Burnout Time Research Articles

Evaluating feasibility of field modeling of fire to calculate fire characteristics in buildings and premises

Introduction. The present paper describes application of a software package using a field model of fire dynamics to calculate fire characteristics in buildings and premises of nuclear power plants (NPP). The authors give necessary justifications for using the software package in performing fire calculations in multifunctional buildings and premises.Aim. To analyze different fire modeling methods, their application and use of the software package for field modeling of fire dynamics to determine the dynamics of fire hazards in complex premises, in facilities with non-uniform fire loads or complex gas exchange processes; to contribute solving the issue of safe distances ensuring that fire cannot spread between equipment elements.Materials and methods. The authors developed and verified a software package to perform calculations using the field model of fire dynamics. The paper presents the basics of the field method for fire modeling in multifunctional premises and the aspects of its application in fire simulation. The presented analytics is substantiated with examples of fire simulation results in real premises of NPPs.Results. Following the analysis of different methods of modeling the dynamics of development and spread of fire hazards, the present paper introduces the possibility of using various methods of fire modeling in the evaluation of fire hazards for buildings and premises. The authors describe the advantages of field modeling method for calculating local parameters of fire. The paper provides information on the software codes to calculate the dynamics of fire and evaluate the thermal effects of fire on building structures.Conclusion. It has been found possible to apply field model of fire dynamics for calculating fire hazards in various buildings, premises and open areas. Calculations using the presented field model enable the sufficiency of fire resistance of building structures and multifunctional premises to be substantiated due to preventing fire spread outside the fire zone during the estimated time of burnout of the total fire load.

Research on Oxy-Fuel Combustion Characteristics of Two Typical Chinese Coals

Oxy–fuel (O2/CO2) combustion technology shows great potential for carbon reduction. However, difference in the combustion atmosphere would affect coal combustion characteristics and pollutant emissions. In order to explore oxy–fuel combustion characteristics, two typical Chinese coals, sub–bituminous and lean coal, were utilized. Based on thermogravimetry and pilot–scale test, the ignition and burnout characteristics under oxy–fuel and air combustion atmosphere were investigated. Besides, the NOx emission characteristics were also investigated on the pilot–scale test. Through experimental results, these two kinds of coal showed different combustion characteristics, mainly due to differences in coal quality. Compared with air combustion, oxy–fuel combustion affected the coal combustion process. Firstly, the ignition temperature of sub–bituminous and lean coal decreased from 418 and 477 °C to 405 and 415 °C, respectively; the burnout temperature also decreased from 855 and 985 °C to 808 and 838 °C, respectively. Then, coal combustion performance was evaluated by comprehensive combustion characteristics (S); with an increase in S from, respectively, 3.659 and 2.013 to 4.826 and 3.545 × 10−8(min−2 × K−3), the combustion performance significantly improved. Then, the char burnout time was advanced for 1~3 min. Similar results were obtained on the pilot–scale test. The ignition temperatures decreased from 505 and 552 to 490 and 512 °C, respectively. Moreover, the char burnout rate increased by 0.5~5% and 2~11%, respectively. Lastly, the NOx concentration in flue gas was 2.2~2.6 and 2.0~2.3 times higher for the two kinds of coal under oxy–fuel combustion.

Combustion of 10–100 μm aluminum droplets in detonation products gases

AbstractWe describe a two‐phase model of combustion effects in aluminized high explosive (HE) charges. It is based on: (i) a Gas Dynamic Model of the expansion of the detonation product gases and their turbulent combustion with air; and (ii) a Heterogeneous Continuum Model of aluminum (Al) droplets and their combustion with the detonation product gases. Initial conditions are based on an analytical similarity solution for a cylindrical Chapman‐Jouguet (CJ) detonation propagating at the CJ detonation velocity. The CJ jump conditions are computed at the thermodynamic equilibrium state by the Cheetah code, assuming the Al droplets are inert. We assume that the Al is 10 % of the charge mass and occurs as droplets at the CJ state. Different initial droplet diameters, ranging from 10 to 100 microns, are studied. A hydrodynamic combustion model based on large Damköhler numbers is employed in this study, . It has a square‐root dependence on the Reynolds number (Re) and inversed‐squared dependence on the droplet diameter ( ). The burnout time ( ) of the Al droplets has a three‐halves dependence on the droplet diameter, . After burnout, the detonation products act as detonation products of the HE charge with active Al. They turbulently mix with air and form a combustion layer on the outer edge of the fireball. Details of the two‐phase model, initial conditions and evolution of the flow field will be described.

Creating an infrastructure to address physician and advanced practice provider burnout at a complex community cancer care delivery system.

11015 Background: Oncology clinicians are at risk for developing burnout due to work-related factors such as high acuity patients, long work hours, limited autonomy, administrative and documentation demands (Copur, 2019; Eelen et al, 2014). The COVID-19 Pandemic has intensified burnout due to rapid and multiple changes in clinical practice, lack of fulfillment, and heightened moral distress and personal challenges (Hlubocky et al 2021). As a multi-center community cancer care system, an infrastructure was created and operationalized to address the work-related factors contributing to burnout. The purpose of the project was improved identification and prioritization of clinician (physician and APP) needs with subsequent targeted intervention. Methods: To measure success, a partnership with the American Medical Association (AMA) was formed to deploy the Mini-Z burnout survey. The survey was administered on July 2-August 20, 2021 to all Medical Oncology physicians and Advanced Practice Providers (APPs), n = 60. The survey was re-deployed from July 13-September 2nd, 2022. Data was collated by the AMA and presented back to executive leadership. Through this survey and follow up focus groups, it was identified that physicians tended to struggle more with the EHR and inability to disconnect from work compared to APPs. Our APPs identified several areas of opportunity including onboarding/orientation, mentorship/professional development, pay and scope of practice. An EHR Well-being Committee was established to evaluate EPIC signal reports to address both system and individual clinician needs. To address APP needs, key factors were addressed in the realm of professional development/orientation, compensation and scope of practice. This was approached with the goal of short-term gains and long-term sustainability. Results: The results indicated a 23.8% improvement in job satisfaction, 4.9% improvement in job stress, and 26.3% improvement in employment outlook. A decrease was also noted in EHR Time outside of work (4.5%) and burnout (16.1%). All areas of improvement met or exceeded national benchmarks. Analysis of these results indicate statistical significance for job satisfaction (p = 0.028, CI 2.8-40.4%) and employment outlook (p = 0.033, CI2.4-45.8%). Results that indicated improvement but were not statistically significant were job stress (p = 0.688, CI 17.6-27.4%), burnout (p = 0.191, CI 7.4-37.5%) and EHR time outside of work (p = 0.806). Conclusions: While the survey data does not account for clinician turnover between 2021 and 2022, initial review indicates a positive impact on job satisfaction and employment outlook which may be an early indication of improved colleague appreciation. Further study, post-pandemic is needed to evaluate effectiveness of care team efficiency and ongoing work to streamline EHR usage.

Effect of red mud additive on the combustion performance of lignite and sulfur fixation behaviors

ABSTRACT To reveal the role of red mud (RM) as the catalyst during the combustion behavior of lignite, two kinds of RM from Bayer red mud (SR) and sintering red mud (GR) were chosen to investigate the catalytic combustion behaviors of lignite under different oxygen contents, the action mechanism and the sulfur fixation performance by the thermogravimetric analysis (TGA) and fixed-bed reactor. Flynn–Wall–Ozawa (FWO) method was used to study the combustion kinetics. The results showed that RM can promote the release of pyrolysis volatiles and significantly improve the ignition performance of coal. Moreover, the improvement effect of RM becomes more noticeable with the increase of O2 content. RM decreased the ignition and burnout temperatures of the char combustion. The types of RM exert different catalytic properties owing to different compositions. Under oxygen-rich conditions, the apparent activation energy in the early stage of coal combustion can be significantly reduced by RM. In addition, RM enhances the peak temperature during constant combustion of coal, improves combustion rate, shortens the burnout time, and remarkably reduces SO2 emission in exhausted gas. About 83.7% SO2 in combustion gas produced at 700°C was reduced at the SR addition of 25 wt%, indicating RM is a potential and cheap catalyst for high-effective coal combustion.

Effects of biomass particles size and shape on combustion process in the swirl-stabilized burner reactor: CFD and machine learning approach

When planning the development of the energy sector, significant attention is given to the energy from the renewable sources, amongst which the biomass has an important role. Computational fluid mechanics and machine learning models are the powerful and efficient tools which allow the analysis of various heat and mass transfer phenomena in energy facilities. In this study, the in-house developed CFD code and machine learning models (Random Forest, Gradient Boosting and Artificial Neural Network) for predicting the biomass trajectories, particle mass burnout and residence time in a swirl burner reactor are presented. Pulverized biomass combustion cases (fine straw, pinewood and switch grass) with various mean diameters (ranging between 60 and 650 μm) and different shape factors (within the range 0–1) are considered. The results of numerical simulations revealed a noticeably nonlinear dependence between the input values (particle types, sizes and shapes) and the output values (particle trajectories, mass burnout and residence time), mostly due to the complex swirling flow in the reactor. For particles with the mean diameters within the ranges considered, the mass burnout of particles generally decreases as the biomass particle shape factor increases. The residence time of pulverized biomass in the reactor shows in most cases a decreasing trend as the particle shape factor increases. Artificial Neural Network showed the best predictions for both particle mass burnout (RMSE = 0.083 and R2 = 0.937) and particle residence time (RMSE = 1.145 s and R2 = 0.900), providing the reliable assessment of these important indicators in the combustion process.

Global prevalence of nursing burnout syndrome and temporal trends for the last 10 years: A meta-analysis of 94 studies covering over 30 countries.

To determine the global prevalence of nursing burnout syndrome and time trends for the last 10 years. The prevalence of burnout syndrome varied greatly in different regions in the last 10 years, so the average prevalence and time trends of nursing burnout syndrome for the last 10 years were not completely clear. A meta-analysis conducted in the PRISMA guidelines. CINAHL, Web of Science, and PubMed were searched for trials on the prevalence of nursing burnout syndrome from 2012 to 2022 systematically. Hoy's quality assessment tool was used to evaluate the risk of bias. The global prevalence of nursing burnout syndrome was estimated, and subgroup analysis was used to explore what caused heterogeneity. Time trends for the last 10 years were evaluated by meta-regression using Stata 11.0. Ninety-four studies reporting the prevalence of nursing burnout were included. The global prevalence of nursing burnout was 30.0% [95% CI: 26.0%-34.0%]. Subgroup analysis indicated that the specialty (p < .001) and the region (p < .001) and the year (p < .001) were sources of the high heterogeneity. Meta-regression indicated that it tended to increase gradually for the last 10 years (t = 3.71, p = .006). The trends increased in Europe (t = 4.23, p = .006), Africa (t = 3.75, p = .006) and obstetrics (t = 3.66, p = .015). However, no statistical significance was found in ICU (t = -.14, p = .893), oncology (t = -0.44, p = .691) and emergency department (t = -0.30, p = .783). A significant number of nurses were found to have moderate-high levels of burnout syndrome for the last 10 years. The meta-analysis also indicated an increased trend over time. Therefore, more attention to the prevalence of nursing burnout syndrome is urgently required. High prevalence of nursing burnout may attract more attention from the public. This analysis may serve as an impetus for relevant policy to change nurses' working conditions and reduce the occurrence of burnout.

“Why Am I Even Here If I Can’t Save the Patients?”: The Frontline Healthcare Workers’ Experience of Burnout during COVID-19 Pandemic in Mthatha, South Africa

Globally, the high prevalence of burnout in healthcare workers (HCWs) is of the utmost concern. Burnout is a state of emotional exhaustion, depersonalization and a decreased sense of personal accomplishment. While the 2019 Coronavirus (COVID-19) exacerbated the burnout prevalence among HCWs, limited studies have explored this phenomenon using qualitative methodologies in the Eastern Cape Province and South Africa generally. This study explored how frontline healthcare workers experienced burnout during the COVID-19 pandemic in Mthatha Regional Hospital. Ten face-to-face in-depth interviews were conducted with non-specialized medical doctors and nurses who directly cared for COVID-19-infected patients during the pandemic in Mthatha Regional Hospital (MRH). In-depth interviews were digitally recorded and transcribed verbatim. Data were managed through NVIVO 12 software before being thematically analyzed using Colaizzi's analysis method. Four main themes emerged from the analysis. These themes were burnout manifestation (emotional strain, detachment and irritability, uncertainty-induced fear, and anxiety, physical exhaustion, yet, low job accomplishment, dread and professional responsibility), precursors of burnout (occupational exposure to high mortality, staff shortages, elongated high patient volume and workload, disease uncertainties and consistent feeling of grief), alleviating factors of burnout (time off work, psychologist intervention, periods of low infection rate and additional staff), and the last theme was every cloud has a silver lining (improved infection prevention and control (IPC) measures, learning to be more empathetic, the passion remains and confidence grows). The COVID-19 pandemic brought about a rapid change in the work environment of healthcare workers who are the backbone of efficient healthcare services, thereby rendering them vulnerable to increased burnout risks. This study provides strategic information for policymakers and managers on developing and strengthening welfare policies to promote and protect frontline health workers' well-being and work functioning.

Effect of turbulent mixing on combustion behaviours of a single biomass pellet

Biomass co-firing in coal-fired power plants is an appealing technology for reducing greenhouse gas emissions due to the abundant biomass resource and low cost of retrofitting the existing power plants. Burning larger biomass particles is inevitable in real boilers due to the energy-consuming grinding process. A profound understanding of the combustion characteristics of larger biomass particles in a strong turbulent gas environment inside the boiler is essential for designing and operating biomass conversion facilities. This paper presents a detailed experimental study of the effects of turbulent mixing on the combustion of biomass particles. An impinging arranged four-fan stirred turbulent furnace was established in the laboratory. Particle image velocimetry (PIV) was adopted to measure the turbulent flow field characteristics under various fan speeds. The combustion behaviours of a 5 mm homemade cylindrical cellulose pellet were investigated under natural convection and turbulent flow at 700 °C. The centre and surface temperature of the particle, the shape and peak temperature of the volatile flame, and the sequential combustion history were measured and analysed. The results show that the turbulent fluctuation velocity Velrms increases linearly with increasing fan speed. Whether the gas environment is natural convection or turbulence has an essential impact on the combustion behaviours of the biomass particle. Increasing turbulence intensity accelerates the heating rate and significantly shortens the burnout time from 94 s to 55 s. The volatile flame area fluctuates randomly and generally decreases with the turbulent intensity due to the dilution of gas-phase volatiles by the turbulent eddies motion. Volatile flame has higher local luminosity and peak combustion temperature at a low turbulent fluctuation velocity of 0 ∼ 0.8 m/s but gradually weakens due to heat dissipation at a higher turbulent fluctuation velocity of 0.8 ∼ 1.6 m/s. The present results are the first to study the combustion behaviours of a single biomass pellet in different turbulent intensities, indicating that the effect of enhanced heat and mass transfer in turbulent environments on biomass combustion is essential and deserves further study.

The study of co-combustion characteristics of coal and duckweed by single particle and TGA methods

Co-combustion of coal and biomass is a feasible technology to reduce CO2 emissions and coal consumption. In this paper, the co-combustion characteristics of coal and three kinds of duckweed (Lemna minor, Wolffia, Spirodela) were studied by a single particle combustion method and thermogravimetric analysis (TGA) method in air. The effects of blending ratio of the duckweed and fuel properties on the ignition delay time, burnout time and flame temperature were studied. The ignition delay time, burnout time and flame temperature all decrease as the blending ratio of duckweed increases. The different volatile content and composition of duckweed will affect the temperature distribution and combustion rate in the combustion stage. Compared with the ash of coal, the ash of duckweed can promote the combustion of coal. During the combustion of blended fuels with volatile removed, different contents of ash have different effects on char combustion, such as combustion temperature range, combustion rate, and temperature at peak combustion rate.

Combustion and mass loss behavior and characteristics of a single biomass pellet positioning at different orientations in a fixed bed reactor

This study aims to investigate the combustion characteristics and mass loss behaviors of rice straw and wheat straw biomass pellets experimentally in a laboratory fixed bed combustor under various operating conditions. High-speed photography was used to record images of the combustion process, and a sensitive balance was utilized for recording the particle mass history during the combustion process in addition to K-type thermocouples for temperature measurements. For both materials, the single pellet was exposed to various air temperatures and different flow rates of air. The orientation of the biomass pellet was positioned at various angles from 0 (horizontal), 30°, 45°, 60° (inclined), and 90° (parallel) to the hot air stream at different flow rates. Both glowing reactions and flameless ignition have been noticed in all experiments at all pellet orientations. All pellets experienced low and high luminosity volatiles without flames, followed by a bright radish color and short-lived combustion of the chars. Although the volatile contents of the two materials are identical, the volatile combustion duration of wheat straw (17–258 s) is less than that of rice straw (20–300 s), which could be due to differences in particle sizes, shapes, and structural compositions. The results also show that increased air temperatures lessen the time it takes for volatile and char to ignite and burn off. It also raises the temperature of surface ignition. Starting from the horizontal position and increasing the orientation angle of the pellet, the volatile and char ignition times increase up to 30° and then drop up to 90°, with angle 45° giving the lowest value. The same pattern was also noticed for volatile and char burnout times. The pellet horizontal position (0°) exhibits reduced combustion and mass loss (%) time intervals. The order of increasing the maximum temperature at the pellet surface was 30° > 60° > 90° angles. Increasing the air temperature reduces the times of char combustion, devolatilization, volatile burnout, and char burnout. As the air flow rate increases, the effect on the combustion parameters alternates between increasing and decreasing values.

Combustion behaviors of pulverized coal MILD-oxy combustion under different steam injection parameters

MILD-oxy combustion under the wet flue gas recirculation mode is of potential in achieving a synergetic control of C/N emissions, whereas its practical realization is restricted by how to efficiently form an in-furnace H2O-rich atmosphere under MILD regime. Towards this issue, this work numerically evaluates the feasibility of applying the direct steam injection method by arranging the individual steam nozzles with different diameters (Dste) on both sides of the primary stream nozzle (i.e., the inner- and outer-steam injections). The effects of incident position and velocity on combustion behaviors are studied. Results show that compared with the advanced confluence of primary and secondary streams in the inner injection cases, outer-steam injection delays the confluence of inlet jets to enhance the in-furnace dilution level. Inner-steam injection is better in inhibiting temperature rise and fluctuation, which facilitates a more uniform distribution of temperature. MILD combustion with diffusion/kinetics-controlled regime is better maintained in the inner injection cases under a small Damkӧhler number. The share of gasification reaction on char consumption in the inner injection cases is higher than that in the outer injection cases, and the burnout time of char is also increased. The increased Dste further enhances the contribution of gasification reaction and prolongs char burnout. Inner-steam injection inhibits the oxidation of fuel-N and enhances NO-reburning in a large low-O2 region as Dste increases, which leads to the lower NO emission concentration. Meanwhile, interaction between NO and fuel-N intermediates is found to play an inevitable role in reducing the overall NO emission.

School Burnout and Depression Symptoms of Polish High School Graduates in the Context of COVID-19 Pandemic

High school graduates usually suffer from stress one month before the final exams. The research’s aim was to compare the depression and burnout symptoms measured in April 2019 (before the pandemic) and in April 2020 (during the pandemic) in the Polish high school students. The results showed that the COVID-19 pandemic affected adolescent girls more than boys, leading to higher rates of depression, student burnout, and imbalanced time perspective. Females perceived lower family acceptance than boys. Males were less depressed and more burned out during the pandemic than before, while girls not only were more burned out but were also more depressed, were imbalanced in their time perspective, and perceived lower family acceptance during the COVID-19 pandemic than before the outbreak.

Three-dimensional full-loop numerical simulation of coal and sludge co-combustion in a circulating fluidized bed

The Dense Discrete Phase Model (DDPM) method is used to simulate the co-combustion process of coal and sludge over the full-loop circulating fluidized bed in a three-dimensional (3D) Eulerian-Lagrangian framework. Both heterogeneous (fuel conversion through pyrolysis and char combustion) and homogeneous reactions (e.g. volatile combustion) are considered. Comparison of the predicted pressure profile, flue gas composition and bed temperature with measurements show good agreement and validate the DDPM methodology for accurate description of the gas–solid flow and combustion process over the full-loop circulating fluidized bed. The results of coal and sludge co-combustion are analysed qualitatively and quantitatively in terms of flow characteristics, gas composition, reaction rate profile, and particle combustion characteristics. Due to the lower density and higher volatile content of the sludge, as the coal-to-sludge feeding ratio decreases, the combustion reaction rate is gradually skewed upwards in the furnace, shifting up also the corresponding gas concentration profiles. For the given fuel sizes, the faster devolatilization rate of coal yields a shorter burnout time than that of the sludge particles. Our work provides an intuitive perspective to the fluidized bed community to boost comprehension on the coal and sludge co-combustion in a full-loop circulating fluidized bed.

The effect of duct size, sample size, and fuel composition on concurrent flame spread over large cellulose samples in microgravity

Concurrent flame spread data for thermally-thin charring solid fuels are presented from Saffire and BASS experiments performed in habitable spacecraft for three duct sizes, five sample sizes, two materials, and two atmospheres. The flame spread rates and flame lengths were strongly affected by duct size even for the relatively large ducts (> 30 cm tall). A transient excess pyrolysis length (i.e., flame length overshoot) was observed for the cotton fabric that burned away, which indicates that the transient excess pyrolysis length phenomenon is caused by more than just the flame moving into the developing boundary layer thickness as was the case with the SIBAL sample. A burnout time, defined as the pyrolysis length divided by the flame spread rate, normalized the pyrolysis length histories into a single curve with a steady burnout time of 22 s for the SIBAL fabric. The transient excess pyrolysis length is hypothesized to be a post-ignition flame growth transient for the essentially two-dimensional flames where the burnout time becomes very long until the preheat and pyrolysis lengths develop. The three-dimensional flames over narrow samples have lateral thermal expansion and lateral oxygen diffusion which allows them to transition to a steady state length without the transient excess pyrolysis length. Surface temperature profiles, nondimensionalized by the pyrolysis length, indicate that the temperature profiles exhibit the same shape across the pyrolysis zone. A surface energy balance calculation in the preheat region revealed that the heat flux increased rapidly at the pyrolysis front to near the critical heat flux for ignition. An estimate of the acceleration of the inviscid core flow in the duct due to thermal expansion and developing boundary layers on the duct walls and the SIBAL sample surface seems to explain the observed spread rate trends across three duct sizes and multiple sample sizes.

The Effects of Work Satisfaction and Work Flexibility on Burnout in Nurses.

The World Health Organization has encouraged improving working conditions for nurses to decrease turnover and increase nurse staffing and nursing capacity. The International Council of Nurses has pointed out that a positive work environment can improve satisfaction and decrease burnout in nurses. However, the effects of working conditions and work satisfaction on burnout in nurses remain unclear. The purpose of this study was to explore the effects of working-condition-related flexibility and work satisfaction on burnout in nurses. A cross-sectional design was employed, and 450 nurses from a single medical center participated in this study. In addition to demographic information, three survey instruments, including the Taiwanese Hospital Nurses' Job Satisfaction Scale, the Working Conditions and Flexible System Scale, and the Maslach Burnout Inventory-Chinese Version, were used to measure working condition flexibility, work satisfaction, and burnout. Descriptive statistics, the Pearson correlation coefficient, and hierarchical linear regression were used to analyze the data. Four hundred thirty-five nurses were enrolled as participants. Most were female, with a mean age of 29 years. Over four fifths (83.1%) were unmarried, and 65.5% had at least 2 years of prior experience working at other hospitals. Although the participants reported experiencing burnout several times per month, they reported feeling satisfied with their work. They noted flexibility related to working conditions, especially task-related flexibility, as important. Four variables (satisfaction/professional autonomy, interpersonal interaction, workload, and working condition flexibility/task flexibility) were found to be significant predictors of emotional exhaustion (adjusted R2 = 0.212). However, only professional autonomy was found to significantly predict a sense of low personal accomplishment (adjusted R2 = .077), whereas nursing competence significantly predicted depersonalization (adjusted R2 = .086). Work satisfaction and flexibility related to working conditions were shown to relate negatively to burnout. Nursing managers should improve the level of satisfaction related to professional autonomy, interpersonal interaction, and workload as well as task flexibility for nurses.

Mathematical models for estimate of the ecological consequences of the impact of the pyrogenic factor on forest ecosystems

There is a need for the development of simple analytical mathematical models of the burning of large forest areas, necessary for the assessment of the ecological consequences of the impact of the pyrogenic factor. Purpose. Develop mathematical models describing the spread of large-scale forest fires aimed at estimate the ecological consequences of the impact of the pyrogenic factor. Methods. Analytical review of research on the problem, theoretical and computational, mathematical modeling. Results. The results of the main parameters analysis of large forest areas combustion are presented. These include the area covered by the fire, the duration of the fire, the burnout time, the specific mass of combustible materials, the energy and power of combustion, the specific calorific value, the intensity of combustion, the movement speed of the combustion front, the influx of combustible materials, etc. Simple analytical mathematical models of large forest areas combustion have been established. These include the following models: a model with a constant growth rate of the fire area, a two-dimensional model, a model with sectorial movement of the combustion front, a model with a linear growth of the length of the combustion front, a model with a quadratic growth of the change rate of the fire area, and a generalized model. A new fire intensity classification has been proposed, containing 1–7 points from extremely low to extreme intensity. The maximum area covered by the fire (10–100 thousand km2), combustion energy (1–10 EJ) and combustion power (0.1–1 PW) have been estimated. Conclusions. Simple analytical mathematical models of the combustion process of large forest surface areas, which are necessary for quantitative assessment of the ecological consequences of fires, have been developed.

Examining the roles of experiential avoidance and cognitive fusion on the effects from mindfulness to athlete burnout: A longitudinal study

ObjectivesAthlete burnout is a maladaptive outcome that is potentially detrimental for performance and wellbeing. Cross-sectional evidence suggests that mindfulness might be associated with athlete burnout via experiential avoidance and cognitive fusion. In the current study, we extend knowledge of these hypothesized mediational pathways using a longitudinal design. MethodsData was collected at three occasions with a three-month interval. A final sample of 280 elite Chinese athletes aged 15–32 years (Mage = 19.13; SD = 2.92; Female = 130) reported their mindfulness at Time 1, experiential avoidance and cognitive fusion at Time 2, and athlete burnout at Time 3. Structural equation modelling was adopted to examine the mediating roles of experiential avoidance and cognitive fusion on the effects from mindfulness to athlete burnout. ResultsWe found statistically meaningful directs effects from mindfulness (Time 1) to experiential avoidance and cognitive fusion (Time 2), which in turn influenced athlete burnout (Time 3). However, the direct effect from mindfulness at Time 1 to athlete burnout at Time 3 was non-significant. The indirect effects of experiential avoidance and cognitive fusion on the effects from mindfulness to athlete burnout were significant, providing longitudinal evidence that these two variables contribute meaningfully to the mindfulness-burnout pathway. ConclusionWith initial evidence for the mediating effects of experiential avoidance and cognitive fusion, future studies could consider using experimental designs to examine the potential changing mechanisms of mindfulness on reducing athlete burnout.

Simulation of char burnout characteristics of biomass/coal blend with a simplified single particle reaction model

A single particle reaction model has been developed to study the char burnout characteristics of co-firing of coal and biomass under air and oxy-fuel combustion conditions. Two types of coal/biomass blend, i.e., Brisbane bituminous coal blended with woodchip, and Loy Yang lignite coal blended with woodchip, have been studied. The model is validated with different sets of experiments and CFD simulation from the literature. The effects of biomass fraction, particle size, oxygen level and gas temperature have been investigated. It is found that increasing biomass blending ratio, oxygen concentration, [O2], or the gas temperature, tg, increases char reactivity and conversion rate and reduces char burnout time. The current numerical study demonstrates that comparing to traditional CFD simulation, the proposed single particle reaction model takes much less simulation time and efforts, while able to provide a deep insight into char burnout characteristics in co-combustion process.

Combustion and Fragmentation Characteristics of Single Wet Coal Slime Particle

ABSTRACT The combustion and fragmentation characteristics of wet coal slime particle are different from that of dried coal particle. In this paper, an understanding of the combustion process of wet coal slime particle through the combined results of the morphology characteristics, mass changes, and gas release pattern is provided. A tube furnace and high-speed camera were used to observe morphological changes of the combustion process of wet coal slime. For comparison, the mass change and gas release pattern of wet coal slime was monitored by a thermogravimetric analyzer and mass spectrometer (TG/MS). The four combustion stages of coal slime were observed for the first time: (1) drying and evaporation, (2) devolatilization and fragmentation, (3) volatile homogeneous combustion, and (4) char heterogeneous combustion. The water content in wet coal slime greatly affected the fragmentation of coal slime, it could build up a great internal pressure when evaporated, which caused the primary fragmentation to occur earlier and be more severe than traditional coals. The temperature and diameter of the slime were considered as factors for the occurrence of fragmentation and the level of it. A larger diameter with a higher furnace temperature resulted in a more severe fragmentation of the wet coal slime. The smaller coal slime at the lower temperatures did not experience the fragmentation stage. Here, the fragmentation and non-fragmentation zones of wet coal slime at different temperatures and different paticle diameters are given, which could be a guide for the combustion of coal slime in CFB(Circulating Fluidized Bed). Also, for larger diameters and lower setting temperatures, the ignition delay time and burnout time of wet coal slime became longer. The gas release pattern of wet coal slime during the combustion process was analyzed, and it was determined that it could be affected greatly by fragmentation. A model of the drying and evaporation stage of wet coal slime was established for the first time by using COMSOL Multiphysics. The results of the theoretical calculations show that there were two evaporation rate peaks of water when fragmentation occurred, which theoretically explained the early stage of the combustion process of wet coal slime, and the results were in agreement with the experiments.