Cyclic Temperature Changes Research Articles

Расчетная оценка причин образования трещин в кожухе воздуховода горячего дутья

The heater of blast furnace intended to provide hot blast and has a metal casing lined inside with refractory bricks. The technological process involves cyclic temperature changes of gas in the heater from 400 to 1200°C with cycle duration of 3 hour. After some operating time, cracks appear in the casing. Internal pressure in the apparatus is low, but nevertheless the cracks are dangerous because the stream of hot (1200°C) oxygen-enriched air can damage surrounding structures. A way to prevent cracks depends on the mechanism of their formation. Three possible reasons of the crack formation were considered: uncompensated forces caused by thermal expansion of the entire structure, vibration and thermal stresses due local uneven heating of the casing. Observable cracks have different orientations and in some cases are located sufficiently close to each other. This pattern is characteristic for thermal cracks and is not typical for cracks caused by mechanical loads and/or vibrations. Numerical analysis shows that the non-uniformity of temperatures may cause the thermal fatigue cracks despite the fact that the non-uniformity observed on the outer surface of the casing is small enough. Fractography had confirmed the thermo-fatigue nature of the cracks. As a possible measure to prevent cracking the usage of 2-layer casing was analyzed; numerical estimations proved potential effectiveness of such solutions.

Numerical Simulation for Hot Dry Rock Geothermal Well Temperature Field

Study on temperature distribution simulation during cementing of hot dry rock (HDR) geothermal well is rare. It has important guiding significance to simulate the construction process of temperature distribution of hot dry rock on site construction. Based on numerical simulation of HDR considering heat-fluid-solid coupling, the influence of temperature distribution on well cementing is analyzed when the drilling fluid cycles and reaches stable state, respectively, and when the cement slurry is injected during the cementing process. It is found that the seepage at the well bottom accelerates the flow velocity of wellbore; the stable temperature change is less than the cyclic temperature change; and the upper and lower temperature variation of the stratum is greater when the cement slurry is injected. Therefore, as to cement retarder involved, the influence of temperature variation on concretion should be considered during cementing of the hot dry rock geothermal well.

CFD simulation and statistical analysis of moisture transfer into an electronic enclosure

Condensation and moisture related problems are the cause of failures in many cases and consequently serious concerns for reliability in electronics industry. Thus, it is important to control the moisture content and the relative humidity inside electronic enclosures. In this work, a computational fluid dynamics (CFD) model is developed to simulate moisture transfer into a typical electronic enclosure. In the first attempt, an isothermal case is developed and compared against the well-known RC circuit analogy considering the behavior of an idealized electronic enclosure. It is shown that the RC method predicts a faster trend for the moisture transfer into the enclosure compared to the CFD. The effect of several important parameters, namely, position of the opening, initial relative humidity inside the enclosure, length and radius of the opening and temperature is studied using the developed CFD model for the isothermal case. The model is then combined with a two level factorial design to identify the significant factors as well as the potential interactions using the numerical simulation results. In the second part of this study, a non-isothermal case is studied, in which the enclosure is exposed to two different conditions, i.e., internal temperature oscillation only and combined cyclic changes of ambient relative humidity and temperature. The results are compared with experimental data from literature, and show that the local climate inside the enclosure responds faster to the temperature changes compared to the RH changes. The trends predicted by the CFD simulations can be used to decide for the right time and position of a commercial adsorbent and/or thermal mass inside the enclosure to control the local climate.

Research on shakedown analysis for functionally graded material plate under thermomechanical loading

ABSTRACTShakedown is an important problem in the design and analysis of functionally graded structures subjected to cyclic, thermal, and mechanical loadings. Subjected to constant mechanical load and cyclic temperature change, static shakedown of a functionally graded material plate and its homogenous counterpart were analyzed in this article with the approach proposed by the authors previously. The functionally graded material plate is composed of an elastoplastic matrix Al and elastic particles SiC, and the particle volume fraction varies through the thickness. The distributions of the effective mechanical and thermal properties of the composites through the thickness are described graded continuously with an exponential law. The results show that a proper and continuously graded distribution of material properties can efficiently improve the shakedown capability of the functionally graded material plate and also show the significance of shakedown analysis and application for functionally graded material plates.

Elastic and Mechanical Fatigue at High Temperatures of High-Alumina Castables with Addition of Partially Stabilized Zirconia

This work evaluates the impact of added zirconia on the thermomechanical and thermoelastic fatigue properties of high-alumina refractory castables. Three testing scenarios are presented in the study: 1) Resonant Frequency Damping Analysis (RFDA) after cyclic temperature changes with and without mechanical load, 2) Refractoriness under Load (RuL) tests, and 3) results of abrupt temperature shifts between two high temperatures in a special thermal shock furnace. The tested refractory formulations were a reference castable based on tabular alumina and two castables each containing 13.75 mass-% of zirconia. The formulations of the zirconia castables had an addition of either fully-stabilized zirconia doped with 8 mol-% yttria (Y-FSZ) or partially-stabilized zirconia doped with 3 mol-% calcia (Ca-PSZ). The Y-FSZ castable displayed elastic and mechanical behaviour by means of RFDA and RuL similar to the reference sample and had good recovery after thermal shock testing. The Ca-PSZ formulation showed some beneficial toughening through energy dissipation of progressing cracks, but after cooling exhibited the matrix fracturing influence of the martensitic zirconia phase transformation which would negatively impact service life of the refractory.

Influence of disorder on ageing and memory effects in non-equilibrium critical dynamics of 3D Ising model relaxing from an ordered state

We have performed a numerical investigation of the influence of disorder on the dynamical non-equilibrium evolution of a 3D site-diluted Ising model from a low-temperature initial state with magnetization m0 = 1. It is shown that two-time dependences of the autocorrelation and integrated response functions for systems with spin concentrations p = 1.0, 0.95, 0.8, 0.6 and 0.5 demonstrate ageing properties with anomalous slowing-down relaxation and violation of the fluctuation-dissipation ratio. It was revealed that during non-equilibrium critical dynamics in the long-time regime the autocorrelation functions for diluted systems are extremely slow due to the pinning of domain walls on impurity sites. We have found that the fluctuation-dissipation ratio for diluted systems with spin concentration p < 1 while the pure system is characterized by . The autocorrelation function power-law delay becomes the same as for the time dependence of the magnetization in the critical point and is characterized by exponent . Also, for diluted systems we reveal memory effects for critical evolution in the ageing regime with realization of cyclic temperature change and quenching at .

Dislocations in MCT heteroepitaxial structures on (013) substrates and possibilities of dislocation density reducing

AbstractDislocations in heterostructures CdTe/ZnTe/GaAs(013) and CdTe/ZnTe/Si(013) were investigated using selective etching and transmission electron microscopy. The calculations of critical film thickness hc were fulfilled for 12 various slip systems, the experimental results were obtained for 4 of them. Misfit dislocations are introduced in a ZnTe film at the stage of formation of the first monolayers. With their introduction, the crystal lattices of the substrate and the film unfold relative each other that is confirmed by X‐ray diffraction measurements. An increase in the dislocation density into the CdTe and HgCdTe films was observed using layer‐by‐layer etching. That is testifies to the annihilation of threading dislocations during the growth of CdTe and MCT films. The dislocation annihilation rate is higher in films grown on GaAs(013) than on Si(013). Perhaps this is due to the higher proportion of gliding dislocations in CdTe films on GaAs substrates (013). It was made annealing of MCT films under cyclic temperature change in such way that activity of MCT components was changed to enhance the non‐conservative motion of dislocations. As a result, the density of penetrating dislocations in the active areas in MCT films on silicon substrates was decreased to the value of 2.5×106 cm‐2. (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

IMPACT OF CYCLICAL CHANGES IN TEMPERATURE ON CIRCADIAN CLOCK GENES EXPRESSION IN Bombyx BmN CELLS.

The physiology and metabolism of poikilothermic insects are under the control of environmental temperature. Temperature is the primary cue for the circadian rhythm. Reports on the timing mechanisms of temperature in lepidopterans are limited. This study used Bombyx mori BmN ovarian cells to investigate the effect of temperature on expression of the main circadian clock genes in a negative feedback loop. A 37°C, 30-min high-temperature stimulation induced transcription of the circadian clock genes Cry1, Cry2, Per, and Tim. The gene expression profiles showed rhythmic oscillations, with shortened oscillatory periods for Cry1 and altered oscillatory phases for Cry1 and Per. Cyclical increases in temperature of 2°C starting at 26°C, 5°C starting at 20 or 25°C, or 10°C starting at 20°C induced cyclical changes in expression and protein from the four circadian clock genes. Cyclical temperature changes with a difference of 10°C had the most influence. In conclusion, cyclical changes in temperature with differences from 2 to 10°C reset and synchronized the circadian clock of silkworm BmN cells. Transcription of the genes for and protein from Cry2 and Per showed a better reset and synchronization with cyclical temperature changes.

鉛フリーはんだに適用される汎用FEAソフトの構成モデルが累積非弾性ひずみ挙動に及ぼす影響

It is important that evaluations of thermal fatigue life of lead-free solder joints under cyclic temperature changes are performed more than before exactly. We have to conduct FE analysis using a constitutive model in order to estimate the fatigue life of solder joints. There, classical isotropic hardening elastic-plastic-creep model, classical kinematic hardening elastic-plastic-creep mode and Anand model are often used because these models are implemented into commercial FEA soft. In this study, as such mechanical properties of the lead-free solder joints, stress-strain curves, stress-strain hystereses and stress-relaxation curves with these temperature dependencies and these rate dependencies were regarded. And, how accuracy simulation results by these model accord with these experimental test data were investigated. Next, using these models, FE structural analysis of solder joints under cyclic temperature change on actual equipment were conducted and the accumulated inelastic strain behavior were gotten. Finally, the characteristics of each constitutive model were connected with these behavior.

ポリシアネート樹脂炭素繊維強化プラスチックスの熱サイクル環境下での損傷評価及び有限要素法を用いた熱応力連成解析

In this study we aim to estimate damage in materials which is used in antenna's radial ribs of new radio astronomy satellite. The materials are carbon fiber reinforced plastics (CFRP) because of their high-specific strength. In space environment, cyclic temperature change is loaded on a structure due to sunshine and eclipse. As a result, severe thermal stress occurs and causes damages in CFRP. The purpose of this study is to evaluate thermal fatigue effects on microscopic damage progress in CFRP. We also conducted finite element analyses to discuss the mechanism of damage behavior.

EDITORIAL

The most significant advance in Molecular Biology area in recent years was due to the development of a technic that provides the unlimited multiplication of DNA molecules (deoxyribonucleic acid – genetic material of most living things). Named PCR (Polymerase Chain Reaction), this technique afforded the progress of several scientific areas. The rapid and accurate diagnosis of diseases by PCR allows for greater effectiveness in the treatment of these diseases. The reliability of this technique is so great, that the identification of a criminal by PCR is accepted as forensic evidence. To perform a PCR reaction, it is necessary a DNA molecule to serve as a template, an enzyme called DNA polymerase and nucleotides, which make up the new DNA strand. In a simplified way, these are the main ingredients, but only mixing them in a test tube is not sufficient to trigger the process of DNA amplification. For this, cyclic temperature variations must occur, such as: a DNA initial denaturation at 94o C for 2 min, 35 cycles of 1 min at 94o C, 1 min at 62o C, 1 min at 72o C, and a final extension for 4 min at 72o C. For the accurate occurrence of these cyclic temperature changes, an equipment called thermocycler was developed. In other words, this revolutionary technique combines enzymatic reactions and a thermodynamic process. Currently most thermocyclers use the Peltier technology, exploiting the properties of semiconductors and providing greater uniformity at different temperatures that result in a high degree of accuracy and reproducibility. Thus, I take the opportunity to encourage research in the field of Thermal Engineering interfaced with Molecular Biology, which, as discussed above, may contribute to major scientific advances in biological sciences, and an improvement in the community's quality of life in general.

Multiphysically coupled thermal–acoustic axisymmetric wave propagation for electron acoustic nondestructive observations

The nondestructive observation using thermoelastic–piezoelectric couplings by the chopped electron beam in the commercial-based scanning electron microscope has been proposed as a scanning electron-induced acoustic microscope (SEAM). Our own-built SEAM has successfully provided some nondestructive observations of micro-defects such as micro-voids, cracks and delamination. In order to investigate the thermal–acoustic wave properties as the principle of observation in SEAM, an axisymmetric thermoelastic–piezoelectric computational model was proposed. Three kinds of governing equations in three dimensions multiphysically coupled among non-Fourier heat conduction, dynamic elasticity and piezoelectricity were first derived and then reduced to the axisymmetric two-dimensional and finally to the one-dimensional equations. The thermal wave and thermal stress wave observed in a monolayer cylinder with the thermal relaxation were first analyzed for both the cases with an almost circular vacancy-like inclusion and without it. The results were in agreement with the analytical prediction, and it was observed that the delay of traveling waves was increased due to the longer transport path as the inclusion radius. A three-multilayer model corresponding to the real measurement system of SEAM was employed to estimate the piezoelectromotive output to the cyclic temperature change on one end face. Fast Fourier transformation of that wave gives us the clear resonance frequencies driven by the thermal-induced disturbance, and thus, the estimated eigenfrequency of the measurement system will be utilized for the higher resolution of the electron acoustic image of SEAM.

The Effect of Environmental Flight Conditions on Damage Propagation in Composite Sandwich Structure

Abstract The aim of the study was to determine the traceability of damage growth caused by inclusions of water in the composite sandwich structure. It was assumed that as a result of temperature changes during the flight and accompanying phase transformation, the zone containing water inclusions increases. The growth is caused by the destruction (mainly the tearing of walls) of the core. As part of the work, this assumption was verified experimentally. For the experiment to be successful it was necessary to simulate actual flight conditions. The simulation involved inducing phase transformations of water in the core cell as a function of time and temperature. Before and after the experiments the non-destructive tests using pulsed thermography were performed. The test results revealed an increase in the number of cells occupied by water. Adequate specimens were designed and manufactured. The study showed that cyclical changes in temperature affected the propagation of water in core sandwich structures. Further, it was found that the increase in the surface area of water-containing inclusions could be monitored using thermographic techniques.

Natural Sleep and Its Seasonal Variations in Three Pre-industrial Societies

How did humans sleep before the modern era? Because the tools to measure sleep under natural conditions were developed long after the invention of the electric devices suspected of delaying and reducing sleep, we investigated sleep in three preindustrial societies [1-3]. We find that all three show similar sleep organization, suggesting that they express core human sleep patterns, most likely characteristic of pre-modern era Homo sapiens. Sleep periods, the times from onset to offset, averaged 6.9-8.5hr, with sleep durations of 5.7-7.1hr, amounts near the low end of those industrial societies [4-7]. There was a difference of nearly 1hr between summer and winter sleep. Daily variation in sleep duration was strongly linked to time of onset, rather than offset. None of these groups began sleep near sunset, onset occurring, on average, 3.3hr after sunset. Awakening was usually before sunrise. The sleep period consistently occurred during the nighttime period of falling environmental temperature, was not interrupted by extended periods of waking, and terminated, with vasoconstriction, near the nadir of daily ambient temperature. The daily cycle of temperature change, largely eliminated from modern sleep environments, may be a potent natural regulator of sleep. Light exposure was maximal in the morning and greatly decreased at noon, indicating that all three groups seek shade at midday and that light activation of the suprachiasmatic nucleus ismaximal in the morning. Napping occurred on<7% of days in winter and <22% of days in summer. Mimicking aspects of the natural environment might be effective in treating certain modern sleep disorders.

Dimensional Responses of Wood Under Cyclical Changing Temperature at Constant Relative Humidity

To investigate dimensional responses of wood under dynamic temperature condition, poplar (populous euramericana Cv.) specimens, 20 mm in radial (R) and tangential (T) directions with two thicknesses of 4 and 10 mm along the grain, were exposed to cyclic temperature changes in square wave between 25℃ and 40℃ at 60% relative humidity (RH) for three different cycling periods of 6 h, 12 h and 24 h. R and T dimensional changes measured during the cycling gave the following results: 1) Transverse dimensional changes of the specimens were generally square but at an opposite phase and lagged behind the imposed temperature changes. The phase lag was inversely correlated with cycling period, but positively related to specimen thickness, while the response amplitude was directly proportional to cycling period, but in a negative correlation with specimen thickness. 2) The specimens showed swelling hysteresis behavior. The heat shrinkage coefficient (HSC) became greater as cycling period increased or specimen thickness decreased. 3) Dimensional changes of the specimens produced deformation accumulation during repeated adsorption and desorption. The deformation accumulating ratio decreased with an increase in cycling period and specimen thickness. 4) Wood suffered 1.5 times as many dimensional changes per unit temperature variation as per unit humidity variation, and this deformation behaved even more seriously under static condition.

Spectrum of heterogeneous nucleation modes in crystallization of Sn-0.7wt%Cu solder: experimental results versus theoretical model calculations

In this paper we analyze both experimentally and theoretically the various possibilities of Sn-0.7wt%Cu solder crystallization and in particular we report, for the first time, low undercooling degrees (1–7 K) for this alloy. The supercooling of Sn-0.7wt%Cu alloy is measured by Differential Scanning Calorimetry experiments performed by using cyclic temperature change of the solder with total melting or with partial melting of the solder. Two different conditions for the solder alloy are used: (1) solder over Cu6Sn5 phase prepared by dipping a Cu sheet into a bath of Sn-0.7wt%Cu liquid alloy at 250 °C for 1 s providing natural interface for the heterogeneous nucleation of Sn crystals and (2) solder alloy without any specially prepared interfaces. At least three categories of undercooling degrees of Sn-Cu alloy are observed according to the experimental conditions. For each undercooling category we try to find the type of the heterogeneous nucleation site responsible for the start of the crystallization. Possible nucleation sites and nucleation modes of the crystallization are explored: (1) in the bulk (homogeneous), (2) at the planar interface liquid alloy/solid Cu6Sn5 surface, (3) as a cap over a spherical particle (a), or as a spherical shell covering a Cu6Sn5 phase sphere (b), (4) in a spherical cavity and (5) in a groove—at the step of the surface. Theoretical and experimental values of undercooling degrees are compared and the sites of the favorable nucleation are proposed for each case.

Thermal and hygric expansion characteristics of mortars and bricks used in the dome structures of Turkish Baths from 14th and 15th centuries

Thermal and hygric expansion characteristics of mortars and bricks from the dome structures of three Turkish Baths from 14th and 15th centuries were investigated. The linear thermal expansion coefficients of the mortars and bricks were determined in the temperature range from −10°C to 50°C and hygric expansion characteristics of the same samples were studied in the relative humidity range from 30% to 80%. The results showed that the thermal and hygric expansion characteristics of mortars used in the dome structures of the studied baths are very similar to those of bricks used within the same structure. The thermal expansion coefficients of the mortars are 2.5% to at most 10% greater than the bricks of the same dome. The linear displacement of the mortars and bricks due to relative humidity changes are less pronounced in comparison with the displacement due to thermal changes, but similarity in the expansion trends in between the mortar and bricks of the same structure is also observed for the hygric expansion test results. Since movement of the materials resulting from cyclic changes in temperature or relative humidity may cause stresses at the interfaces where different materials are in contact, eventually resulting in cracks and detachments, it is important to consider the thermal and hygric expansion behavior of the original materials during the selection of repair materials to be used in the conservation works of these dome structures.

온도변화가 모래 및 화강풍화토의 입자구조 및 강도 특성에 미치는 영향

본 논문에서는 지열활용 지반구조물 적용시 주변 지반에 부과되는 온도변화 사이클이 흙의 물리적 역학적 특성에 미치는 영향에 대한 내용을 다루었다. 이를 위해 모래와 화강풍화토를 대상으로 다양한 온도변화 조건을 구현하고 이에 따른 흙의 입자구조 및 열전도특성 변화 경향을 고찰하였다. 아울러 다양한 온도변화에 노출된 시료를 이용하여 시편을 조성한 후 삼축압축시험을 수행하고 그 결과를 토대로 온도변화가 시편의 응력-변형률-강도 톡성에 미치는 영향을 검토하였다. 그 결과 온도변화 사이클은 흙의 입자구조 및 열전도율에 큰 영향을 미치지 않는 것으로 검토되었다. 또한 임의 반복 사이클 <TEX>$N_{hc}$</TEX>에 있어 가열시간이 <TEX>$H_d=2{\sim}8hrs$</TEX> 변화함에 따라 최대 축차응력이 15%이상 감소하는 것으로 나타나 가열-냉각 반복작용에 의한 흙의 강도특성 변화는 흙의 종류에 따라 달라 질수 있는 것으로 검토되었다. This paper presents the results of an investigation into the effect of forced temperature change cycles on physical and mechanical properties of sand and weathered granite soil. The effect of forced temperature change cylecs on the particle arrangement and the thermal conductivity was first investigated. A series of triaxial compression tests on the soils were also performed to look into the effect of temperature change cycles on the stress-strain-strength behavior. The results indicated that the forced temperature change cycle does not significantly affect the particle arrangement and thermal conductivity. It is shown however that the heating duration showed some effect on the deviatoric stress at failure while no significant effect due to the number of heating-cooling cycle was observed.

Probabilistic assessment of failure risk of the building envelope thermally insulated from the inside

Thermal insulation of external walls is designed in particular to reduce energy performance of buildings. Insulation placed on the outer side of walls act as an effective protection against the external environment. On the contrary placing the thermal insulation layer on the inner side of the building envelope is quite hazardous as the internal insulation does not fulfil the protective function. It actually exposes the bearing layer of the building envelope to the immediate effect of the environment and therefore it enhances the negative impacts of the cyclic temperature changes on structural system of the building. This paper focuses on probability risk of development of failures on such construction depending on variable boundary conditions (rigidity of the structure, strength of the materials, and range of the temperature load). Besides this there is also comparison of probability and deterministic approach to the evaluation of static reliability of the building constructions. Using of probabilistic approach in this context is still very rare. The aim of this paper is to analyse the effects of internal insulation on load bearing system of buildings, and to verify the applicability of probabilistic methods in the analysis of structural reliability. Like the deterministic approach, it draws attention to the high risk of failure of the structures insulated from the inside. At the same time, however, it shows the high demands of the probabilistic method on the amount of input data. If the data are not available, it is possible to replace some of them results of deterministic method; this approach has negative consequences in mutual dependency of accuracy of achieved results.

Alterations in Human Liver Metabolome during Prolonged Cryostorage.

Tissue metabolomics requires high sample quality that crucially depends on the biobanking storage protocol. Hence, we systematically analyzed the influence of realistic storage scenarios on the liver metabolome with different storage temperatures and repeated transfer of samples between storage and retrieval environments, simulating the repeated temperature changes affecting unrelated samples stored in the same container as the sample that is to be retrieved. By cycling between storage (-80 °C freezer, liquid nitrogen, cold nitrogen gas) and retrieval (room temperature, -80 °C), assuming three cycles per day and sample, we simulated biobank storage between 3 months and 10 years. Liver tissue metabolome was analyzed by liquid chromatography/mass spectrometry. Most metabolite concentrations changed <5% for the first "year" of time-compressed biobanking simulation, predominantly due to hydrolysis of peptides and lipids. Interestingly, storage temperature affected metabolite concentrations only little, while there was a linear dependence on the number of temperature change cycles. Elevated sample temperature during (prolonged) retrieval time led to a distinctly different signature of metabolite changes that were induced by cycling. Our findings allow giving recommendations for optimized storage protocols and provide signatures that allow detection of deviations from protocol.