Ventilation Conditions Research Articles

Oxidant concentrations and photochemistry in a vehicle cabin.

Indoor air quality (IAQ) in vehicles can be important to people's health, especially for those whose occupations require them to spend extensive time in vehicles. To date, research on vehicle IAQ has primarily focused on direct emissions as opposed to chemistry happening in vehicle cabins. In this work, we conducted time-resolved measurements of the oxidants and oxidant precursors ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), and nitrous acid (HONO) inside the cabin of a 2012 Toyota Rav4 under varying ventilation conditions (i.e., car off, car on with passive ventilation, car on with mechanical ventilation via the recirculating fan, and car on with mechanical ventilation via the direct fan). Ozone levels inside the vehicle were significantly lower than outdoors under most conditions, and were approximately half the outdoor levels when the direct fan was in operation. Nitric oxide and NO2 concentrations were very low both inside the vehicle and outdoors. Nitrous acid levels in the vehicle were lower than reported values in other indoor environments, though much higher than expected outdoor levels. We also investigated the potential for photochemical production of radicals in the vehicle. Time- and wavelength-resolved solar irradiance spectra were collected, and steady state hydroxyl radical (OH) and nitrate radical (NO3) concentrations were calculated. Steady state OH concentrations were predicted to be similar to those in air masses in residences illuminated by sunlight, suggesting the importance of HONO photolysis in vehicles. Conversely, nitrate radicals (NO3) were not considered significant indoor oxidants in our study due to rapid titration by NO. Overall, our findings emphasize the importance of both air exchange and photochemistry in shaping the composition of air inside vehicles.

Distribution Characteristics and Prediction of Temperature and Relative Humidity in a South China Greenhouse

South China has a climate characteristic of high temperature and high humidity, and the temperature and relative humidity inside a Venlo greenhouse are higher than those in the atmosphere. This paper studied the effect of ventilation conditions on the spatial and temporal distribution of temperature and relative humidity in a Venlo greenhouse. Two ventilation conditions, with and without a fan-pad system, were studied. A GA + BP neural network was applied to predict the temperature and relative humidity in fan-pad ventilation in the greenhouse. The results show that the temperature in the Venlo greenhouse ranged from 15.8 °C to 48.5 °C, and the relative humidity ranged from 24.9% to 100% during the tomato-planting cycle. The percentage of days when the temperature exceeded 35 °C was 67.3%, and the percentage of days when the average relative humidity exceeded 70% was 83.7%. The maximum temperature differences between the three heights under NV (Natural Ventilation) and FPV (Fan-pad Ventilation) conditions were 3.4 °C and 4.5 °C, respectively. The maximum relative humidity differences between the three heights under NV and FPV conditions were 8.4% and 21.7%, respectively. The maximum temperature difference in the longitudinal section under the FPV conditions was 3.2 °C, while the relative humidity was 11.4%. The cooling efficiency of the fan-pad system ranged from 16.6% to 70.2%. The non-uniform coefficients of the temperature under the FPV conditions were higher than those under the NV conditions, while the nonuniform coefficients of the relative humidity were the highest during the day. The R2, MAE, MAPE and RMSE of the temperature-testing model were 0.91, 0.94, 0.11, and 1.33, respectively, while those of relative humidity model were 0.93, 2.83, 0.10, and 3.86, respectively. The results provide a reference for the design and management of Venlo greenhouses in South China.

Empirical study on the influence of initial relative humidity on wood crib fire behavior in compartment under varied natural ventilation conditions

This empirical study investigates the influence of initial relative humidity (RH) variations (35 % and 95 %) on key fire behavior parameters, specifically focusing on the fully developed stage, occurrences of flashover, and the temperature of the upper gas layer. Wooden cribs weighing 10 kg–40 kg are used as fuel in a compartment with three openings to establish different natural ventilation conditions. The experimental findings reveal that increasing the initial RH within the chamber leads to a delay in the onset of the fire growth phase. Furthermore, it induces two noticeable effects on the fully developed fire stage: a reduction in its duration by up to 50 % and a delay in its initiation by at least 30 s. While heightened initial RH does not prevent flashover, it effectively postpones its occurrence by a minimum of 40 s. Experiments with maximum fuel loads demonstrate negligible effects of increased RH on the maximum temperature, even under varying ventilation conditions. Conversely, lower fuel loads exhibit a significant decline in temperature with rising humidity, notably from 626 °C to 474 °C. The quantitative and qualitative insights derived from this study have considerable potential to inform the development of more effective fire suppression strategies in enclosed compartments.

Coupled indoor air quality and dynamic thermal modelling to assess the potential impacts of standalone HEPA filter units in classrooms

The quality of the classroom environment, including ventilation, air quality and thermal conditions, has an important impact on children’s health and academic achievement. The use of portable HEPA filter air cleaners is widely suggested as a strategy to mitigate exposure to particulate matter and airborne viruses. However, there is a need to quantify the relative benefits of such devices including the impacts on energy use. We present a simple coupled dynamic thermal and air quality model and apply it to naturally ventilated classrooms, representative of modern and Victorian era construction. We consider the addition of HEPA filters with, and without, reduced opening of windows, and explore concentrations of carbon dioxide (CO2), particulate matter PM2.5, airborne viral RNA, classroom temperature and energy use. Results indicate the addition of HEPA filters was predicted to reduce PM2.5 by 40–60 % and viral RNA by 30–50 % depending on the classroom design and window opening behaviour. The energy cost of running HEPA filters is likely to be only 1 %–2 % of the classroom heating costs. In scenarios when HEPA filters were on and window opening was reduced (to account for the additional clean air delivery rate of the filters), the heating cost was predicted to be reduced by as much as − 13 %, and these maximum reductions grew to − 46 % in wintertime simulations. In these scenarios the HEPA filters result in a notable reduction in PM2.5 and viral RNA, but the CO2 concentration is significantly higher. The model provides a mechanism for exploring the relative impact of ventilation and air cleaning strategies on both exposures and energy costs, enabling an understanding of where trade-offs lie.

Evaluation of microclimate in dairy farms using different model typologies in computational fluid dynamics analyses

Ventilation plays a key role in the livestock buildings since it is important to guarantee a comfortable environment and adequate indoor air quality for the animals. Naturally ventilated barns are usually characterized by high variability in the ventilation conditions. Moreover, the ventilation efficiency can be very different in different areas of a barn because of the different presence of the animals. On the other hand, appropriate ventilation is an essential requirement to ensure animal welfare and efficient and sustainable production since a proper ventilation is the most efficient way to remove undesirable air pollutants and to obtain a comfortable microclimate for the welfare of the animals. In this regard, the computational fluid dynamic (CFD) simulations represent a powerful and useful tool because they can be used to assess ventilation and microclimate conditions. In this context, the present study has the object to assess whether different CFD modelling approaches (i.e. model with animals modelled as obstacles with closed volume and model enriched with cows modelled as obstacles capable of exchanging heat with the surrounding air volume) show differences in relation to the climatic conditions inside a naturally ventilated dairy barn. The comparison of the results, set in terms of indoor air temperature and air velocity contours of the two different models, arises that if a precise definition of the microclimatic features is necessary, in order to correlate them with production parameters or assess animal welfare indexes, thermal simplification is not acceptable since can lead to completely misleading conclusions and incorrect evaluations. Then, only adopting CFD models considering the animal thermal behaviour is possible to obtain effective information both for the proper barn system management and for the creation of useful tools driving the farmers' choices.

Large-scale experimental study on the average temperature distribution model of fire smoke under mechanical ventilation in the flat space

Mechanical ventilation is essential to ensure the safety of persons, equipment, and structures in cruise ship fire incidents. The mass loss rate, smoke temperature, and comprehensive heat transfer coefficient during large-scale fire experiments are researched in cruise ship flat space. The results indicate that the mass loss rate of four pool fires with different sizes presents different rules in mechanical ventilation conditions compared with open conditions. In addition, the vertical distribution of temperature appears to be stratification, which aligns with the “dual-zone model”. The horizontal distribution of the temperature has a “mutation point”. With the mutation point as the boundary, the temperature drops rapidly from the fire source to the mutation point and decreases more slowly. Furthermore, the distribution model of comprehensive heat transfer coefficient and average temperature are established. The comprehensive heat transfer coefficient is in direct proportion to the 1.00 power of heat release rate and inversely in proportion to the 0.69 power of the number of mechanical ventilation. However, the average temperature is in direct proportion to the 0.52 power of heat release rate and inversely in proportion to the 1.40 power of the number of mechanical ventilation.

Combined acoustic metamaterial design based on multi-channel Fano resonance effect

In response to the increasing traffic noise problem, we designed a combined acoustic metamaterial (CAM) based on the multi-channel Fano resonance principle. By utilizing the Fano resonance coupling between the acoustic spiral structure and the hollow structure, efficient sound insulation under effective ventilation conditions is achieved. Simulation results of acoustic transmission loss show that the acoustic transmission loss of CAM is more than 13 dB in the frequency band of 520–989 Hz. The broadband sound insulation characteristic can block the oblique angle incident sound waves from different angles. Simulation results of the elastic strain energy and acoustic pressure field validate the sound insulation mechanism of the Fano resonance of the combined acoustic metamaterial. The experimental results in the impedance tube generally agree with the simulation results. To explore the possibility of wider engineering applications of CAM, we propose a combined CAM and CAM0.7 structure. The results show that a series structure of acoustic metamaterials can be selected to further realize broadband sound insulation within 500–1574 Hz.

Machine learning-driven real-time identification of large-space building fires and forecast of temperature development

In firefighting, real-time knowledge of fire dynamics is crucial yet often unavailable. The building geometry and measured gas temperatures are integrated to ascertain fire states and predict temperature evolution, utilizing a machine learning framework that combines long short-term memory networks and transfer learning. The model is pre-trained on datasets with 1000 samples from parametric fire models and 200 from field simulations, enabling real-time predictions with on-site data. Numerical simulations in portal frame buildings demonstrate over 95% accuracy in identifying fire states and 90% in predicting gas temperatures. A method using correlation coefficients and standard deviations effectively detects damaged thermocouples with over 96% accuracy, given a damage ratio below 30%. Validation in two real fire scenarios showed more than 92% accuracy in locating fires and over 89% in forecasting gas temperatures 20 min ahead, which costs 2.14 s and 1.83 s, respectively. The machine learning framework also exhibits robustness to changes in ventilation conditions by making temperature predictions using reliability theory. The proposed framework provides clear information about the state and development of the fire to firefighters and is useful for promoting smart firefighting.

Analysis of ventilation conditions in the rumoh aceh exhibition museum

Analysis of ventilation conditions in the rumoh aceh exhibition museum

Impact analysis of dust evolution pattern and determination of key ventilation parameters in highland highway construction tunnels

In order to study the influence of ventilation parameters on the ventilation of plateau highway construction tunnels, a highway tunnel construction section in Yunnan is taken as the research background, and Fluent software is used for simulation. The results of the study show that: under the conditions of press-in ventilation, the wind speed in the center of the vortex area in the wind flow field is smaller than the wind speed in the surrounding area, and with the diffusion of the flow field, the average wind speed in the tunnel section gradually decreases, and ultimately stabilizes at the level of 0.5 m/s. After blasting, the dust mass concentration on the return side of the tunnel is higher than that on the duct side. Dust with a particle size of 30 μm or more settled rapidly within 100 m from the boring face, while dust with a particle size of 30 μm or less gradually diffused outward under the action of the wind flow. In the vicinity of the tunnel boring face, reducing the distance from the air outlet to the boring face and increasing the air velocity can improve the dust removal effect. This conclusion can provide theoretical basis and certain guidance for the evolution of dust and dust prevention in the tunnel construction process in plateau area.

Formation and Transport of Secondary Contaminants Associated with Germicidal Ultraviolet Light Systems in an Occupied Classroom.

Germicidal ultraviolet light (GUV) systems are designed to control airborne pathogen transmission in buildings. However, it is important to acknowledge that certain conditions and system configurations may lead GUV systems to produce air contaminants including oxidants and secondary organic aerosols (SOA). In this study, we modeled the formation and dispersion of oxidants and secondary contaminants generated by the operation of GUV systems employing ultraviolet C 254 and 222 nm. Using a three-dimensional computational fluid dynamics model, we examined the breathing zone concentrations of chemical species in an occupied classroom. Our findings indicate that operating GUV 222 leads to an approximate increase of 10 ppb in O3 concentration and 5.2 μg·m-3 in SOA concentration compared to a condition without GUV operation, while GUV 254 increases the SOA concentration by about 1.2 μg·m-3, with a minimal impact on the O3 concentration. Furthermore, increasing the UV fluence rate of GUV 222 from 1 to 5 μW·cm-2 results in up to 80% increase in the oxidants and SOA concentrations. For GUV 254, elevating the UV fluence rate from 30 to 50 μW·cm-2 or doubling the radiating volume results in up to 50% increase in the SOA concentration. Note that indoor airflow patterns, particularly buoyancy-driven airflow (or displacement ventilation), lead to 15-45% lower SOA concentrations in the breathing zone compared to well-mixed airflow. The results also reveal that when the ventilation rate is below 2 h-1, operating GUV 254 has a smaller impact on human exposure to secondary contaminants than GUV 222. However, GUV 254 may generate more contaminants than GUV 222 when operating at high indoor O3 levels (>15 ppb). These results suggest that the design of GUV systems should consider indoor O3 levels and room ventilation conditions.

Meteorology-driven trends in PM2.5 concentrations and related health burden over India

As a heavily polluted country, India has made great efforts on mitigating severe PM2.5 pollution during last several years. Quantifying meteorological impacts on PM2.5 pollution and related health burden is essential to accurately assess pollution control effects and therefore provides a reference for air quality policy in India. This study identifies meteorological influences on PM2.5 trends and related mortality during 2014–2021 in five Indian megacities (Chennai, Kolkata, Hyderabad, Mumbai, Delhi). Decreasing trends in PM2.5 concentrations are observed in all cities and seasons with the maximum trend of −7.24 μg m−3 yr−1 in Delhi during winter. Meteorology causes PM2.5 decreases in all cities and seasons with meteorology-driven downward trends of −6.51 ∼ −0.36 μg m−3 yr−1. Meteorology dominates PM2.5 decreases in Delhi during summer/monsoon and Chennai/Mumbai/Delhi during winter, where meteorology-driven PM2.5 trends contribute 65% ∼ 105% of observed PM2.5 decreases. Better ventilation condition is identified as the primary meteorological factor for PM2.5 decrease. Anthropogenic emissions almost play positive roles in improving India's PM2.5 air quality, confirming the effectiveness of pollution control measures in India during recent years. Meteorological conditions dominate decreases in PM2.5-related deaths in 25% of cities and seasons. The most significant meteorology-driven PM2.5-related mortality trend of −127.12 deaths yr−1 occurs in Delhi during winter.

Is there a connection between spine alignment, chest mobility, shoulder joint and respiratory parameters of patients with ankylosing spondylitis?

IntroductionAnkylosing spondylitis is chronic progressive disease, which decrease functions of musculoskeletal system including chest area. Those changes influences respiratory mechanics, worsen conditions of proper ventilation of lungs.ObjectivesRating of functional and respiratory parameters and dependence between them at patients with ankylosing spondylitis.Materials & methodsThe study included 45 patients with diagnosed ankylosing spondylitis. Chest and upper limbs mobility, resting spinal curvature alignment were assessed, and respiratory parameters were measured in a plethysmographic chamber JAGGER MasterScreen Body.ResultsAnkylosing spondylitis patients had lower respiratory parameters especially sReff, and FRC. Restriction of chest and upper limbs mobility was also demonstrated. Forward head extension was observed based on the occipital wall test. Correlations between functional parameters and correlations between functional and respiratory parameters were shown, in particular MIP, MEP, sReff, Rtot, TLC, ERV.ConclusionsThe study confirmed a decrease in functional and respiratory parameters in the examined patients with ankylosing spondylitis compared to the applicable standards. A significant relationship was found between functional parameters in the upper body and respiratory parameters, which worsen with increasing thoracic dysfunction. The obtained results indicate the directions of therapy that should be taken into account to improve respiratory parameters and reduce respiratory dysfunction in these patients. Chest-focused physiotherapy appears to be an important element in improving function in patients with ankylosing spondylitis.

Evaluation of radiation dose associated with underground uranium mining activities in east Singhbhum, Jharkhand, India

This paper presents the effect of ventilation parameters on the 222Rn inhalation dose in an underground uranium mine located in east Singhbhum of Jharkhand, India. This study reveals that the airflow rate variable statistically significantly predicts the 222Rn dose variable in the mine. On the other hand, no significant effect of other ventilation parameters such as barometric pressure, dry-bulb, and wet-bulb temperatures on 222Rn inhalation dose in the stopes was observed due to negligible variations in their values. Therefore, the airflow rate plays a significant role in reducing the effective radiation dose level in mines. In this study, the Equivalent Equilibrium Radon concentration (EER) and total effective radiation dose received by the miners involved in different mining activities in the various locations of the mine were found to be in ranges of 130–420 Bq m−3 and 0–3.17 mSv y−1, respectively. It also reveals that the miners involved in the stope preparation and timbering were exposed to more radiation than other mining activities. Under the existing ventilation conditions, the total effective radiation dose was far below the safe limit of 20 mSv y−1 recommended by the International Commission of Radiological Protection.

Numerical investigation of different building configurations for improving outdoor spatial ventilation conditions in strip-type residential neighbourhoods

Understanding the influence of building configurations on spatial wind flows is essential for architects to optimize urban ventilation in the design process. However, the design changes in urban form are abundant and many detailed design variations were not examined. This study aims to explore the potential of spatial forms to improve wind conditions in strip-type residential neighbourhoods. Several specific building design variations were investigated using computational fluid dynamic (CFD) simulations. The ventilation performance indicators including spatial averaged wind velocity (<V>), purging flow rate (PFR), and net escape velocity (NEV) were adopted to quantify the effects of design changes on spatial ventilation efficiency of overall and local residential spaces. The results show that the buildings with staggers of residential units could have a noticeable impact on the overall residential space, especially when the wind direction is inclined or parallel to the corridor space between the strip buildings. The PFR and < V > values of the residential space can be reduced by 19% and 18%. Building length variation and square setting can be beneficial to the ventilation conditions of the local residential spaces.

Does the Addition of Oral Sampling Improve Waveform Capnography When Compared to Traditional Nasal Sampling in Open-Airway Patients?

BackgroundEnd-tidal carbon dioxide (EtCO2) is an invaluable anesthesia measure due to minimal delay in monitoring ventilation. Oral and Maxillofacial Surgery (OMS) presents special challenges because oral exhalations are not sampled effectively via nasal cannula normally used to avoid interfering with procedures. PurposeThe purpose of the study was to compare EtCO2 waveforms obtained in subjects using nasal monitoring and combined nasal and oral monitoring under simulated ventilatory conditions. Study design, setting, sampleA single-blinded, randomized crossover controlled study was conducted at the University of Illinois Chicago with healthy volunteers, who were blinded to the monitoring system used. Inclusion criteria required subjects be >18 years of age, be consentable and English-speaking. Exclusion criteria required no airway abnormalities, no edentulism, no conditions that preclude undergoing an OMS procedure under sedation. Predictor variableThe primary predictor variable was the EtCO2 monitoring system: nasal with a standard nasal cannula, and combined with a nasal cannula and oral device. The secondary predictor variable evaluated three ventilatory states (nasal breathing, oral breathing, apnea) in each arm, standardizing by maintaining consistent breath counts across observation periods. Main outcome variableThe main outcome variable was the number of waveforms recorded over 30 seconds for nasal and combined monitoring. Each recording was standardized by dividing it by the baseline waveforms and multiplying by 20. Higher values, closer to baseline, were considered more accurate depictions of ventilation. CovariatesCovariates were body mass index (BMI), age, sex, Mallampati score, and breathing method. AnalysesANOVA, ANCOVA, and MANOVA were performed. P-value<0.05 was considered statistically significant. ResultsThe sample included 25 subjects (18 male, 7 female) with mean age 29.9+7.98 years and BMI 23.9+3.51 kg/m2. Combined sampling detected more waveforms during nasal and oral breathing (p<0.001). Higher BMI correlated with reduced waveform capture during nasal sampling in oral breathing (p=0.013). Combined sampling detected more waveforms during nasal breathing (p=0.005) in subjects with BMI < 23.5 kg/m2. Mallampati score correlated with increased waveforms during nasal breathing. Conclusions and RelevanceOral EtCO2 sampling may improve accuracy of capnography waveform capture. Further clinical studies in sedated subjects undergoing OMS procedures are needed.

A new ventilation performance index considering relative changes in environmental parameters: A numerical study

The ventilation index plays a crucial role in evaluating and selecting ventilation systems. However, existing studies focus only on the "effectiveness" of ventilation systems but usually ignore the "extent of the effect" caused by ventilation, and no relevant indexes are available. To address this issue, this study aims to propose a new ventilation index named the equivalent ventilation number (EVN), which considers the relative change in environmental parameters. The application potential of the EVN index was numerically examined in a virtual hospital ward setting with varying air changes per hour (ACH), thermal loads, air distribution patterns, contaminant source intensities, and local air supply rates. The results demonstrate that the highest average temperature-based EVN and CO2-based EVN are obtained when ACH increases from 6 h−1 to 12 h−1 and local supply air velocity increases from 0 m/s to 1 m/s, with values of 0.66 and 1.49 respectively. Furthermore, EVN values differ across different ventilation conditions and locations. The effect of changing ventilation conditions on ventilation performance assessed by heat removal effectiveness and temperature-based EVN, as well as contaminant removal effectiveness and CO2-based EVN, is opposite in 4 out of 10 cases and 3 out of 10 cases, respectively. The average EVN values calculated based on temperature and contaminant changes differ among all cases, with the largest difference of 1.2. The proposed EVN is anticipated to be an effective index for quantifying and comparing the "extent of the effect" caused by ventilation systems under various ventilation conditions.

Feasibility assessment of a clean and efficient fire extinguishing system for pottery jar liquor warehouses

Clean fire extinguishing systems applicable to the pottery jar liquor warehouse are in demand. In this study, taking 53vol% liquor as the research subject, fire models of various clean fire extinguishing systems comprising water mist, liquid carbon dioxide (LCO2) and liquid nitrogen (LN2) were established using a fire dynamic simulator to determine their fire extinguishing effect. A feasibility assessment of systems was performed under different fire source types, fire source sizes, and ventilation conditions. The fire extinguishing efficiency was analyzed in terms of the fire extinguishing time, oxygen concentration, and space temperature. The results showed that the success rate of the LCO2 and LN2 fire extinguishing systems was 100%, whereas the success rate of the water mist fire extinguishing system was 95%. In terms of reducing the oxygen concentration at the bottom of the space and the temperature in the space, the LCO2 system exhibited the best performance, followed by the LN2 system, and lastly the water mist. Under different ventilation conditions and fire source types, the LCO2 fire extinguishing system was least affected, whereas the effectiveness of the water mist fire extinguishing system reduced under natural ventilation conditions, and the extinguishing efficiency of the LN2 fire extinguishing system was affected by the fire source type. Overall, the LCO2 system presented more advantages in extinguishing fires in pottery jar liquor warehouses and can provide a new idea for the development and application of clean and efficient fire extinguishing systems.

Factor analysis and GA-BP-ANN prediction of nitrogen diffusion behavior in underground laboratory under ventilation conditions

Nitrogen is widely used in various laboratories as a suppressive gas and a protective gas. Once nitrogen leaks and accumulates in a such confined space, it will bring serious threats to the experimental staff. Especially in underground tunnels or underground laboratories where there is no natural wind, the threat is more intense. In this work, the ventilation design factors and potential leakage factors are identified by taking the leakage and diffusion of a large liquid nitrogen tank in China Jinping Underground Laboratory (CJPL) as an example. Based on computational fluid dynamics (CFD) research, the effects of fresh air inlet position, fresh air velocity, exhaust outlet position, leakage hole position, leakage hole size, and leaked nitrogen mass flow rate on nitrogen diffusion behavior in specific environments are discussed in detail from the perspectives of nitrogen concentration field and nitrogen diffusion characteristics. The influencing factors are parameterized, and the Latin hypercube sampling (LHS) is used to uniformly sample within the specified range of each factor to obtain samples that can represent the whole sample space. The nitrogen concentration is measured by numerical value, and the nitrogen diffusion characteristics are measured by category. The GA-BP-ANN numerical regression and classification regression models for nitrogen concentration prediction and nitrogen diffusion characteristics prediction are established. By using various rating indicators to evaluate the performance of the trained model, it is found that models have high accuracy and recognition rate, indicating that it is effective in predicting and determining the concentration value and diffusion characteristics of nitrogen according to ventilation factors and potential leakage factors. The research results can provide a theoretical reference for the parametric design of the ventilation system.

Acceleration analysis and unsteady mathematical prediction of flame spread over thermal insulation layer in u-shaped building façade fires

As one of the most commonly used energy-saving methods in buildings, thermal insulation layer is widely used in building façade and it also endangers the human safety in buildings due to its combustibility. U-shaped facade is a commonly used structure in high-rise buildings since it could improve both the light and ventilation conditions indoors. This paper investigated the flame acceleration over the thermal insulation in u-shaped building facade fires. It was found that the flame spread rate over u-shaped facade had an exponential growth with time as the direction of preheating zone location is the same direction of the heat transfer from the pyrolysis zone. The air entrainment and the upward induced airflow played an important role in the acceleration. As the side wall length increased or the back wall length decreased, the flame spread rate accelerated more rapidly. Furthermore, a mathematical prediction model of the unsteady flame spread rate over u-shaped structure façade was established and validated through experiments. This study provides technical guidance for the fire safety design of building facade.