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Heating Cycle (heating + cycle)
Selected AbstractsFly ash concrete subjected to thermal cyclic loadsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2010M. S. KHAN ABSTRACT The present study describes the behaviour of concrete as well as fly ash concrete when subjected to varying number of high temperature heating cycles. A Concrete mix (1:2.37:2.98) with 340 kg/m3 cement and,w/cm,ratio 0.45 was prepared. Cement was replaced by varying percentages (0%, 20%, 40%, 50% and 60%) of fly ash by weight of cement. The concrete was subjected to a constant temperature of 200°C for 7, 14, 21 and 28 heating cycles. One heating cycle corresponds to 8 h heating and subsequent cooling in 24 h. Subsequently the effect of temperature on the properties of the concrete was investigated and compared with that of the properties of unheated concrete. The compressive strength of plain as well as fly ash concrete increased when it was subjected to thermal cyclic loads. Moreover, the compressive strength increased with an increase in number of heating cycles. Thermal conductivity of concrete was found to decrease with an increase in the fly ash content. [source] Studies on glass transition temperature of mono and bilayer protein films plasticized by glycerol and olive oilJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Babak Ghanbarzadeh Abstract Thermomechanical and thermal properties of whey protein, maize prolamin protein (zein), and the laminated whey protein,zein films were studied. The dynamic mechanical (thermal) analysis (DMTA) results showed that the single zein film had higher Tg than single whey protein and zein,whey laminated films. The shift in the Tg values of films from 31.2°C in whey protein film and 88.5°C in the zein film to 82.8°C in the laminated whey protein,zein films may be implied some interaction formation between the two polymers. The small tan , peaks were observed at ,50°C in zein,glycerol films and at ,22.37°C in the whey protein films and can be related to ,-relaxation phenomena or presence of glycerol rich region in polymer matrix. Zein-olive oil and zein,whey protein,olive oil films showed tan , peaks corresponded the Tg values at 113.8, and 92.4°C, respectively. Thus, replacing of glycerol with olive oil in film composition increased Tg. A good correspondence was obtained when DSC results were compared with the tan , peaks in DMTA measurements. DSC thermograms suggested that plasticizers and biopolymers remained a homogeneous material throughout the cooling and heating cycle. The results showed that Tg of zein,glycerol films predicted by Couchman and Karasz equation is very close to value obtained by DSC experiments. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Determination of the Minimum Time for Binder Removal and Optimum Geometry for Three-Dimensional Porous Green BodiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2003Stephen J. Lombardo A model is developed to optimize two aspects of the thermal removal of binder from green ceramic components. The model, which accounts for flow in porous media arising from the thermal decomposition of binder in three-dimensional bodies with anisotropic permeability, describes the pressure within the body as a function of position, time, and temperature during the heating cycle. The model is used with variational calculus to predict the heating profile that minimizes the cycle time for the thermal removal of binder. The model is also used to determine which body geometry maximizes the buildup of pressure in parallelepipeds, a common shape of multilayer ceramic capacitors. [source] Role of Length Scale on Pressure Increase and Yield of Poly(vinyl butyral),Barium Titanate,Platinum Multilayer Ceramic Capacitors during Binder BurnoutJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000Leo C.-K. The binder-burnout kinetics of poly(vinyl) butyral from BaTiO3 multilayer ceramic capacitors with platinum metal electrodes were analyzed by combining thermogravimetric analysis with infrared spectroscopy. The rate of weight loss was accelerated when both BaTiO3 and platinum metal were present, and the presence of both metal and ceramic enhanced the production of CO2. The activation energy and pre-exponential factor were determined by analysis of the weight-loss data with a first-order kinetics model. Then, the decomposition kinetics were incorporated into a coupled heat- and mass-transport model to predict pressure increases as a function of the heating cycle. The heating cycles determined in this manner then were used to evaluate the yield of capacitors 1.3,3.8 cm long and 0.3,1.3 cm high. The optimum yield was realized at an aspect ratio (height:length) of 1:3. [source] Morphological, thermal, rheological and retrogradation properties of potato starch fractions varying in granule sizeJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 10 2004Narpinder Singh Abstract The physicochemical properties of small, medium and large starch granules separated from four potato cultivars were investigated to reveal whether functional properties differed among the various size classes of the starches. Large-size fractions showed higher amylose content and light transmittance and lower swelling power than small-size fractions. The granules from the three fractions had diameters of 5,20, 25,40 and 40,85 µm respectively. The large and medium granules were ellipsoidal to irregular or cuboidal while the small granules were spherical or ellipsoidal in shape. The transition temperatures and gelatinisation temperature range of the fractionated starches increased while the enthalpy of gelatinisation decreased with decreasing granule size. Rheological parameters such as peak storage (G,) and loss (G,) moduli increased in the order small-, medium- and large-granule starches when subjected to temperature sweep testing. The breakdown in peak G, during the heating cycle and retrogradation during storage were found to be highest for large- and lowest for small-size fractions. The differences in functional properties among the different size fractions suggested that the granule size distribution is an important parameter that can influence the behaviour of potato starch during processing. Copyright © 2004 Society of Chemical Industry [source] Dual functionality of PTSA as electrolyte and dopant in the electrochemical synthesis of polyaniline, and its effect on electrical propertiesPOLYMER INTERNATIONAL, Issue 7 2007Sambhu Bhadra Abstract The electrochemical synthesis of polyaniline (PAni) powder was carried out from an aqueous solution of 0.15 mol L,1 aniline with varying concentrations of p -toluenesulphonic acid (PTSA) at room temperature. The PAni samples thus obtained were characterized using DC and AC conductivity, dielectric properties, infrared spectroscopy, thermogravimetric analysis, X-ray analysis, scanning electron microscopy and ultraviolet spectroscopy. Results showed that PTSA is acting both as electrolyte and doping agent. With an increase in the PTSA concentration, there is more polaron formation, and this means an increase in charge carrier concentration and mobility. This accounts for the increase in conductivity and improved dielectric properties of the resultant PAni. The polymer was subjected to a heating and cooling cycle. The change in conductivity during the heating cycle is quite different from that during the cooling cycle, indicating some kind of hysteresis phenomenon occurring in the system. Moreover there is a net decrease in room temperature conductivity of PAni when subjected to the heating,cooling cycle. This may be due to the oxidation of PAni and generation of some kind of disorder in the structure of PAni during the heating,cooling process. Copyright © 2007 Society of Chemical Industry [source] Fly ash concrete subjected to thermal cyclic loadsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2010M. S. KHAN ABSTRACT The present study describes the behaviour of concrete as well as fly ash concrete when subjected to varying number of high temperature heating cycles. A Concrete mix (1:2.37:2.98) with 340 kg/m3 cement and,w/cm,ratio 0.45 was prepared. Cement was replaced by varying percentages (0%, 20%, 40%, 50% and 60%) of fly ash by weight of cement. The concrete was subjected to a constant temperature of 200°C for 7, 14, 21 and 28 heating cycles. One heating cycle corresponds to 8 h heating and subsequent cooling in 24 h. Subsequently the effect of temperature on the properties of the concrete was investigated and compared with that of the properties of unheated concrete. The compressive strength of plain as well as fly ash concrete increased when it was subjected to thermal cyclic loads. Moreover, the compressive strength increased with an increase in number of heating cycles. Thermal conductivity of concrete was found to decrease with an increase in the fly ash content. [source] Latitudinal height couplings between single tropopause and 500 and 100 hPa within the Southern HemisphereINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2010Adrián E. Yuchechen Abstract In order to provide further insights into the relationships between the tropopause and different mandatory levels, this paper discusses the coupling between standardized tropopause height anomalies (STHAs) and standardized 500-hPa and 100-hPa height anomalies (S5HAs and S1HAs, respectively) within the ,climatic year' for three sets of upper-air stations located approximately along 20°S, 30°S and 45°S. Data used in this research consists in a radiosonde database spanning the period 1973,2007. The mandatory levels are supposed to be included in each radiosonde profile. The tropopause, on the other hand, is calculated from the significant levels available for each sounding using the lapse rate definition. After applying a selection procedure, a basic statistical analysis combined with Fourier analysis is carried out in order to build up the standardized variables. Empirical orthogonal functions (EOFs) in S-mode are used to get the normal modes of oscillation as well as their time evolution, for STHA/S5HA as well as for STHA/S1HA coupling, separately, within the aforementioned latitudes. Overall, there are definite cycles in the time evolution associated with each EOF structure at all three latitudes, the semi-annual wave playing the most important role in most of the cases. Nevertheless, 20°S seems to be the only latitude driven by diabatic heating cycles in the middle atmosphere. Certainly, EOF1 at this latitude has a semi-annual behaviour and seems to be strongly influenced by the tropical convection seasonality. Apparently, the convectively driven release of latent heat in the middle troposphere affects the time evolution of the EOF1 structure. By contrast, the vertical propagation of planetary waves is raised as a possible explanation for the EOF1 and EOF2 behaviour at latitudes beyond 20°S, in view of the close connection existent between the semi-annual oscillation (SAO) and the reversion in the direction of the zonal wind. Copyright © 2009 Royal Meteorological Society [source] In situ Raman monitoring of chromium oxide scale growth for stress determinationJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2001Julie Mougin Raman spectra of a growing chromia (Cr2O3) layer generated by oxidation of pure chromium at 750 °C under 150 mbar of oxygen were recorded in situ every 5 min. The wavenumber evolution of the main Raman band versus oxidation time was interpreted in terms of mechanical stress development. Comparison with Raman spectra of a fully relaxed spalled chromia layer submitted to high-pressure and high-temperature treatments showed that internal compressive stresses develop during the growth, varying from ,2.1 GPa when the scale is very thin to ,2.4 GPa when the scale reaches a thickness of 0.6 µm. Relaxation phenomena seem to take place during isothermal oxidation. During cooling, thermal stresses are induced, which are purely elastic according to the perfect reversibility of cooling,heating cycles. Copyright © 2001 John Wiley & Sons, Ltd. [source] High-Intensity Discharge Lamp with Mo,SiO2 Functionally Graded MaterialJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006Ayumu Umemoto We show the invention of the new type of hermetically sealed high-intensity discharge lamps, made of Mo,SiO2 functionally graded material (FGM) as an electrode and a sealing component. In the case of high-intensity discharge lamps with Mo,SiO2 FGM (FGM lamp), the thermal expansion coefficient between Mo and SiO2 is functionally graded so that it tolerates a large number of heating cycles, with no cooling system required. Furthermore, lamps survive without breakage. The W electrode is totally separated from the lamp envelope by the FGM, so that no leakage of the luminous elements or gases takes place, when a large gas pressure exists inside a lamp. [source] | |||||||||||||