Papers by Keyword: Heat Capacity

Abstract: For the first time, the time dependences of the temperature of aluminum, zinc and zinc-aluminum alloys alloyed with II A group elements under spontaneous cooling mode were obtained; an anomalous course and two characteristic times of the cooling process were found, and their mechanism was explained; the temperature dependence of the thermophysical properties of the investigated metals and alloys was established; the temperature dependence of the coefficients of convective heat transfer and radiation of Al, Zn and Zn55Al and Zn5Al alloys was experimentally determined; the influence of the concentration of II A group elements and temperature on the heat capacity and thermodynamic functions of Zn55Al and Zn5Al alloys was revealed.

Abstract: In this study, the temperature increase of the Ti-17 alloy (Ti–5Al–2Sn–2Zr–4Cr–4Mo, wt.%) during isothermal forging in the (α + β) dual-phase region was investigated using large-size workpieces forged between hot dies in a 1500-ton forging press. The temperature increase was predicted using finite element analysis (FEA). The tip of a thermocouple was inserted into the center of the workpiece (diameter: 100 mm; height: 50 mm). The forging temperatures were 1023 K (750 °C) and 1073 K (800 °C) in the (α + β) dual-phase region. The strain rate was 0.05 s⁻¹ and 0.5 s⁻¹ at each temperature. Meanwhile, the compression percentage was 75%. The true stress–true strain curves were inversely obtained by fitting the load–stroke curves using the FEA. The predicted temperature was in a good agreement with that in the experimental results when the value of 1.0 was used as the conversion factor for plastic deformation energy to heat energy in the FEA under the current forging conditions. At the strain rate of 0.5 s⁻¹, the temperature instantly increased to a β-transus temperature in 3 s at 1073 K (800 °C). In contrast, the temperature logarithmically increased at both 1023 K (750 °C) and 1073 K (800 °C) at 0.05 s⁻¹ in 28 s (e.g., 42 K at 1023 K (750 °C)). The obtained true stress–true strain curves indicate that flow softening occurred during the forgings, which is attributed to dynamic recrystallization and/or dynamic recovery. The temperature increase in the Ti-17 alloy was smaller than that in the Ti–6Al–4V alloy under the same forging condition.

Abstract: The syntactic foams based on polymethylphenylsiloxane resin filled by hollow glass microspheres were developed for using in different applications of construction industry. Thermophysical properties of the developed syntactic foams were analyzed in this work. According to the study results, with an increase of polymethylphenylsiloxane content in the syntactic foam, the thermal conductivity and the specific heat capacity increased. The coefficient of thermal linear expansion was dependent on the ratio of the components, reaching the lowest value for the composites with a minimum binder content.

Abstract: The number of researches on steel fiber reinforced concrete (SFRC) fire resistance is insignificant. For the calculation of building structures for fire resistance, it is necessary to use the thermophysical characteristics of concrete: thermal conductivity, heat capacity and thermal diffusivity. The physicomechanical characteristics of SFRC depend on the volumetric content of the fiber in it. This paper presents the results of studies of thermophysical properties of SFRC. The studied SFRC had a high-strength self-compacting cement-sand matrix and a different percentage of fiber content (from 0 to 6%). The experiments were carried out for SFRC with steel wavy fiber 15 mm long and 0.3 mm in diameter. As a result of experimental studies, it was discovered that with an increase in the volumetric content of the fiber, a decrease in the values of heat flow, thermal conductivity and thermal diffusivity coefficients, specific heat capacity is observed and the thermal resistance of SFRC increases.

Abstract: At present time complex alloyed brasses are widely used for manufacturing of parts worked in fray conditions. The mechanical and service properties of this alloys are provided by presence of different structural constituents in the structure of alloys. The wear resistance is a basic property of complex alloyed brasses. The information on actual problems in the industrial production of cast bars, semi-finished products and [ pfrts]-непонятно] of complex alloyed brasses is presented in the article. In accordance with the increasing requirements of consumers to reliability and service life of parts the complex alloyed brass Cu62Zn31.6Mn3Al2Si0.8Ni0.4Cr0.2 was proposed as a material for production of parts. The development of technology of melting and semi-continuous casting of complex alloyed brass is an important problem. Moreover, for estimation of thermal contition of ingot and simulation of the process of solidification of the ingot, it is necessary to know thermal physic and physical characteristics of an alloy. Therefore, the research on determination of heat conductivity, heat capacity and density of complex alloyed brass, depending on temperature, was carried out. The obtained experimental data can be used to thermos-technical calculation of thermal contition of ingot and simulation of the process of solidification of ingot during semi-continuous casting for the purpose of determination of technological parameters of casting.

Abstract: The possibility of applying a hyperbolic model for calculating thermodynamic characteristics (the standard molar heat capacity, standard molar entropy) to the V–O system is shown. For calculation of the molar specific heat and entropy within the bounds of the model the general concept has been used: a thermodynamic parameter is divided into two components. The first component depends on the molar mass of a compound, the second one is determined by inter particle interaction. The dependence of the inverse value for the interaction heat capacity (entropy) on composition is of linear character within one region of quasi-equilibrium solid solutions (one region combines compounds with the same or similar structure type).The use of the model allowed refining the available experimental data on vanadium oxides and predicting the values of thermodynamic characteristics for compounds poorly studied in experiment.

Abstract: Thermal characteristic of insulation concretes is one of the key components in materials selection especially in civil constructions. In this article, non–tabulated material parameters of some innovative highly-insulating non-structural concretes are presented. The specific volumetric heat capacity, specific heat capacity, parameter of temperature diffusivity and thermal mass parameter of the innovative highly-insulating cementitious composites were determined. The experiments were conducted using a prototype automated calorimetric chamber. The measurement results are compared with those obtained by using a commercial multifunctional instrument (Isomet 2114) and are accompanied by the measurement of other significant thermal parameters of the cementitious composites under investigation. The results indicated that there is potential of using the newly created types of concrete for insulation purposes.

Abstract: Synthetic fibers are being replaced gradually by natural materials such as lignocellulosic fibers. Compared to synthetic fibers, natural fibers have shown advantages in environmental, societal, economical and technical aspects. Thus, there is a growing worldwide interest in the use of those fibers. The banana fiber, extracted from the pseudo-stem of the plant, displays significant properties yet to be studied. Few thermal properties on banana fiber as reinforcement of epoxy matrix were fully evaluated. Therefore, the present work had as its objective to investigate, by photoacoustic spectroscopy and photothermal techniques the thermal diffusivity, specific heat capacity and thermal conductivity of epoxy composites reinforced with banana fibers .The epoxy matrix was added with up to 30% in volume of continuous and aligned banana fibers. The results indicated that these composites have good insulation capacity.

Abstract: Transient thermal analysis is a very useful tool for thermal evaluation to realize the stable operation of SiC power modules which are operated at higher temperatures than conventional Si power modules. A transient thermal analysis system to investigate the thermal characteristics of SiC power modules at high temperature is presented. We have found that precise temperature measurement at the initial stage of the junction temperature decay curve is necessary in order to evaluate the thermal resistance and heat capacity of the die attach, since the thermal diffusivity of SiC is larger than that of Si and the temperature distribution of SiC die was considered. Using the proposed transient thermal analysis method, the thermal resistance and heat capacity of the AuGe die attach under the SiC-SBD was successfully evaluated at temperatures up to 250 °C.

Abstract: By method of dynamic calorimetry, in the temperature range between 298,15 and 673 K, isobaric heat capacity of polycrystalline ferrites Bі₂СаFe₄O₁₀, BіMgFe₂O_5.5, Bі₂MgFe₄O₁₀ was experimentally studied. Mathematical processing of experimental data made it possible to derive polynomial equation of temperature dependence of ferrites heat capacity for respective temperature ranges, in dependencies C⁰_p~f (T) of ferrite Bі₂СаFe₄O₁₀ a jump was detected in heat capacity at 625K associated with phase transitions of type II. The values of the thermodynamic functions C⁰_p(Т), H⁰(T) – Н⁰(298,15), C⁰(T), F^hh(Т) have been calculated. Standard values of thermodynamic functions were determined using the method of ion increments. The results obtained broaden thermodynamic data bank for complex inorganic crystalline compounds.