Wyniki wyszukiwania - BazTech

1

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.

2

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.

3

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.

4

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.

5

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.

6

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.

7

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.

8

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.

9

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.

10

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

|

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.

11

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.

12

Investigation of thermal properties of novel phase change material mixtures (octadecane-diamond) with laser flash analysis

Sierakowski Mateusz, Godlewski Wojciech, Domański Roman, Kapuściński Jakub, Wiśniewski Tomasz, Kubiś Michał

Journal of KONES

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2019

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Vol. 26, No. 4

211--218

EN

Phase change materials (PCMs) are widely used in numerous engineering fields because of their good heat storage properties and high latent heat of fusion. However, a big group of them has low thermal conductivity and diffusivity, which poses a problem when it comes to effective and relatively fast heat transfer and accumulation. Therefore, their use is limited to systems that do not need to be heated or cooled rapidly. That is why they are used as thermal energy storage systems in both large scale in power plants and smaller scale in residential facilities. Although, if PCMs are meant to play an important role in electronics cooling, heat dissipation, or temperature stabilization in places where the access to cooling water is limited, such as electric automotive industry or hybrid aviation, a number of modifications and improvements needs to be introduced. Investigation whether additional materials of better thermal properties will affect the thermal properties of PCM is therefore of a big interest. An example of such material is diamond powder, which is a popular additive used in abradants. Its thermal diffusivity and conductivity is significantly higher than for a pure PCM. The article presents the results of an analysis of the effect of diamond powder on thermal conductivity and diffusivity of phase change materials in the case of octadecane.

13

Investigation of the effect of diamond powder on the thermal properties of octadecane using differential scanning calorimetry

Godlewski Wojciech, Sierakowski Mateusz, Domański Roman, Kapuściński Jakub

Journal of KONES

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2019

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Vol. 26, No. 3

39--45

EN

The purpose of this work was to examine the effect of diamond powder on the thermal properties of phase change materials on the example of octadecane. The experiment involved mixing of diamond powder with a specific granulation with the aforementioned representative of the alkanes group. Two different grain sizes were used: 50 and 250 micrometres. The change of specific heat, latent heat of phase change and degree of supercoiling in newly formed mixtures was compared to the pure forms of the phase-change materials used. Initial mixing with a glass-stirring rod showed strong stratification for each granulation due to the low viscosity of the mixture and too large differences between component densities. It was decided to add amorphous silicon dioxide to the mixtures, which increases density of the mixture. The optimal percentage of amorphous silicon dioxide was estimated experimentally. Measurements of thermal parameters were carried out using DSC technology. The results of the tests of specific heat and latent phase transition heat showed that with the increasing content of diamond, the specific heat of the mixture decreases almost twice, and the latent heat can decrease by up to three times. The effect of diamond powder on reducing the degree of supercoiling of the mixture was also observed. An important observation was that the mixture with higher granulation of diamond powder had greater tendency for sedimentation. This method could be used to increase thermal conductivity and diffusivity of phase change materials and make them viable for use in systems that require cooling at high rate or temperature stabilization, such as control systems in electronic vehicles or aviation industry and at the same time decrease the degree of supercoiling which could increase the efficiency of system.

14

Badania termofizyczne materiałów zmiennofazowych w aspekcie ich zastosowań w układach do odzysku ciepła odpadowego

Smusz R., Wilk J., Tychanicz-Kwiecień M., Gil P., Bałon P.

Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika

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2018

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z. 90 [298], nr 1

67--75

PL

W artykule zaprezentowano wyniki badań eksperymentalnych właściwości termofizycznych wybranych materiałów zmiennofazowych PCM (ang. Phase Change Material). Znajomość właściwości cieplnych materiałów zmiennofazowych jest niezbędna przy projektowaniu urządzeń akumulujących ciepło lub układów do odzysku ciepła odpadowego. Opracowywana koncepcja takiego urządzenia pracującego dodatkowo w układzie z odzyskiem ciepła odpadowego była podstawą do prowadzonych badań. W ramach pracy zostały wykonane pomiary przewodności, dyfuzyjności cieplnej, ciepła właściwego oraz gęstości. Badane materiały to: wosk plastyczny, cerezyna niskotopliwa oraz ksylitol i erytrytol. Do badań właściwości cieplnych materiałów zastosowano metodę gorącego drutu.

EN

This paper presents the results of experimental investigation of thermophysical properties of selected phase change materials (PCM). It is essential for design heat-storage devices which utilize such materials. The basis of presented investigation was the concept of heat-storage device in cooperation with waste heat recovery unit. The investigated parameters were: thermal conductivity, diffusivity, specific heat and density. The following materials were tested: plastic wax, ceresin, xylithol and erythritol. Thermophysical parameters were obtained with the use of transient hot wire method. To investigate the thermal properties of materials the hot wire method was used.

15

Pomiary dyfuzyjności cieplnej z zastosowaniem termografii aktywnej

Pawlak S.

Stal, Metale & Nowe Technologie

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2018

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nr 9-10

113--116

PL

W artykule przedstawiono procedurę pomiarów dyfuzyjności cieplnej z zastosowaniem termografii aktywnej na przykładzie badań wybranych materiałów polimerowych. Badania termograficzne wykonano, stosując oryginalne stanowisko pomiarowe własnej konstrukcji. Na podstawie zarejestrowanych sekwencji obrazów termograficznych utworzono wykresy zmian temperatury w czasie, które posłużyły do wyznaczenia dyfuzyjności cieplnej, zgodnie z metodą Parkera.

EN

The subject of the study was the application of active thermography for the thermal diffusivity measurements of selected polymer materials. The active thermography experiment was performed using an original apparatus of the author’s own design. Based on the recorded sequences of thermal images the temperature variations versus time plots were created to determine the thermal diffusivity values according to the Parker’s method. The article also presents the effect of specimen thickness on the obtained experimental values of thermal diffusivity.

16

Investigations of Thermal Diffusivity of Material of Compressor Blade of Turbine Jet Engine Using Modified Temperature Oscillation Method

Omen Ł., Panas A.

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

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2018

|

Vol. 9, Nr 1 (31)

79--92

EN

The modified temperature oscillation method was applied for investigation of thermal diffusivity of the aviation turbine engine’s part. The studies resulted in characterization of the applied method and experimental procedures performance. They were motivated by a need of determination of thermophysical data of the investigated material. The acquired thermal diffusivity data enabled identification of the material’s type and will be applied as input data for numerical analyses on thermo-mechanical loads of the structure. The investigated specimen was a sample of material from the first stage compressor’s blade of the AŁ-21F3 turbine engine. The measurements were conducted within the range of 5°C to 95°C. The thermal diffusivity was calculated from both the amplitude and phase responses to the harmonic excitation from exact analytical solution of the appropriate heat conduction problem. The appropriate transcendental equations describing the response signal amplitude attenuation and phase shift were solved applying iterative procedures. The analysis confirmed the effectiveness of the research methods and enabled to identify the material as titanium alloy.

PL

W pracy omówiono wykorzystanie zmodyfikowanej metody wymuszeń okresowych do określenia dyfuzyjności cieplnej materiału konstrukcyjnego lotniczego silnika odrzutowego oraz przedstawiono zastosowane procedury badań. Bezpośrednią przyczyną podjęcia badań była konieczność identyfikacji i udokumentowania danych materiałowych do ich późniejszego wykorzystania w modelowaniu numerycznym obciążeń termomechanicznych konstrukcji. Długofalowo wykonane badania mają służyć opracowaniu szybkiej i skutecznej nieniszczącej metody określania właściwości cieplnofizycznych elementów konstrukcyjnych napędów lotniczych. Obiektem badań była próbka materiału pobrana z łopatki wirnikowej pierwszego stopnia sprężarki turbinowego silnika odrzutowego AŁ–21F3. Badania wykonano dla przedziału temperatury od 5 °C do 95 °C. Wartość dyfuzyjności cieplnej określono wykorzystując tzw. amplitudowe i fazowe cechy odpowiedzi na wymuszenie quasi-sinusoidalne. Analiza otrzymanych wyników potwierdziła skuteczność zastosowanej metody badań i pozwoliła na zidentyfikowanie badanego materiału, jako stopu tytanu.

17

Thermophysical properties of 904L austenitic steel

Nasiłowska B., Bogdanowicz Z., Terpiłowski J., Pańcikiewicz K.

Metallurgy and Foundry Engineering

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2018

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Vol. 44, no. 2

61--71

EN

This paper presents the results of the structural investigations and thermophysical properties of 904L steel parent material. Experimental studies on the structure of 904L steel proved a pure austenitic structure. Both the experimental research and analysis of the thermophysical properties of 904L steel were complemented with the results of the thermal conductivity calculations for the tested material. The paper presents a brief description of the measurements, the procedures for evaluating the data, and a set of the obtained results.

PL

W pracy przedstawiono wyniki badań strukturalnych i właściwości cieplnofizyczne materiału rodzimego stali 904L. Badania eksperymentalne struktury stali 904L wykazały strukturę czysto austenityczną. Badania doświadczalne i analizę właściwości cieplnofizycznych stali 904L uzupełniono wynikami obliczeń przewodności cieplnej badanego materiału. W pracy przedstawiono zwięzły opis wykonywanych pomiarów, charakterystykę procedur opracowania danych oraz komplet uzyskanych wyników.

18

Natural convection in a hydrodynamically and thermally anisotropic non-rectangular porous cavity: effect of internal heat generation/absorption

Chandran P., Sacheti N. C., Bhadauria B. S., Singh A. K.

International Journal of Applied Mechanics and Engineering

|

2018

|

Vol. 23, no. 3

595--609

EN

Laminar natural convection in a trapezoidal porous vertical cavity has been investigated in this work. It is assumed that the porous enclosure is filled up with a permeable material subject to hydrodynamic and thermal anisotropy, the flow being governed by the Darcy law as applicable to a non-isotropic medium. It is further assumed that (i) there is heating at the left vertical wall and cooling at the right wall of the enclosure and (ii) the flow domain is subject to the presence of heat source or heat sink. The partial differential equations governing the resulting free convection have been solved numerically in the non-dimensional forms. There arises a number of parameters relating to buoyancy, internal heating, cavity aspect ratio and inclination of the upper surface to the horizontal. The influence of these parameters has been illustrated and analyzed through contours of streamlines and isotherms. We have also discussed the role of internal heating as well as anisotropy on the heat transfer characteristics.

19

Thermophysical properties of selected vermicular graphite cast iron alloy

Homa M., Sobczak N., Turalska P., Bruzda G., Bacior M., Warmuzek M., Polkowska A.

Prace Instytutu Odlewnictwa

|

2017

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Vol. 57, no. 4

345--350

EN

The paper presents the results of thermophysical properties of selected vermicular graphite cast iron with nominal chemical composition of 3.70 C; 2.30 Si; 0.44 Mn; 0.054 P; 0.015 S; 0.017 Mg (wt. %). The comparative studies of the alloy were performed using differential scanning calorimetry, dilatometry and laser flash analysis. The calorimetric investigations proved that upon the heating to melting temperature (~1200°C), four endothermic transformations take place: 1) ferromagnetic → paramagnetic at 742°C, 2) pearlite → austenite at 824.2°C, 3) allotropic transformation of bcc ferrite to fcc austenite at 802°C, 4) melting at 1173.1°C. The character of the dilatometric curve shows small deviation at the temperature above 810°C corresponding to the pearlite → austenite transformation. The values of thermal diffusivity and thermal conductivity change throughout the entire examined temperature range. Both curves showed a changeover from negative to positive trends between 700 and 800°C. This effect might be associated with the pearlite → austenite transformation.

20

Copper-Carbon Nanoforms Composites - Processing, Microstructure and Thermal Properties

Pietrzak K., Gładki A., Frydman K., Wójcik-Grzybek D., Strojny-Nędza A., Wejrzanowski T.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2B

1307--1310

EN

The main current of publication is focused around the issues and problems associated with the formation of composite materials with Cu matrix and reinforcing phases in the various carbon nanoforms. The core of the research has been focused on thermal conductivity of these composites types. This parameter globally reflects the state of the structure, quality of raw materials and the technology used during the formation of composite materials. Vanishingly low affinity of copper for carbon, multilayered forms of graphene, the existence of critical values of graphene volume in the composite are not conducive to the classic procedures of composites designing. As a result, the expected, significant increase in thermal conductivity of composites is not greater than for pure copper matrix. Present paper especially includes: (i) data of obtaining procedure of copper/graphene mixtures, (ii) data of sintering process, (iii) the results of structure investigations and of thermal properties. Structural analysis revealed the homogenous distribution of graphene in copper matrix, the thermal analysis indicate the existence of carbon phase critical concentration, where improvement of thermal diffusivity to pure copper can occur.