Changes In Thermodynamic Characteristics Research Articles

Poly(vinyl chloride) plasticates modified by polystyrene: features of preparation, morphology and properties

The influence of component composition and the nature of plasticizer on the features of intermolecular interactions in the system poly(vinyl chloride)–polystyrene–diester phthalate was established. It was found that polystyrene macromolecules are actively involved in interactions with both poly(vinyl chloride) macromolecules and plasticizer molecules, forming associates of slightly smaller size. It was noted that the wetting angle of the surface by plasticizer and the work of adhesion largely depend on the nature of a plasticizer and a polymer dissolved in it. This indicates a significant effect of the nature and content of the polymer modifier on the compatibility of poly(vinyl chloride) and plasticizer and changes in thermodynamic characteristics of the system. The influence of the nature and content of polystyrene modifier on physicochemical features of the migration process of diester phthalate plasticizer from modified poly(vinyl chloride) plasticate as well as on its morphological features was studied. It was found that the thermodynamic compatibility of the components is significantly affected by the wettability of the surface of fine polymer particles with liquid plasticizers, which, in turn, affects the release (migration) of the plasticizer from poly(vinyl chloride) plastics during operation of products based on them. Pre-dissolution of suspension polystyrene or acrylonitrile butadiene styrene plastic in the plasticizer, regardless of its nature, leads to a significant reduction in the value of migration.

Insights into aging mechanism of Ti-metal based pyrotechnics and changes in thermo-kinetic characteristics

Metal fuels with high energy density have been receiving attention recently as alternatives to fossil fuels in propulsion systems, power generation applications, and energy storage technology. However, to adopt metal fuels for such purposes, maintaining the designed performance level and greater reliability are required. Thus, aging analysis as well as thermal analysis of metal fuels must be conducted thoroughly prior to such practical applications. In order to identify an aging mechanism, the present paper investigates the variation in both thermodynamic characteristics and reaction kinetics of titanium hydride potassium perchlorate (THPP) under aging. Some chemical and physical defects of aged samples were also found by x-ray photoelectron spectrometer (XPS) and field emission scanning electron microscope (FE-SEM). The influence of aging on combustion reactions of THPP was elucidated by carrying out the non-isothermal differential scanning calorimetry (DSC) and thermogravimetry (TGA). Based on the changes in thermodynamic characteristics and reaction kinetics, the altered reaction mechanism due to aging was investigated. Certain samples aged under humid environments had different activation energy pathways for reaction progress due to an increased amount of TiO2, which can give rise to severe changes in lifetime and stability after all.

Exergetic analysis of heat pump units for various climate conditions

The article deals with exergetic analysis of a heat pump for climate of Russian North-West. The dependencies between the parts of the pump and its general characteristic are shown. The influence of ambient temperature, condensation temperature, and low-grade heat source on the working efficiency of heat pump units is analyzed. The changes in thermodynamic characteristics of the heat pump at ambient temperature decreasing form 0°C to –15°C are identified. The coefficient of performance is seen to decrease two times, the coefficient of transformation – by 1.4 times; overall exergetic coefficient of performance increases by 18 %. Working efficiency and coefficient of performance of the unit in general, and the ones of compressor, compensator, evaporator and thermal expansion valve are determined. The results of the research are of use for increasing efficiency of heat pumps.

Predicted model of magnetocaloric effect in BiFeO3-based multiferroics

Structure, magnetic properties and magnetocaloric effect in synthesized Bi-based multiferroics with a partial isovalent substitution of bismuth (III) cations for rare-earth elements (R = La, Nd, Sm, Eu, Gd, Dy, Er) have been studied. The samples have been prepared by the solid-state reaction method under cold pressing at high pressure (4 GPa). Proposed, for the first time, has been a modified phenomenological model for describing temperature dependences of magnetization and investigating a magnetocaloric effect within “weak ferromagnetic-antiferromagnetic” and “antiferromagnetic-paramagnetic” magnetic phase transition regions. Systematic changes of thermodynamic characteristics have been found out to depend on the degree of replacement and the type of a substituted cation.

Изменения термодинамических свойств клея, обработаного электромагнитным полем СВЧ

Изменения термодинамических свойств клея, обработаного электромагнитным полем СВЧ

On the spatial nonuniformity of some parameters of global variations in the recent climate

The near-surface temperature began rising in the mid-1970s, and the planetary field of atmospheric pressure considerably rearranged. The average pressure fields and temperatures for two successive 25-year periods prior to and after the rearrangement are compared in this work. Temperature fluctuations between the periods are shown to be in good agreement with variations in the atmospheric circulation due to rearrangement of the barometric field. A decrease in the near-surface temperature average for the periods was observed in regions with an air mass influx from higher latitudes with an increase in wind speeds over the ocean. A rise in the temperature took place in reversed situations. Early in the 21st century, a gradual relapse of the system to the situation antedating the last quarter of the 20th century was noticed. According to [1], long-term atmospheric processes are inevitably global—only the planet as a whole can serve as a “natural synoptic region” for them. The processes correspond to the scale of the general circulation of the atmosphere. The global nature of climatic processes is evidenced by the observed quasi-synchronous changes in thermodynamic characteristics of the ocean‐atmosphere subsystem in the Pacific and Atlantic [2, 3] and Pacific and Indian [4, 5] oceans; in the high, middle, and low latitudes [6]; and in the Western and Eastern [7] hemispheres. Our investigations along with the study of individual properties and peculiarities of the climatic system are aimed at acquiring the whole pattern of its interdecadal variability and establishing general causes that form the basis of the observed climatic fluctuations, as well as physical mechanisms which maintain the variability. We consider in this work the peculiar features of the recent global climate dynamics in the period referred to as the global warming. Variations that took place in that period in the fields of the atmospheric pressure and near-surface temperature have been analyzed and natural processes that could cause those variations have been considered. Used as basic data in diagnostic calculations of oceanic and atmospheric climatically significant characteristics were global monthly fields of atmospheric pressure at sea level [http://www.cdc.noaa.gov/Pressure/Gridded/] and anomalies of the near-surface temperature [http://www. cru.uea/ak/cru/data/temperature/] for the period of 1950‐2007. Due to scanty data on observations north of 80 ° N and south of 70 ° S, the results of the analysis of the corresponding hydrometeorological fields in these zones should be taken with caution. The lack of data and, hence, inadequate reliability of the investigation results hold true for other regions as well, for instance, in central Africa. Global warming attracted particular attention in the 1970s, when a substantial rearrangement of the planetary field of atmospheric pressure took place [8‐10]. This situation formed the basis for the methods used in this work. To get nonrandom, statistically secured quantitative estimates of the above-mentioned rearrangement, we determined differences of global climatic fields of atmospheric pressure at sea level and the near-surface temperature averaged for two 25-year time intervals: 1975‐1999 and 1950‐1974. The field differences ∆ X ( ϕ , λ , z 0 ) were determined according to the formula

Influences of Large-scale Atmospheric Circulation and Local Sea Surface Temperature on Convective Activity over the Sea of Japan in December

The characteristics of the anomalous winter climate around Japan in December 2005, including abnormally heavy snowfall, were analyzed from the viewpoint of interannual variation using reanalysis data for 50 years. The anomalous snowfall near the Sea of Japan in 2005 is attributed to an anomalous air-mass modification over the Sea of Japan, the large changes of thermodynamic characteristics due to the warmth of the Sea of Japan. Thermodynamic budget analyses showed that the air-mass modification in December 2005 over the Sea of Japan was the strongest in more than 40 years. Air-mass modification over the Sea of Japan was strongly related with a large-scale atmospheric north-south dipole pattern consisting of a northern high covering Siberia and a southern low covering a wide area of Japan in the 500 hPa height field in the positive phase (SJ pattern). In addition, the local SST variability during late autumn was significantly related to air-mass modification. However, the Arctic Oscillation was not significantly correlated with the air-mass modification over the Sea of Japan on an interannual timescale.

Heat of formation of liquid copper alloys with 3d-transition metals

A calorimetric method is used to study the enthalpy of mixing in liquid copper alloys with 3d-metals. Results are compared with published information. The change in thermodynamic properties along the 3d-row is not uniform. The regularities obtained are associated with the type of phase diagrams. It is demonstrated that the change in thermodynamic characteristics is determined by features of the electron structure of the components.