Thermal Stress Levels Research Articles

Determination of the optimal cross-sectional size of a flat plate solar collector

The article is devoted to the determination of thermal stresses in a flat plate solar collector and the calculation of its optimal size. The solution is found when moving to an elliptical coordinate system. The obtained result is useful because by varying the geometric shape of the cross-section, it is possible to reduce the level of thermal stresses that occur, and, consequently, to increase the reliability and durability of the solar collector design.

The effect of urban greening on pedestrian’s thermal comfort and walking behaviour

The urban heat island (UHI) phenomenon is becoming increasingly severe due to unprecedented urbanization and global warming paces. The increasing heat stress threatens the environment, the health of residents, and also the city the walkability. However, greenspace can generate a cooling effect to mitigate the UHI. To gain a better understanding of how urban greening contributes to the optimization of outdoor thermal comfort and the improvement of city walkability, this study investigates the relationships between outdoor thermal environment, the thermal comfort of pedestrians, and their traveling behaviours. Thermal environment was simulated using a microclimatic computational fluid dynamic (CFD) model – ENVI-met. Travel behaviour of pedestrians was simulated through agent-based modelling (ABM). A total of 337 pedestrians were monitored and interviewed across several outdoor sites with different urban morphologies in Hong Kong, along with the simultaneous collection of site-specific climatic data. Based on the data, relationships between outdoor thermal conditions, human thermal perceptions, and walking speeds were analysed exploratively and quantitatively. It is found that the walking speed of pedestrians is notably reduced with increased thermal stress levels. The walking speed can be well predicted by a polynomial regression model (R2=0.719), artificial neural network (ANN) models (R2=0.907), and a deep neural network (DNN) model (R2=0.931). Street trees can improve outdoor thermal comfort effectively (a maximum reduction of the mean radiant temperature at 4.23 °C and a maximum reduction of the universal thermal index at 0.88 °C). Simulation results of ABM demonstrate that street trees can cause a reduction in perceived travel time (PTT) of up to 3 s per 100 m. The research findings are expected to mitigate urban warming and constitute thermally comfortable and walkable outdoor environments.

Coral Oasis on Con Dao Islands: A Potential Refuge of Healthy Corals in the Offshore Waters of Vietnam?

Coral reefs of Vietnam are highly threatened by a combination of anthropogenic impacts and natural disturbances. As a result, preservation of the remaining reefs is a major governmental concern. Con Dao Islands, located in the coastal area of southern Vietnam in the South China Sea, still possess diverse and healthy coral communities. Coral surveys conducted in 2017–2020 on six sites within the marine protected area of Con Dao National Park revealed extensive coral cover (62.8–95.5%) and diversity (168 stony coral species). Coral communities were mostly dominated by Acroporidae followed by Poritidae and Fungiidae. Temporal dynamics over a 3-year period exhibited no significant decrease in the cover of dominant coral taxa, despite the severe thermal anomaly in 2019 and subsequent moderate coral bleaching, suggesting that the local corals may be successfully acclimating to the current level of thermal stress, although further study of coral adaptation in this region is warranted. High diversity and coral cover, together with the potential of resistance and resilience to repeated thermal stress in coral communities of the Con Dao Archipelago, highlights the need for authorities to pay special attention to this area and to expand conservational efforts to preserve this unique natural site.

Determination of thermal comfort among nurses working with personal protective equipment in COVID-19 clinics.

This study aimed to determine thermal comfort among nurses working with personal protective equipment in COVID-19 clinic. In this study, a descriptive design was carried out between June and September 2020. Sample of the study consisted of 246 nurses (77.6%) who worked in the COVID-19 clinics with personal protective equipment. We used a questionnaire to determine thermal comfort of nurses; a follow-up form to determine the factors affecting thermal comfort; and the ASHRAE Thermal Sensation Scale. Four measurements and follow-ups were made three times. More than half of nurses complained of ambient temperature and ventilation, one-third complained of humidity and nearly half complained of poor air quality. The mean thermal comfort score of nurses working in COVID-19 clinics was 1.19 (SD = 0.75). The thermal comfort of the nurses was negatively affected in all measurements except before wearing personal protective equipment. The highest scores were measured leaving the patient room and before removing personal protective equipment (M = 2.65, SD = 0.58). The thermal comfort, work performance and stress levels of the nurses were negatively affected by working with personal protective equipment. This study reveals the necessity of improving the working conditions of nurses, including working hours, environment and personal protective equipment.

Identifying sensitive population associated with summer extreme heat in Beijing

Severe high-temperature leads significant risks of human health under the highly population concentration and climate change. The thermal sensitivity to high temperature is needed to be quantified associated with different population characteristics. Thermal condition was quantified by universal thermal climate index (UTCI) and thermal sensitivity was identified by thermal sensation votes (TSV), thermal comfort votes, and thermal unacceptability votes based on 667 questionnaires in Beijing, China. This study designated four indicators, i.e., neutral temperature, neutral temperature range, tolerance temperature, and tolerance temperature range to analyze the effects of individual characteristics on thermal sensitivity. A one-way ANOVA was used to identify the effects of long-term adaptation and psychological factors. Results showed that: (1) Older residents had a higher neutral temperature, narrow tolerance temperature range, and lower tolerance temperature of 1.2 °C UTCI than younger residents. (2) People with chronic disease had a narrow tolerance temperature range and lower tolerance temperature of 1.3 °C UTCI than healthy ones; (3) The proportion of people who voted strong thermal sensation (TSV≥2) rated the highest in building areas, while the proportion decreased 31.6% in spaces with dense trees; (4) Residential history and city attractiveness had significant impacts on mean thermal sensation votes and mean thermal comfort votes, excluding the effect of thermal stress level. This study provided useful implications of specific adaption for summer extreme heat according to different population characteristics.

A remote coral reef shows macroalgal succession following a mass bleaching event

Coral reefs worldwide are exposed to increased levels of thermal stress due to global warming. A coral reef at the remote island of Kapou (Lisianski) in Papahānaumokuākea experienced an unprecedented level of heat stress in 2014, which resulted in coral bleaching and subsequent mass mortality that resulted in nearly 100 % loss of live coral cover. Here, we describe successional changes in benthic communities occurring on the reef from 2014 to 2021 based on our surveys utilizing underwater photogrammetric techniques. Despite having > 85 % Montipora live coral cover before the bleaching event, the newly available substrata created by the loss of coral were quickly colonized by the green macroalga Halimeda, along with an ephemeral bloom of the green macroalga Boodlea in 2016. While Halimeda continued to increase in benthic cover, other algae (Neomeris, Asparagopsis and unidentified filamentous red and green algae) also started colonizing the reef between 2017 and 2021. Erosion of the reef substrata was evident in both in-situ and three-dimensional surveys in 2015 following the bleaching event and has continued to progress through time. The high abundance of Halimeda may indicate a slow process of coral recovery, but the overall benthic diversity increased in 2021 due to the presence of other algae and an increase in hard substrata and turf algal cover. New colonies of Montipora coral were also observed during annual surveys following the bleaching-induced mortality. Future monitoring efforts should continue to track coral and algal communities and survey herbivorous fish and reef binders that play important ecological roles in algal control, reef erosion and sediment binding. Such efforts should reveal interactions among these different ecological processes that enable reef succession following mass coral mortality.

Thermal stress during late gestation impairs postnatal growth and provides background for genotype-environment interaction in Hereford-Braford and Angus-Brangus cattle

Heat stress suffered by pregnant cows can impair fetal development and have negative consequences for the future performance of calves. Thus, our objective was to determine the effect of heat stress during late gestation on birth weight (BW) and postnatal growth traits of Hereford-Braford and Angus-Brangus cattle from Brazil. In addition, we employ a reaction norm model to investigate the genotype by environment interaction (G × E) due to thermal stress in late gestation. The average temperature and humidity index of the last 60 days of gestation (THIg) was chosen as an environmental descriptor. The BW of animals was considerably lower for extreme low and high values of THIg. In contrast, the average daily gain from birth to weaning (ADG) and muscling score at weaning (MUS) were gradually reduced by increasing THIg values by -0.0014 kg /day/THIg -0.0119 units/THIg, respectively. The variation observed for the estimates of variances, direct and maternal heritability for BW, ADG, and MUS suggest that there is substantial heterogeneity of genetic variances along the environmental gradient. Thus, differences in response to selection are expected depending on the level of thermal stress where selection candidates are evaluated. Genetic correlation estimates for direct and maternal effects between distant THIg values differed from unity or were negative for all traits. This was another strong indication that few of the same genes are responsible for the same trait in contrasting thermal environments during late pregnancy. In this sense, the thermal environment during late gestation provides background for G × E and should be appropriately considered in genetic evaluations of Hereford-Braford and Angus-Brangus cattle reared on pasture in (sub)tropical regions.

Effects of Creating Street Greenery in Urban Pedestrian Roads on Microclimates and Particulate Matter Concentrations

Urbanization can increase artificial coverage rates and emissions by causing increases in traffic, which represents a serious health risk to pedestrians. To create pedestrian-friendly environments in urban canyons, this study examined their microclimates and air quality; methods to improve the pedestrian environment were also explored, based on the current street green space practices in Seoul, Korea. Under these current standards, the physiologically equivalent temperature (PET) of the pedestrian roads was predicted to decrease by 1.29–1.44 °C, but this was insufficient to adjust the thermal stress level. The air temperature of the pedestrian road declined slightly; fine dust concentrations increased, and ozone concentrations decreased. The effects of increasing the planting occupancy on the pedestrian environment were then simulated, which resulted in decreases in PET of 3.04–3.49 °C, depending on the floor area ratio, thereby effectively lowering the thermal stress stage. The particulate matter concentrations increased, however, and the air quality deteriorated. Therefore, street greenery planning alone cannot sufficiently improve both the microclimate and air quality of urban pedestrian roads. Thus, it is necessary to plan street greenery spaces in parallel with measures to improve air quality.

The application of the physiologically equivalent temperature to determine impacts of locally defined extreme heat events within vulnerable dwellings during the 2020 summer in Ankara

• PET proved more effective to quantify indoor/outdoor heat stress relationship. • New extreme heat event thresholds proved critical to identify thermal stress exposure. • Forced convective cooling alone improved indoor thermal stress levels. • Cause-and-effect patterns between indoor/outdoor heat stress identified via PET. This study addresses the limited work related to Heat Stress (HS) vulnerability within indoor/outdoor contexts and its relationship with local Extreme Heat Events (EHEs). Centred upon Ankara, the study focuses on building upon its weaker approach to human thermophysiological vulnerabilities in an era of climate change, and unregulated urban densification. Through newly defined local EHEs, the physiologically equivalent temperature (PET) (and its cumulative derivatives), were utilised to develop the limited approaches that utilise Energy Based Models in the scope of EHE risk management. The study was undertaken by processing hourly data from 2008 to 2020 from Ankara's Meteorological Station, and Esenboga Meteorological Station. At a finer 10 min resolution, an interior Kestrel Heat-stress Station was used to assess summer thermal conditions in 2020 within a thermally vulnerable, yet still very frequent, residential Turkish construction typology. Among other outcomes, the results indicated the permanency of indoor PET that remained above 27 °C during non EHE periods. In the case of a Very Hot Day (VHD 33 ), PET remained between 29 and 32.9 °C for almost 24 h. The thermal index also indicated how forced convective cooling led to indoor reductions of PET by 3–4 K, and in duration of such HS levels to less than 2 h.

Marine protected areas do not buffer corals from bleaching under global warming

BackgroundThe rising temperature of the oceans has been identified as the primary driver of mass coral reef declines via coral bleaching (expulsion of photosynthetic endosymbionts). Marine protected areas (MPAs) have been implemented throughout the oceans with the aim of mitigating the impact of local stressors, enhancing fish biomass, and sustaining biodiversity overall. In coral reef regions specifically, protection from local stressors and the enhanced ecosystem function contributed by MPAs are expected to increase coral resistance to global-scale stressors such as marine heatwaves. However, MPAs still suffer from limitations in design, or fail to be adequately enforced, potentially reducing their intended efficacy. Here, we address the hypothesis that the local-scale benefits resulting from MPAs moderate coral bleaching under global warming related stress.ResultsBayesian analyses reveal that bleaching is expected to occur in both larger and older MPAs when corals are under thermal stress from marine heatwaves (quantified as Degree Heating Weeks, DHW), but this is partially moderated in comparison to the effects of DHW alone. Further analyses failed to identify differences in bleaching prevalence in MPAs relative to non-MPAs for coral reefs experiencing different levels of thermal stress. Finally, no difference in temperatures where bleaching occurs between MPA and non-MPA sites was found.ConclusionsOur findings suggest that bleaching is likely to occur under global warming regardless of protected status. Thus, while protected areas have key roles for maintaining ecosystem function and local livelihoods, combatting the source of global warming remains the best way to prevent the decline of coral reefs via coral bleaching.

An Electro-Thermal Model for LFP Cells: Calibration Procedure and Validation

Lithium batteries for energy storage systems are a prominent solution for both stationary and mobile applications. Electro-thermal modelling of the cell is a useful tool for monitoring voltage and temperature in order to predict battery behaviour especially in cases of critical operative conditions. This paper provides a modelling approach focusing on the calibration of parameters of an electro-thermal model for large prismatic LFP lithium cells. The designed model is tuned by means of experimental tests that identify a set of parameters that are function of a cell’s state-of-charge and temperature. The model outputs are voltage, cell surface, and internal temperature profiles, which are validated against experimental data referring to realistic working conditions, even providing an intense level of thermal stress. The model accuracy is marked by a voltage mean average error lower than 1% and a mean cell surface temperature deviation lower than 1 K.

Expression profiling of rosmarinic acid biosynthetic genes and some physiological responses from Mentha piperita L. under salinity and heat stress.

Peppermint is of great economic importance, mainly due to its valuable essential oils. The present study aimed to compare the expression level of genes coding for proteins involved in the rosmarinic acid biosynthesis pathway and some physiological responses in peppermint under three levels of salinity (0, 60 and 120mM) and two levels of thermal stresses (at 25°C, optimal plant heat, and 35°C, for thermal stress). The results showed that salinity at 25°C resulted in an increased relative level of phenolic compounds, proline and antioxidant activity by 1.88, 1.92 and 2.58 times after 72h respectively at salinity of 120mM. Rosmarinic acid as well as soluble sugar, chlorophyll and K+/N+ ratio showed a decreasing trend by 3.2, 1.8, 4.6 and 9 times after 72h respectively at salinity of 120mM at 35°C. Gene expression analysis showed a significant increase in HPPR and C4H expression and a significant decrease in RAS expression in plants subjected to simultaneous stresses. The higher levels of C4H and HPPR expression indicate the roles of these genes in defense processes and the effects of phenolic compounds in inhibiting oxidative stress. Our results may help increase knowledge about the stress-dependent alterations in gene expression profiles and physiological patterns in plants. This information may be used for medicinal plant improvement programs aimed at increasing rosmarinic acid production.

Mechanisms of crack healing in dense Yb-Si-O environmental barrier coatings by plasma spray-physical vapor deposition

Due to high thermal stress level and low strain tolerance, through-thickness cracks are generally observed in plasma-sprayed environmental barrier coatings (EBCs) with dense microstructures, providing shortcuts to water vapor volatilization and molten salt penetration during service in combustion environments of gas turbines. In this study, crack-free and dense Yb-Si-O EBCs were successfully prepared by plasma spray-physical vapor deposition (PS-PVD) and annealing treatment. Closure and healing of through-thickness crack were observed via scanning electron microscopy, while phase transformation and sintering behavior were characterized by X-ray diffraction and nanoindentation. Furthermore, crack healing mechanisms of dense PS-PVD EBCs were elucidated utilizing a microstructure-based finite element model with physically-based constitutive relation. This work provides a foundation for the development of high-performance EBCs and thermal/environmental barrier coating (T/EBC) systems.

Chronic Pain in Spanish Wildland Firefighters.

The work performed by wildland firefighters (WFFs) is very demanding owing to the conditions in which they have to operate. It has been reported that these professionals walk long distances over unstable and steep terrain carrying heavy loads, handle tools manually and repeatedly and are subject to a high level of thermal stress. Under such conditions, the risk of developing chronic pain (CP) is high, although despite this, there are no available data pertaining to CP among WFFs, to the best of our knowledge. As such, the aim of this study is to describe CP in Spanish helitack crews, for which purpose 221 WFFs (203 men and 18 women) completed an online self-report questionnaire. Approximately 60% of WFFs reported suffering from CP, of which 45.5% had CP in more than one body region at the same time. Age and length of service were associated with the probability of suffering from CP. Likewise, the age and height of WFFs and weight of the protective equipment used increased the prevalence of CP. Lastly, gender and job position affected CP location, with women and forepersons reporting greater prevalence of CP in the lower limbs. To conclude, the results obtained suggest the major prevalence of CP among Spanish WFFs, with current data suggesting in turn the importance that age, stature, gender, length of service, weight of protective equipment and job position have on the prevalence and location of CP.

Nature of metal drop displacement during deposit welding elements of railway transport

The transformation of the microstructure of the heat-strengthened steel 65G section deposited with an electrode with a low-carbon rod is complex. Increased hardness values of individual areas contribute to an increase in the abrasive wear resistance of the part. The presence of a fusion zone ensures the resistance of the deposited area of an element on railway transport to cracking. The use of electrodes with a low-carbon rod is advisable when carrying out surfacing reinforcement of heat-hardened steels. The authors obtained mathematical expressions for the speed of displacement of a metal drop falling from the electrode material and the path it traverses when deposit welding elements on railway transport. They show that the displacement of this drop is accompanied by acceleration followed by deceleration. In electromagnetic deposit welding, the experimental assessment of the level of circumferential and radial residual thermal stresses during deposit welding of a coating on a hollow cylinder is of considerable practical interest. As an example, the calculation and experimental analysis of the stress state during deposit welding of the cylinder on the inner surface is made. He showed that residual compressive stresses, significant in magnitude, are formed on the outer surface. The method, which is limited to cutting the cylinder along the generatrix, without subsequent layer-by-layer removal of metal from its inner surface, is a simple and effective method for determining the circumferential residual stresses that provides the required accuracy.

Elastic-Plastic stress analysis in the pole fixation of an electric generator

Hydroelectric power plants are currently the most efficient large scale electric energy producers. Therefore, there are many opportunities for construction of new hydroelectric power plants throughout the world, which makes the study and design of improved electric power generators a priority. The core equipment of an electric power plant is the electric power generator, which can deliver hundreds of MW of electric power, while withstanding high levels of mechanical and thermal stresses under high rotation speeds. Therefore, the design of the electric generator, especially the rotor component, must ensure structural integrity, safety of operation, and an extended lifetime of 30–40 years. To achieve the safe and reliable operation of the generator, one of its components that must be designed after a detailed and comprehensive stress analysis is the rotor pole fixation. When the hydroelectric generator operates under high stress conditions, due to frequent start-stop cycles, structural elements such as the rotor poles fixations could operate beyond their endurance limit and could be exposed to the risk of failure. This paper presents an elastic–plastic finite element analysis of the mechanical response of the pole fixation, part of an assembly with three hammerheads of a hydroelectric generator rotor, under various loading conditions. The elastic–plastic stress analysis leads to a safe design at much higher operational loads compared to a linear elastic analysis and may be further used to study the effect of crack appearance in the plastic zone, preventing a catastrophic failure of the generator.

Faults in Modular Multilevel Cascade Converters–Part II: Fault Tolerance, Fault Detection and Diagnosis, and System Reconfiguration

Modular Multilevel Cascade Converters (MMCCs) are considered a promising power electronics topology in industry. Their scalability allows to reach (ultra/very) high voltage levels with low harmonic content and high efficiency and makes MMCCs an ideal solution for high-power applications; such as electrical drives, solid-state transformers and high-voltage direct-current (HVDC) transmission systems. However, the high levels of thermal, electrical and mechanical stress on the power electronics devices and the large number of components (e.g. capacitors or semiconductors) make MMCCs prone to faults. Fault detection and diagnosis (FDD) in combination with fault isolation and system reconfiguration techniques, based on cell redundancy, can increase the reliability, availability and safety of MMCCs, which is crucial for their utilization in critical energy applications. This second part of the paper comprehensively surveys: (i) fault tolerance and fault detection & diagnosis (FDD; e.g. expert system, model- or hardware and data-based FDD methods) and (ii) system reconfiguration strategies (e.g. cold- or hot-redundant) for MMCCs. Finally, the state-of-the-art, challenges and future research trends and opportunities towards reliable MMCC-based systems are revealed.

Faults in Modular Multilevel Cascade Converters—Part I: Reliability, Failure Mechanisms, and Fault Impact Analysis

Modular Multilevel Cascade Converters (MMCCs) are considered a promising power electronics topology in industry. Their scalability allows to reach (ultra/very) high voltage levels with low harmonic content and high efficiency and makes MMCCs an ideal solution for high-power applications; such as electrical drives, solid-state transformers and high-voltage direct-current (HVDC) transmission systems. However, the high levels of thermal, electrical and mechanical stress on the power electronics devices and the large number of components (e.g. capacitors or semiconductors) make MMCCs prone to faults reducing its reliability. In this first part of the paper, a comprehensive overview of reliability on MMCCs, failure mechanisms and fault impact analysis in MMCCs, including failure rates and fault modes is presented. Also a set of tables which collect all information to easily detect and identify faults in MMCCs is presented.

Assessment of possibility of thermal fracture in layered ceramic composite

The internal stresses in a disk-shaped ceramic composite sample consisting of five ZrB2 – 20% SiC layers with various additives of ZrO2 after cooling down from the sintering temperature are analyzed. The problem is solved numerically using the finite element method. Three versions of the simulation were performed. In the first two simulations, it was supposed that all the properties of the composite constituents are temperature independent and correspond to the temperature of sintering and room temperature, respectively. In the third simulation, we take into account the dependence of the physical and mechanical characteristics of the composite components on the temperature. Comparing the results reveals a profound effect of the temperature dependence of the properties. The residual thermal stresses determined on different sides of the layer interfaces vary in hundreds of MPa. The tensile residual thermal stress level is shown to be high enough for possible cracking of the ceramic layered composite after cooling.

Effect of the heat treatment mode of high chrome iron rolling mills on chrome redistribution in the stress field

Heat treatment is an important stage in the technology of rolling rolls, due to the fact that the thermal stresses that occur during rapid or uneven heating summing up with the rather high residual stresses after casting, create a risk of cracking. Goal. The aim is improving the quality of rolling rolls by varying the modes of heat treatment. Therefore, it is important to assess the level of thermal stress. Method. Evaluation of thermal stresses arising in heating and cooling in the heat treatment process that summing up to the relatively high residual stresses after casting, creates the risk of fractures. The profile of the distribution of chromium in the cross section of the working layer at each time under the action of the stress gradient that occurs during heat treatment of the roll is obtained by calculation. Results To ensure a minimum temperature difference between the surface and the core, it is necessary to reduce the heating and cooling rate, as well as increase the duration of exposure at a given temperature. Reducing the cooling rate from 17 to 3.7°C/h decreases the temperature difference at the surface and in the center of the roll and the intensity of thermal stresses from 29 to 7 MPa. It is established that the rate of heating and cooling should not exceed 10– 15° C/h, and exposure to annealing should be at least 5–7 hours. Scientific novelty. The modes of heat treatment of rolling rolls with a high-chromium cast iron working layer are designed by estimating the level of thermal stresses. The profile of distribution of chromium after various modes of heat treatment is calculated analytically and its mode at which the most uniform distribution of chromium on section of a working layer remains is offered. Practical significance. The developed technique allows to calculate analytically the profile of distribution of chromium after various modes of heat treatment and to choose such a mode at which the most uniform distribution of chromium remains on the section of a working layer.