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1
Content available Influence of heat generation/absorption on mixed convection flow behaviour in the presence of Lorentz forces in a vertical micro circular duct having time periodic boundary conditions: steady periodic regime
Aina B., Isa S.
International Journal of Applied Mechanics and Engineering
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2020
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Vol. 25, no. 4
1--21
EN
The problem of mixed convection flow of a heat generating/absorbing fluid in the presence existence of Lorentz forces in a vertical micro circular subjected to a periodic sinusoidal temperature change at the surface has been studied taking the first-order slip and jump effects into consideration. The research analysis is carried out by considering a fully developed parallel flow and steady periodic regime. The governing equations, together with the constraint equations which arise from the definition of mean velocity and temperature, are written in a dimensionless form and mapped into equations in the complex domain. One obtains two independent boundary value problems, which provide the mean value and the oscillating term of the velocity and temperature distributions. These boundary value problems are solved analytically. A parametric study of some of the physical parameters involved in the problem is conducted. The results of this research revealed that the magnetic field has a damping impact on the flow and results in decreases in fluid velocity for both air and water. Furthermore, the presence of the heat generation parameter is seen to enhance the temperature distribution and this is reflected as an increase in the magnitude of the oscillation dimensionless velocity, whereas in the presence of heat absorption a reversed trend occurs.
2
Content available New Possibilities in Thermal Analysis of Molding Materials
Svidró J., Diószegi A.
Journal of Casting & Materials Engineering
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2018
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Vol. 2, no. 4
67--70
EN
Molding material-related studies within the research activities concerning foundry technology have always been limited despite the significant effect of molding mixtures on the quality of cast parts. One reason behind this trend is the difficulty in interpreting the results of such complex systems like molds and cores. This paper provides a new possibility for studying the heat-absorption performance of materials used as molding media in metal casting processes. By further developing the Fourier thermal analysis method of cores and molds introduced by earlier studies, the investigation of unbonded sand has become available. The heat-absorption properties of the components can be hereby separated and studied respectively. Thermal analyses were performed on sphere-shaped resin-bonded cores with various binder levels as well as on unbonded sand samples. The temperature data collected from two points of the samples were then used for the calculation of the novel thermophysical properties. The results revealed not only quantitative but qualitative differences in the characteristics of the binder decomposition processes, providing a deeper understanding on the thermal behavior of molding materials. The outcome of the research provides more accurate data, which is the key for the improved simulation of casting processes.
3
Content available Fractional heat conduction in an infinite rod with heat absorption proportional to temperature
Povstenko Y., Klekot J.
Scientific Issues of Jan Długosz University in Częstochowa. Mathematics
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2017
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Vol. 22
61--71
EN
The one-dimensional time-fractional heat conduction equation with heat absorption (heat release) proportional to temperature is considered. The Caputo time-fractional derivative is utilyzed. The fundamental solutions to the Cauchy and source problems are obtained using the Laplace transform with respect to time and the exponential Fourier transform with respect to the spatial coordinate. The numerical results are illustrated graphically.
4
Content available The fundamental solutions to the central symmetric time-fractional heat conduction equation with heat absorption
Povstenko Y., Klekot J.
Journal of Applied Mathematics and Computational Mechanics
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2017
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Vol. 16, nr 2
101--112
EN
The time-fractional heat conduction equation with heat absorption proportional to temperature is considered in the case of central symmetry. The fundamental solutions to the Cauchy problem and to the source problem are obtained using the integral transform technique. The numerical results are presented graphically.
5
Intensyfikacja przejmowania ciepła przez opromieniowane ściany wymienników z natryskanymi powłokami o wysokiej absorpcyjności i przewodności cieplnej
Morel S.
Hutnik, Wiadomości Hutnicze
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2016
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Vol. 83, nr 5
258--262
PL
Przytoczono wartości współczynników emisyjności materiałów metalowych i ceramicznych oraz powłok. Dokonano analitycznych obliczeń wpływu współczynnika emisyjności wzajemnej: czynnik nagrzewający (płomień) - ściana bez powłok, a następnie czynnik nagrzewający (płomień) ściana z powłoką (czynnik nagrzewany) na wartości strumienia wymienianego ciepła. W oparciu o wyniki pomiarów podstawowych właściwości powłok wytypowano najbardziej przydatne do natryskiwania ścian pieców i wymienników warunkujące intensyfikację wymiany ciepła. Powłokami tymi natryskano ściany laboratoryjnego kotła odzysknicowego i dokonano pomiarów wartości strumieni ciepła przejmowanego przez wodę chłodzącą − przepływającą w rurach kotła pokrytych różnymi rodzajami powłok. Obliczenia analityczne i badania laboratoryjne potwierdzono wynikami eksploatacji przemysłowej w elementach urządzeń hutniczych.
EN
The values of emissivity coefficients are given for the materials of metal and ceramic coatings. Analytical calculations have been made for the effect of the heating medium (flame) – uncoated wall and then heating medium (flame) – coated wall mutual emissivity coefficients on the values of the exchanged heat flux. Based on the measurement results for the main coating properties, coatings were selected which were the most suitable for spraying the walls of furnaces and heat exchangers, and determined the intensification of heat exchange. These coatings were used to spray the walls of a laboratory waste-heat boiler, and then measurements were taken for the values of the fluxes of heat absorbed by the cooling water flowing in the boiler tubes covered with different type coatings. The analytical calculations and the laboratory tests have been confirmed by the results of full-scale operation on the elements of metallurgical equipment.
6
Content available remote MHD natural convection flow past an impulsively moving vertical plate with ramped wall temperature in the presence of thermal diffusion with heat absorption
Seth G. S., Ansari Md. S.
International Journal of Applied Mechanics and Engineering
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2010
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Vol. 15, no 1
199-215
EN
Hydromagnetic natural convection flow of a viscous incompressible electrically conducting and heat-absorbing fluid past an impulsively moving vertical plate with ramped wall temperature in a porous medium, in the presence of thermal diffusion, is studied. The exact solution of momentum and energy equations, under the Boussinesq approximation, is obtained in closed form by the Laplace transform technique. The expressions for the skin friction and Nusselt number are also derived. The variations in fluid velocity and temperature are shown graphically whereas numerical values of skin friction and the Nusselt number are presented in tabular form for various values of pertinent flow parameters. The natural convection flow near a ramped temperature plate is also compared with the flow near an isothermal plate.
7
Content available remote Estimation of the Overall Heat - transfer Coefficient Through a Textile Layer
Ziegler S., Kucharska-Kot J.
Fibres & Textiles in Eastern Europe
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2006
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Vol. 14, no. 5 (59)
103--106
EN
The article justifies the use of calculative determination of the heat transfer coefficient k, on the basis of immutable parameters of the textile layer such as thermal conductivity and thickness. A method of elaborating the heat transfer coefficient is described, and examples of calculations are presented for randomly selected samples of clothing woven fabrics. It was proved possible to make a calculative estimation of the influence of changes on the parameters of the textile layer, as well as the conditions of use on the value of the heat transfer coefficient. No estimation of the woven fabrics tested from the point of view of their properties was carried out. A brief description of a device for measuring the thermal conductivity coefficient and the heat transfer coefficient of flat textile products is presented.
PL
W artykule wykazano celowość obliczeniowego określania współczynnika przenikania ciepła k, na podstawie stałych parametrów warstwy odzieży: przewodności cieplnej i grubości warstwy. Przedstawiono metodę obliczania współczynnika k i wykonano obliczenia dla wybranych próbek tkanin odzieżowych. Przedstawiono opis przyrządu do pomiaru współczynnika przewodności cieplnej i współczynnika przenikania ciepła płaskich wyrobów włókienniczych. Wyniki pomiarów porównawczych wykazały dostateczną zgodność obliczeń z pomiarami. Wykazano możliwość obliczeniowej oceny wpływu zmian parametrów warstwy odzieży i warunków użytkowania na wartość współczynnika przenikania ciepła.
8
Content available remote lntensification of heat absorption by radiated walls sprayed with coatings of high thermal absorptivity and conductivity
Morel S., Morel S.
Metallurgy and Foundry Engineering
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1998
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T. 24, no. 4
287--297
EN
The values of emissivity coefficients are given for the materials of metal and ceramic coatings. Analytical calculations have been made for the effect of the heating medium (flam c) - uncoated wall and then heating medium (flame) - coated wall mutual emissivity coefficients on the values of the exchanged heat flux. Based on the measurement results for the main coating propertics, coatings were selected which were the most suitable for spraying the walls of furnaces and heat exchangers, and determined the intensification of heat exchange. These coatings were used to spray the walls of a laboratory waste-heat boiler, and then measurements were taken for the values of the fluxes of heat absorbed by the cooling water flowing in the boiler tubes covered with different type coatings. The analytical calculations and the laboratory tests have been confirrned by the results of full-scale operation on the elements of metallurgical equipment.
PL
W pracy przytoczono wartości współczynników emisyjności materiałów metalowych i ceramicznych oraz powłok. Dokonano analitycznych obliczeń wpływu współczynnika emisyjności wzajemnej: czynnik nagrzewający (płomień) - ściana bez powłok, a następnic czynnik nagrzewający (płomień) ściana z powłoką (czynnik nagrzewany) na wartości strumienia wymienianego ciepła. W oparciu o wyniki pomiarów podstawowych własności powłok wytypowano najbardziej przydatne do natryskiwania ścian pieców i wymienników, warunkujące intensyfikację wymiany ciepła. Powłokami tymi natryskano ściany laboratoryjnego kotła odzysknicowego i dokonano pomiarów wartości strumieni ciepła, przejmowanego przez wodę chłodzącą - przepływającą w rurach kotła, pokrytych różnymi rodzajami powłok. Obliczenia analityczne i badania laboratoryjne potwierdzono wynikami eksploatacji przemysłowej w elementach urządzeń hutniczych.
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