Vent Sizing Research Articles

A hybrid numerical approach for characterising airflow and temperature distribution in a ventilated pallet of heat-generating products: Application to cheese

Temperature control throughout the cold chain is of crucial importance in the preservation of the quality of cheese. As a result of cheese heat generation, both natural and forced convection need to be considered. This numerical study aimed to characterise the airflow and temperature fields within a ventilated pallet of heat-generating cheeses. An original computational fluid dynamics (CFD) hybrid approach was developed. This approach is based on a combination of a porous media approach for the contents of the boxes and a direct CFD approach for the outer cardboard walls, including vent size and position. The computational domain is limited to one pallet level. The simulations were conducted on a steady state for two upwind air velocities 0.31 m/s and 0.73 m/s and three generated heat fluxes 0.05 W, 0.15 W, and 0.3 W per product item (250 g). The model was validated by comparison with experimental results related to velocity and product temperature profiles obtained on a full-scale experimental set-up. The hybrid approach shows good accuracy while reducing the mesh size and the computational time in comparison with the direct CFD approach.

Effects of Vent Size and Pressure on Hydrogen Explosion Dynamic Characteristics.

Explosion venting is an effective method to reduce the explosion damage; in order to study the mechanism of an explosion venting process in internal and external space, this paper investigates the influence of vent parameters on hydrogen-air explosion in a rectangular duct through numerical simulation. The model including the internal and external space is first constructed, and then the explosion dynamic behaviors of the full flow field are analyzed under different vent pressures and sizes. The study aims to reveal the coupling effect of the flame, pressure, and flow field on hydrogen explosion venting. The results indicate that the explosion intensity increases with the growth of the vent pressure and the reduction of the vent size. The maximum external overpressure increases to 2.6 and 2.3 times as the vent pressure increased to 10 times or vent size reduced by 90%. The flame and combustible gas mixture evolve from a mushroom cloud into a jet form as the vent size decreases, and vortexes formed at the flame front suppress flame propagation. However, the flame speed increases significantly as the flame passes the vent under the impact of larger pressure gradient, which results in a more violent turbulence intensity and secondary external explosion.

Effect of vent size on vented H2/N2/air deflagration

In this work, the coupling of explosion venting (vent size) and inerting (N2) on H2/air deflagration was investigated. Experiments were carried out in a vertical rectangular duct with an upper opening at an initial temperature and pressure of 280 K and 101 kPa, and a vent coefficient Kv was employed to replace the vent size to elucidate its effect on pressure buildup and flame propagation during H2/N2/air deflagration. In the present study, the internal pressure profile is monitored by three pressure sensors, PS1-3, which are installed at the bottom, center, and top of the duct, respectively, and the external pressure profile is obtained by PS4. The results show that the maximum internal overpressure (pmax) recorded by PS1-3 all increase with increasing Kv, but pmax obtained from PS2 and PS3 tend to increase linearly. For a given Kv, the maximum and minimum amplitudes of pmax are measured by PS1 and PS3, respectively. Specifically, the greater the distance between the pressure sensor and the upper opening, the greater the amplitude of pmax. The relationship between the maximum reduced explosion pressure (pred) and Kv is investigated, where pred is defined as the highest pmax for a specific Kv. As Kv increases from 2.2 to 11.9, pred increases from 26.25 kPa to 88 kPa. The maximum external flame velocity (Vext) increases from 83 m/s to 454 m/s with increasing Kv from 2.2 to 11.9. The amplitude of the maximum external overpressure (pext) first increases and decreases with an increase in Kv from 2.2 to 11.9. The formation time (Δt) of pext decreases and then increases and finally decreases with increasing Kv from 2.2 to 11.9. When Kv is increased from 2.2 to 4.1, all external fireballs are presented as mushroom shapes, but the external fireballs are gradually transformed into jet shapes for Kv ≥7.8. Two pressure oscillations, including Helmholtz oscillations and acoustic oscillations, are found. Acoustic oscillations are found in all tests, but Helmholtz oscillations are only observed for Kv ≤ 4.1.

Prediction of peak overpressure from hydrogen-air cloud explosions in vented cylindrical vessels

Hydrogen as one of the most promising clean energies, has received a lot of attention. Intensive research has been devoted to developing techniques for the effective usage of hydrogen energy. However, hydrogen is prone to gas explosion incidents, which may impose significant threats to people and structures in the vicinity. Blast overpressure is one of the main hazards from hydrogen explosion incidents. A simplified evaluation method for the prediction of peak overpressure from hydrogen-air cloud explosions in vented cylindrical vessels is proposed. Detailed three-dimension numerical models of vented cylindrical vessels with premixed hydrogen-air clouds were generated and validated with testing data. The numerical simulation results were used to establish the empirical correlation between peak overpressure and cylindrical vessels parameters including length and diameter, vent size and vent activation pressure. The influence of ambient temperature in the vented cylindrical vessels on the peak overpressure is also discussed. The simplified prediction method could be used for quick and reliable prediction of the peak blast overpressures in vented cylindrical vessels from accidental hydrogen explosions.

Temperature evolution and flame behavior inside a ceiling-vented compartment with different fire source locations under the effect of wind

This work presents an experimental investigation on ceiling-vented compartment fire behavior and thermal characteristics with different fire source locations under the effect of wind associated by CFD simulations. Experiments were carried out under the ambient wind condition, and the fire source was respectively set at windward side, center and leeward side. Results show that: (1) In no-wind cases, a critical heat release rate is found at which the inside temperature decreases with the increasing of fire heat release rate indicating flame flows outside. The critical HRR for fire source attached to sidewall is slightly larger than that when the fire source is located at compartment center, and it increases as vent dimension increases. (2) In ambient wind condition, there is a travelling process that the flame transfers from windward side to leeward side with the increasing of fire HRR. The critical HRR for the transition increases as vent size increases, and decreases as wind speed increases, and is basically independent of fire source location, which is proved to be related to air inflow rate. A Froude number is proposed to characterize the wind effect based on air inflow analysis, and the critical HRR for transition is represented well by the Froude number.

An attention temporal convolutional network-based hybrid approach to simulating indoor air pollutants and their determinants in classroom and office spaces

Accurately assessing and source tracing indoor air quality (IAQ) is crucial for implementing targeted interventions to improve IAQ. This study aimed to investigate the concentrations and underlying determinants of multiple indoor air pollutants in classrooms and office spaces of educational buildings and develop a robust model for precise IAQ assessment and simulation. A walkthrough-based inspection with continuous monitoring of indoor and outdoor PM2.5, PM10, NO2, and O3 was conducted in ten educational buildings in Gainesville, Florida. IAQ dynamics and determinants were systematically compared across spaces to discern setting-specific patterns. An Evolutionary Polynomial Regression method-assisted Attention Temporal Convolution Network (EPR-ATCN) model was developed to assess and predict IAQ. The results revealed that the influencing factors of indoor pollutants in classrooms and offices were similar, but the contribution proportion and weight of each factor differed. Street distance, wall damage, indoor relative humidity, and air conditioning vent size were identified as key determinants for most indoor pollutants. The EPR-ATCN models significantly outperformed Multiple Linear Regression (MLR) and Artificial Neural Network (ANN) ANN-based models in simulating indoor environments of both classrooms (RMSE: 1.6, 2.4 and 4.9) and offices (RMSE: 1.3, 2.9 and 5.1). Follow-up studies exploring IAQ in similar architectural and environmental settings may accordingly reference these findings.

Improving the efficiency of the trombe wall by integrating multi-fold glazing and sustainable materials: Ifrane, Morocco as a case study

The Trombe wall is renowned for its effectiveness in passive heating during winter, but it can lead to overheating in summer. To address this issue, this study investigates a Trombe wall with fully opening glazing during the summer season, employing multi-fold glazing. The research, conducted in Ifrane, Morocco, focuses on a residential building using the Conduction Finite Difference Method within the DesignBuilder software, and examines three configurations: a reference configuration, classic Trombe wall, and Trombe wall with multi-fold glazing. The results demonstrate that the last configuration achieves a 63 % (24,94 kWh/m2) reduction in total energy consumption compared to the reference configuration and a 34 % (7,62 kWh/m2) reduction compared to the classic Trombe wall. Additionally, the implementation of sustainable ecological biomaterials, such as timber instead of concrete, is explored to reduce CO2 emissions. Further analysis of the Trombe wall with multi-fold glazing is conducted by considering five parameters: glazing type, emissivity, vent size, insulation, and PCM thicknesses. These parameters are examined across five different variables. Reducing emissivity leads to reductions of 51 % and 30 % in heating energy consumption and discomfort hours, respectively. Modifying the type of glazing results in an 11 % reduction in heating energy consumption. Increasing insulation thickness leads to notable reductions of 15 % in heating energy consumption and 6 % in discomfort hours. Conversely, increasing PCM thickness and vent size yields had minimal impact on total energy consumption, each resulting in a 1 % reduction. This research provides insights into optimizing Trombe walls by integrating multi-fold glazing to address summer overheating issues and by exploring additional parameters to enhance system performance.

Single Room Fire Traceability and Prediction Models Based on Deep Learning Methods

ABSTRACT When a fire occurs, fast recognition on key information of the fire based on limited data available and predict fire smoke motion trends from limited fire information is desirable to develop effective emergency strategies. The proposed models include fire intensity traceability model and fire position traceability model based on Back Propagation Neural Network (BPNN). Smoke prediction model is proposed based on Transpose Convolutional Neural Network (TCNN). The numerical model is first validated by the single-room fire test, and then a numerical database of 165 transient room-fire scenarios is established under various fire locations, fire sizes, and vent sizes. The model test is conducted in new fire intensity and vent size scenarios, with R2 coefficients of 0.965 and 0.95, respectively. The experimental data validation shows that relative errors were less than 10%. The position traceability model has Kappa values of 0.758 and 0.75. The average visibility error values of the smoke prediction model’s output images in the validation of the test set generally fall within the range of ± 1.5 m. The results indicate that the models have good accuracy and strong adaptability to different compartment fire scenarios which can provides effective support for fire rescue and emergency strategy development in fire scenes.

Adiabatic thermal runaway and safety relief design for hexamethylene diisocyanate reaction system

Runaway reaction may occur for hexamethylene-diisocyanate (HDI) with two active NCO groups during the reactions or storage and transportation when run into device failure, operation error and other unexpected environments, which would damage equipment or even cause explosions. Adiabatic experiments for HDI using Vent Sizing Package 2 (VSP2) is conducted and temperature and pressure changes over time, as well as the maximum temperature rise rate and maximum pressure rise rate, are obtained. The results show that the initial exothermic temperature of the system is 50°C, and the maximum temperature is 232°C and the heat of reaction is 414.7 kJ/kg, so the severity level of HDI is classified as "medium" according to the assessment criteria for the severity of a runaway reaction. The relief type of the reaction system is determined to be a gas system by analysis of the pressure change curve during heating and cooling processes, along with the temperature at the point of loss of control, and calculated by the DIERS method and Leung's correction method through Python programming, which is applied to determine the required safety relief device for an industrial scenarios, and the minimum relief area is calculated to be 0.0028m2 and 0.0019m2, respectively. The study verifies the higher reliability of the safety relief design for runaway reactions based on VSP2 experimental data.

Research on the Explosion Venting Effect and Influencing Factors of Gas Explosion in Urban Shallow Pipe Trenches

ABSTRACT In this study, two groups of gas explosion venting tests were conducted based on a large-scale pipe trench test system (30 m length), and the numerical model of pipe trench was established through the FLACS software, which was verified by the corresponding experimental data, and then the explosion process and load distribution characteristics of the gas explosion in pipe trenches were further analyzed by varying the number, location, and size of the top vent and the size of the end opening. The results showed that the explosion flame and overpressure time-history oscillate significantly without top vents, and the peak impulse decreases while the peak pressure first increases and then decreases axially along the pipe trench, mainly attributed to the relative positions of the precursor and flame wave. The top vents can significantly block the flame propagation and weaken the oscillation phenomenon, but the attenuation of the peak overpressure is mainly limited to the upstream of the vents, so it is necessary to set multiple consecutive top vents to effectively reduce the overall explosive load. The overall peak stress and peak impulse can be attenuated by 12% and 57% respectively with 3 top vents, but the downstream peak stress even tends to increase with only one top vent. In addition, the explosion venting effect of top vents can be ignored with the small size (0.2 m × 0.2 m), the explosion venting effect of the end opening is also limited to a small range (12 m) upstream of it.

Experimental and numerical study on the explosion characteristics of syngas under different venting conditions

To explore ways to mitigate the harm and damage caused by syngas explosions and provide a theoretical basis for the safe and widespread use of syngas, the explosion characteristics of syngas under different venting conditions were experimentally and numerically investigated in our work. Five venting configurations were established based on the location and size of the lateral vent. The combined effects of venting conditions and hydrogen concentrations on explosion characteristics were concerned. Results showed the lateral vent significantly impacted the flame front structure, flame propagation velocity, and overpressure. Moreover, the formation and development of tulip flame could be affected by the lateral vent and hydrogen concentration. The presence of a lateral vent reduced both the flame propagation velocity and overpressure. With increasing hydrogen concentration, the drop ratio of the maximum flame propagation velocity did not increase, whereas the drop ratio of the maximum overpressure increased for the same venting condition. Finally, the internal mechanism of syngas venting explosion under different venting conditions was revealed by numerical simulation. In short, the research results provided the theoretical basis for the safe utilization of syngas in the industrial production field.

Experimental study of self-extinguishing behavior of hydrogen jet fires in the confined space with a ceiling vent

With the widespread utilization of hydrogen energy, the hydrogen safety issues, especially hydrogen jet fires, should be much paid attention to, since the latter present high temperature and radiation in confined space. Hydrogen jet fire experiments were conducted with various release rates and vent sizes in a confined space with ceiling vent to investigate the hydrogen jet flame height, oxygen concentration, and self-extinguishing time. The results show that, the large vent sizes with low hydrogen release rates result in well-ventilated hydrogen jet fires. As the vent size decreases or the hydrogen release rate increases, the hydrogen jet flame evolves from a well-ventilated one to one having self-extinguishing behavior with under-ventilation. The combustion process can be divided into four stages: the growth stage, the quasi-steady stage, the stretch stage and the self-extinguishing stage. The flame height increases with the hydrogen release rate at the quasi-steady stage, and the vent size has almost no effect. However, in the case of under-ventilation, the flame height at the stretch stage is determined by the joint actions of vent size and hydrogen release rate, and the flame height is positively connected with the size of the ceiling vent. The oxygen concentration and self-extinguishing time decrease dramatically as the vent size and hydrogen release rate increase. The parameter Q˙VA1/3 is proposed to reflect the coupling effects of hydrogen release rate and vent size, and the correlations of oxygen concentration and self-extinguishing time are determined with Q˙VA1/3.

Effects of Air Vent Size and Location Design on Air Supply Efficiency in Flood Discharge Tunnel Operations

Effects of Air Vent Size and Location Design on Air Supply Efficiency in Flood Discharge Tunnel Operations

Taguchi method-based evaluation of thermal hazard of lift-off pyrotechnics under various storage conditions

This study employed the Taguchi method and analysis of variance to investigate the factors that influence the deterioration of the lift-off pyrotechnics when they are stored under various relative humidity (RH) and temperature conditions. A field emission scanning electron microscope and an energy-dispersive X-ray spectroscope were used to observe the microstructures and elements of pyrotechnic samples. Differential scanning calorimetry (DSC) and Vent Sizing Package 2 (VSP2) were applied to measure the relationship between the trace heat flow of the samples and temperature as well as the thermal runaway reactions in a pseudo-adiabatic environment. A DSC analysis and a thermodynamic ASTM E698 analysis were combined to explore the safety of lift-off pyrotechnics and the related thermal hazards.The energy-dispersive X-ray spectroscopy and DSC experimental results revealed that KNO3 is highly soluble. However, when RH and exposure time increased, the surface dissolution of oxidants decreased the height of the second exothermic peak, resulting in incomplete combustion and ignition failure. The ASTM E698 thermokinetic analysis results indicated that the apparent activation energy (Ea) of the samples increased substantially after being immersed in deionized water. Notably, the Ea of colored smoke increased from 46.88 to 155.91 kJ/mol, indicating that the examined pyrotechnics were more sensitive to a decrease in temperature than to an increase in humidity. A large amount of water can be used to alleviate the reactivity of pyrotechnics and thus reduce pyrotechnic hazards. The VSP2 analysis results indicated that the self-boosting rate of the samples was greater under 40% RH than under pristine conditions; however, this rate decreased substantially under 80% RH and after immersion in deionized water. The results of the Taguchi experiment and analysis of variance revealed that humidity contributed 63.60% and 50.86% to Ea and maximum pressure, respectively. Accordingly, controlling humidity should be prioritized to diminish the hazard of storing pyrotechnics.

Experimental study on the overpressure variation and flame mode of premixed fuel-air deflagration in a semi-closed enclosure

A small scale combustible gas venting explosion experimental system with a volume of 0.002 m3/0.0035 m3 was established, and the venting explosion experiments of ‘petroleum fuel vapor-air mixture’ under various vent sizes were conducted. The characteristics of overpressure and flame parameters under different vent sizes were obtained and the different venting modes were classified. The research results show that the overpressure history of petroleum fuel vapor/air mixture during the venting explosion process could be divided into four types, and four typical overpressure peaks induced by various phenomena were captured. With increasing venting coefficient Kv, the number of overpressure peaks decreases, but the value of overpressures gradually increases. When the value of Kv was relatively small (Kv ≤ 3.329) a ball or mushroom flame cloud was formed in the external field. When the value of Kv was comparatively large (4.560 ≤ Kv), a jet-like flame was formed in the external field. With the increase of the venting coefficient Kv, the internal maximum overpressure peak, the external maximum overpressure peak along vertical direction, the external flame height dimensionless number along the vertical direction and the external flame speed dimensionless number along the vertical direction showed an increasing trend, while the external flame diameter dimensionless number along the horizontal direction and the external flame speed dimensionless number along horizontal direction showed an decreasing trend. If treat ‘the least number of overpressure peaks’ and ‘the external explosion doesn’t occur’ as the ideal state of the venting explosion process, the vent opening needs to be set to ensure that 4.560 ≤ Kv ≤ 8.585.

Improving size and selectivity of blue swimming crab (Portunus pelagicus) by using collapsible trap with escape vents in Pamekasan, Madura Island

Blue Swimming Crab (Portunus pelagicus) is high export value product from Indonesia that usually exported as pasteurized crabmeat in cans, and has high consumer demand. Blue swimming crab production still depends on wild catch, so that it will threaten the existence of them in the sea. The use of traps will cause almost all sizes of blue swimming crabs to be caught (accidentally) including those that are still small (not suitable for catching). This study aims to analyze the effectiveness of the escape vent in collapsible traps to reduce small catches of blue swimming crabs in the Pamekasan area. This research was carried out from August 2021 - January 2022 in the southern waters of Pamekasan. The method used is descriptive analysis and the effectiveness analysis of collapsible traps with a size (length x width) of escape vents is 4,5 x 3,5 cm. The study carried out 106 females and 85 males with a total weight of 22,908 kg and the carapace width ranged from 9,7 to 15,8 cm. The effectiveness of escape vents is 98,65%, which is the higher value (closer to 100%) the more benefits it will give to sustainability of blue swimming crabs in the Pamekasan area.

Restraint System Optimizations Using Diverse Human Body Models in Frontal Crashes

<div><b>Objective:</b> This study aimed to optimize restraint systems and improve safety equity by using parametric human body models (HBMs) and vehicle models accounting for variations in occupant size and shape as well as vehicle type.</div> <div><b>Methodology:</b> A diverse set of finite element (FE) HBMs were developed by morphing the GHBMC midsize male simplified model into statistically predicted skeleton and body shape geometries with varied age, stature, and body mass index (BMI). A parametric vehicle model was equipped with driver, front passenger, knee, and curtain airbags along with seat belts with pretensioner(s) and load limiter and has been validated against US-NCAP results from four vehicles (Corolla, Accord, RAV4, F150). Ten student groups were formed for this study, and each group picked a vehicle model, occupant side (driver vs. passenger), and an occupant model among the 60 HBMs. About 200 frontal crash simulations were performed with 10 combinations of vehicles (n = 4) and occupants (m = 8). The airbag inflation, airbag vent size, seatbelt load limiter, and steering column collapse force were varied to reach better occupant protection. The joint injury probability (Pjoint) combining head, neck, chest, and lower extremity injury risks was used for the design optimization. Injury risk curves were scaled based on the skeleton size and shape of each HBM.</div> <div><b>Results and Conclusions:</b> We observed that tall and heavier male occupants tend to strike through the airbag leading to higher head injury risk; older and female occupants tend to sustain higher chest injury risk, while obese occupants tend to have higher lower extremity injury risk. After design optimizations, the average <i>P</i>joint was reduced from 0.576 ± 0.218 to 0.343 ± 0.044. The airbag inflation and venting were found to be highly effective in head protection, while the belt load limit and steering column force were sensitive to chest injury risks. Conflicting parameter effects were found between head and chest injuries and among different occupants, highlighting the complexity of achieving safety equity across a diverse population. This study demonstrated the benefit of adaptive restraint systems for a diverse population.</div>

Calculation of vent sizing for emergency relief system with modified DIERS method: an analysis of thermal decomposition runaway of cumene hydroperoxide system

Calculation of vent sizing for emergency relief system with modified DIERS method: an analysis of thermal decomposition runaway of cumene hydroperoxide system

A multi-scale experiment analysis of air entrainment and heat exhaust coefficient under lateral smoke exhaust in tunnel fires

This study investigated the air entrainment caused by a lateral smoke exhaust system via full-scale and model-scale tests. A particular phenomenon, shear flow, was observed downstream of the exhaust vent. The phenomenon of shear flow was more intense when the exhaust velocity increased, which destroyed the smoke layer stratification and strengthened the air entrainment. Plug-holing and shear flow intensified air entrainment, and the functional relationship between air entrainment, Froude number, and dimensionless exhaust vent size was established. The relationship between the air entrainment and heat exhaust efficiency was studied, and it was found that the heat exhaust coefficient was positively related to the air entrainment. The functional relationship between the heat exhaust coefficient and air entrainment for different lateral exhaust vent sizes was presented. In addition, we observed that lateral smoke exhaust exhibit little effect on the centerline temperature distribution. A model that can be used to describe the centerline temperature distribution with lateral smoke exhaust systems was developed.

A thermal hazard risk evaluation of emulsion polymerisation and vinyl acetate monomers in the latex manufacturing process

Latex is extensively used in industrial products. However, completing some processes at scale leads to unacceptable levels of risk that need to be quantified and mitigated. Systemic risks must be eliminated wherever possible, and safety takes priority over efficiency and quality. To assess the process risks accurately, four raw materials were examined in this study: polyvinyl acetate (PVA), latex process-initiator-ammonium persulfate (APS) and hydrogen peroxide (H2O2), and vinyl acetate monomer (VAM). The physicochemical composition of the PVA latex process was determined via calorimeters, including differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2). The calorimetry results showed that the protective colloid was a critical component in the polymerisation reaction. In addition, when adding initiators to the system, it is vital to observe the normal ratio of materials and keep the stirring system operating. The scenario system also simulated the effects of shutting down various inhibitory programs, including the build-up of free radicals that could result in a runaway reaction when the initiator was added in excess. On the other hand, the result of the risk matrix displayed as a medium level, indicating that although the probability of an accident is low, the resulting severity is at disaster level. As a result, this study provides process safety engineers with a reliable frame of reference for assessing the potential dangers in the PVA latex manufacturing process.