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.

Designs for Reliability and Failure Mode Prevention of Electrical Feedthroughs in Integrated Downhole Logging Tools

To enable an electrical feedthrough integrated down-hole logging tool to maintain high reliability during its logging service in any hostile wellbores, it is critical to apply some guidelines for the electrical feedthrough designs. This paper introduces a safety factor-based design guideline to ensure an integrated electrical feedthrough has sufficient compression or thermomechanical stress amplitude in the stress well against potential logging failures. It is preferred to have a safety actor of 1.5–2.0 for an electrical feedthrough at lowest temperature, such as −60°C, and a safety actor of 2.5–5.0 at operating temperature range of 200–260°C. Moreover, the designed ambient pressure capability should be 1.5–2.0 times higher than the maximum downhole pressure, such as 25,000–30,000 PSI. To validate this thermomechanical stress model, several electrical feedthrough prototypes have been tested under simulated 200–260°C and 31,000–34,000 PSI downhole conditions. The observed testing data have demonstrated that there is a maximum allowable operating pressure for an electrical feedthrough operating at a specific downhole temperature. It is clearly demonstrated that an electrical feed-through may operate up to 60,000 PSI at ambient temperature in a real-life application, but it may actually operate up to 30,000–35,000 PSI at 200–260°C downhole temperatures.

Theoretical Modeling for the Thermal Stability of Solid Targets in a Positron-Driven Muon Collider

A future multi-TeV muon collider requires new ideas to tackle the problems of muon production, accumulation and acceleration. In the Low EMittance Muon Accelerator concept a 45 GeV positron beam, stored in an accumulation ring with high energy acceptance and low angular divergence, is extracted and driven to a target system in order to produce muon pairs near the kinematic threshold. However, this scheme requires an intensity of the impinging positron beam so high that the energy dissipation and the target maintenance are crucial aspects to be investigated. Both peak temperature rises and thermomechanical shocks are related to the beam spot size at the target for a given material: these aspects are setting a lower bound on the beam spot size itself. The purpose of this paper is to provide a fully theoretical approach to predict the temperature increase, the thermal gradients, and the induced thermomechanical stress on targets, generated by a sequence of 45 GeV positron bunches. A case study is here presented for Beryllium and Graphite targets. We first discuss the Monte Carlo simulations to evaluate the heat deposited on the targets after a single bunch of 3 × 1011 positrons for different beam sizes. Then a theoretical model is developed to simulate the temperature increase of the targets subjected to very fast sequences of positron pulses, over different timescales, from ps regime to hundreds of seconds. Finally a simple approach is provided to estimate the induced thermomechanical stresses in the target, together with simple criteria to be fulfilled (i.e., Christensen safety factor) to prevent the crack formation mechanism.

Relationship between mechanical behavior and microstructure evolution of sintered metallic brake pad under impact of thermomechanical stress

It is well known that on the brake pad material, the triptych microstructure-properties-solicitations is the key to better understand the phenomena caused by braking stress. The challenging issues are the evolution of this triptych, i.e., the impact of thermal stress and mechanical stress on the microstructure which undoubtedly induces changes in properties. In order to solve the issues without tackling them in all their complexity, this study proposes an experimental approach where physics is decoupled but inspired by the braking sequence in terms of applied temperature gradient and braking loads. Two experimental tests were carried out. The first one is the thermal solicitation test where a temperature gradient from 400°C to 540°C was applied to the material. The second one is the thermomechanical test where a compressive load at 20 MPa was applied under the same thermal gradient. The experiment time is fixed for two minutes, equivalent to the time of one braking stroke. The referred material is sintered metallic composite, which is widely used as brake pad material for high-energy railways. As result, it shows that coupled thermomechanical stress has a greater impact on the material properties than decoupled one. This impact is related to the microstructure where graphite inclusions play an important role.

Extrusion Processing of Pure Chokeberry (Aronia melanocarpa) Pomace: Impact on Dietary Fiber Profile and Bioactive Compounds

The partial substitution of starch with dietary fiber (DF) in extruded ready-to-eat texturized (RTE) cereals has been suggested as a strategy to reduce the high glycemic index of these food products. Here, we study the impact of extrusion processing on pure chokeberry (Aronia melanocarpa) pomace powder (CPP) rich in DF and polyphenols (PP) focusing on the content and profile of the DF fractions, stability of PP, and techno-functional properties of the extrudates. Using a co-rotating twin-screw extruder, different screw speeds were applied to CPP with different water contents (cw), which resulted in specific mechanical energies (SME) in the range of 145–222 Whkg−1 and material temperatures (TM) in the range of 123–155 °C. High molecular weight soluble DF contents slightly increase with increasing thermomechanical stress up to 16.1 ± 0.8 g/100 g dm as compared to CPP (11.5 ± 1.2 g/100 g dm), but total DF (TDF) contents (58.6 ± 0.8 g/100 g dm) did not change. DF structural analysis revealed extrusion-based changes in the portions of pectic polysaccharides (type I rhamnogalacturonan) in the soluble and insoluble DF fractions. Contents of thermolabile anthocyanins decrease linearly with SME and temperature from 1.80 ± 0.09 g/100 g dm in CPP to 0.24 ± 0.06 g/100 g dm (222 Whkg−1, 155 °C), but phenolic acids and flavonoids appear to be largely unaffected. Resulting techno-functional (water absorption and water solubility) and physical properties related to the sensory characteristics (expansion, hardness, and color) of pure CPP extrudates support the expectation that granulated CPP extrudates may be a suitable food ingredient rich in DF and PP.

INFLUENCE OF REGIME AND OPERATIONAL FACTORS ON THE DAMPER SYSTEM OF THE SALI-ENT-POLE SYNCHRONOUS MACHINE ROTOR

The physical processes in the damping system of the salient-pole synchronous machine rotor, which cause the gradual destruction of its structure, have been studied. In particular, the distributions of currents, temperatures and thermomechanical stresses in the damping system rods during its operation in asynchronous and asymmetric modes of operation, as well as in case of rotor eccentricity. A field mathematical model has been developed that takes into account the combined action of three physical fields of different nature: electromagnetic, temperaturic, and thermomechanical stress fields, and allows estimating heating and thermomechanical loads in the damping system of the rotor of the salient-pole synchronous machine. According to the results of the analysis, the heating and thermomechanical loads of the structural elements were determined and recommendations for its structural improvement were given. References 9, figures 9, tables 1.

The Wear of Seal Fins during High-Speed Rub between Labyrinth Seal Fins and Honeycomb Stators at Different Incursion Rates

Labyrinth seals as a noncontact sealing technology are widely used in aero-engine. To improve the efficiency of the aero-engine, the clearance between the rotor and stator must be as small as possible. However, the change of the clearance between the rotor and stator because of thermal expansion, vibration, mechanical loading may lead to undesirable high-speed rub, which will lead to the cracking of the seal fins. This paper focuses on the wear of the seal fin after the rub and presents the rubbing tests between seal fins and the metal honeycomb under rubbing speed of 380 m/s and incursion rates between 20 and 180 μm/s, with an incursion depth of 1500 μm and a temperature of 350 °C. The rubbing force and temperature were recorded, and the seal fins were checked by SEM and EDS. The results show that the wear mechanism of seal fins changed from oxidation wear and adhesive wear to delamination wear and then to metal wear with the increasing incursion rate. The axial cracks appeared on the worn surface of the seal fins due to the cracking of tribo-layers under periodic thermomechanical stress. The wear mechanism of the seal fin also has a great influence on the rubbing force and temperature.

Impact of Heat Transfer on Transient Stress Fields in Power Plant Boiler Components

In boilers operating in modern power plants, thick-walled elements of complex shapes, such as valves, superheater headers, T-pipes, Y-pipes, four-way pipes, and elbows, are especially prone to fatigue processes. Higher operation parameters and more frequent startups may speed up fatigue damage in these elements. Such damage is a local phenomenon and is caused by thermomechanical fatigue (TMF). This paper presents a method designed for predicting the behavior of components subjected to variable temperature and mechanical loading conditions. This method combines the results of measurements of operating parameters of devices under industrial conditions with those obtained using finite element modeling (FEM). Particular attention was given to the influence of the time-dependent heat transfer coefficient on the local thermomechanical stress–strain behavior of the material. It was stated that heat transfer conditions have a significant impact on local transient stresses and depend on the operation parameters of boilers. Consistency of the temperature changes as a function of time, determined in industrial conditions and calculated on the basis of the model approach, was obtained. This developed and described in the work approach enables defining the conditions of heat transfer on the surface of models of considered components.