Very-high Temperature Research Articles

Effect of drying profiles on surface structure changes of durum wheat pasta during the boiling process

The aim of this study was to investigate the effect of different drying conditions on structural changes of durum wheat pasta during the boiling process. Boiled pasta samples with different drying conditions were evaluated under the same water absorption level in order to more consistently elucidate the effect on cooking properties. The evaluated properties were cooking loss, surface structure of the boiled pasta as observed by fluorescence microscopy, and surface roughness as assessed by a combination of laser microscopy and principal component analysis. Furthermore, the smoothness of samples was evaluated by sensory evaluation. Cooking loss was lower in VHT (very high temperature drying)- than in LT (low temperature drying)-boiled pasta. Structural observation of the pasta surface revealed that the swelling of starch granules was suppressed and a dense gluten network structure was maintained at the outer periphery in VHT-boiled pasta compared to LT-boiled pasta. Analysis of surface roughness indicated that the surface of VHT-boiled pasta was smoother than that of LT-boiled pasta, which was in agreement with the result of sensory evaluation of pasta smoothness.

Inhibited radiation transmittance and enhanced thermal stability of silica aerogels under very-high temperature

Silica aerogels are applied extensively in thermal insulation due to their extra-low density and thermal conductivity. However, this can be heavily undermined under high temperature, especially beyond 700–800 °C, due to not only a high transparency for radiation heat transfer, but also an instability caused by nanoparticle collapse. The present study demonstrated a solution to this problem by two steps. Firstly, the size effect of nanoparticles is explored by experimentally preparing unconventional samples composed of large-diameter particles (larger than 20 nm). The prepared sample microstructures and radiative characteristics are investigated by SEM apparatus and FTIR measurements, respectively. Additionally, based on the fractal structures reconstructed using the Diffusion-Limited Colloid Aggregation (DLCA) method, the effects of particle size on thermal stability of silica aerogels are theoretically investigated and the light shielding performance is numerically analyzed by the Generalized Multiparticle Mie-solution (GMM) method. The simulation and experimental results indicate that the enhanced size of nanoparticles can improve the radiative inhibition and thermal stability property under high temperature significantly. However, the ideal above should be refined as it brings an increasing contribution of conduction heat transfer. Thus, a novel structure of core-mantle nanoparticle is proposed to retain the excellent resistance in radiation but avoid an increased thermal conduction. The present work may pave a new direction for developing aerogels under extreme temperature conditions, compared with the widely-used opacifier addition.

Benefits, Drawbacks, and Future Trends of Brayton Helium Gas Turbine Cycles for Gas-Cooled Fast Reactor and Very-High Temperature Reactor Generation IV Nuclear Power Plants

Abstract Numerous studies are on-going on to understand the performance of generation IV (Gen IV) nuclear power plants (NPPs). The objective is to determine optimum operating conditions for efficiency and economic reasons in line with the goals of Gen IV. For Gen IV concepts such as the gas-cooled fast reactors (GFRs) and very-high temperature reactors (VHTRs), the choice of cycle configuration is influenced by component choices, the component configuration and the choice of coolant. The purpose of this paper to present and review current cycles being considered—the simple cycle recuperated (SCR) and the intercooled cycle recuperated (ICR). For both cycles, helium is considered as the coolant in a closed Brayton gas turbine configuration. Comparisons are made for design point (DP) and off-design point (ODP) analyses to emphasize the pros and cons of each cycle. This paper also discusses potential future trends, include higher reactor core outlet temperatures (COT) in excess of 1000 °C and the simplified cycle configurations.

Design of an experimental facility with a unit cell test section for studies of the lower plenum in prismatic high temperature gas reactors

One proposed design for a Generation IV reactor is the very-high temperature reactor (VHTR), which employs helium as the primary coolant. Although many advantages exist with this design, a number of challenges remain. One such area of concern is the turbulent mixing of non-isothermal flows in the lower plenum, where an array of coolant jets collectively mix and traverse around a series of structural support posts before exiting the core. Neighboring jets in the lower plenum could experience temperature differences as high as 300–400 K, causing potential hot streaking in the support posts. Additional problems could occur further downstream if the level of non-uniformity in the temperatures is too high (e.g, inducing thermal stresses on gas turbine blades). Therefore, it is important that adequate tools exist to predict the turbulent mixing within the VHTR lower plenum. This task remains difficult to achieve due to the complex geometry and flow physics that dictate the mixing. Various modeling approaches can only be assessed using data acquired from a carefully designed experimental facility. This paper presents details of such a facility, where high-fidelity measurements can be acquired for a scaled portion of the lower plenum defined herein as a “unit cell”, which consists of a hexagonal array of jets whose flow is directed into a test section with support posts positioned between neighboring jets, and subjected to a crossflow. Through adjusting velocity and temperature conditions at the jet inlets, different locations within the lower plenum can be experimentally simulated. System response quantities (SRQs) include both temperature and velocity measurements, captured via multiple thermocouples embedded in each post, and particle image velocimetry (PIV), respectively. These SRQs provide assessment metrics for both the momentum and energy models present in current computational solvers, and therefore the experimental facility is a valuable source for validation data. Another benefit is a more comprehensive understanding of the thermal-hydraulic loading conditions and flow physics present in the VHTR lower plenum.

A concept of wireless and passive very-high temperature sensor

There is a need for sensors capable operating at temperatures above 1000 °C. We describe an innovative sensor that might achieve this goal. The sensor comprises two main elements: a thermocouple and a surface acoustic wave (SAW) strain sensor. The cold junction of the thermocouple is electrically connected to a highly piezoelectric thin layer, deposited on top of a SAW substrate. In operation, the voltage generated by the temperature gradient between the hot (>1000 °C) and cold junction (<350 °C) generates a strain field in the layer, which is mechanically transmitted to the substrate. This modifies the SAW propagation conditions and therefore the sensors' radiofrequency response. The change depends on the applied voltage and thus on the hot junction temperature. As SAW devices are passive elements that can be remotely interrogated, it becomes possible to infer the hot junction temperature from the radiofrequency response, i.e., to remotely read temperatures above 1000 °C, without embedded electronics. In this paper, we demonstrate the feasibility of this concept, using AlN layers deposited on Y-Z Lithium Niobate (LN). The achieved sensitivity of 80 Hz/V at 400 MHz is constant over a wide voltage range. Numerical simulations were performed to compute the main properties of the demonstrators and suggest optimization strategies. Improvements are expected from the use of stronger piezoelectric layers, such as AlScN or Pb(Ti,Zr)O3 (PZT), which could increase the sensitivity by factors of 3 and 20, as estimated from their transverse piezoelectric coefficients. As a first step in this direction, thin PZT layers have been deposited on Y-Z LN.

Use of activated carbon to remove undesirable residual amylase from refinery streams

In recent years, there has been increased world-wide concern over residual (carry-over) activity of mostly high temperature (HT) and very high temperature (VHT) stable amylases in white, refined sugars from refineries to various food and end-user industries. HT and VHT stable amylases were developed for much larger markets than the sugar industry with harsher processing conditions. There is an urgent need in the sugar industry to be able to remove or inactivate residual, active amylases either in factory or refinery streams or both. A survey of refineries that used amylase and had activated carbon systems for decolorizing, revealed they did not have any customer complaints for residual amylase. The use of high performance activated carbons to remove residual amylase activity was investigated using a Phadebas® method created for the sugar industry to measure residual amylase in syrups. Ability to remove residual amylase protein was dependent on the surface area of the powdered activated carbons as well as mixing (retention) time. The activated carbon also had the additional benefit of removing color and insoluble starch.

Use of activated carbon to remove undesirable residual amylase from refinery streams

In recent years, there has been increased world-wide concern over residual (carry-over) activity of mostly high temperature (HT) and very high temperature (VHT) stable amylases in white, refined sugars from refineries to various food and end-user industries. HT and VHT stable amylases were developed for much larger markets than the sugar industry with harsher processing conditions. There is an urgent need in the sugar industry to be able to remove or inactivate residual, active amylases either in factory or refinery streams or both. A survey of refineries that used amylase and had activated carbon systems for decolorizing, revealed they did not have any customer complaints for residual amylase. The use of high performance activated carbons to remove residual amylase activity was investigated using a Phadebas® method created for the sugar industry to measure residual amylase in syrups. Ability to remove residual amylase protein was dependent on the surface area of the powdered activated carbons as well as mixing (retention) time. The activated carbon also had the additional benefit of removing color and insoluble starch.

Gas-Phase Structures of Ketene and Acetic Acid from Acetic Anhydride Using Very-High-Temperature Gas Electron Diffraction.

The gas-phase molecular structure of ketene has been determined using samples generated by the pyrolysis of acetic anhydride (giving acetic acid and ketene), using one permutation of the very-high-temperature (VHT) inlet nozzle system designed and constructed for the gas electron diffraction (GED) apparatus based at the University of Canterbury. The gas-phase structures of acetic anhydride, acetic acid, and ketene are presented and compared to previous electron diffraction and microwave spectroscopy data to show improvements in data extraction and manipulation with current methods. Acetic anhydride was modeled with two conformers, rather than a complex dynamic model as in the previous study, to allow for inclusion of multiple pyrolysis products. The redetermined gas-phase structure of acetic anhydride (obtained using the structure analysis restrained by ab initio calculations for electron diffraction method) was compared to that from the original study, providing an improvement on the description of the low vibrational torsions compared to the dynamic model. Parameters for ketene and acetic acid (both generated by the pyrolysis of acetic anhydride) were also refined with higher accuracy than previously reported in GED studies, with structural parameter comparisons being made to prior experimental and theoretical studies.

Enhanced thermoelectric properties of samarium boride

SmB62 single crystals were successfully grown by the floating zone (FZ) method. The high-temperature thermoelectric properties were investigated, together with magnetic properties and specific heat at low-temperature. The electrical resistivity, ρ, shows variable-range-hopping (VRH) behavior with significantly lower values than other rare-earth RB62 (RB66) compounds. An effective magnetic moment, μeff, of 0.42 μB/Sm was estimated, which if straightforwardly taken indicates a mixed valency for SmB62 with Sm2+:Sm3+ = 1:1, which is the first ever indicated for RB66-type compounds. Localization length of the VRH at the Fermi level, ξ, was estimated to be 3.33 Å indicating that carriers in SmB62 are much less localized than in YB66 which has 0.56 Å. The thermoelectric behavior of SmB62 is striking, with ρ reduced by two orders of magnitude while maintaining large Seebeck coefficients, and as a result the power factor is ∼30 times higher than other rare-earth phases. Overall the figure of merit ZT amounts to ∼0.13 at 1050 K, with an extrapolated value of ∼0.4 at 1500 K, an expected working temperature for topping cycles in thermal power plants; that gives a ∼40 times enhancement for Sm. Since there are few thermoelectric materials applicable for very-high temperature applications, this discovery gives new interest in the samarium higher borides.

Hot-Spot Formation in Energetic Materials Confined in Wavy-Rough Domains

We obtain very-high temperature profiles that resemble hot spots after numerically tuning the geometric as well as material parameters. Approximate solutions for steady temperature distribution of exotic materials with temperature-dependent thermal absorptivities inside microannuli with small amplitude wavy-rough surfaces were derived considering a quasilinear partial differential equation by the boundary perturbation approach. Our results can give useful clues about the storage of solid fuels as well as energy creation via fine-tuned hot-spot formation.

Effect of oat β-glucan fiber powder and vacuum-drying on cooking quality and physical properties of pasta

Oat β-glucan fiber powder was added to pasta dough at levels of 40, 80, 120, 160, and 200 g/kg. Pasta was dried at very high temperature and in a vacuum dryer. The cooking quality was evaluated based on the swelling index, water uptake, and cooking loss measurement. Further tests were carried out to determine the color, hardness, adhesiveness, total dietary fiber (TDF), and β-glucan content in pasta. The results showed that vacuum-drying had a significant impact on the cooking quality and physical properties of pasta. Water uptake and swelling index were higher and the cooking loss was lower in vacuum-dried pasta than in pasta dried using very high temperature (VHT) technology. The swelling index, water uptake, and cooking loss were significantly higher in samples with oat β-glucan fiber powder compared to control. Pasta with oat powder was darker, softer, and less sticky than semolina pasta. Lightness of vacuum-dried samples was higher while redness was lower than in conventionally dried samples.

Research on Material Irradiation in HANARO

HANARO (High-Flux Advanced Neutron Application Reactor) is a 30MWth multi-purpose research reactor generating a very high neutron flux for scientific and technical applications. Since its initial criticality in Feb. 1995, it has worked as a national neutron source for neutron beam research, RI production and related research, material and fuel irradiation research, and neutron transmutation doping. The installation of a cold neutron source and related beam instrument makes HANARO serve as a regional source for beam research as well. As Korea is developing nuclear power systems and fuels, irradiation research is a main utilization subject in HANARO, and irradiation facilities have been actively utilized for various nuclear fuel and material irradiation tests requested by users from research institutes, universities, and industries. Most of the irradiation tests were related to the R & D relevant to the ageing management and safety evaluation of the present nuclear power reactors. Korea is conducting R & D programs relevant to new nuclear systems including a research reactor, System-integrated Modular Advanced Reactor (SMART), and future nuclear systems such as a very high temperature reactor system (VHTR) and sodium cooled fast reactor system (SFR). To effectively support the R&D for new nuclear systems, advanced irradiation technologies such as high-temperature irradiation, instrumentation, and long-term irradiation are being developed. In addition, research on the irradiation characteristics of super-conductor materials and new chemical materials is being conducted as a part of fundamental research.

The re-determination of the molecular structure of antimony(iii) oxide using very-high-temperature gas electron diffraction (VHT–GED)

The molecular structure of a fundamental binary compound [antimony(III) oxide] has been re-determined to a far higher accuracy and precision than previously reported. The structure is compared to those determined by various ab initio methods, X-ray diffraction and to a previous gas-phase structure determined by electron diffraction prior to modern-day developments for data extraction and manipulation. The experiments utilised a new very-high-temperature (VHT) inlet nozzle system that has been designed and constructed for the gas electron diffraction (GED) apparatus now based at the University of Canterbury (formerly at the University of Edinburgh). The VHT-GED system is capable of heating samples to temperatures of up to 1100 K. The VHT system was tested by studying the gas-phase structure of antimony(III) oxide. Data were collected at 750 K and the contents of the gas flow analysed by mass spectrometry. In the gas phase at this temperature, antimony(III) oxide (Sb(2)O(3)) exists as a dimer (Sb(4)O(6)) with tetrahedral symmetry. The Sb-O bond length (r(a3,1)) was determined to be 195.66(4) pm and the O-Sb-O bond angle was 98.15(3)°. Unusually, the Sb-O bond length observed from X-ray diffraction investigation of Sb(4)O(6) was longer than the gas phase bond length [197.7(1) pm as compared to 195.66(4) pm].

Effects of Different Drying Conditions on Water Absorption and Gelatinization Properties of Pasta

Three flat pasta types dried by low temperature (LT), high temperature (HT), and very high temperature (VHT) drying profiles were analyzed. The starch properties of these pastas, cooked at different temperatures for different times, were investigated. The starch properties were examined by observing starch swelling with a scanning electron microscope (SEM), identifying the phase difference with an ultrasonic device, and determining the water absorption and gelatinization rate with the BAP method and X-ray diffraction. The SEM images revealed expanded and gelatinized starch granules during cooking pasta and increased with drying temperature. The water absorption of pasta increased with cooking temperatures and times, and the trend was LT > HT > VHT-dried pasta. The gelatinization rate of pasta increased with cooking time and temperature. The X-ray diffractograms of pasta cooked less than 12 min showed typical A-type X-ray diffraction patterns, while in pasta cooked for 12 min, V-type diffraction was observed. Uncooked pasta showed an enhanced peak at about 2θ = 20°, which indicated the generation of high levels of amylose–lipid complexes. The present study found that these changes occurred during drying and may affect pasta starch characteristics.

Sherwood number correlation for nuclear graphite gasification at high temperature

Gasification of nuclear graphite in the unlikely event of massive air ingress in High-Temperature and Very-High Temperature gas-cooled Reactors is a safety concern, requiring accurate and reliable predictions of the erosion rate of the external surface and within volume pores. At low temperature, gasification occurs within the open pores gradually degrading the mechanical strength of graphite components. Gasification shifts gradually to the external surface with increasing temperature. At high temperatures, although the rates of chemical reactions increase exponentially with temperature, they are limited by the oxygen diffusion to the external surface. A semi-empirical Sh correlation is developed to calculate the oxygen diffusion velocity. It is based on an extensive database of reported measurements of the convective heat transfer coefficient for heated wires and cylinders in air, water and paraffin oil flows at 0.006 ≤ Re ≤ 2.42 × 105 and 0.068 ≤ Pr ≤ 35.2 and the mass transfer coefficient at 4.8 ≤ Re ≤ 104 and Sc = 0.609 and 1300–2000. The database also includes reported values of the averaged Sh for gasification of a cylinder of V483T nuclear grade graphite (300 mm long and 200 mm in dia.) at 1141–1393 K in ascending cross-flow of nitrogen gas containing 5 vol.% oxygen at 533 ≤ Re ≤ 1660. The Sh correlation is within ±8% of the compiled 807 data points and applicable to both internal and external parallel and cross-flow conditions. When implemented in a chemical-reaction kinetics model, the calculated gasification rates are consistent with reported measurements for different size specimens of nuclear graphite grades NBG-18, NBG-25, IG-11, IG-110 and IG-430 at intermediate and high temperatures in atmospheric air (0.08 ≤ Re ≤ 30).

Constraints and deception in the isotopic record; the crustal evolution of the west Musgrave Province, central Australia

The Hf and Nd isotopic evolution of the Musgrave Province, central Australia, is used to constrain the timing of crust formation and lithospheric organisation of Proterozoic Australia. The dataset from this region challenges two widely held tenets of Hf and Nd isotope systematics, namely; that crust formation events can only be identified as periods when crystallisation ages correspond to model ages, and that linear Hf evolution arrays away from depleted mantle (along crustal Lu/Hf or Sm/Nd slopes) reflect reworking of the same source.Hf isotopes in Musgrave Province zircon crystals indicate two major crust formation events at c. 1900Ma and at 1600–1550Ma. Although no juvenile rocks or crystals are known from c. 1900Ma, radiogenic addition into the crust at this time is required to account for consistent Nd and Hf evolution patterns, which show no indication of an initially heterogeneous source. Oxygen isotopes in zircon grains confirm that much of the c. 1900Ma Hf isotopic signal is not compromised by mixtures. Furthermore, the correspondence between mantle extraction and the commencement of reworking of Archean material supports new crust generation at c. 1900Ma and a coupling between lower and upper crustal processes. The c. 1900Ma timing of juvenile addition is dissimilar to that in the Albany–Fraser and Arunta Orogens and may reflect continental arc development on the margin of a southern continent.The general Hf isotopic evolution trend of the Musgrave Province apparently reflects reworking from a dominant c. 1900Ma source with some additional unradiogenic and radiogenic input through time. However, in the 1220–1050Ma interval this apparent isotopic evolution contrasts with geological observations that indicate input of voluminous mantle-derived material. Intracontinental rifts and other regions with sustained very-high temperature crustal recycling processes generate magmatic provinces with extreme HFSE-enrichment. This can have a profound influence on isotopic evolution trends, suppressing typical juvenile addition patterns. Isotopic mixture modelling indicates that a significant volume of mantle derived material can be accommodated within HFSE enriched magmas without diverging isotopic signatures from apparent reworking trends. In the Musgrave Province, the crust had become so HFSE enriched during the prolonged Musgrave Orogeny (1220–1150Ma) that it was insensitive to mantle input, which is estimated to have been as much as 85% during this event.

Very-High Temperature (200 $^{\circ}$C) and High-Speed Operation of Cascade GaN-Based Green Light- Emitting Diodes With an InGaN Insertion Layer

We demonstrate a novel type of linear cascade green light-emitting diode (LED) arrays as a light source for in-car or harsh environment plastic optical fiber (POF) communications. To further enhance its dynamic and static performance, an InGaN layer is inserted between an n-type GaN cladding layer and InGaN-GaN multiple quantum wells as an efficient current spreading layer. Compared with the control device without that layer, our three-LED cascade array demonstrates a smaller turn-on voltage (9.3 versus 11 V at 20 mA) and a larger output power (25.5 versus 22.5 mW at 180 mA), corresponding to an enhancement of around 31% in wall-plug efficiency. Furthermore, under the constant voltage bias of an in-car battery (12 V), our three-LED array exhibits an electrical-to-optical 3-dB bandwidth (100 versus 40 MHz) performance superior to that of the control device. Even under high-temperature dynamic operation, we observe that the InGaN insertion layer gives strong enhancement of modulation speed with negligible degradation of the output power, unlike the red resonant-cavity LEDs conventionally used for POF. We achieve 200-Mb/s error-free transmission at 200°C which is the highest operation temperature among all the reported high-speed LEDs.

Sex reversal and growth performance in juvenile females of the freshwater crayfish Cherax quadricarinatus (Parastacidae): effect of increasing temperature and androgenic gland extract in the diet

Monosex male culture of C. quadricarinatus is proposed for increasing yields because males reach a larger size at harvest than females. An experiment was done to evaluate the effects of androgenic gland extract and temperature on sex reversal and somatic growth in early juvenile females. Females were exposed to the following experimental conditions: C: control food and temperature maintained at 26 ± 1°C; HT (high temperature): control food and temperature maintained at 28.5 ± 1°C; VHT (very high temperature): control food and temperature maintained at 31 ± 1°C; AG: food with enriched with androgenic gland (1/10 dose for each juvenile per day) and temperature maintained at (26 ± 1)°C. The juveniles were weighed, sexed, and growth increment (GI) and growth rate (GR) were calculated twice a month. The HT and AG groups differed from the C group in GI and GR indicating a greater somatic growth. At the end of the experiment, the HT and AG groups had similar weight but only the HT group had enhanced oocyte diameter, with some vitellogenic oocytes compared to the C group. In the HT group, there was significant sex reversal, as indicated by development of male and intersex male characteristics in different individuals. Both temperature and AG diet have a high potential for culture of this species because of their enhancement of somatic growth; higher temperature increases the proportion of males, a desirable characteristic of cultured populations.

Effects of industrial pasta drying temperatures on starch properties and pasta quality

Effects of industrial pasta drying temperatures on various starch properties and the quality of pasta were investigated. A short cut pasta (fusilli) was processed from durum semolina and dried by high temperature (HT) and very high temperature (VHT) drying cycles. Starch properties were examined by Rapid Visco Analyzer, differential scanning calorimeter, X-ray diffractometer and polarized light microscope. Cooking quality was evaluated by determining cooking loss (CL) into cooking water, total organic matter (TOM) in washing water after cooking, and sensory evaluation. The X-ray diffractograms of semolina samples showed typical A-type diffraction patterns. The diffractograms of pasta products using HT and VHT drying were similar. However, an additional small peak appeared at about 2θ=20° for both drying cycles, indicating the formation of a V-type X-ray diffraction pattern. All starch granules of semolina displayed a clear “Maltese cross” under polarized light, but approximately 20% of starch granules of HT- and VHT-dried pasta samples either partially or completely lost their birefringence. Starch from VHT-dried pasta had greater RVA peak viscosity and breakdown viscosity than HT-dried pasta. Both gelatinization enthalpy and peak temperature of HT-dried pasta were significantly lower than those of VHT-dried pasta. The HT-dried pasta had lower quality scores based on TOM and CL values and sensory evaluation as compared with the VHT-dried pasta. The present study indicated that the changes in starch during HT and VHT drying may affect the pasta cooking quality.

Study of the Maillard reaction in model systems under conditions related to the industrial process of pasta thermal VHT treatment

Non-enzymatic browning (NEB) due to the Maillard reaction (MR) was studied in a closed starch/glucose/lysine model system (20 g kg−1 glucose, 10 g kg−1 lysine) in order to analyse conditions favouring reactivity during an industrial process of pasta VHT (very high temperature) thermal treatment. The closed model pastes gave data on the NEB progress during the pasta drying cycle as a function of temperature, time and water activity (aw). Indicators such as headspace CO 2 , optical density and colour showed an increase of MR as the initial aw increased from 0.50 to 0.91. During the initial stages of drying, a combination of high temperatures and high aw led to the most likely conditions for NEB. © 1999 Society of Chemical Industry