Extreme Thermal Environments Research Articles

Thermal Stability Analysis of the Mg/TeO2 Ignition Composition after 180 °C Exposure

In order to satisfy the performance requirements of the pyrotechnic ignition composition of a space mission under an extreme thermal environment, it is necessary to analyze and verify the thermal stability of magnesium/tellurium dioxide (Mg/TeO2) ignition composition at a temperature of 180 °C. The thermal stability of the ignition composition of Mg/TeO2 and its components after exposure to 180 °C for 2–10 days was studied by means of apparent morphology analysis, differential scanning calorimetry (DSC), X-ray diffraction (XRD), content change analysis, and the P-t curve test. The results showed that after exposure to 180 °C for 2–10 days, no obvious changes, such as ruptures, expansion, or shrinkage, were found by optical microscope, and no changes in morphology and surface details were found by scanning electron microscope (SEM). XRD showed that no other new substance was found in the mixture except magnesium hydroxide (Mg (OH)2). DSC showed that the main reaction peak temperature of the ignition composition of Mg/TeO2 was after 500 °C and that no endothermic/exothermic reaction occurred before 380 °C. The exothermic pre-reaction took place at 381 °C to 470 °C, the weight loss ratio was within 0.71%, the content of the magnesium component varied from 0.49% to 0.90%, the peak pressure attenuation of the ignition composition of 360-mesh Mg/TeO2 was 8.07%, and the pressure rise time was basically unchanged. The results showed that the ignition composition of Mg/TeO2 had good thermal stability after exposure to 180 °C temperatures.

Evaluation of Candidate Thermal Protection System Materials for Indian Manned Mission Gaganyaan in Plasma Wind Tunnel Facility

During atmospheric reentry of a manned crew module, the vehicle experiences severe thermal environments due to aerodynamic heating. Protection of crew module necessitates thermal protection systems (TPS) which shield the vehicle structure from the extreme thermal environments. Ground based testing in Plasma Wind Tunnels play a vital role in selection and qualification of TPS for re-entry missions. Three candidate TPS materials identified for the Gaganyaan mission of ISRO are evaluated in Plasma Wind Tunnel facility under simulated reentry environments. Tests are conducted at expected peak heat flux and total heat load conditions and performance of materials are compared based on thermal response and material surface recession characteristics.

Occupation-Specific Physical Demands And Physiological Strain Of American Football Referees While Officiating

Occupational incidences of sudden cardiac death (SCD) are greater among workers that experience high levels of physical exertion, physiological strain, and extreme thermal environments. American football referees fall under this distinction, yet are underrepresented in occupational research. PURPOSE: To bridge this gap by quantifying the physical demands and physiological strain they experience while officiating. METHODS: Twelve male officials (mean±SD; age=43±11 y, body mass index [BMI]=31.9±7.2 kg/m2, 67% white), across 3 games, provided urine samples for urine specific gravity (USG) determination, ingested core temperature (Tc) pills, and wore GPS-enabled performance monitoring systems. Outdoor conditions were monitored using a weather meter. Analyses included descriptive statistics and bivariate correlations. RESULTS: Games lasted ≈2.5 h and evening weather conditions were typical of the Southeastern US (wet bulb globe temperature: 23.5±2.2°C, relative humidity: 72.5±9.2%). Across all 3 games, 58% of officials were hypohydrated (USG>1.020); they covered an average of 5.5±1.6 km (total distance) at a speed of 1.9±0.3 kmph, with corresponding Tc and heart rate (HR) values of 37.4±0.4°C (peak Tc=38.3±0.4°C) and 132±16 bpm (peak HR: 169.2±17.5 bpm), respectively, across all referees and over the entire sampling period. Higher relative humidity at the start of each game was associated with greater physiological strain (average HR: r=0.61, P=0.04; peak HR: r=0.56, P=0.06). Pre-game hydration status (r=0.50, P=0.09) and BMI (r=0.50, P=0.09) tended to elicit greater physiological strain (defined as the proportion of the game spent above 85% of age-predicted maximal HR). CONCLUSIONS: Football referees experience elevated levels of physiological strain while performing officiating duties. Individual and environmental factors appear to influence levels of strain and should be explored in a larger and more diverse sample of referees to identify patterns and develop strategies to best mitigate strain and prevent SCD.

A Review on Temperature-Dependent Electrochemical Properties, Aging, and Performance of Lithium-Ion Cells

Temperature heavily affects the behavior of any energy storage chemistries. In particular, lithium-ion batteries (LIBs) play a significant role in almost all storage application fields, including Electric Vehicles (EVs). Therefore, a full comprehension of the influence of the temperature on the key cell components and their governing equations is mandatory for the effective integration of LIBs into the application. If the battery is exposed to extreme thermal environments or the desired temperature cannot be maintained, the rates of chemical reactions and/or the mobility of the active species may change drastically. The alteration of properties of LIBs with temperature may create at best a performance problem and at worst a safety problem. Despite the presence of many reports on LIBs in the literature, their industrial realization has still been difficult, as the technologies developed in different labs have not been standardized yet. Thus, the field requires a systematic analysis of the effect of temperature on the critical properties of LIBs. In this paper, we report a comprehensive review of the effect of temperature on the properties of LIBs such as performance, cycle life, and safety. In addition, we focus on the alterations in resistances, energy losses, physicochemical properties, and aging mechanism when the temperature of LIBs are not under control.

Ultra-low density three-dimensional nano-silicon carbide architecture with high temperature resistance and mechanical strength

Silicon carbide nanotube/nanowires (SiCNT/NWs) exhibit excellent mechanical properties in extreme thermal and oxidative environments. Here, we demonstrate an easily scalable process to synthesize millimeter-sized three-dimensional architectures using SiCNT/NW building blocks to create materials with excellent mechanical strength, stiffness, and resiliency with ultra-low density. The structure of these macro-materials is initially synthesized using carbon nanotubes, then utilizing the shape memory synthesis (SMS) method are converted to nano-silicon carbide. It is proposed that using this technique, any micro-structure can initially be created with nano-carbon building blocks, optimized for the necessary morphological features of a specific application. Here, the synthesis and subsequent SiCNT/NW conversion of carbon nanotube spheres and graphene foam, demonstrates the ability to use a simple, cost-effective conversion method to create a material that can mechanically perform in extreme environments.

Strong electron-phonon coupling induced anomalous phonon transport in ultrahigh temperature ceramics ZrB2 and TiB2

Ultrahigh temperature ZrB2- and TiB2-based ceramics are widely used in extreme thermal environment. Yet, open questions remain pertaining to their lattice thermal conductivity (кph). In this work we investigate the phonon transport of ZrB2 and TiB2 by systematically evaluating the phonon-phonon interaction (PPI), electron-phonon interaction (EPI) and grain boundary scattering (GBS) from the atomistic level using first-principles. Upon including EPI, the room-temperature кph of ZrB2 and TiB2 is significantly reduced by 38.16% and 52.34%, respectively, and agrees excellently with experimental measurement. Such giant reduction arises from the strong EPI for the heat-carrying acoustic phonons due to phonon anomaly and the existence of Fermi nesting vectors along high symmetry line in the Brillouin zone. Following the Casimir model, the GBS further decreases кph of ZrB2 even by 49.27% for small grain boundary spacing of 50 nm and theoretical calculations agree well with experiments. Thus, GBS crucially influences phonon transport, which explains the large deviation of previous experimental measurements on кph for ZrB2-based ceramics. Moreover, the combined influence of EPI and GBS results in the anomalous phonon transport where кph is almost temperature-independent over a large temperature range, consistent with experimental observations. This work directly reveals the phonon transport mechanism for high temperature ceramics ZrB2 and TiB2, gains deep insight into the large variation in the previously reported кph and provides guidance to engineer it for practical applications.

Numerical Study of High Performance Ablative Thermal Protect System by Adding Phase Change Material

Under extreme thermal environment, ablation process of thermal protection system is a key issue in atmospheric re-entry and hypersonic flight vehicles; it displays a strong coupling between ablation mass, velocity and heat transfer. This article presents a method for combining the ablating and melting process, building a right triangle carbon-carbon model for ablation mixed with octadecane phase change material to absorb the heat of combustion delaying the movement of burning interface. For the moving of boundary, it is treated by the modified Stefan model coupled with chemical reaction and thermal radiation at the front leading boundary. The governing equation of heat transfer considering the melting process of phase change material is given by referring the enthalpy method. The effect of volume ratio and aerodynamic heating on the ablation interface and net heat flux on the interface are investigated. Result shows that high volume ratio of the phase change material delays the movement of the interface, and decreases the net heat flux of the interface; on the other hand, high aerodynamic heat accelerates the movement of the interface and increases the interface net heat flux at a given time point. This study can give a rule on how the volume ratio of phase change material influence the ablative process quantitatively.

A 3.3 Å‐Resolution Structure of Hyperthermophilic Respiratory Complex III Reveals the Mechanism of Its Thermal Stability

AbstractRespiratory chain complexes convert energy by coupling electron flow to transmembrane proton translocation. Owing to a lack of atomic structures of cytochrome bc1 complex (Complex III) from thermophilic bacteria, little is known about the adaptations of this macromolecular machine to hyperthermophilic environments. In this study, we purified the cytochrome bc1 complex of Aquifex aeolicus, one of the most extreme thermophilic bacteria known, and determined its structure with and without an inhibitor at 3.3 Å resolution. Several residues unique for thermophilic bacteria were detected that provide additional stabilization for the structure. An extra transmembrane helix at the N‐terminus of cyt. c1 was found to greatly enhance the interaction between cyt. b and cyt. c1, and to bind a phospholipid molecule to stabilize the complex in the membrane. These results provide the structural basis for the hyperstability of the cytochrome bc1 complex in an extreme thermal environment.

A 3.3 Å-Resolution Structure of Hyperthermophilic Respiratory Complex III Reveals the Mechanism of Its Thermal Stability.

Respiratory chain complexes convert energy by coupling electron flow to transmembrane proton translocation. Owing to a lack of atomic structures of cytochrome bc 1 complex (Complex III) from thermophilic bacteria, little is known about the adaptations of this macromolecular machine to hyperthermophilic environments. In this study, we purified the cytochrome bc1 complex of Aquifex aeolicus, one of the most extreme thermophilic bacteria known, and determined its structure with and without an inhibitor at 3.3 Å resolution. Several residues unique for thermophilic bacteria were detected that provide additional stabilization for the structure. An extra transmembrane helix at the N‐terminus of cyt. c 1 was found to greatly enhance the interaction between cyt. b and cyt. c 1, and to bind a phospholipid molecule to stabilize the complex in the membrane. These results provide the structural basis for the hyperstability of the cytochrome bc1 complex in an extreme thermal environment.

Carbon pillars are stronger than diamond yet elastic

Researchers have constructed microscopic carbon structures that boast the best combination of strength and elasticity of any material studied to date (Nat. Nanotechnol. 2019, DOI: 10.1038/s41565-019-0486-y). The tiny carbon pillars are stronger by weight than most existing materials and can bounce back after being pressed to half their size. The columns are also lightweight and heat resistant, making them ideal for use in aerospace components, engines, and nuclear reactor parts. Engineers could use these microscopic structures as building blocks for macroscopic materials, says Julia R. Greer, a materials scientist at the California Institute of Technology. With the pillars’ unique combination of properties, “you could build robust parts for any extreme thermal mechanical environment,” she says. The words strong and rubbery do not typically go together for materials. Strong materials are usually hard, while elastic materials that can recover their original shape after being deformed are pliable. Combining ...

Numerical analysis of response of a fuze to cook-off

ABSTRACTA fuze may be exposed to extreme thermal environments during its life cycle, such as high temperature resulting from burning of leaked fuel, or accidental deflagration (or explosion) of shells. It is essential to study the response of fuzes under cook-off conditions to reduce possible economic loss and casualties. Cook-off tests are an important experimental method to test and evaluate the thermal sensitivity of shells and fuzes at present, and extensive research has been done on the subject. However, it is not economical to conduct many experiments in the early stage of product development due to high cost and risk. Herein, numerical simulations are conducted to analyze the response of a fuze to cook-off. Thermal-decomposition models for HMX- and TATB-based polymer-bonded explosives proposed by Tarver are applied in the numerical models. In addition, the influence of various factors on simulation results, such as heating rate, package of the fuze, type of high explosives within the fuze is analyzed quantitatively. The law is summarized and can be used for future development of similar products.

Trait variation in extreme thermal environments under constant and fluctuating temperatures.

Climate change is increasingly exposing populations to rare and novel environmental conditions. Theory suggests that extreme conditions will expose cryptic phenotypes, with a concomitant increase in trait variation. Although some empirical support for this exists, it is also well established that physiological mechanisms (e.g. heat shock protein expression) change when organisms are exposed to constant versus fluctuating temperatures. To determine the effect of common, rare and novel temperatures on the release of hidden variation, we exposed fathead minnows, Pimephales promelas, to five fluctuating and four constant temperature regimes (constant treatments: 23.5, 25, 28.5 and 31°C; all fluctuating treatments shared a minimum temperature of 22°C at 00.00 and a maximum of 25, 28, 31, 34 or 37°C at 12.00). We measured each individual's length weekly over 60 days, critical thermal maximum (CTmax), five morphometric traits (eye anterior-posterior distance, pelvic fin length, pectoral fin length, pelvic fin ray count and pectoral fin ray count) and fluctuating asymmetry (FA, absolute difference between left and right morphometric measurements; FA is typically associated with stress). Length-at-age in both constant and fluctuating conditions decreased with temperature, and this trait's variance decreased with temperature under fluctuating conditions but increased and then decreased in constant temperatures. CTmax in both treatments increased with increasing water temperature, while its variance decreased in warmer waters. No consistent pattern in mean or variance was found across morphometric traits or FA. Our results suggest that, for fathead minnows, variance can decrease in important traits (e.g. length-at-age and CTmax) as the environment becomes more stressful, so it may be difficult to establish comprehensive rules for the effects of rarer or stressful environments on trait variation. This article is part of the theme issue 'The role of plasticity in phenotypic adaptation to rapid environmental change'.

Preliminary Thermal Design and Analysis of Lunar Lander for Night Survival

A lunar lander is exposed to extreme lunar thermal environments with a nighttime of 14.75 earth days. Thus, a proper thermal design is an important task to guarantee a successful lunar mission. This paper describes a preliminary thermal design and analysis results of a lunar lander to ensure its survivability during lunar night. The effectiveness of the thermal designs of a lunar lander with various thermal hardwares was numerically investigated according to the landing candidate areas to determine which design is the most feasible for night survival. In addition, we analyzed the mechanical safety of the solder joint of electronic components in accordance with the operating temperature range, because it is an important factor for reducing the system power budget during night survival.

Advanced Ablative composites for Aerospace applications

The external surface of a re-entry space vehicle experiences high heat flux and temperatures of the order of 2500°C during re-entry into the atmosphere and the internal contour of a rocket motor nozzle has to encounter temperatures above 2000°C during its operation. Special Thermal Protection Systems (TPS) are employed to protect the rocket hardware and re-entry capsule from such extreme thermal environments. Ablative composites are cost-effective and well-proven candidates for such applications. However, processing, characterisation and qualification of ablatives are quite complex and involves long cycle times.Ablation is a heat and mass transfer process in which a large amount of heat is dissipated in a very short period of time with sacrificial loss of material. Ablative composites are polymeric composites where the reinforcement is generally a fibre with high melting point like Carbon or Silica and the matrix is a high char yielding resin like phenolics. In this paper, the process of ablation, the physical and chemical changes and the process of synthesis of ablatives are clearly elaborated. The recent advances in design, development, characterisation and testing of carbon and silica phenolics are explained with examples.The process sequence and customised equipments used for the synthesis and characterisation are described. The raw materials, critical process parameters, quality control mechanisms, non-destructive testing methods etc are covered. The defects which were observed during the realisation and the corrective measures taken to solve them are explained.Different laminate and subscale level tests have been done to qualify the process and verify the design margins. Finally a full scale rocket engine test is carried out for qualification before induction into an operational launch vehicle.

Thermal Design, Analysis and Packaging of an Airborne Multi-output Power Supply Unit

Design of airborne multi-output power supply unit (MOPS) is restricted by space, weight and predefined geometry of air flow path. The unit is cooled by ram air and hence, exposed to the extreme external thermal environment that changes typically from +55°C to -40°C, from ground to cruising altitude within a few minutes. Hence the design should meet the thermal requirements of the electronics inside the packaging adequately, for both the positive and negative extremities of the temperature, so that device limiting temperatures are not exceeded. At the same time, it must accommodate the necessary circuitry. Details of the thermal and mechanical design and performance of the MOPS unit at various altitudes, hot spot location, flow requirements and optimal heat sink design are presented in this paper.

Functionalized boron nitride membranes with multipurpose and super-stable semi-permeability in solvents

Multipurpose and super-stable molecular sieving membranes exhibit great potential for mixture separation at low energy cost within extreme chemical and thermal environments.

Highly porous nano-SiC with very low thermal conductivity and excellent high temperature behavior

Highly porous nano-SiC is fabricated by partial sintering and decarburizing process using SiC nano-powders as starting materials and graphite flakes as pore forming agents. The prepared porous nano-SiC ceramics possess multiple pore structures, including well-distributed meso-pores in the skeleton and interconnected flakelike micro-pores. The samples prepared at 1800°C have relatively low thermal conductivities of 5.61∼0.25Wm−1K−1 with porosities of 55.5–76.1%. While the samples sintered at 1500°C with porosities between 54.0% to 76.3% show very low thermal conductivities of 0.74∼0.14Wm−1K−1, which is attributed to the integrated nano-scale phonon-scattering mechanisms and duplex pore structures. Porous nano-SiC ceramics also show good retention of elastic stiffness up to 1350°C and low thermal conductivity at 1400°C. Our results shed light on porous nano-SiC as a promising thermal insulator used in extreme thermal and chemical environments.

Numerical Study on Flow and Cooling Characteristics for Supersonic Film Cooling

ABSTRACTWith the booming performances of the gas turbine engine, the turbine vane of the gas turbine engine experiences more extreme thermal environment with supersonic flows. The film cooling applied in the supersonic flow condition has essential difference from that used in the subsonic flow condition in the flow characteristics and cooling effectiveness. This article focused on the film cooling of two parallel flows (primary flow and coolant flow) with supersonic or subsonic velocity, respectively. The results show that: on the condition of supersonic primary flow and subsonic coolant flow, the coolant flow with lower momentum is sheared and dragged by the higher momentum primary flow because of the viscous property of fluid． At the meantime, the thermal and momentum of the primary flow transfers into the coolant flow rapidly． It causes the great damage of the film coverage, and the decrease of the cooling effectiveness dramatically． In contrast, on the condition of supersonic primary flow and supersonic coolant flow, the film coverage of the supersonic coolant flow can last further far than that of the subsonic coolant flow on the same blowing ratio． The turbulence kinetic energy seems to be depressed by the shorten of velocity difference of two supersonic flow. Therefore, the cooling effectiveness is enhanced by 45% for the supersonic primary and coolant flow.

Design of Thermally Stressed Panels Subject to Transonic Flutter Constraints

The objective of this study is to design a two-dimensional panel subject to transonic flutter constraints in the presence of an extreme thermal environment. The unsteady aerodynamic model is based on a high-order stabilized finite element formulation of the Euler equations. The linearized dynamic instability problem is converted into the flutter-stability problem, and an iterative procedure is used to identify the flutter velocity at a given design point. The design variables include the lengthwise thickness and density distributions, with the objective function as the minimization of structural mass. The first set of designs are obtained for an unstressed panel with flutter constraints at Mach 1.1 and Mach 2.0, and it is found that the optimal thickness distribution closely mimics the amplitude of the constraining flutter mode. The thermally stressed panel is designed for aeroelastic stability about the nonlinear static equilibrium. It is found that the optimum mass of the thermally stressed panels is lower than the optimum mass of the unstressed panels due to the additional stiffening from the transverse deformations.

A thermally-invariant, additively manufactured, high-power graphene resistor for flexible electronics

Solution processed two-dimensional (2D) layered materials and their integration with additive manufacturing techniques, such as ink-jet printing, is a facile approach for incorporating these exotic materials into device platforms for flexible electronics. In this work, graphene ink formulations are successfully utilized toward the design and fabrication of high-power resistive structures that are printed on both rigid and flexible substrates and have the potential to deliver close to 10 W of power. A near-flat, negative temperature coefficient of resistivity (TCR) is measured with an activation energy Ea ~ 2.4 meV for electron hopping, which is 100× lower compared to Ea values for high TCR materials. The TCR and Ea values are amongst the lowest reported for 2D layered material systems. The thermal-invariance of resistivity for such high-power graphene printed resistors is attractive for applications, for example to provide a stable heating source for flexible electronics over extreme thermal environments. The transport characteristics of the ink-jet printed features is modeled as a composite structure in order to explain the thermal response which appears to be mediated via defects in the sonicated graphite, and correlates well to inferences made from Raman spectroscopy and transmission electron microscopy analysis conducted on the printed graphene structures. In order to fabricate such functional structures with ink-jet printing, the active nozzle number, printing passes, and annealing conditions are shown to play an important role to determine line resolution, and also dictate the morphological and electronic transport characteristics of the printed graphene features.