Heating Zone Research Articles

An investigation into heat storage by adopting local climate zones and nocturnal-diurnal urban heat island differences in the Tokyo Prefecture

• Urban heat island diurnal-nocturnal difference adopted as relative heat storage indicator. • Seasonal local climate zone (LCZ) and relative heat storage correlation is analyzed. • Relative height slope data is combined with LCZs for heat storage analysis. • Higher-rise LCZs are suggested to have larger relative heat storage effects than lower-rise. • Compact LCZs are suggested to have larger relative heat storage effects than open. This study aims to identify urban forms that are prone to heat storage in the Tokyo Prefecture in Japan. First, local climate zones (LCZ) were identified with 100 m pixel resolution using Landsat 8 data. LCZs include urban forms that are predominantly defined by building compactness and height. The spatial distribution of urban heat island intensity was obtained using LCZs and MODIS 100 m resolution land surface temperatures from 2013 to 2021. The difference between diurnal and nocturnal heat island intensity (∆UHI) was evaluated as an indicator of the relative heat storage effect between the LCZs. Lower ∆UHIs suggest increased relative heat-storage capacities. Seasonal average ∆UHIs for compact and super high-rise, high-rise, mid-rise, and low-rise LCZs were 3.1 °C, 4.1 °C, 5.8 °C, and 8.3 °C, respectively. Additionally, ∆UHIs for open and super high-rise, high-rise, and mid-rise LCZs were 5.8 °C, 6.4 °C, and 7.8 °C, respectively. Slope data also validated the LCZ height. LCZ and slope analyzes found lower ∆UHI magnitudes in all LCZs with high-rise buildings. Also, compact LCZs had lower ∆UHI magnitudes than open LCZs at corresponding heights. Therefore, higher-rise and compact LCZs are suggested to have larger relative heat storage effects than lower-rise and open LCZs.

Study on the mechanism of shock wave and boundary layer interaction control using high-frequency pulsed arc discharge plasma

This paper studies the response characteristics of shock wave and boundary layer interaction (SWBLI) controlled by high-frequency pulsed arc discharge (PAD) in a Mach 2.5 flow. The dynamic evolution of SWBLI disturbed by arc plasma energy deposition was captured, and the controlling mechanism under different exciting power and frequency was explored. The results showed that the blast wave induced by PADs had a strong impact on SWBLI structures and distorted the separation shock wave. During the downstream propagation, the controlling gas bubbles (CGBs) delivered a continuous thermal excitation to the boundary layer and reached the maximum penetration depth near the semi-cylinder. The arc discharge in the SWBLI region induced larger energy deposition, which made the heating zone obtain the highest initial temperature and longest heating duration. Under the plasma condition of 1 × 1011 W/m3/15 kHz, both the upstream part of the shear layer and the foot portion of the reattachment shock wave were removed. When setting the excitation to 2.5 × 1010 W/m3/60 kHz, a thermal exciting surface of merged CGBs was formed and the separation shock wave was completely replaced by an equivalent compression-wave system. A better drag-reduction effect on the flow field would be produced by the actuator with an increased operating power or frequency, and a drag reduction rate of nearly 25.5% was achieved under the 2.5 × 1010 W/m3/60 kHz control condition.

Influence of slip effect on viscous dissipation heat and lubrication characteristics of Gas Journal Bearing: A multiscale analysis

As operating under quite high bearing speed with quite narrow clearance, the slip effect generally inevitable exists and closely relates to the performance of Gas Journal Bearing (GJB). However, singly the conventional macroscopic method may not be capable of fully exploring the influence of slip effect and seize tiny details such as slip velocity and flow vortex. In this article, both the Lattice Boltzmann Method (LBM) and the Reynolds equation method are applied to analyze the distributions of lubricant viscous dissipation heat, velocity, slip velocity, pressure, journal position and film thickness versus different operating parameters at multiscale. It shows that the slip effect weakens the squeezing function on lubricant film, reduces the viscous dissipation heat peaks, consumes the maximum pressure peaks, and decreases the bearing capacity, which is more obvious at larger Knudsen number. At higher bearing speed, the high viscous dissipation heat and pressure zone rapidly magnifies, in contrast, under larger bearing load, the high viscous dissipation heat zone concentrates.

Processing of Leucaena Leucocepphala for renewable energy with catalytic fast pyrolysis

This research aimed processing of Leucaena Leucocepphala in a fluidized-bed reactor with catalysts for renewable energy. The reaction was tested over different type of catalysts such as natural zeolite, kaolin and dolomite. These catalysts were loaded under the heating zone with a supplementary hot filter. The rate of feedstock added in the reactor was 1 kg/h and the pyrolysis temperature was 500 °C. Product yields was calculated after each experiment was completed.The results demonstrated an optimum bio-oil yield of 65.1 wt% after undergoing fast pyrolysis. A reduction in bio-oil yield was observed when natural zeolite, kaolin and dolomite was employed during fast pyrolysis. The minimum bio-oil yield recorded for the dolomite catalyst was 54.5 wt%. On the other hand, kaolin catalyst produces a maximum bio-oil yield of 59.6 wt%. The organic content of bio-oil from kaolin catalyst increased significantly compared with other catalysts. Addition of an ESP condenser, instead of water-cooled condenser resulted in bio-oil with the highest heating value (HHV). Higher heating value of bio-oil derived from natural zeolite catalyst maximized at 35.8 MJ/kg and 37.3 MJ/kg, respectively. The range of hydrocarbon component of bio-oil was C15–C44 for ESP condenser and C12–C35 for water-cooled condenser. The availability of bio-oil was optimized when natural zeolite catalyst added into the process. On the other hand, density and viscosity of bio-oil was increased when dolomite catalyst was used. Additionally, the presence of dolomite catalyst reduced acidic compounds such as 2-Octenoic acid (C8H14O2) and Methyl propiolate (C4H4O2) in the bio-oil. Bio-oil yield was found to be significantly improved by the large pore diameter and small surface area of the catalyst. Among the three catalysts in was observed that kaolin catalyst gave the highest bio-oil yield. Natural zeolite catalyst was found to improved bio-oil product’s thermal quality. However, bio-oil with better viscosity and lower acidity was produced from the dolomite catalyst.

Transient numerical study on injecting PCM in buildings along with extra comfort ventilation: Use of artificial neural network to decline energy utilization

Strict standards in medical complexes forced the air conditioning designers to approve a system that adjusts temperature and CO2 levels. In this study, medical complex energy analysis was discussed by introducing two cases, i.e., internal and external improvers. Using numerical approaches the energy analysis was performed and consequently using CFD-based approaches, the internal temoerature distribution was simulated. Monthly analysis showed that PCM has a positive effect each month. The heating zone and cooling zone for the medical complex with PCM were 15751 and 129923 kBtu per hour less than the normal medical complex. In the external improver section, a program was developed to adjust the building's ventilation in three scenarios: part-load, full-load, and extra load. Although in the first and second scenarios, the goal of ventilation was to create comfortable conditions, in the third scenario, the goal of extra ventilation was to reduce energy consumption. Excessive ventilation kept the room in comfortable conditions by distributing fresh air at the desired temperature. Owing to injecting extra ventilated fresh air, the changes in the heating zone were not significant while the cooling zone parameter decreased by 2639 kBtu per hour. To forecast the thermal behavior of the medical complex with PCM, the neural network was implemented.

A surfactant-free approach: Novel one-step ultrasonic nebulizer spray method to generate amphiphilic Janus particles

HypothesisA solvent evaporation-induced phase separation method, which is based on the preferential partitioning of two or more immiscible materials after solvent evaporation on providing heat, has been one of the main strategies for synthesis of Janus particles (JPs). Considering this approach, it should be possible to synthesize surfactant free-JPs in continuous flow by the ultrasonic nebulizer spray method. ExperimentsTwo polymers, polystyrene and polymethylmethacrylate, were dissolved in dichloromethane, and droplets of a precursor solution generated by an ultrasonic nebulizer were then conveyed through a borosilicate glass cylinder with two heating zones. The solvent evaporation-induced phase separation occurred in a single flow process, which resulted in the preferential partitioning of two incompatible polymers in the droplets, leading to the formation of the spherical bicompartmental JPs. FindingsThe successful fabrication of spherical JPs was observed at high polymer concentrations (1.5 and 2.0 wt%), and at elevated temperature (40–75 °C). The fluorescent compartmentalization of JPs was confirmed. Furthermore, the interfacial arrangement of JPs at oil–water interface was studied. A detailed explanation of theoretical prediction of interfacial configurations of JPs was provided. Lastly, the generated JPs were proved as Pickering stabilizers at the oil–water interface.

Failure modes and mechanisms of layered h-BN under local energy injection

Layered h-BN may serve as an important dielectric and thermal management material in the next-generation nanoelectronics, in which its interactions with electron beam play an important role in device performance and reliability. Previous studies report variations in the failure strength and mode. In this study, using molecular dynamics simulations, we study the effect of local heat injection due to the electron beam and h-BN interaction on the failure start time and failure mode. It is found that at the same heat injection rate, the failure start time decreases with the increase in the layer number. With the introduction of point defects in the heating zone, the failure always starts from the defect site, and the start time can be significantly shortened. For monolayer h-BN, failure always starts within the layer, and once failure starts, its propagation is through melting or vaporization of the h-BN atoms, and no swelling occurs. For multiple layers, once failure starts within the h-BN film, swelling occurs first. With continued heating, the large pressure induced by melting and vaporization can cause the burst of the layers above, leading to the formation of a pit. In the presence of multiple defects within the heating zone, these defects can interact, causing a further reduction in the failure start time. We also reveal the relation of beam power with layer-by-layer failure mode and swelling/pit formation mode. The present work not only reproduces many interesting experimental observations, but also reveal several interesting mechanisms responsible for the failure processes and modes. It is expected that the findings revealed here may provide useful references for the design and engineering of h-BN for device applications.

Parameter study of the grid spacer position on subcooled boiling in an upward vertical tube at low pressures

One of the principal issues in the phase change heat transfer at the vertical channel that changes the vapour fraction in the two-phase system is the presence of a grid spacer which prompts the temperature and velocity jump. In this study, the subcooled fluid stream rising inside the annular tube with grid spacer has been concentrated to investigate the effect of its location on changes in the gas volume fraction ratio, grid spacer temperature, and fluid flow jumping. The system of non-equilibrium two-phase flow of liquid-vapour exposed to an external heat transfer is modelled by mass, Euler-Euler model momentum, and energy equation of each phase. Validation of developed code is done by experimental results. Results show that extending the gas volume part as a result of a grid spacer presence decreases the Nusselt number, in conclusion, a temperature jump will occur. In the same manner, the presence of the grid spacer changes fluid streamlines. In this assessment, by contemplating the grid spacer in the vertical annular tube, the rising of fluid velocity in the vertical direction is demonstrated. As well the results show that the presence of a grid spacer moves to the liquid stage is less redirected conversely with vapour stage stream because of having more power; along these lines, around the completion of the grid spacer in the channel, the proportion of vapour volume fraction near the divider rises strongly. It has moreover been observed that if there are grid spacer inside the vertical annular tube, there will be no gigantic change in the liquid stream and gas volume division in various parts of the vertical annular tube when stood out from the customary vertical annular tube. The results demonstrate that the grid spacer before the heating zone will not change the vapour volume fraction inside the tube. The worst case happens for the grid spacer near the middle of the heated zone. The local peaks happen after the grid spacer when it is located after the heated zone.

Microstructure anomaly upon high temperature exposure and its influence on the mechanical properties of a modified 9Cr-1Mo steel weld

The present work evaluates the microstructure stability of modified 9Cr-1Mo steel welds when subjected to high temperature exposure (HTE) at 775 °C for different times (5, 100, 500, and 1000 h). Prior to HTE, a post weld heat treatment (PWHT) at 760 °C for 2 h was performed. Upon HTE, the individual weld zones viz., weld metal (WM), coarse-grain heat affected zone (CGHAZ) and fine-grain heat affected zone (FGHAZ) demonstrate distinct microstructural variations in terms of precipitate size, grain size and substructure (lath/block/packet boundaries) fractions. The least- and the highest-microstructure stability are respectively seen in FGHAZ and WM after HTE. A detailed investigation involving electron backscattered diffraction (EBSD) and high-resolution transmission electron microscopy (HR-TEM) confirm that a pronounced recovery of the substructure in FGHAZ happens due to enhanced diffusion along the higher fraction of prior-austenite grain boundaries (PAGBs), leading to M23C6 precipitate coarsening and substantial grain growth. The microstructure degradation upon HTE for 1000 h had eventually resulted in deterioration of mechanical properties, where the hardness reduced the most for FGHAZ (~34%), while the least for WM (~7%). Similarly, after HTE, the tensile strength and toughness had deteriorated by ~67% and ~57%, respectively, from the PWHT condition. Fractography further confirms the pronounced degradation after HTE as they result in failure from FGHAZ.

Model of transition zone evolution between coating and substrate under intense short thermal impulse

In the present work a model of the evolution of the composition of the transition zone between the material and the pre-applied coating under conditions of intense short-term thermal impulse is proposed. The pulse times are assumed to be comparable to the relaxation times of the heat and mass fluxes. This led to the need to account for finite rates of heat and mass propagation in the model, leading to hyperbolic transfer equations. The phenomena of thermodiffusion (Soret effect) and diffusive thermal conductivity (Dufour effect) and some possible chemical reactions leading to a change in the transition zone composition are also taken into account. This nonlinear model problem illustrates the necessity of the really coupled problem solution to reveal the feature of cross-effects in irreversible conditions. It was found that due to the wave heating and the wave nature of the movement of elements, chemical reactions can start during the action of a short pulse outside the heating zone expected only due to thermal conductivity.

Integrated control strategy of district heating system based on load forecasting and indoor temperature measurement

District heating system (DHS) plays an important role in attaining sustainable energy systems, which can conveniently provide energy-efficient space heating. At present, it is common that heat source and stations are operated and regulated separately by different owners. Their own technicians adjust the operation parameters empirically with fine-tune according to users’ complaint. This kind of isolated and extensive regulation often results in imbalance of supply and demand featuring in large indoor temperature fluctuation and waste of energy. In order to tackle this problem, this paper proposes an integrated control strategy based on load forecasting and correction according to indoor temperature measurement. Firstly, regulation period and regulation time nodes of heat source and stations are determined. Then, water supply temperature of heat source and heat stations are predicted respectively. The predicted water supply temperature of heat stations is corrected by the measured average indoor temperature under their own heating zone, while the overall average is used to correct the predicted water supply temperature of the heat source. Field study in a realistic DHS project shows that the proposed method effectively improved the users’ thermal comfort reducing indoor temperature non-uniformity coefficient from 0.0310 to 0.0196. Hydraulic instability index reduced from 0.63 to 0.19 which means pipe network pressure fluctuation is mitigated. An energy saving rate about 6.75% was yield which is quite considerable.

Experimental and Theoretical Studies on Water-Added Thermal Processing of Model Biosyngas for Improving Hydrogen Production and Restraining Soot Formation

The upgrading of biosyngas to convert methane into syngas is a necessary step for hydrogen production from biomass. However, this process is highly energy-demanding. In this study, a model biosyngas containing H2, CH4, CO, and CO2 were thermally treated between 1200 and 1500 °C. The gas mixture, comprised of H2 (33 vol %), CH4 (12 vol %), CO (28 vol %), CO2 (25 vol %), and He (2 vol %), was diluted with argon and the effect of reaction temperature (1200–1500 °C), water addition (0–44.3 mol %), and residence time (23, 46, and 76 μs in corresponding to flow rates of 1500, 2500, and 5000 mL/min at normal temperature and pressure, respectively) were studied. A possible reaction scheme for the upgrading of the model gas is proposed based on the kinetic simulation with CHEMKIN. The main reaction pathways involve dry reforming of methane and reverse water-gas shift (WGS) reactions. The kinetic simulation explained the finding that CO production was negatively influenced by the water content via the WGS reaction. The main side reaction is the methane pyrolysis reaction which causes the formation of carbon. The carbon formed in the reforming was characterized by SEM and Raman spectroscopy. SiO2 needle-like microdomains are observed at the top of the reactor heating zone, while the central part of the heating zone was covered by carbon with a disordered, amorphous, low-density soot structure. It is proposed that the SiO2 species formed by the chemical reaction between the reactor wall material and the reactants act as a support to anchor the carbon formed.

Root-Zone Heat Priming Effects on Maximum Quantum Efficiency of PSII, Productivity, Root Morphology and Nutritional Quality of Two Aeroponically Grown Leafy Greens in a Tropical Greenhouse.

This study investigated the effects of root zone (RZ) heat priming on Eruca sativa (cv. Arugula) and Lactuca sativa (cv. Canasta) in a tropical greenhouse by exposing them to three different RZ temperatures (RZTs). For the first group, plants were grown at 25 °C-RZT for 36 days. The second group of plants was grown at 25 °C-RZT for 10 days before transferring to 38 °C-RZT for 10 days and then to 42 °C-RZT for another 16 days (primed). For the third group, plants were grown at 25 °C-RZT for 20 days and for the last 16 days were transferred to 42 °C-RZT (non-primed). RZ heat priming did not affect the leaf expansion of Arugula while the leaf expansion was slower in RZ heat primed Canasta compared to 25 °C-RZT plants. After transferring to 42 °C-RZT in the later stage, RZ heat primed Arugula had similar productivity but a larger root system with higher nutritional quality at harvest and during postharvest storage compared to those of 25 °C-RZT plants. After subjection to 42 °C-RZT, although RZ heat priming enhanced its nutritional quality, the productivity of Canasta was compromised. The results of this study suggest that it is feasible to enhance productivity and nutritional quality of leafy greens at lower production cost through RZT management.

Fabrication of low-loss adiabatic optical microfibers using an attainable arc-discharge fiber tapering setup

Based on an attainable cost-effective homemade arc-discharge fiber heating and pulling setup, a fast and highly controllable process for fabricating low-loss adiabatic optical microfibers (AMFs) is presented. For this purpose, two linear translation stages driven at the same direction with different speeds stretch and shift a silica fiber through a heating arc-discharge zone induced between two tungsten electrodes. In this process, the amplitude of the inducing arc voltage and the relative positions of the electrodes and the tapering fiber adjust the characteristics of the heating zone. This technique is relatively fast and takes only about 55 s to form a low-loss (<0.2 dB) AMF. By this setup, the fabricated microfiber samples with the input and output transitions of about 12 mm lengths and the waists diameters of 3, 5, and 8μm exhibit very low insertion losses of 0.16, 0.13, and 0.07 dB, respectively. The adiabaticity of the resultant microfibers is experimentally examined by monitoring their spectral responses and is theoretically investigated based on fiber tapers adiabaticity criteria. Finally, as an important application of the microfibers, two knot resonator configurations are manually implemented on the 5μm AMFs, and their external sensitivities are investigated using the ethanol/water solutions of different concentrations. This study shows the functionality of an affordable arc-discharge setup and appropriate process for fabricating high-performance AMFs, which could be useful for their future applications.

Global Droplet Heat Transfer in Oxygen Steelmaking Process

Generated droplets in a basic oxygen furnace (BOF) process create an interfacial area between metal and slag/emulsion that helps in heat transfer during different stages of the blowing period. Previous studies have developed extensive models to understand bloating behavior and overall refining kinetics contributed by the droplets in a BOF process. Except for the recent study on single droplet heat transfer by the current authors, no studies in the open literature have addressed the heat transfer contributed by droplets in a BOF. The present work is an extension of single droplet heat transfer, wherein a global droplet heat transfer model is developed by integrating kinetic and dynamic aspects of generated droplets during the blowing period. The model was developed based on previous chemical kinetic studies and input values from plant trials. The results from the global droplet heat transfer model are integrated into the overall zone heat balance calculations to predict the temperature evolution profile of hot spot, slag, and hot metal zones during the blowing period. The results highlight that the hot spot temperature ranges from 1900 °C to 2090 °C, with a peak value of around 2300 °C observed during the middle of the blow. Furthermore, computing the overall droplet heat transfer efficiency, it was observed that the droplets transfer 90% of the heat to the slag up to the first 10 min of the blow, and then the heat transfer efficiency drops towards the end of the blow.

Tidally driven tectonic activity as a parameter in exoplanet habitability

Context.The habitability of an exoplanet is defined by its ability to support surface liquid water. The long-term carbon cycle plays an important role in regulating planetary temperature, thus supporting the conditions for the preservation of surface liquid water and, consequently, the habitability of exoplanets.Aims.On Earth, plate tectonics play an integral role in driving the long-term carbon cycle; however, on tidally locked rocky exoplanets, alternative tectonic mechanisms driven by tidal stress and tidal heating could serve this purpose in an analogous way.Methods.We calculated tidal stress and tidal heating rates to model the likelihood of tectonic activity maintaining stable climates suitable for surface liquid water on tidally locked rocky exoplanets with radii ofRp≤ 1.23R⊕.Results.Applying the tidal models to our sample of 767 tidally locked rocky exoplanets reveals that ~10% of exoplanets, including Proxima Cen b and GJ 1061 d from the circumstellar habitable zone (CHZ), pass the tidal stress subduction threshold for mobile lid tectonic activity and simultaneously reside within the optimal tidal heating zone. This subset of exoplanets could sustain tidally induced temperate mobile lid tectonic activity that is comparable to plate tectonics on Earth, aiding in maintaining the presence of surface liquid water. Furthermore, ~40% of exoplanets from our sample located in the CHZ would be unable to maintain the tectonic activity needed to stabilise the climate and are unlikely to retain surface liquid water. When broadening our modelling to establish the overlap between tidal stress, tidal heating, and the CHZ to discover optimal regions to target for future observations, we determined that tidally driven tectonic activity conducive to the maintenance of surface liquid water occurs predominantly around M dwarfs. We identified intersections, where both mobile lid and optimal tidal heating could be sustained on eccentric (e&gt; 0.1) Earth-sized exoplanets (Rp= 1.0-1.23R⊕) orbiting in the CHZ of low-mass M dwarfs.

The role of temperature profile during the pyrolysis of end-of-life-tyres in an industrially relevant conditions auger plant

Pyrolysis is a chemical recycling process of interest as a means to achieve a sustainable circular economy for end-of-life tyres (ELTs). In the pyrolysis process, ELTs are converted into tyre pyrolysis gas (TPG), tyre pyrolysis oil (TPO) and raw recovered carbon black (RRCB). This work investigates for the first time the effect of different temperature profiles by using a single-auger pyrolysis reactor in an industrially relevant scale (TRL-5). Since the development of this process at this representative scale is quite limited and the temperature profile has not been previously studied, the results achieved in this work can provide a useful database for the development of this process at industrial scale. For this purpose, two different sources of ELTs, commercial truck tyres (CTTs) and passenger car tyres (PCTs), were used. Accordingly, the experimental campaign was conducted using two different incremental temperature profiles (425-550-775 °C and 600-700-800 °C) based on those that can be replicated in an industrial-scale auger pyrolysis plant. For the sake of comparison, two isothermal heating conditions (500-500-500 °C and 600-600-600 °C) were also tested. The results confirmed the remarkable influence of temperature profile on both the distribution and properties of products. The 425-550-775 °C temperature profile was found to enhance limonene production, which is associated with the minimisation of secondary reactions in the first heating zone of the reactor. Additionally, there were very low carbonaceous deposits found in the RRCB because of the high severity of devolatilisation conditions in the third heating zone of the reactor. On the other hand, when the temperature profile was raised, the production of single-ring aromatics, particularly benzene, toluene, ethylbenzene and xylenes (BTEX) significantly increased in the TPO at the expense of limonene. Thus, from this strategy, it is possible to tune the properties of the products depending on the requirements of the application in a single step, getting closer for circular economy in the ELT recycling domain.

Watching the Cryosphere Thaw: Seismic Monitoring of Permafrost Degradation Using Distributed Acoustic Sensing During a Controlled Heating Experiment

AbstractPermafrost degradation is rapidly increasing in response to a warming Arctic climate, altering landscapes and damaging critical infrastructure. Solutions for monitoring permafrost thaw dynamics are essential to understand biogeochemical feedbacks as well as to issue warnings for hazardous geotechnical conditions. We investigate the feasibility of permafrost monitoring using permanently installed fiber‐optic seismic networks. We conducted a 2‐month seismic monitoring campaign during a controlled thaw experiment using a permanent surface orbital vibrator (SOV) and a 2D‐array of distributed acoustic sensing (DAS) cables, and observed significant (15%) shear‐wave velocity (Vs) reductions and approximately 2 m depression of the permafrost table beneath the heating zone. These observations were validated by time‐lapse horizontal‐to‐vertical spectral ratio (HVSR) analysis from three co‐located broadband seismometers. The combination of SOV and DAS provided unique seismic observations for permafrost monitoring at the field scale, as well as a basis for design and development of early warning systems for permafrost thaw.

Microstructure characteristics and mechanical properties of Al2O3/MgAl2O4 directionally solidified eutectic ceramic

ABSTRACT Al2O3/MgAl2O4 directionally solidified eutectic ceramic (DSEC) rods with Φ 10 mm were prepared with induction heating zone melting (IHZM) method. The phase components of the DSEC were composed of MgAl2O4 phase growing along the preferred orientation 〈311〉 and Al2O3 phases growing along the preferred orientation 〈110〉. In the DSEC, the Al2O3 phase is the matrix phase mixed with part of MgAl2O4 phase and the other part of MgAl2O4 phase forms slice structure. Both the DSEC density and hardness decrease with the increase of the growth rate, due to the increase of micropores in DSEC with the higher growth rate. However, its fracture toughness improved due to the fine interface spacing toughening and the dispersion toughening. The highest hardness and fracture toughness of DSEC are 19.3 GPa and 3.74 MPa·m1/2, respectively, the toughening effect could be attributed to the crack deflection and bifurcation hindering the propagation of crack in DSEC.

Modeling optical floating zone crystal growth in a high-pressure, single-lamp furnace

An optical floating zone (OFZ) model is developed, validated, and applied to obtain initial results for crystal growth in a novel high-pressure, single-lamp furnace. Computation with a realistic irradiation profile for zone heating results in dramatically different growth behavior than predicted using idealized Gaussian heating, though the discontinuities of the realistic profile prove challenging from a computational perspective. System pressure significantly affects buoyant flows in the surrounding atmosphere. Both driving force and flow strength increase nonlinearly with pressure, with the Grashof number growing with the cube of pressure and the Reynolds number scaling with pressure to the 3/2 power. For pressures of 100 bar and greater, flows of the surrounding phase strongly cool the growth sample, leading to significantly shorter melt zones, more deflected melt-solid interfaces, and weaker flows in the melt zone. Such effects reduce the likelihood of achieving stable growth conditions under very high pressure in this OFZ system.