Peak Temperature Research Articles

Effect of x-ray irradiation on magnetocaloric materials, (MnNiSi)1-x(Fe2Ge)x and LaFe13-x-yMnxSiyHz

Abstract Understanding the behavior of magnetocaloric materials when exposed to high-energy x-ray irradiation is pivotal for advancing magnetic cooling technologies under extreme environments. This study investigates the magnetic and structural changes of two well-studied magnetocaloric materials, (MnNiSi)1−x(Fe2Ge)x composition (x = 0.34) and LaFe13-x-yMnxSiyHz composition (x = 0.30,y = 0.1.26 and z = 1.53) alloys upon irradiation. The alloys were exposed to x-ray radiation with a dosage of a continuous sweeping rate of ∼>120 Gy min−1 and an absorbed dose of 35 kGy . Both the samples didn’t show any observable crystal change after irradiation. There was a considerable change in magnetization at low applied magnetic fields in magnetization versus temperature measurements from 2.72 emu g−1 to 4.01 emu g−1 in the irradiated (MnNiSi)1−x(Fe2Ge)x sample and 4.41 emu g−1 to 5.49 emu/g for the LaFe13-x-yMnxSiyHz alloys. The Magnetization versus magnetic field isotherms near transition temperature exhibited irradiation-induced magnetic hysteresis for the (MnNiSi)1−x(Fe2Ge)x (x = 0.34) while the LaFe13-x-yMnxSiyHz samples did not result in any irradiation-induced magnetic hysteresis. In both the samples the magnitude of entropy change did not change due to irradiation however, the peak entropy change shifted to different temperatures in both the samples, (MnNiSi)1−x(Fe2Ge)x (x = 0.34), showed a maximum entropy change, ΔSmag of ∼ 11.139 J/kgK at 317.5 K compared to ΔSmag of ∼ 11.349 J/kgK at Tave peak of 312.5 K for the irradiated sample. LaFe13-x-yMnxSiyHz, pristine sample exhibited a maximum magnetic entropy change, ΔSmag ∼ 18.663 J/kgK, with the corresponding peak temperature, Tave peak, of 295 K compared to ΔSmag ∼ 18.736 J/kgK, at Tave peak of 300 K. It was determined that irradiation applied to the samples did not induce any structural or magnetic phase changes in the selected compositions but rather modified the magnetic properties marginally.

The Role of α−β Quartz Transition in Fluid Storage in Crust From the Evidence of Electrical Conductivity

AbstractAqueous fluids are extensively present in the middle to lower crust, as revealed by seismic and magnetotelluric soundings. The α−β quartz phase transition significantly affects many physical properties and leads to substantial microcracks that can provide pathways for the migration of crustal fluids. A systematic investigation of macroscopic physical properties and microstructure of quartz is crucial to elucidate their correlation. In the present study, the effects of water content, trace elements, orientations, and phase transition on the electrical conductivity of quartz were thoroughly evaluated at 400−900°C and 1 GPa. Individual annealing experiments were simultaneously conducted on quartz single crystals at different peak temperatures and 1 GPa to investigate the evolution and spatial distribution of microcracks using X‐ray microtomography (CT) and backscattered electron imaging. We found that trace element content and orientations, rather than H2O, are the dominant factors controlling the conductivity of quartz. The distinct changes in conductivity of single crystals at around α−β phase transition temperature are attributed to the transformation of microcracks from isolated to interconnected networks, as confirmed by two‐dimensional (2‐D) and three‐dimensional (3‐D) microstructure images. Based on the variation in electrical conductivity and microstructure across the transition, it thus is proposed that the intragranular microcracks caused by quartz phase transition can serve as fluid or melt pathways within highly conductive zones present in the middle to lower crust, while α‐quartz acts as an impermeable cap.

Passive battery thermal management and thermal safety protection based on hydrated salt composite phase change materials

Lithium-ion batteries (LIBs) are progressing towards higher energy densities, extended lifespans, and improved safety. However, battery thermal management systems are facing increased demand owing to high-rate charging and discharging, dynamic operating conditions, and heightened thermal safety concerns. Therefore, this paper proposes a novel composite phase change material (CPCM) comprising Na2SO4-10H2O as the core phase change material (PCM) and expanded graphite as the thermal conductivity enhancer. The CPCM offers high latent heat, superior thermal conductivity, and a two-stage temperature control function for battery thermal management and safety. The optimal mass CPCM ratio, determined through comprehensive characterization and thermal property tests, resulted in a melting point of 29.05°C, latent heat of 183.7 J.g−1, and high thermal conductivity of 3.926 W.m−1.K−1. During normal LIB operations, the CPCM efficiently absorbs and transfers heat, reducing the peak LIB temperature from 66 to 34°C at 15°C ambient temperature during a 3.7C high-rate discharge. Under dynamic conditions, the peak temperatures across the three cycles were consistently controlled at 36.7, 36.4, and 35.8°C, respectively. In a thermal runaway state, the thermochemical heat storage of hydrated salt dehydration effectively slowed LIB temperature increase, delaying the time to reach 130°C by 187 s. Suppression of the temperature rise outside the CPCM, combined with an extended dehydration plateau of up to 320 s, prevented the occurrence and propagation of thermal runaway in the battery.

Effect of viscous dissipation in heating/cooling of grade three fluid in a pipe subjected to uniform surface temperature

Forced convection in Newtonian and non-Newtonian fluids flowing through pipes maintained at uniform heat flux or uniform wall temperature are important for understanding heat transfer characteristics in design and thermal management of heat exchangers. Convective heat transfer in both Newtonian and non-Newtonian fluids flowing through pipes and parallel plates, subjected to uniform wall heat flux condition, were extensively studied by researchers. But for uniform wall temperature, studies on non-Newtonian fluids in pipes are rarely considered. Forced convective heating and cooling of a third-grade fluid, flowing in a pipe subjected to uniform (constant) wall temperature is considered. Effect of viscous dissipation is included in the energy equation. Separate energy conservation equations for heating and cooling are formulated and their dimensionless forms are obtained. Numerical solutions by shooting technique are obtained for the governing equations. The same equations are also solved by the least square method and semi-analytical solutions are yielded. Least square method is a widely used semi-analytical tool used for solving non-linear differential equations. Results of the numerical solution and semi-analytical solutions are compared and are observed to be in close agreement. This validates the numerical solution. Few important observations are presented. For heating, when the non-Newtonian parameter increases from 0 – 0.1, the peak temperature drops from 1.15 – 0.55 which occurs at the centre. In case of cooling, when non-Newtonian parameter increases from 0 – 0.1, the difference in central line temperature and wall temperature increases to 0.17 from 0.09. For change in the non-Newtonian parameter from 0.2 – 0.3, both for heating and cooling the peak temperature change is not drastic. Heat transfer coefficient, in case of heating, differs by nearly 3.5 when the non-Newtonian parameter increases from 0 – 0.1.

Halogen-free epoxy flame retardant & promoter with diimidazole skeleton improves overall properties of epoxy resins

In order to solve the widespread problem in the field of flame retardancy epoxy(FREP), for the deterioration of the overall properties, we designed a novel structural flame retardant & promoter DOPO-CDI and synthesized it using a simple nucleophilic addition one-step method, which exhibits remarkable flame retardant and curing promotion, the flame retardant and promote mechanism of DOPO-CDI on neat EP is illustrated in Fig 0a, which obtained excellent overall properties shown in Fig 0b. Compared with neat epoxy, it has high flame retardancy, low additives results in an limiting oxygen index(LOI) of up to 37.5 % and a V-0 rating of UL-94, a lower curing exothermic peak temperature, a shorter curing time. And in terms of mechanical properties, the excellent strength of epoxy has been further enhanced, flexural strength and tensile strength are increased by 13.3 % and 21.6 % respectively. Moreover, the toughness of epoxy, which is generally lacking, has been greatly improved, in particular, compared with neat epoxy, the impact strength of epoxy with 3 wt% DOPO-CDI increased by 103.6 %. Unlike most FREP, glass transition temperature(Tg) of the epoxy with the introduction of DOPO-CDI raises to 165.6 °C, which is a significant improvement compared to that of the neat epoxy, in terms of combustion behavior, DOPO-CDI has a considerable inhibitory effect on the combustion exotherm and smoke emission. This work explores a way to balance processing, mechanical and thermal properties when preparing FREP, which has great potential for application.

Experimental Study and Neural Network Predictions of Early-Age Behavior of Microexpansion Concrete in Large-Diameter Steel Tube Columns

The improved mechanical performance of concrete-filled steel tube (CFST) components has led to their widespread application in megastructures. Therein, CFST hybrid arch bridge has become an optimal selection of large span bridges. Nonetheless, for massive concrete poured in CFST members with large diameter, the thermal cracking and sustained rising temperature caused by early hydration heat of core concrete are urgently required to be studied. The two large-diameter CFST columns in this work, each having a diameter of 2.1 m, had their temperature and strain fields recorded in-situ. An existing CFST arch bridge served as the model for the two CFST columns’ design. Additionally, early-age characteristics of several scaled CFST columns with varying diameters were documented. A multi-field finite element (FE) model that combines linked chemical (hydration), heat, and mechanical fields is suggested in order to properly characterize the evolutions of temperature and strain fields. The model is validated by comparing the in-situ measurements with the numerical results. Finally, to investigate the affect factors on the hydration temperature of core concrete in CFST columns, early-age hydration behaviors of CFST columns was simulated using the validated FE models input parameters as water to cement ratio (w/c), cement dosage, heat release of cement and diameter of CFST columns. Based on the numerical results under the input parameters mentioned, the LSTM neural network was constructed, and the hydration temperature variances computed by FE models were selected as the input dataset. Afterwards, the temperature variance of core concrete of CFST columns was predicted using the established LSTM network. It is discovered that the LSTM neural network that was previously constructed was able to predict the peak temperature of CFST columns as well as the hydration temperature of CFST specimens with respect to time.

Design and modeling of PV-integrated Double Skin Facades and application to retrofit buildings

Double Skin Façade (DSF) system comprises two glazing layers with a ventilated cavity. Integrating photovoltaic (PV) modules within the outer layer of DSFs offers an efficient method for electricity generation. Current tools for modeling and analyzing DSF systems are complex and resource-intensive, lacking the capability to evaluate the performance of innovative PV-DSF systems during the early design stage. This study develops a mathematical model to evaluate the electrical and thermal performance of PV-DSF systems, considering architectural design elements such as PV color and relative orientation. Based on an energy balance approach, the model is particularly suited for designing PV-DSF systems in heritage buildings, which often have color and relative orientation constraints. The model is applied to assess the performance of PV-DSF systems with conventional clear glass PV and colored front glass PV modules under the climatic conditions of Montreal, Canada. Results indicated that conventional clear glass PV module exhibit higher PV cell temperature than colored PV modules due to greater transmissivity, with peak temperature differences at noon of 5.5 °C, 6.2 °C, and 6.5 °C for orange, blue, and gray PV modules, respectively. On the contrary, the influence of PV's color front glass on room air temperature is non-significant. Furthermore, the optimal orientation for maximum energy yield is not always south-facing; it depends on the hourly distribution of the beam, diffuse solar irradiation, and ambient air temperature. For Montreal, west-facing DSFs produce more electrical and thermal energy on a summer design day because the hourly distribution of beam radiation is skewed towards afternoon hours.

Influence of secondary peak temperature on simulated ICCGHAZ microstructure and toughness of high-strength low-alloy steels

Abstract The ICCGHAZ specimens of laser-arc hybrid welding under various secondary peak temperatures were prepared using welding thermal simulation technology. Investigations were conducted into how the toughness and microstructure of the simulated ICCGHAZ specimens were correlated with the secondary peak temperature. Results showed that the size, distribution, and morphology of the M-A constituents in the ICCGHAZ specimens were primarily influenced by the secondary peak temperature. With this temperature at 760 °C, the blocky M-A constituents mostly aggregated into chains along the grain boundaries. As the secondary peak temperature reached 800 °C, while the blocky M-A constituents typically stayed close to the grain boundaries, the necklace M-A constituents began dispersing. The former austenite grain boundaries vanished as the M-A constituents migrated outward when the temperature further rose to 840 °C. At secondary peak temperatures of 760 °C and 800 °C, the volume proportion of the M-A constituents was 2.9% and 3.2%, respectively. In comparison, the volume fraction rapidly decreased to 0.9% at 840 °C. The size of the M-A constituents shrank as the secondary peak temperature rose, whereas the crack initiation energy Ei, crack propagation energy Ep, and impact energy Et increased. The toughness of the ICCGHAZ specimen was diminished because of the grain boundary necklace distribution characterization and the large size of the M-A constituents.

A Multi-scale Framework for Advancing Battery Safety Through Early Calorimetric Analysis of Materials and Components

Batteries are the cornerstone of the global shift toward electrification, powering applications from passenger transportation, like electric vehicles (EVs), to load shifting of renewable energy generation at the grid level. The demand for batteries is accelerating, and is projected to nearly quadruple by 2030. In response to increasing battery demands, in particular demand for longer range EVs, higher energy density and specific energy alternatives to conventional Li-ion battery technologies are being researched. However, higher energy density directly correlates with an increased potential for higher peak temperatures on failure. In addition, safety evaluation of conventional and new battery technologies generally occurs late in development, often at the commercialization stage when mandated by stakeholders or industry standards. This approach can be costly and challenging as it may require a change to manufacturing processes, a re-design of the battery, and even a change in chemistry to meet safety requirements. This is critical; scale-up efforts alone can take tens to hundreds of millions of dollars and >5 years to achieve. Safety risks discovered after commercialization can significantly exacerbate those figures. Furthermore, safety is still a major risk with already commercialized Li-ion batteries. These risks hinder adoption, slow commercialization, and when they become issues, the outcome may result in recalls, fires, injuries, and even fatalities. Providing additional levers to proactively mitigate safety risk at the materials and components scale (e.g., composite cathode) will lead to considerable time and money savings in the long run.

Canopy temperatures strongly overestimate leaf thermal safety margins of tropical trees.

Current estimates of temperature effects on plants mostly rely on air temperature, although it can significantly deviate from leaf temperature (Tleaf). To address this, some studies have used canopy temperature (Tcan). However, Tcan fails to capture the fine-scale variation in Tleaf among leaves and species in diverse canopies. We used infrared radiometers to study Tleaf and Tcan and how they deviate from air temperature (ΔTleaf and ΔTcan) in multispecies tropical tree plantations at three sites along an elevation and temperature gradient in Rwanda. Our results showed high Tleaf (up to c. 50°C) and ΔTleaf (on average 8-10°C and up to c.20°C) of sun-exposed leaves during 10:00 h-15:00 h, being close to or exceeding photosynthetic heat tolerance thresholds. These values greatly exceeded simultaneously measured values of Tcan and ΔTcan, respectively, leading to strongly overestimated leaf thermal safety margins if basing those on Tcan data. Stomatal conductance and leaf size affected Tleaf and Tcan in line with their expected influences on leaf energy balance. Our findings highlight the importance of leaf traits for leaf thermoregulation and show that monitoring Tcan is not enough to capture the peak temperatures and heat stress experienced by individual leaves of different species in tropical forest canopies.

Thermal fields induced by oscillating laser beams versus non-oscillating equivalent laser beams — A numerical study

In high power laser material processing, like laser transformation hardening, laser welding or laser cladding, tailoring the laser intensity profile is a method to improve stability of the laser material process and/or improve the processing results. A method to tailor the laser intensity profile in real-time is using a Galvanometer Scanner to quickly and iteratively oscillate the focal spot of the laser beam over a predefined path. Due to the oscillating nature of this beam shaping method, the temporal heat input will differ from the temporal heat input by an equivalent non-oscillated laser intensity distribution. Mathematically this equivalent non-oscillated beam profile is the convolution of the laser intensity distribution of the oscillated focal spot and the predefined oscillation path. This work presents simulation results of laser induced thermal fields. The thermal fields induced by oscillated laser beams at different frequencies are compared with the thermal field induced by the equivalent non-oscillated beam. These comparisons show that even at the highest oscillation frequencies the oscillated and equivalent non-oscillated laser beams induce significantly different in temperature fields (e.g. up to 325 K peak temperature difference) and different cooling rates (105 K/s and 5500 K/s respectively).

Experimental investigation on the thermal enhancement of spherical macro-encapsulated phase change material assisted soil heat accumulators

Reserved cavities during construction have the potential to serve as the space to efficiently harness shallow geothermal energy resources in light of the underground spaces' rapid expansion. Earth-air heat exchanger technology is an effective way among all the technologies. However, as the heat storage capacity of the surrounding soil gradually diminishes due to the long-term operation of the system, it is recommended to incorporate phase change materials (PCMs) with a stabilized heat storage capacity to improve the overall thermal performance of the system. This research specifically recommends back-filling macro-encapsulated PCMs measuring 15–25 mm in order to prevent backfill contamination caused by PCM leakage. The shells and cores of the PCMs are polypropylene spheres and n-heptadecane. Different volume proportions of macro-encapsulated PCMs are used in the design of modified soil accumulators. 27 groups of orthogonal array experimental tables were made using the Taguchi method to test the improved heat accumulator's performance with different heating sources. According to the results, adding PCMs causes the peak temperature to change and increases overall energy storage by 7.2 %. The most significant factor is the soil moisture content, which accounts for 62.47 % of the overall impact of the PCM's heat storage ratio and total heat storage capacity. With a contribution of 20.41 %, the PCM ratio is ranked second. Furthermore, optimization options for the primary parameters that impact the total heat storage and heat storage ratio of the PCM are offered. This paper offers references for the potential use of the PCM-assisted EAHE system design in real-world engineering applications.

Gulf Stream intrusion and deep current upwelling drive dynamic patterns of temperature and food supply within cold‐water coral reefs

AbstractOne of the most significant features of the Northwest Atlantic, the Gulf Stream influences high magnitude environmental fluctuations in deep habitats across the South Atlantic Bight. Amid this variability, the Blake Plateau harbors extensive reefs formed by cold‐water corals that were previously assumed to rely on narrow ranges of temperature, currents, and particulate supply. A benthic lander collected near‐bed conditions at the Richardson Reef Complex, a cold‐water reef dominated by the scleractinian Desmophyllum pertusum at 830 m within the path of the Gulf Stream. Specific behavior of the Gulf Stream resulted in recurring environmental patterns at depth. During offshore meanders, deep stream components intruded onto the reef and caused rapid (3.74°C per hour) temperature increases up to 10.8°C (> 5°C above the site mean) and increased chlorophyll. Within 2 d of peak temperatures, intrusions were replaced by strong, turbid upwelling currents that rapidly cooled the site to temperature minima (4.13°C). While considerable environmental variability from the Gulf Stream may otherwise implicate a thermally stressful setting for corals, high‐temperature events were likely mitigated by their short duration (< 37.4 h) and physical coupling with enhanced organic material. This hypothesis was supported by high‐density clustering of D. pertusum occurrences within 50 km around the Gulf Stream's position along the South Atlantic Bight. This suggests that cold‐water corals experiencing environmental variability can be sustained by relationships between food supply, temperature, and currents that vary in strength along stochastic time scales, shedding further light on the niche of cold‐water corals.

Impact of Aerogel Barrier on Liquid‐Cooled Lithium‐Ion Battery Thermal Management System's Cooling Efficiency

Thermal runaway propagation (TRP) in lithium batteries poses significant risks to energy‐storage systems. Therefore, it is necessary to incorporate insulating materials between the batteries to prevent the TRP. However, the incorporation of insulating materials will impact the battery thermal management system (BTMS). In this article, the influence of aerogel insulation on liquid‐cooled BTMS is analyzed employing experiments and simulations. In the experiment results, it is revealed that aerogel reduces heat dissipation from liquid‐cooled battery packs, leading to elevated peak temperatures and steeper temperature gradients. Simulation of battery pack discharge warming based on the 3D model shows that the result matches very well with that in the experiment., indicating a maximum temperature rise from 34.92 to 42.57 °C at 2C when aerogel thickness is increased to 5 mm, alongside a temperature differential expansion from 11.11 to 17.50 °C. Nonetheless, beyond 3 mm thickness, further increases in aerogel thickness cause negligible (<0.1 °C) temperature alterations, defining the saturation thickness of aerogel. Furthermore, maintaining consistent thickness and stacking more aerogel layers do not mitigate its detrimental effects. Interestingly, augmenting the battery's through‐thickness thermal conductivity counteracts the adverse outcomes of aerogel usage.

Poly(lactic acid)/poly(vinyl butyral) composites containing kaolin modified by acids and calcination

AbstractThe compatibility between two distinct polymers in the blend is important to maximize various properties of the blends. This study investigated the effects of kaolin modifications through acid and calcination treatments on the compatibility, molecular weight, its distribution, and various properties of poly(lactic acid) (PLA)/poly(vinyl butyral) (PVB) blends. In addition, the incorporation of the modified kaolin as a compatibilizer into the blends enhanced their mechanical and thermal properties, addressing the challenges of immiscibility between distinct polymers. The experimental approach included the utilization of scanning electron microscopy, gel permeation chromatography, differential scanning calorimetry, x‐ray diffraction, Fourier transform infrared spectroscopy, rheometer, and melt flow index to examine the structural, molecular, and thermal, mechanical and rheological behaviors of the composites. The changes in various molecular weights were correlated with other properties. The incorporation of surface‐treated kaolin into the blend improved the compatibility between PLA and PVB, exhibiting a singular melting temperature peak and a less distinct interface between two different polymers. This research contributed to the development of sustainable material solutions by demonstrating the potential of modified inorganic fillers in improving the performance of biodegradable polymer blends.

Effects of ammonia energy ratio and PODE injection timing on combustion and emissions in a PODE/ammonia RCCI engine

The application of ammonia as an alternative carbon-free fuel has attracted increasing attention. In this paper, the effects and mechanisms of ammonia energy ratio (AER) and polyoxymethylene dimethyl ethers (PODE) injection timing on the combustion and emissions characteristics of a PODE/ammonia RCCI engine are investigated by both experimental and numerical methods. Results show that increasing AER from 10% to 40% leads to the delayed low temperature heat release (LTHR) due to reduced OH radical generated by PODE and the competition between PODE and ammonia for OH radical consumption. The larger AER increases the indicated thermal efficiency (ITE) by lowering combustion temperature and reducing heat transfer losses at the cost of higher hydrocarbon (HC), carbon monoxide (CO), and unburned NH3 emissions. The reduction of fuel-based nitrogen oxide (NOx) emissions with a larger AER is attributed to the enhanced in-cylinder thermal denitrification reactions. The delayed start of injection (SOI) from −60 °CA ATDC to −45 °CA ATDC leads to the higher peak in-cylinder pressure and temperature, resulting in the larger heat transfer losses and lower ITE. The impact of retarding SOI on NOx is insignificant under the combined effect of more thermal NO formation, less fuel-based NO generation, and weakened denitrification reactions. Additionally, nitrous oxide (N2O) shows dominant effects on the total greenhouse gas (GHG) emissions, and increasing AER or advancing injection timing produces more GHG. Under low loads and low AERs, although the introduction of ammonia helps to improve ITE, more researches are required to further reduce exhaust emissions.

A Novel Concept of Nano-Enhanced Phase Change Material.

In the actual context of growing concerns over sustainability and energy efficiency, Phase Change Materials (PCMs) have gained attention as promising solutions for enhancing energy storage and release efficiency. On another hand, materials based on graphene oxide (GO) have proven antibacterial activity, biocompatibility, efficiency in microbial growth inhibition, and pollutant removal. Integrating nanoparticles into PCMs and creating Nano-Enhanced Phase Change Materials (NEPCMs) have opened new horizons for optimizing the performance of these systems and sustainable development. The key objective of this work is to gain insight into NECPMs, which are used in solar wall systems to enhance solar energy storage. Paraffin RT31 was mixed with Cu nanoparticles, graphene oxide (GO), and Cu-decorated GO (Cu@GO) at loading ratios ranging from 1% to 4% (w/w nanoparticles with respect to RT31). The compositions were characterized through Differential Scanning Calorimetry (DSC) and rheology tests. The decoration of the carbon-based nanoparticles was performed using the ultrasonication procedure, and the decoration efficiency was confirmed through X-ray Photoelectron Spectroscopy (XPS). The rheologic measurements were performed to correlate the flow behavior of the NEPCM with their composition at various temperatures. The study methodically investigated these composites' latent heat values, phase change peak temperatures, and solidification phase change temperatures. Compared to pure paraffin, the solidification of the formulations obtained using Cu@GO exhibits the largest increase in latent heat, with a 12.07% growth at a concentration of 2%. Additionally, at a 4% concentration of NEPCM, the largest increase in thermal conductivity was attained, namely 12.5%.

Analysis of micro-hole formation in titanium nanofilms using a low power CW laser

This study investigates the mechanisms and dynamics governing microhole formation in titanium nanofilms under the influence of a continuous-wave low-power laser emitting at 1070 nm. Two distinct configurations were explored: one in which the laser interacted with the titanium film in an air environment (referred to as configuration AM), and the other in which the laser beam passed through glass before reaching the titanium film (referred to as configuration SM). Our experiments demonstrated that microhole formation is possible in both configurations. However, the threshold powers, hole characteristics, and time scales involved differ significantly between AM and SM configurations. Temperature distribution simulations, based on a linear absorption model, revealed notable differences in peak temperatures between these two configurations, primarily attributed to variations in focal spot size and Fresnel losses. These temperature variations resulted in significantly different mechanisms of material removal in both configurations. In the AM configuration, the boiling temperature was not achieved, even at the highest power; however, a melting pool was formed at powers exceeding 50 mW. Thus, the primary driver of microhole formation was the Marangoni effect, which caused molten material to flow tangentially towards the edges of the molten pool. Furthermore, titanium oxidation was identified as a competing process contributing to changes in optical transparency and potentially inhibiting the complete formation of holes. Conversely, within the SM configuration, boiling temperatures are easily achieved, leading to localized boiling and the formation of gas bubbles near the glass–titanium interface. As a result, the rupture of the bubble through the capping molten layer led to a vigorous expulsion of both gas and material, allowing for the creation of microholes even at remarkably low laser power levels (10 mW). Notably, in this configuration, the influence of titanium oxidation is negligible due to the relatively short time scale involved (hundreds of microseconds).

Self-powered sensors utilizing single-pillar thermocells with pyrolytic graphite sheet electrodes: harvesting body heat and solar thermal energy

This study investigates the development of self-powered sensors employing single-pillar thermocells to harness body heat and solar thermal energy. A pyrolytic graphite sheet was selected for its low water vapor permeability, and its surface was modified to be hydrophilic to minimize interfacial resistance. Two types of DC–DC converters, Asahi Kasei Microdevices AP4473 and matrix mercury, underwent evaluation for compatibility with these thermocells. The compact 1.5 cm3 (1 cm × 1 cm × 1.5 cm) device effectively powered the AP4473 converter, illuminating a light-emitting diode. A larger device (2.5 cm × 2.5 cm × 1.5 cm) efficiently drove the matrix mercury converter, enabling the operation of bluetooth low-power sensors. These self-powered sensors wirelessly provided humidity and temperature data using solar thermal energy for approximately 4 h per day during peak temperature differences in January. This study showcases the potential of thermocells for sustainable energy harvesting and suggests avenues for future research, such as exploring alternative heat sources like geothermal energy to power these sensors.

A quantitative theory for heterogeneous combustion of nonvolatile metal particles in the diffusion-limited regime

The paper presents an analytical theory quantitatively describing the heterogeneous combustion of nonvolatile (metal) particles in the diffusion-limited regime. It is assumed that the particle is suspended in an unconfined, isobaric, quiescent gaseous mixture and the chemisorption of the oxygen takes place evenly on the particle surface. The analytical solution of the particle burn time is derived from the conservation equations of the gas-phase described in a spherical coordinate system with the utilization of constant thermophysical properties, evaluated at a reference film layer. This solution inherently takes the Stefan flow into account. The approximate expression of the time-dependent particle temperature is solved from the conservation of the particle enthalpy by neglecting the higher order terms in the Taylor expansion of the product of the transient particle density and diameter squared. Coupling the solutions for the burn time and time-dependent particle temperature provides quantitative results when initial and boundary conditions are specified. The theory is employed to predict the burn time and temperature of 10–100 μm iron particles, which are then compared with measurements, as the first validation case. The theoretical burn time agrees with the experiments almost perfectly at both low and high oxygen levels. The calculated particle temperature matches the measurements fairly well at relatively low oxygen mole fractions, whereas the theory overpredict the particle peak temperature due to the neglect of evaporation and the possible transition of the combustion regime.Novelty and significance statementFor the first time, we present a comprehensive and quantitative analytical theory elucidating the heterogeneous combustion of nonvolatile (metal) particles in the diffusion-limited regime. This novel theoretical model exhibits a remarkable capacity for quantitative prediction, obviating the need for supplementary information from numerical simulations or experimental data. The derivation process of analytical solutions for burn time and time-dependent particle temperature from conservation equations is elaborated, offering transparency and insight into the model’s foundations. To demonstrate the practical utility of the theory, we apply it to analyze the combustion of iron particles, providing valuable mathematical perspectives on the underlying processes. The model’s predictions for burn time and temperature align closely with experimental results, offering a partial validation of the theory within the realm of its applicable assumptions. This pioneering work contributes a robust and versatile analytical framework, advancing our understanding of diffusion-limited combustion phenomena of nonvolatile particles.