Papers by Keyword: Heat Conductivity

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 paper presents data on the use of the alkaline aluminosilicate binder-based adhesive of the system Na₂O•Al₂O₃•(4-6)SiO₂•(17-20)H₂O for gluing and fire protection of structural timber elements. The results of the study of thermoresistant phases in the reaction products of the alkaline aluminosilicates are reported and discussed. The results allowed to show that at SiO₂/Al₂O₃ between 5 and 6 the zeolite-like phases of heulandite types, which, under action of temperatures, are able to form a porous aluminosilicate artificial stone with low thermal conductivity (λ=0.09 Wt/m•К, DSTU B V.2.7-105-2000 (GOST 7076-99)) are formed in the reaction products. The use of the developed aluminosilicate adhesives allow for to classify the structural timber elements as hardly burnable and hardly flammable materials (GOST 12.1.044-1989, EN 13823 + A1: 2014-12, ASTM E119-07). They have the following characteristics: water resistance D3 (EN 204:2001), resistance in splitting up 7.8 MPa (GOST 16483.5-1973), adhesion in normal pull-off test up to 2.6 MPa (GOST 32299-2013 (ISO 4624:2002)).

Abstract: The paper deals with change patterns of heat-efficient concrete depending on the content of artificial granulated aggregate and water. The obtained results allow analyzing the quantity and degree of influence of each factor on physical-mechanical properties of concrete and defining its structure.

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: The work is devoted to effective and ecological technologies for the application of functional structured materials for roads, railways, airfields on permafrost with forced cooling of the sub-soil foundation. The physical and mathematical simulation of the thermal state of frozen ground with single and double-layer coatings was performed. The temperature profiles of a model combine roadbed on the longstanding permafrost have been calculated at winter conditions of the Northern Hemisphere. This roadbed include an upper surface coating with low thermal conductivity and high emissivity in the long-wavelength IR range at convective-radiative heat exchange. The second high-conductive subsurface coating is laid on the underlying sub-soil and ensures its cooling as the “heat pump”. The efficiency of the proposed technology of roadbed construction based on the use of non-toxic waste of numerous industrial productions. The carried out research will be in demand for the specialists of transport support, engineering glaciology, in the field of climatology, oceanology, construction, environmental measures, and also in the presentation of financial and economic forecasts of the prospects for the development of polar and subpolar regions, the Arctic and the Antarctic, and high-mountain.

Abstract: Ion-beam deposition of amorphous Ge layers on different substrates (silicon and quartz) has been performed. Deposited amorphous Ge layers were subjected to pulsed laser annealing (λ = 0.69 μm, τ = 80 ns). Simultaneously the optical probing of the Ge surface was carried out. The computer simulation of heating processes and phase transitions was performed taking into account the temperature dependences of film and substrates’ parameters and phase transition energies. The results of the dynamics of heating, melting, crystallization and plasma formation processes are well described by simulation data. It is shown that the threshold values for radiation power density and phase transition rates are determined mainly by thermophysical parameters of the substrates and thermal contact between Ge melt and substrate.

Abstract: Air pre-heater and economizer are heat transfer surfaces in which air temperature and water temperature are raised by transferring heat from other media such as flue gas. Hot air is necessary for rapid combustion in the furnace and also for drying coal in milling plants. So an essential boiler accessory which serves this purpose is air pre-heater. The air pre-heater is not essential for operation of steam generator, but they are used where a study of cost indicates that money can be saved or efficient combustion can be obtained by their use. The decision for its adoption can be made when the financial advantages is weighed against the capital cost of heater. The efficiency of the boiler increases with the increase in the temperature of the combustion air used in the furnace. This is achieved by the increased temperature of the flue gas in the air preheater and economizer zone. This paper deals with the different ways to obtain the maximum heat from the flue gas travelling through the air preheater and the economizer zone to improve the boiler efficiency.

Abstract: The article describes the calculation method of the payback period for the thermal protection measures. These measures are aimed at the increasing of thermal protection level achieved by the additional thermal insulation of the existing building's walls. The example of the calculation for the certain settlement with the specified climatic variables is also provided in the article.

Abstract: Calculation of payback periods of the energy saving actions directed on increase of level of thermal protection of external enclosure structures of buildings is given. Economic efficiency of investments in energy saving actions is analyzed and the model allowing to carry out the specified analysis is offered. Recommendations about reduction of payback periods are provided.Article also is devoted definition of optimum, economically well-founded thickness of a insulant in systems of rear ventilated facades. Are resulted thermotechnical and economic calculations. The optimum thickness of the insulant in the given systems is offered.A number of the energy saving actions is necessary for economy of thermal energy, allowing to eliminate defects of protecting designs or to reduce their influence on building heatconsumption. Construction of hinged ventilated facades at simultaneous introduction of automated individual thermal points with automatic equipment dependent on weather [1] can become an example of the engineering decision on increase of heat-shielding properties of protecting walls.

Abstract: In order to discuss the effect of energy saving of heat-reflective insulation coating on exterior walls of building, the wall temperature change of two test rooms with heat insulation or not in Hangzhou has been monitored in summer, and the heat flux data of east, south and west walls were analyzed. The results indicate that the reflective coatings reduce the exterior surface temperature by up to 7 to 8°C. The reduction in heat gain of east, south and west walls is significant, which is the cooling effect. The total surface heat gain of exterior walls without reflective coatings is 2.44 times larger than those without them. In particular, the heat gain of walls with reflective coatings is nearly 5.27 times more than that of walls without reflective coatings. The reduction in electricity consumption of air-conditioning system in the building with reflective coatings is 2.5KWh/m² per month by calculation, which well proves the energy saving effect of reflective coatings.