence of measurement conditions on the determined values of thermal parameters of different types of concrete

Garbalińska Halina, Matys Małgorzata

Archives of Civil Engineering

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2024

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Vol. 70, nr 2

493--511

EN

In recent years, great emphasis has been placed on the introduction of energy-saving solutions to the construction sector. Building envelopes made of concrete with a specially selected composition give great opportunities in this regard. As part of a wide-ranging experiment, the authors undertook to diagnose how much thermal conductivity, volumetric specific heat and thermal diffusivity can be improved with an aerating admixture and different types of aggregates. Three groups of composites were tested: B1 – on stone aggregate, B2 – on expanded clay aggregate, B3 – on sintered fly ash aggregate. Each of the groups was divided into 4 formulations made without an aerating admixture and with its increasingly higher content of 0.8, 1.1, 1.4% in relation to the weight of cement. The thermal parameters were measured on the top (T) and bottom (B) surfaces of 36 rectangular samples (3 samples from each of the 12 mixtures) with the ISOMET 2104 apparatus. Diagnostic tests concerning the influence of measurement conditions were carried out on dry and water-saturated samples. It has been proven that for each composite and in both conditions, the values of thermal parameters determined on the lower surfaces will not correctly describe the properties of the real structure present in the main volume of the element. Only measurements carried out on surfaces with a structure corresponding to the interior of the element provide adequate data that can be used in decision-making processes and in numerical simulations to assess the real thermal qualities of building envelopes.

PL

W ostatnich latach kładzie się duży nacisk na wprowadzenie energooszczędnych rozwiązań do sektora budownictwa. Duże możliwości w tym względzie dają przegrody budowlane wykonane z betonów o specjalnie dobranym składzie. Autorki w ramach szeroko zakrojonego eksperymentu podjęły się zdiagnozowania, na ile można poprawić przewodność cieplną λ, objętościowe ciepło właściwe CV oraz dyfuzyjność termiczną za pomocą domieszki napowietrzającej oraz różnego rodzaju kruszyw. Badaniom poddano trzy grupy kompozytów: B1 – na kruszywie kamiennym, B2 – na kruszywie keramzytowym, B3 – na kruszywie popiołoporytowym. Równocześnie każda z grup została podzielona na 4 receptury wykonane bez domieszki napowietrzającej oraz z coraz to wyższą jej zawartością wynoszącą 0.8, 1.1, 1.4% w stosunku do masy cementu. Badania parametrów cieplnych zrealizowano techniką niestacjonarną wykorzystując aparat ISOMET 2104. Pomiary przeprowadzono na górnych i dolnych powierzchniach 36 próbek prostopadłościennych (po 3 próbki z każdej z 12 mieszanek), wykonując je na każdej z powierzchni dwukrotnie. Górne powierzchnie reprezentowały faktyczną strukturę występującą we wnętrzu każdego z badanych kompozytów. Dolne powierzchnie ukształtowane na styku z dnem formy odznaczały się na tyle zmienioną strukturą, że w bardzo istotny sposób zmieniały wartości sczytywanych na nich parametrów. Badania diagnostyczne, dotyczące wpływu warunków pomiarowych, przeprowadzono na próbkach suchych i nasyconych wodą. Udowodniono, że w przypadku każdego kompozytu i w każdych warunkach wilgotnościowych, wyznaczone na dolnych powierzchniach wartości parametrów cieplnych nie będą prawidłowo opisywać właściwości realnej struktury występującej w zasadniczej objętości tego elementu.

8

Testing the thermal properties of the insulating structures of a flight data recorder

Panas Andrzej J., Szczepaniak Robert, Krupińska Anna, Łęczycki Krzysztof, Nowakowski Mirosław

Acta Mechanica et Automatica

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2024

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Vol. 18, no. 2

244--251

EN

This paper deals with the problems faced during the research on the insulating structures used in the thermal shielding of flight recorders. These structures are characterised by specific properties determined by, among other aspects, their porosity. The complex and coupled heat-exchange phenomena occurring under the operating conditions of the recorders, and in numerous cases combined with mass exchange, require dedicated test methods. The paper characterises the origin of the research problem, presents a methodology for comprehensive testing of the thermal propertiesand uses the example of determining the insulating properties of the Promalight microporous structure ®-1000R. The authors focussed on thermal diffusivity tests performed by means of the oscillatory excitation method. The measurements were conducted on a test stand to determine the effect the type of gas filling had on the porous structure and the pore filling gaspressure effect on the temperature characteristics of apparent thermal diffusivity. The authors also conducted research on the structure’s resistance to direct flame exposure. The analysis of the obtained results enable recognition and characterisation of the key phenomena of heat and mass transfer; the numerical results exert a significant influence on their application.

9

Własności termofizyczne wybranych stali lufowych

Koniorczyk Piotr, Zieliński Mateusz

Problemy Techniki Uzbrojenia

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2023

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R, 52, z. 164

19--41

PL

Artykuł poświęcono badaniom własności termofizycznych, tzn. dyfuzyjności cieplnej, przewodności cieplnej, rozszerzalności cieplnej oraz ciepła właściwego wybranych stali lufowych. W typowych stalach lufowych, np. 30HN2MFA występuje przemiana strukturalna w temp. około 730℃, w której zachodzi skurcz materiału. Sposobem na podwyższenie trwałości luf jest zmiana rodzaju stali na taki, w którym ta przemiana nie zachodzi lub ma miejsce, ale w wyższych temperaturach. W pracy przedstawiono wyniki badań eksperymentalnych wszystkich wymienionych powyżej własności termofizycznych pięciu wybranych stali lufowych, tzn. 38HMJ, 30HN2MFA, DUPLEX 2205, WCL oraz MARAGING 350. Pomiary wykonano w zakresie temperatury od pokojowej do około 1100℃. W ten sposób utworzono bazę danych własności termofizycznych tych stali jako dane wejściowe do wykonania obliczeń wymiany ciepła w lufach broni strzeleckiej i armat.

EN

This paper is devoted to the study of thermophysical properties, i.e. thermal diffusivity, thermal conductivity, thermal expansion and specific heat of selected barrel steels.In typical barrel steels, e.g.30HN2MFA, a structural trans-formation occurs at about 730℃, at which material shrinkage occurs. The way to increase the durability of the barrels is to change the steel grade to one in which this transformation does not occur or does occur, but at higher temperatures. The paper presents the results of experimental studies of all the above-mentioned thermophysical properties of five selected barrel steels, i.e. 38HMJ, 30HN2MFA, DUPLEX 2205, WCL and MARAGING 350. Measurements were made in the range from room temperature to about 1100°C. In this way, a data-base of thermophysical properties of these steels was created as input data for the calculation of heat transfer in the barrels of small arms and cannons.

10

Combined Effect of Silicon Dioxide and Titanium Dioxide Nanoparticles on Concrete Properties

Al-Rbaihat Raed, Al-Marafi Mohammad Nour

Journal of Ecological Engineering

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2023

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Vol. 24, nr 12

319--335

EN

Nanoconcrete is an attractive research area because of its recent practical applications in building materials technologies. This study investigates the individual and combined effects of using nanoparticles in concrete mixtures as a cement substitute. Microscopic images are also used to determine changes in the microstructure of modified concrete in the present study. Concrete’s thermal and mechanical properties, including thermal conductivity (k), specific heat capacity (C), thermal diffusivity (α), and compressive strength (σ), are the leading concrete characteristics examined. The current study used different percentages (0%, 1%, 3%, and 5%) of nano-SiO2, nano-TiO2, and combined nano-SiO2/TiO2 particles as cement substitutes for 7 and 28 days of curing to examine the characteristics of nanoconcrete compared to conventional concrete (CC). The results indicated that adding individual nanoparticles to CC could improve concrete’s thermal and mechanical properties. Among the investigated nanomaterials (nano-SiO2, nano-TiO2, and combined nano-SiO2/TiO2 particles), nano-SiO2 was superior in that context. The optimal thermal properties of nanoconcrete were achieved when 5% nano-SiO2 (C-S5 specimen) was added. The k and α coefficients of sample C-S5 compared to the CC specimen were reduced by 65.6% and 80.3%, respectively, while the C coefficient was increased by 12.8%. Meanwhile, the optimal compressive strength coefficient of nanoconcrete was achieved when 3% nano-SiO2 (C-S3 specimen) was added, where the compressive strength coefficient of sample C-S3 compared to sample CC was increased by 19.6%. In contrast, for the combined effect, the thermal properties of concrete were improved, but the compressive strength coefficient of concrete was reduced. Overall, the present experimental findings offer valuable information about the impact of nanotechnology on high-performance concrete to save energy in buildings.

11

Study of the periodic thermal contact between exhaust valve and its seat in an internal combustion engine

Zemmouri Amina, Azzouz Salaheddine, Benchadli Djillali, Ayad Amar, Chaoui Kamel

Eksploatacja i Niezawodność

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2023

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Vol. 25, no. 2

art. no. 162911

EN

The focus of internal combustion engine development for urban vehicles is shifting towards reducing materials by making them lighter. In order to maintain thermal and flow levels, a model was developed to study the thermal behavior of valve seats during periodic contact, which can also help improve engine performance and fuel efficiency. The model, composed of two cylindrical bars in periodic contact, takes into account the evolution and topography of the contact surface. The model's performance was evaluated through various experimental studies and showed a maximum difference of 5.05% with experimental values, in good agreement with previous literature. The results showed that heat flux increases with increasing contact frequency and thermal diffusivity affects conductive transfer. This model can be used by manufacturers to evaluate cylinder head temperature and by the automotive industry to improve heat transfer in engines.

12

The Possibility of Using the Finite Element Method for Determining Thermal Diffusivity on the Example of Nickel Using the Classic and The Modified Pulse Method

Szczepaniak Robert, Terpiłowski Janusz, Woroniak Grzegorz

Advances in Science and Technology. Research Journal

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2023

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Vol. 17, no. 6

274--287

EN

The main purpose of the work is to present the possibility of using the finite element method implemented in the COMSOL 3.5a program in the heat transfer symmetry 2D module to determine thermal diffusivity by the classic and modified pulse methods. The method of determining the thermal diffusivity by means of measuring and recording the course of the temperature difference between the extreme surfaces of the tested sample and changes in the temperature increase on the back surface after a laser shot at its front surface, assuming that the sample is adiabatic for a representative experimental course at a given temperature, is discussed. This paper presents the basic metrological conditions for the implementation of the modified pulse method for testing the temperature characteristics of thermal diffusivity on the example of nickel. The heat pulse generated by the laser method at the extreme surface of the sample for a thermostatic temperature of 341.8 °C was simulated. Using the inverse problem in both the classic and modified methods, the thermal diffusivity of the material in question was determined and these results were compared with the experimentally obtained values. The values of thermal diffusivity differ from those obtained experimentally by 3.3% for the classic method and approximately 2.5% for the modified method. A preliminary analysis of the influence of the number of nodal points on the numerical results obtained was also carried out and the results for the number of nodes between 64 and 17,000 change by only 1.1%. The paper presents a combination of experimental and numerical studies which is useful in science and simplifies the process of time-consuming experimental studies.

13

Investigation of Carbon Nanotube Particles Addition Effect on the Dispersed Composite Structure Thermal Diffusivity

Omen Łukasz, Szczepaniak Robert, Panas Andrzej J.

Advances in Science and Technology. Research Journal

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2023

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Vol. 17, no. 5

280--288

EN

The article addresses the issue of the possibility of improving the thermal transport parameters of an epoxy resin, such as thermal diffusivity (TD) and thermal conductivity (TC), by the addition of carbon nanotubes (CNT) as a high thermal conductivity filler. In the case presented here, the effect of the addition of high TC carbon nanotubes to commercial epoxy resin LH145 cured with H147 hardener was investigated experimentally. The main parameter studied was thermal diffusivity. Measurements were carried out for samples of epoxy resin and epoxy resin matrix composites with dispersed CNTs with a volume fraction of carbon nanotubes ranging from 1% to 6%. A modified Ångström temperature oscillation method was used to obtain TD. Basic measurements were performed in the temperature range from 20 ºC to 80 ºC while maintaining high temperature resolution that allows to observe the TD changes with the temperature change. During extended temperature range additional differential scanning calorimetry studies, the effects after curing of the epoxy resin were also characterized. As a result, the temperature dependence of thermal conductivity was determined and data for determining thermal conductivity was obtained. However, the analysis of the obtained results did not show a significant dependence of the studied parameters on the amount of CNT additive for the studied compositions.

14

The Influence of Ag2Te Addition on Thermoelectric Properties of Bismuth Telluride

Drzewowska Sylwia, Lan Tian-Wey, Onderka Bogusław

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 1

5--15

EN

The resistivity, Seebeck coefficient and thermal diffusivity were determined for BiTe3 + Ag2Te composite mixtures. Subsequent measurements were carried out in the temperature range from 20 to 270°C, and for compositions from pure Bi2Te3 to xAg2Te = 0.65 selected along the pseudo-binary section of Ag-Bi-Te ternary system. It was found that conductivity vs. temperature dependence shows visible jump between 140 and 150°C in samples with highest Ag2Te content, which is due to monoclinic => cubic Ag2Te phase transformation. Measured Seebeck coefficient is negative for all samples indicating they are n-type semiconductors. Evaluated power factor is of the order 1.52·10-3 and it decreases with increasing Ag2Te content (at. %). Recalculated thermal conductivity is of the order of unity in W/(m K), and is decreasing with Ag2Te addition. Finally, evaluated Figure of Merit is 0.43 at 100°C and decreases with temperature rise.

15

Determination of thermal diffusivity values based on the inverse problem of heat conduction - numerical analysis

Adamowicz Adam

Acta Mechanica et Automatica

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2022

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Vol. 16, no. 4

399--407

EN

This paper presents a discussion on the accuracy of the method of determining the thermal diffusivity of solids using the solution of the inverse heat conduction equation. A new measurement data processing procedure was proposed to improve the effectiveness of the method. Using the numerical model, an analysis of the sensitivity of the method of thermal diffusivity determination to changes in operational and environmental parameters of the test was carried out. The obtained results showed that the method was insensitive to the parameters of the thermal excitation impulse, the thickness of the tested sample, and the significant influence of convection cooling on its accuracy. The work was completed with the formulation of general conclusions concerning the conditions for determining the thermal diffusivity of materials with the use of the described method.

16

Practical aspects of heat conduction simulation in household heating optimization tasks

Duda Jan Tadeusz

Science, Technology and Innovation

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2019

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Vol. 5, no. 2

9--22

EN

Mathematical model selection for simulation heat conduction processes in household heating optimization task is considered. The essence of the matter is that the heat transfer dynamics properties are very diversified, so simulation procedure formulae and parameters should be properly selected to avoid excessive modeling errors with reasonable calculation time being held. The typical state-space model and analytical formulae for step response of the heat conduction across a homogeneous wall are presented and compared in terms of modeling errors. Formal and numerical problems of heat losses simulation are discussed. Semi-analytical step-response formulae for multilayer walls are derived and their accuracy is compared with effects of simulation based on the state-space model. Some recommendations for time and space discetization parameters are given.

17

Estimation of thermal diffusivity of building elements based on temperature measurement for periodically changing boundary conditions

Owczarek Mariusz, Baryłka Adam

Rynek Energii

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2019

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Nr 5

76--79

EN

Thermal diffusivity, also called the temperature equalisation coefficient, is the basic parameter in the Fourier equation for non stationary heat exchange. In construction, its value is needed to calculate heat losses in a transient state. Building elements made, for example, of reinforced concrete have a non-homogeneous structure. For such cases, values available in the literature may differ significantly from the specific object to be modelled. More precise values of thermal diffusivity can be obtained from measurements for a given element. Since these are usually large items, the measurement method should take into account the material in the entire volume of the element. Proposals for such a method based solely on measuring the temperature at several depths in the sample are presented. In the case of external walls of the building, the sinusoidal temperature variation in the 24-hour cycle is natural. The periodic temperature variability was simulated with a one-dimensional flow in a wall with assumed thermal diffusivity. Then, the value of this diffusivity from the calculated temperatures was determined. The obtained results of diffusivity are presented depending on the boundary condition. A minimum relative error rate of 2 to 6 percent was obtained. Using the data presented in the article, conclusions can be drawn as to the conditions that must be met to determine the diffusive value in actual measurements with the required accuracy. The results obtained indicate that this method is worth further research.

PL

Dyfuzyjność cieplna, zwana też współczynnikiem wyrównania temperatury jest podstawowym parametrem w równaniu Fouriera dla niestacjonarnej wymiany ciepła. W budownictwie jej wartość jest potrzebna dla obliczenia strat ciepła w stanie nieustalonym. Elementy budowlane wykonane na przykład z żelbetu mają strukturę niejednorodną. Dla takich przypadków wartości tablicowe z literatury mogą się znacznie różnić od konkretnego obiektu, dla którego modelujemy wymianę ciepła. Dokładniejsze wartości dyfuzyjności cieplnej można uzyskać z pomiarów dla danego elementu. Ponieważ są to zwykle elementy o dużych rozmiarach metoda pomiaru powinna brać pod uwagę materiał w całej objętości elementu. Przedstawiono propozycje takiej metody opierającej się wyłącznie na pomiarze temperatury na kilku głębokościach w próbce. W przypadku ścian zewnętrznych budynku naturalna jest sinusoidalna zmienność temperatury w cyklu dobowym. Symulowano okresową zmienność temperatury przy jednowymiarowym przepływie w ścianie o założonej dyfuzyjności cieplnej. Następnie wyznaczono wartość tej dyfuzyjności z obliczonych temperatur. Przedstawiono otrzymane wyniki dyfuzyjności w zależności od warunku brzegowego. Otrzymano minimalną wartość błędu względnego od 2 do 6 procent. Za pomocą danych przedstawionych w artykule można wyciągnąć wnioski co do warunków jakie muszą być spełnione, aby wyznaczyć wartość dyfuzyjności w rzeczywistych pomiarach z wymaganą dokładnością. Otrzymane wyniki wskazują, że metoda ta jest warta dalszych badań.

18

Mixing characteristics of the subarctic front in the Kuroshio-Oyashio confluence region

Zhu Ke-Lan, Chen Xi, Mao Ke-Feng, Hu Dong, Hong Sen, Li Yan

Oceanologia

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2019

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No. 61 (1)

103--113

EN

This paper analyzes the mixing characteristics of the Subarctic Front (SAF) in the Kuroshio-Oyashio Confluence Region based on temperature, salinity, and current data obtained from surveys and remote sensing in June 2016. The frontal zone of the observed area is at 145°-151°E, 38°-41°N. The front is distributed between 25.5-26.7 σ0 in a band pattern inclined from north to south and is deeper in the south. The region shallower than 200 m and distributed along the isopycnal of 25.9-26.1σ0 has thestrongest horizontal temperature andsalinity gradients, andthe largest of the former can reach over 0.7°C/km. Diapycnal mixing of the SAF ismainly turbulent; it is stronger in the north than in the south. The region with stronger turbulence (Kρ > 10-3.5 m2/s) is distributed mainly in water layers within and under the front (26.1-26.7σ0), showing that the SAF is shallower in the north and deeper in the south along the front. Symmetric instability may be the main factor causing strong turbulent mixing in the frontal zone.Double diffusion mixing is stronger in the south than in the north; the region with stronger double diffusion (K0 > 10-4.5 m2/s) is distributed mainly in water layers within and above the front (25-26.5σ0) on the southern side of the SAF. These water layers are dominated mainly by „salt-fingering'' double diffusion, with only a few water layers dominated by „diffusive layering'' double diffusion mixing in middle and lower waters deeper than 300 m.

19

An experimental method for estimating the thermal diffusivity of building elements, depending on the resolution of temperature measurement

Owczarek Mariusz

Modern Engineering

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2019

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1

28--33

EN

Thermal diffusivity, also known as temperature equalization coefficient, is the basic parameter in the Fourier equation for non-stationary heat exchange. Its values are known for homogeneous materials with a specific composition. Building elements made of reinforced concrete, for example, have a heterogeneous structure. For such cases, table values from the literature may differ significantly from the specific object for in real constructions. More accurate thermal diffusivity values can be obtained from measurements for a given element. Since these are usually large sized elements, the measurement method should take into account the material in the entire volume of the element. Proposals for such a method based solely on temperature measurement at several depths in the sample were presented. It consists in solving the inverse problem assuming a polynomial solution of the Fourier equation. An attempt was made to validate the method through a numerical experiment. Temperature variability was simulated with one-dimensional flow in the wall with assumed thermal diffusivity. Then the value of this diffusivity was determined from the calculated temperatures. On the inside of the partition, a constant temperature was maintained and on the outside it changed periodically. The dependence of the error in the obtained diffusivity value on the precision of temperature results was analyzed. Depending on the precision of the calculations, a minimum relative error of 2 to 6 percent was obtained. With the help of the data presented in the article, conclusions can be drawn as to the conditions that must be met to determine the value of diffusivity in real measurements with the required accuracy. The obtained results indicate that this method is worth further research.

20

Optical and thermal properties of TeO2–B2O3–Gd2O3 glass systems

Eevon C., Halimah M. K., Azlan M. N., El-Mallawany R., Hii S. L.

Materials Science Poland

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2019

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Vol. 37, No. 4

517--525

EN

New glass samples with composition (1 – x)[(TeO₂)₇₀(B₂O₃)₃₀] – x(Gd₂O₃) with x = 0.2, 0.4, 0.6, 0.8 and 1.0 in mol% have been synthesized by conventional melt-quenching techniques. X-ray diffraction (XRD) studies were performed in order to confirm the amorphous nature of the samples. The density of the samples has been found to vary with the Gd₂O₃ content, whereas an opposite trend has been observed in the molar volume. The analysis of Fourier Transform Infrared (FT-IR) spectroscopy of the samples showed that the glass network is mainly built of TeO, TeO₄, BO₃ and BO₄ units. The addition of Gd₂O₃ changed the refractive index, optical band gap and Urbach energy of the glass samples. The thermal properties of the studied glasses were investigated by measuring the thermal diffusivity of the samples by using photoflash method at room temperature.