Papers by Keyword: Heat Release

Abstract: The paper discusses the results of studying the hardening process of a gypsum-based composite material using a thermal imager. Thermal imaging research involves periodically obtaining thermal images of hardening material with pronounced hydration exotherm. It is assumed that the intensity of hydration and heat release depend on the state of the heterogeneous system, the structure of the forming material and the degree of aggregation of particles of hydrating components. The resulting images contain both visible and hidden information about the physical and chemical processes occurring in the material. To fully obtain such information, computer image processing methods were used. Intensity histograms were constructed and analyzed, for which regular changes were observed in the process of structure formation. As a generalization of the observed patterns, a working hypothesis is proposed about the filling of scales of physicochemical characteristics and, in particular, large-scale structural scales, in the process of structure formation. An image processing algorithm has been developed that makes it possible to construct isothermal cells‒areas of material with the same temperature. The geometric characteristics of the resulting areas, forming a partition of the study area, were studied by an automated method and reflected using histograms. The interpretation of the influence of a changing temperature distribution on the properties of a material is based on the idea of an approximate correspondence between a network of temperature cells and a Voronoi network that defines regions of a disordered structure. The spatiotemporal features of thermal processes are considered, indicating a possible decrease in the strength characteristics of the material.

Abstract: The paper presents the experimental data on the cement effect typeon the effects of heat generation during the 3D-printable cement materials’setting and hardening. Materials made on the basis of cements CEMI 42.5 RandCEMI 52.5 R, differing in phase contentC₃Ain combination with viscosity modifiers of various compositions,have been studied. To control setting kinetics, a penetrometer test was used, hardening kinetics was evaluated by testing the samples for compressive strength after 1, 3, 7, 14, 28 days of hardening. It was found that the useof CEMI 52.5 Rhigh in compositionC₃Acauses a significant heating of the mixture already after its setting, which is not observed when using ordinary CEMI 42.5R. The combination of a highly active aluminosilicate modifier with high-strength cement causes a technologically unacceptable reduction in the setting time and open time of mixtures.

Abstract: The paper presents the results of the determination of the effect of a photocatalytic composite material (PCM) with the composition SiO₂‒TiO₂ on the main properties of white Portland cement: heat release during hydration, phase composition and microstructural features of cement stone, pressure strength and self-cleaning ability. PCM was synthesized by a sol-gel method based on tetrabutoxytitanium and finely dispersed diatomite powder and 15% cement was added instead. The presence of PCM in the cement system provided the reduction of the induction period of cement hydration, consolidation of the microstructure of the cement stone with the products of the pozzolanic reaction, the ability to photocatalytic self-cleaning of the cement stone surface.

Abstract: The effects of external heat radiation on combustion and toxic gas release characteristics of flame retardant cables, which were XLPE insulated, flame retardant PVC sheathed and steel armoured cables, were investigated. The combustion characteristics of the level A and the level C flame retardant cables were explored by the cone calorimeter. For the level C cables, heat release rate (HRR) and CO concentration in cable fires increased and the ignition time decreased with increase of the external radiation heat flux. For level A cables, the HRR and CO concentration showed two-stage variations with the external radiation heat flux. When the external radiation heat flux was smaller than 35 kW/m², the cable self-extinguished quickly after the ignition. When the external radiation heat flux was larger than 50 kW/m², the cables showed continuous burning phenomena after the ignition. The level A cable had smaller HRRs compared with that of the level C cable under the same external radiation heat flux. However, the CO concentration of level A cable was remarkably higher than that of the level C cable in the present study. The high CO release rate of cable with well flame retardant ability under large external radiation heat flux requires more caution in the cable fires.

Abstract: In the current study, combustion characteristics were evaluated using mahua biodiesel blends at different compression ratios on a direct injection CI engine. Non edible mahua oil was transesterified into biodiesel by two stage technique. Combustion parameters were evaluated for B5, B10 and B20 blends of mahua biodiesel with diesel and they were compared with straight diesel at compression ratios of 16, 17 and 18.Compression ratio was varied without altering the combustion chamber geometry and the static spill timing was set to 23° bTDC. Parameters like In cylinder pressure, heat release rate, rate of pressure rise and cumulative heat release were evaluated in this study at 100% engine loading conditions. Higher peak cylinder pressure and heat release was observed at higher compression ratios. The ignition delay of the blends were slightly higher compared to diesel at all CR tested. Peak cylinder pressure of the blends was slightly higher at CR 18. The ignition delay was also observed to be lower at higher compression ratio. The peak pressure was observed closer to TDC at higher compression ratios for all fuels tested.

Abstract: Computational simulation for the combustion process in a DI diesel engine was performed through a code made by the author [1]. Two conditions of different injection pressure were examined in the simulation. The injection pressures are 150 MPa and 500 MPa. The combustion phenomenon was modeled as a combined process of formation of a combustible mixture and a chemical reaction. The rate of mixture formation was assumed to be dependent on the turbulence characteristics and the concentration of species in each computational cell. The rate of chemical reaction is described as an Arrhenius equation. The result agrees with the experimental result qualitatively, and the effect of injection pressure on the combustion process is well predicted.

Abstract: Energy-saving and emission-reducing must be achieved based on the reliable performance of fire safety. External thermal insulation material is the main component of external thermal insulation system, and also the main combustion participants when a fire occurs; the combustion performance is an important factor affecting the fire scale of external thermal insulation system. The main material and heat release principle was introduced in this paper, tests were carried out, and fire hazard was analyzed based on large amount of test data. The research will provide theoretical support for external insulation material choice, system construction, fire prevention and rescue.

Abstract: In this article, an improved procedure based on ISO 5660-1 and ASTM E1474 was developed to ensure the effectiveness and reliability of cone calorimeter test of textile fabrics. In order to improve the instability for some easy shrinking fabrics exposed under heat in cone calorimeter test, an iron wire grid was applied to cover the top surface of polypropylene nonwovens and polyester fabrics to avoid drastic distortion caused by heating irritation. Results showed that the iron wire grid could avoid the distortion of the easy shrinking samples and stable test process, also success probability and results repeatability were also improved. A guiding effect was found during the test caused by the grid, which leaded to a better uniformity of polymer melt under the thermal or even on fire.

Abstract: Influence of different flame retardants on the heat release performance of the rigid polyurethane foam (RPF) was studied in this paper. It was found that adding antimony trioxide (ATT) in RPF, heat release rate of RPF was slightly reduced, total heat release was significantly decreased but peak of heat release temperature was decreased. Therefore, ATT was not an excellent flame retardant for RPF. When adding ammonium polyphosphate (APP) in RPF, total heat release of RPF was significantly decreased, ignition temperature was significantly improved and heat release rate was not changed. Melamine polyphosphate (MPOP) could quickly reduce total heat release of RPF so its flame retardant effect was the best. Nitrogen-based flame retardants could reduce peak of heat release rate of RPF. APP, MPOP and nitrogen-based flame retardants were all better flame retardants for RPF. Small amount of magnesium hydroxide (MH) could increase total heat release of RPF.

Abstract: A thermal emission layer was coated on the aluminum chassis of a concentrator photovoltaic (CPV) module. The cell temperature in the CPV mini-module with the white thermal emission coating was 3 - 5°C lower than that in the CPV mini-module without the thermal emission coating. The effect of the high-radiation layer was remarkable. In spite of the high emissivity of the black thermal emission coating, the effect of the black coating was not remarkable. This is because the scattered light from environment is absorbed by the black coating and the CPV mini-module is heated. The color of CPV is important and the white coating is better than the black coating.