The two-dimensional problem of heat conduction in a cylindrical sample of material is solved numerically when a short heat pulse acts on its surface and the heated region is in the form of a circle. It is shown that t...
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The two-dimensional problem of heat conduction in a cylindrical sample of material is solved numerically when a short heat pulse acts on its surface and the heated region is in the form of a circle. It is shown that the use of a laser beam with a transverse cross section of rectangular form gives a considerably smaller error in determining the thermal characteristics.
The problem of the three-dimensional nonstationary temperature field of a sample of material when a thermal pulse of short duration acts on its surface is solved numerically. The scales of the errors in determining th...
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The problem of the three-dimensional nonstationary temperature field of a sample of material when a thermal pulse of short duration acts on its surface is solved numerically. The scales of the errors in determining the thermal characteristics of the material by a pulse method due to the assumption that heat transfer in the sample is a one-dimensional process, is estimated. The limits of the ranges of possible variation of the ratio of the area of the heated surface of the sample and the zone of thermal heating, which ensure minimum errors in determining the thermal characteristics, are established.
The errors in determining the thermal characteristics of a semitransparent material by a pulsed method are determined by comparing the results of a numerical solution of the problem of the steady temperature field of ...
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The errors in determining the thermal characteristics of a semitransparent material by a pulsed method are determined by comparing the results of a numerical solution of the problem of the steady temperature field of a sample when a collimated laser pulse of finite duration acts on its surface with the true values of the thermal diffusivity, thermal conductivity, and specific heat capacity.
The adsorption isotherms of selected compounds are our main source of information on the mechanisms of adsorption processes. Thus, the selection of the methods used to determine adsorption isotherm data and to evaluat...
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The adsorption isotherms of selected compounds are our main source of information on the mechanisms of adsorption processes. Thus, the selection of the methods used to determine adsorption isotherm data and to evaluate the errors made is critical. Three chromatographic methods were evaluated, frontal analysis (FA), frontal analysis by characteristic point (FACP), and the pulse or perturbation method (PM), and their accuracies were compared. Using the equilibrium-dispersive (ED) model of chromatography. breakthrough curves of single components were generated corresponding to three different adsorption isotherm models: the Langmuir, the bi-Langmuir, and the Moreau isotherms. For each breakthrough curve, the best conventional procedures of each method (FA, FACP, PM) were used to calculate the corresponding data point, using typical values of the parameters of each isotherm model, for four different values of the column efficiency (N = 500,1000, 2000, and 10,000). Then, the data points were fitted to each isotherm model and the corresponding isotherm parameters were compared to those of the initial isotherm model. When isotherm data are derived with a chromatographic method, they may suffer from two types of errors: (1) the errors made in deriving the experimental data points from the chromatographic records;(2) the errors made in selecting an incorrect isotherm model and fitting to it the experimental data. Both errors decrease significantly with increasing column efficiency with FA and FACP, but not with PM. (C) 2008 Elsevier B.V. All rights reserved.
A pulse method is described by which the thermal diffusivity and the specific heat can be measured with a bead microthermistor, a carbon bolometer, and a heater film. The thermal conductivities of several semiconducto...
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Transient heat transfer is studied and compared in two planeparallel composite walls and one EPIDIAN 53 epoxy resin wall acting as a matrix for both composites. The first of the two walls is made of carbonepoxy compos...
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Transient heat transfer is studied and compared in two planeparallel composite walls and one EPIDIAN 53 epoxy resin wall acting as a matrix for both composites. The first of the two walls is made of carbonepoxy composite;the other wall is made of glass-epoxy composite, both with comparable thickness of about 1 mm and the same number of carbon and glass fabric layers (four layers). The study was conducted for temperatures in the range of 20-120 degrees C. The results of the study of thermal diffusivity which characterizes the material as a heat conductor under transient conditions have a preliminary character. Three series of tests were conducted for each wall. Each series took about 24 h. The results from the three series were approximated using linear functions and were found between (0.7-1.35) x 1 0(-7)m(2)/s. In the whole range of temperature variation, the thermal diffusivity values for carbon-epoxy composite are from 1.2 to 1.5 times higher than those for the other two materials with nearly the same thermal diffusivity characteristics.
This paper presents the possibility of modifying the microstructure of anodic hard coatings on aluminium alloys by applying a pulsed method in the process of their electrochemical deposition. Anodic hard coatings were...
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ISBN:
(纸本)9788087294925
This paper presents the possibility of modifying the microstructure of anodic hard coatings on aluminium alloys by applying a pulsed method in the process of their electrochemical deposition. Anodic hard coatings were formed on an aluminium alloy intended for plastic working. The electrolytic process was conducted using the pulsed method with a rectangular current waveform in time, applying variable frequencies, current densities and duty cycles of the waveform. Examination of the microstructure of the anodic hard coatings was carried out by image analysis of the images obtained by means of SEM from fractures of the coatings. The obtained results indicate that the application of the pulse anodizing method results in the occurrence of local changes in the microstructure of the anodic hard coatings.
The effect of the time of flight of neutrons escaping from the moderator on the measured time dependence of the neutron density, which in turn serves for determining the decay constant α, has been analyzed. The measu...
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