Toward full simulations for a liquid metal blanket. Part 2: Computations of MHD flows with volumetric heating for a PbLi blanket prototype at Ha~104 and Gr~1012

On the pathway toward full simulations for a liquid metal blanket, this Part 2 extends a previous study of purely MHD flows in a DCLL blanket in Ref. 1 [Chen, L., Smolentsev, S., and Ni, M. J. (2020)] to more general conditions when the MHD flow is coupled with heat transfer. The simulated prototypic blanket module includes all components of a real liquid metal blanket system, such as supply ducts, inlet and outlet manifolds, multiple poloidal ducts and a U-turn zone. Volumetric heating generated by fusion neutrons is added to simulate thermal effects in the flowing PbLi breeder. The MHD flow equations and the energy equation are solved with a DNS-type finite-volume code “MHD-UCAS” on a very fine mesh of 470×10^6 cells. The applied magnetic field is 5 T (Hartmann number Ha~10^4), the PbLi velocity in the poloidal ducts is 10 cm/s (Reynolds number Re~10^5), whereas the maximum volumetric heating is 30 MW/m^3 (Grashof number Gr~10^12). Four cases have been simulated, including forced- and mixed-convection flows, and either an electrically conducting or insulating blanket structure. Various comparisons are made between the four computed cases and also against the purely MHD flows computed earlier in Ref. \cite{1} with regards to the (1) MHD pressure drop, (2) flow balancing, (3) temperature field, (4) flows in particular blanket components, and (5) 3D and turbulent flow effects. The strongest buoyancy effects were found in the poloidal ducts. In the electrically non- conducting blanket, the buoyancy forces lead to significant modifications of the flow structure, such as formation of reverse flows, whereas their effect on the MHD pressure drop is relatively small. In the electrically conducting blanket case, the buoyancy effects on the flow and MHD pressure drop are almost negligible.

Onset of Thermal Instabilities in the Plane Poiseuille Flow of Weakly Elastic Fluids: Viscous Dissipation Effects

The onset of thermal instabilities in the plane Poiseuille flow of weakly elastic fluids is examined through a linear stability analysis by taking into account the effects of viscous dissipation. The destabilizing thermal gradients may come from the different temperatures imposed on the external boundaries and/or from the volumetric heating induced by viscous dissipation. The rheological properties of the viscoelastic fluid are modeled using the Oldroyd-B constitutive equation. As in the Newtonian fluid case, the most unstable structures are found to be stationary longitudinal rolls (modes with axes aligned along the streamwise direction). For such structures, it is shown that the viscoelastic contribution to viscous dissipation may be reduced to one unique parameter: γ=λ1(1−Γ), where λ1 and Γ represent the relaxation time and the viscosity ratio of the viscoelastic fluid, respectively. It is found that the influence of the elasticity parameter γ on the linear stability characteristics is non-monotonic. The fluid elasticity stabilizes (destabilizes) the basic Poiseuille flow if γ<γ* (γ>γ*) where γ* is a particular value of γ that we have determined. It is also shown that when the temperature gradient imposed on the external boundaries is zero, the critical Reynolds number for the onset of such viscous dissipation/viscoelastic-induced instability may be well below the one needed to trigger the pure hydrodynamic instability in weakly elastic solutions.

Thermal Analyses of Nanowarming-Assisted Recovery of the Heart From Cryopreservation by Vitrification

This study explores thermal design aspects of nanowarming-assisted recovery of the heart from indefinite cryogenic storage, where nanowarming is the volumetric heating effect of ferromagnetic nanoparticles excited by a radio-frequency electromagnet field. This study uses computation means, while focusing on the human heart and the rat heart models. The underlying nanoparticle loading characteristics are adopted from a recent, proof-of-concept experimental study. While uniformly distributed nanoparticles can lead to uniform rewarming, and thereby minimize adverse effects associated with ice crystallization and thermomechanical stress, the combined effects of heart anatomy and nanoparticle loading limitations present practical challenges which this study comes to address. Results of this study demonstrate that under less-than-ideal conditions, nonuniform nanoparticles warming may lead to a subcritical rewarming rate in some parts of the domain, excessive heating in others, and increased exposure potential to cryoprotective agents (CPAs) toxicity. Nonetheless, results of this study also demonstrate that computerized planning of the cryopreservation protocol and container design can help mitigate the associated adverse effects, with examples relating to adjusting the CPA and/or nanoparticle concentration, and selecting heart container geometry and size. In conclusion, nanowarming provides superior conditions for organ recovery from cryogenic storage, which comes with an elevated complexity of protocol planning and optimization.

DEVELOPMENT AND ANALYSIS OF AN INTEGRATED MILD/PARTIAL GASIFICATION COMBINED (IMPGC) CYCLE

Around 50% of the world's electrical power supply comes from the Rankine cycle, and the majority of existing Rankine cycle plants are driven by coal. Given how unattractive coal is as an energy resource in spite of its high energy content, it becomes necessary to find a way to utilize coal in a cleaner and more efficient manner. Designed as a potential retrofit option for existing Rankine cycle plants, the Integrated Mild/Partial Gasification Combined (IMPGC) Cycle is an attractive concept in cycle design that can greatly increase the efficiency of coal-based power plants, particularly for retrofitting an old Rankine cycle plant. Compared to the Integrated Gasification Combined Cycle (IGCC), IMPGC uses mild gasification to purposefully leave most of the volatile matters within the feedstock intact (hence, yielding more chemical energy) compared to full gasification and uses partial gasification to leave some of the remaining char un-gasified compared to complete gasification. The larger hydrocarbons left over from the mild gasification process grant the resulting syngas a higher volumetric heating value, leading to a more efficient overall cycle performance. This is made possible due to the invention of a warm gas cleanup process invented by Research Triangle Institute (RTI), called the High Temperature Desulfurization Process (HTDP), which was recently commercialized. The leftover char can then be burned in a conventional boiler to boost the steam output of the bottom cycle, further increasing the efficiency of the plant, capable of achieving a thermal efficiency of 47.9% (LHV). This paper will first analyze the individual concepts used to create the baseline IMPGC model, including the mild and partial gasification processes themselves, the warm gas cleanup system, and the integration of the boiler with the heat recovery steam generator (HRSG). This baseline will then be compared with four other common types of power plants, including subcritical and ultra-supercritical (USC) Rankine cycles, IGCC, and natural gas. The results show that IMPGC consistently outperforms all other forms of coal-based power. IMPGC is more efficient than the standard subcritical Rankine cycle by nine percentage points, more than a USC Rankine cycle by nearly four points, and more than IGCC by seven points.

Quality Formation of Adzuki Bean Baked: From Acrylamide to Volatiles under Microwave Heating and Drum Roasting

Baked adzuki beans are rich in tantalizing odor and nutritional components, such as protein, dietary fiber, vitamin B, and minerals. To analyze the final quality of baked beans, the acrylamide and volatile formation of adzuki beans were investigated under the conditions of microwave baking and drum roasting. The results indicate that the acrylamide formation in baked adzuki beans obeys the exponential growth function during the baking process, where a rapid increase in acrylamide content occurs at a critical temperature and low moisture content. The critical temperature that leads to a sudden increase in acrylamide content is 116.5 °C for the moisture content of 5.6% (w.b.) in microwave baking and 91.6 °C for the moisture content of 6.1% (w.b.) in drum roasting. The microwave-baked adzuki beans had a higher formation of the kinetics of acrylamide than that of drum-roasted beans due to the microwave volumetric heating mode. The acrylamide content in baked adzuki beans had a significant correlation with their color due to the Maillard reaction. A color difference of 11.1 and 3.6 may be introduced to evaluate the starting point of the increase in acrylamide content under microwave baking and drum roasting, respectively. Heating processes, including microwave baking and drum roasting, for adzuki beans generate characteristic volatile compounds such as furan, pyrazine, ketone, alcohols, aldehydes, esters, pyrroles, sulfocompound, phenols, and pyridine. Regarding flavor formation, beans baked via drum roasting showed better flavor quality than microwave-baked beans.

Effects of Radio Frequency Tempering on the Texture of Frozen Tilapia Fillets

Radio frequency (RF) tempering has been proposed as a new alternative method for tempering frozen products because of its advantages of rapid and volumetric heating. In this study, the texture of RF-tempered frozen tilapia fillets was determined under different RF conditions, the effects of related factors on the texture were analyzed, and the mechanisms by which RF tempering affected the texture of the tempered fillets were evaluated. The results show that the springiness (from 0.84 mm to 0.79 mm), cohesiveness (from 0.64 mm to 0.57 mm), and resilience (from 0.33 mm to 0.25 mm) decreased as the electrode gap was increased and the power remained at 600 W, while the shear force increased as the power was increased for the 12 cm electrode gap (from 15.18 N to 16.98 N), and the myofibril fragmentation index (MFI) values were markedly higher at 600 W than at 300 W or 900 W (p < 0.05). In addition, the tempering uniformity had a positive effect on hardness and chewiness. The statistical analysis showed that the texture after RF tempering under different RF conditions correlated relatively strongly with the free water content, cooking loss, and migration of bound water to immobilized water. The decrease in free water and bound water migration to immobilized water resulted in a significant increase in cohesiveness and resilience.

Automated control of the production process of antifriction polymer materials

This paper presents a technique of controlling the process of oil filling of polymer and composite materials, which allows automated determination of volumetric heating of a polymer or composite sample for the purpose of drying. The differentiation of the obtained results, presented in graphical form, made it possible to quickly analyze the dynamics of temperature changes in the thickness of the material, the change of which determines the rates and time of impregnation to a certain depth of the body of the polymer or composite sample in figure 1. According to the developed methodology, studies of the impregnation of the oil filler of a mixture of M8-B motor oil and hexane were carried out. For each experiment, time dependences of the impregnation rate were obtained. Based on the work carried out, the optimal proportion of a mixture of hexane and engine oil and the most favourable temperature conditions were determined. At the end of the research, the assumption about the possibility of using this technique for the purpose of its industrial use in the technology of oil filling of antifriction products made of polymer and composite materials was confirmed.

Investigation of Different Post-Harvest Treatments on the Quality of Almond Kernels during Ambient Storage

Maintaining almond kernel quality during and after harvest is crucial in producing premium kernel product for Australian and international markets. In this study, we investigated the effects of different post-harvest treatments on changes in moisture content, texture, colour, nutritional profile and flavour of almond kernels over a storage period of 9 months under ambient conditions. Post-harvest treatments included steam pasteurization, volumetric heating pasteurization, oven roasting and dry roasting, which were compared with raw kernels. Moisture and texture analysis revealed that the average values within each treatment group did not change significantly over 9 months, although the breaking force required to create an initial crack in the kernel structure were markedly lower for Steam Pasteurized (SP) and Oven Roasted (OR) samples after 9 months. Sensory analysis conducted by a trained panel of experts revealed that the chewiness of raw samples increased over time, and both toasted and roasted characteristics were low. For OR and Dry Roasted (DR) samples the chewiness was low and roasted and toasted properties were higher. Average overall enjoyment score given to samples as a part of sensory testing was higher for Volumetric Heating Pasteurization (VHP) and DR at start of the storage (control) and stayed higher than others after 6 and 9 month of storage. Testing of nutritional content of samples showed changes in alpha tocopherol content in roasted samples. However, DR samples had higher content in comparison with OR samples. Volumetric heating treatment didn’t diminish tocopherol content of samples in comparison with raw samples while the average alpha tocopherol content of SP over first 3 month of storage was lower. Both SP and OR samples showed lower fat percentage in comparison with raw, VHP and DR. A reduction was observed in Lightness (L*) values for all samples tested. Among the tested treatments OR samples had darker kernels and Raw and VHP samples had lightest colours. The testing results showed the potential of volumetric heating pasteurization and roasting in maintaining quality of kernel over bulk storage period.

INVESTIGATION OF THE INFLUENCE OF MICROWAVE RADIATION ON THE PROPERTIES OF GRANULAR HEAT INSULATION MATERIALS BASED ON LIQUID GLASS

The main methods of improving the performance of granular thermal insulationmaterials based on liquid glass are chemical methods of their modification, which are based onchanging their structure through the use of special ingredients. At the same time, there is a need to introduce often a large number of components and individual technological operations, which is notalways technological. One of the promising methods of changing the physical state of substancesunder the action of an electromagnetic field is non-thermal treatment of microwave radiation. Theadvantages of using microwave radiation in comparison with the generally accepted methods ofmodification of materials are the transformation of their structure without significant changes in thetechnological process and the need to use additional components. Due to volumetric heating and themechanism of non-thermal action of microwave radiation on processing objects the duration of theirheating considerably decreases. When microwave heating of a liquid glass composition part of theenergy of electromagnetic radiation is converted into heat, which contributes to the intense swellingof the material, and the other part is aimed at structural changes in the material, which improve itsproperties due to the non-thermal effect of microwave radiation. Studies show that the best set ofperformance properties have granular materials obtained under the action of microwave radiationat a power of 650 W, which corresponds to a temperature of 110-120 0C. The required duration ofsuch heat treatment is 6-7 minutes. The closest to them in terms of coefficient of swelling are materialsobtained by convective heating at a temperature of 200 0C for 1 hour, but their physical andmechanical properties are much lower. Thus, it can be noted that the use of microwave radiationallows to obtain granular thermal insulation materials with a better set of performance properties atlower energy costs for their production.

USE OF MICROWAVE RADIATION FOR SEPARATION OF LIQUID GLASS HEAT INSULATION MATERIALS

The study of the thermal insulation market of Ukraine showed that the market is dominated by aerated concrete and silicates, which are used as thermal insulation materials at an average density of 300-500 kg / m3. Their disadvantages include high values of water absorption and hygroscopicity, as well as very low flexural strength, because this material does not have elasticity and the use of small bending forces leads to its cracking. Foam glass has a set of operational properties that meet the highest regulatory requirements. Foam glass is the strongest of all effective thermal insulation materials, but this material is fragile. It is sensitive to vibration - induced damage. In addition, the technology of production of foam glass is quite complex and requires high energy consumption, as a consequence, the cost of this material is high. Therefore, it was important to develop thermal insulation material with the appropriate level of performance while reducing production costs. This was achieved by using energy-saving microwave technology to swell liquid glass materials. This technology is based on the simultaneous swelling of the liquid glass granulate and the binder under microwave radiation, which, due to the volumetric heating of the liquid glass composition, allows to obtain a strong monolithic material with a rigid, homogeneous and mostly closed-porous structure. The production of thermal insulation materials is proposed to be carried out on the basis of liquid glass granulate, because the introduction of granules reduces the deformability and shrinkage of the material and prevents its cracking, increases its strength, because the granular material has a certain plastic deformation, reduces water hygroscopicity. granules swell to form a compacted shell, which slows down the absorption kinetics of water and its vapor. The monolithic granules are proposed to be carried out with a binder that foams not only due to the release of water, but also with the help of a gasifier, because this technology will allow uniform distribution of the binder in the intergranular space, thus forming a more homogeneous structure of the material, which has a positive effect on its physical and mechanical characteristics.