Vent Sizing Research Articles

Thermal hazard studies on aqueous ethylene oxide solution using DSC, VSP2, and the pressure-proof TAM IV

Ethylene oxide is a most versatile and critical raw chemical and intermediate. However, the strained ring of ethylene oxide is liable to be cleaved, potentially leading to industrial disasters at high temperatures, such as severe explosions, fires, and toxic releases. In this study, nonisothermal, adiabatic, and isothermal tests were performed to determine the inherent properties of aqueous ethylene oxide solution (AEOS) with regard to its safety. Differential scanning calorimetry and vent sizing package 2 were used to investigate its thermal decomposition and pseudo-adiabatic runaway reaction, respectively. Isothermally exothermic behavior was detected by using the thermal activity monitor IV. Kinetic equations were applied to calculate the apparent activation energy of AEOS (at conversion degrees of 10, 11, 12, 13,…, and 90%), with its value in the range 59.6–85.0 kJ mol−1. The Arrhenius method was also used to ascertain the frequency factor. As the conversion degree increased, the apparent activation energy and frequency factor gradually decreased. The flash point of AEOS was tested to determine its fire and explosion hazard potential. From the perspective of proactive loss prevention, these results are salient for the safer thermal handling of AEOS.

Experimental and theoretical study of the pressure wave generation in railway tunnels with vented tunnel portals

The aim of this study is to enhance the knowledge of the generation of pressure waves in railway tunnels and to adopt a method of predicting the influence of vented tunnel portals.Pressure waves in railway tunnels generated by the entry of a train into a tunnel entail many disadvantages and therefore have to be reduced.The experimental study was performed at the Tunnel Simulation Facility Göttingen, a moving-model rig. The influence of the train velocity, size and the head length, as well as the influence of the geometry of the tunnel portal and the number and size of portal vents on the pressure waves were investigated regarding the minimisation of the pressure gradient inside the tunnel. The air outflow through the vents was studied using PIV, especially the amount of air leaving the portal through each vent and the geometry of the stream tube.Furthermore, an acoustical analogy was used to predict the pressure-time history inside a model tunnel equipped with the different types of tunnel portals during the passage of the train. Empirical parameters, which are necessary for the estimation, were assessed both theoretically and experimentally. The given theory was adapted to a realistic train with underbody.

Blast from pressurized carbon dioxide released into a vented atmospheric chamber

This study describes the blast from pressurized carbon dioxide $$(\hbox {CO}_{2})$$ released from a high-pressure reservoir into an openly vented atmospheric chamber. Small-scale experiments with pure vapor and liquid/vapor mixtures were conducted and compared with simulations. A motivation was to investigate the effects of vent size and liquid content on the peak overpressure and impulse response in the atmospheric chamber. The comparison of vapor-phase $$\hbox {CO}_{2}$$ test results with simulations showed good agreement. This numerical code described single-phase gas dynamics inside a closed chamber, but did not model any phase transitions. Hence, the simulations described a vapor-only test into an unvented chamber. Nevertheless, the simulations reproduced the incident shock wave, the shock reflections, and the jet release inside the atmospheric chamber. The rapid phase transition did not contribute to the initial shock strength in the current test geometry. The evaporation rate was too low to contribute to the measured peak overpressure that was in the range of 15–20 kPa. The simulation results produced a calculated peak overpressure of 12 kPa. The liquid tests showed a significantly higher impulse compared to tests with pure vapor. Reducing the vent opening from 0.1 to $$0.01\,\hbox {m}^{2}$$ resulted in a slightly higher impulse calculated at 100 ms. The influence of the vent area on the calculated impulse was significant in the vapor-phase tests, but not so clear in the liquid/vapor mixture tests.

Using picosatellites for 4-D imaging of volcanic clouds: Proof of concept using ISS photography of the 2009 Sarychev Peak eruption

Volcanic ash clouds can present an aviation hazard over distances of thousands of kilometres and, to help to mitigate this hazard, advanced numerical models are used to forecast ash dispersion in the atmosphere. However, forecast accuracy is usually limited by uncertainties in initial conditions such as the eruption rate and the vertical distribution of ash injected above the volcano. Here, we demonstrate the potential of the Telematics Earth Observation Mission (TOM) picosatellite formation, due for launch in 2020, to provide valuable information for constraining ash cloud dispersion models through simultaneous image acquisition from three satellites. TOM will carry commercial frame cameras. Using photogrammetric simulations, we show that such data should enable ash cloud heights to be determined with a precision (~30–140 m depending on configuration) comparable to the vertical resolution of lidar observations (30–180 m depending on the cloud height). To support these estimates, we processed photographs taken from the International Space Station of the 2009 Sarychev Peak eruption, as a proxy for TOM imagery. Structure-from-motion photogrammetric software successfully reconstructed the 3-D form of the ascending ash cloud, as well as surrounding cloud layers. Direct estimates of the precision of the ash cloud height measurements, as well as comparisons between independently processed image sets, indicate that a vertical measurement precision of ~200 m was achieved. Image sets acquired at different times captured the plume dynamics and enabled a mean ascent velocity of 14 m s−1 to be estimated for regions above 7 km. In contrast, the uppermost regions of the column (at a measured cloud top height of ~11 km) were not ascending significantly, enabling us to constrain a 1-D plume ascent model, from which estimates for the vent size (50 m) and eruption mass flux (2.6 × 106 kg s−1) could be made. Thus, we demonstrate that nanosatellite imagery has the potential for substantially reducing uncertainties in ash dispersion models by providing valuable information on eruptive conditions.

Combustion of 1-butylimidazolium nitrate via DSC, TG, VSP2, FTIR, and GC/MS: An approach for thermal hazard, property and prediction assessment

Abstract Ionic liquids (ILs) possess negligible vapor pressure, a low toxicity, a low melting point, and a vast liquid temperature range, rendering them as favorable candidates for new alternative solvents. However, some recent studies showed that ILs are flammable during thermal upsets. To explore the overall spontaneous combustion under upset conditions, we propose a safer method to investigate the IL’s thermal hazards. Gas chromatography/mass spectrometry, Fourier transform infrared spectrometry, and flash point analysis results indicated that 1-butylimidazolium nitrate ([BIM][NO3]) exhibits combustible characteristics and low thermal stability at high temperatures (over ca. 150.0 °C) during thermal decomposition. Meanwhile, differential scanning calorimetry, thermogravimetry, and vent sizing package 2 (VSP2) tests were used to describe the thermal properties of [BIM][NO3]. The thermokinetic parameters were further acquired by using an isoconversional method. The results demonstrate that the suitable combination of anion and cation might yield energetic ILs.

Effect of vent conditions on internal overpressure time-history during a vented explosion

Vented explosion experiments of ethylene-air mixtures were conducted in a custom-designed 2 × 1.2 × 0.6 m3 steel chamber under three vent conditions to study the effect of vent size and vent type on overpressure under different concentrations. The experiment results show that vented explosion behaviors are related to various vent conditions. The rupture pressure of vent film at different concentrations are the same with static vent pressure while the rupture pressure of vent panel increases as the concentration approaches the stoichiometric concentration. Double-peak pressure curves were recorded under small size vent conditions, while overpressure curves with only one peak were recorded under large size venting. Analysis indicates that the peak overpressure and rate of pressure increase under large size venting are mainly affected by the rupture pressure and the concentration of combustible gas, respectively. Moreover, secondary explosion, due to the backflow of external gas, will occur in high concentrations under large size vent conditions. In the case of small size vent condition, the value of first peak P1 is mainly determined by the rupture pressure, while the value of second peak P2, and the rates of increase to P1 and P2 are mainly affected by the concentration. There is a clear difference between the recorded values of P2 at two measurement points, which indicates that there is a pressure gradient induced by small size vent conditions due to the change of flow cross-section. This work provide a practical reference for the safety design of the explosion venting.

Overview of hydrogen combustion experiments performed in a large scale vented vessel at Canadian Nuclear Laboratories

Hydrogen combustion inside a post-accident containment environment may pose a threat to the integrity of the containment structure and equipment. In CANDU reactors, combustion-generated overpressures in an accident will be relieved by venting to adjacent from one compartment volumes through relief panels or existing openings. To have a better understanding of the fundamental mechanisms that control the overpressures resulting from a vented hydrogen deflagration, a 120 m3 large scale vented combustion test facility was constructed at Canadian Nuclear Laboratories. A number of experiments have been completed in this facility to investigate hydrogen combustion behavior simulated in a post-accident reactor containment environment. A selected number of experimental results are presented in this paper to demonstrate several parameter effects on vented combustion dynamics by varying the number of chambers (single, two or three interconnected), volume and vent size, initial turbulence (quiescent vs. turbulent), initial temperature and steam concentration, mixture uniformity (well mixed vs. highly stratified), vent locations, and number of igniters. These results have provided useful insights for hydrogen management for the Canadian nuclear industry and CANDU utilities participating in the CANDU Owners Group research program. Most experimental data have been used for validation of combustion models and development of user guidelines.

Combustion phenomena of pool fire in a ceiling vent compartment: the vent far away from the fire source

Abstract To study the combustion phenomena of pool fire in a ceiling vent compartment where vent is far away from the fire source, experiments in cabin with a size of 1.8m×1.2m×1.2m were conducted. The influence of ceiling vent size and pool fire source area upon mass loss rate, compartment temperature and gas exchange pattern at vent was researched. The internal connection between flame shape and vent flow pattern was provided. The result showed: ceiling vent size had major impact on vent flow pattern. As the ceiling vent size increased, the air flow into the compartment through vent augmented, either. Yet it had little impact on combustion rate. In the meantime, the change of vent size affected compartment temperature in a small scale, which was much more implicated by the change of fire source size. The average compartment temperature increased linearly according to the fire source area.

Natural Ventilation of Smoke Subject to Wind Pressure Within Fire Safety Engineering Approach

This paper presents an analytical model able to explore the design method of natural smoke evacuation through an exhaust vent subject to wind pressure. The proposed model can be used to determine the flow rate of smoke and the optimal section of the exhaust vent according to the geometric parameters of the room, the heat release rate and the pressure exerted by the wind forces at the exhaust vent. The numerical resolutions of the mathematical equations of the model were performed using the dichotomy method. The proposed analytical approach is built progressively by, (i) the examination of interaction forces between buoyancy forces and wind pressure forces, (ii) a numerical validation of the analytical model using the numerical simulation software Fire Dynamics Simulator, and (iii) proposal of a method of approximation of the optimal section of the exhaust vent for a maximum smoke evacuation rate. The results show very satisfactory and provide adequate prediction of the optimal size of the exhaust vent between the theoretical approximation and various configurations of numerical simulation. The feasibility and effectiveness of the proposed approach lead to an accurate and reliable analytical model able to analyze the influence of the size of natural smoke evacuation vents subjected to the pressure of wind forces.

On the Analysis of Flame Pulsation and Fire Induced Vent Flow Oscillatory Behaviors in Confined Enclosures with Horizontal Openings

Abstract This paper undertakes a comprehensive analysis of flame pulsation behavior and vent flow oscillatory behavior in a confined enclosure. Experiments are carried out in a small scale confined compartment with a horizontal opening, and several configurations characterized by different pool diameters and ceiling vent sizes are considered. Flame pulsation and horizontal vent flow oscillatory behaviors are investigated during the experiments, and visualization recordings were collected. Results indicate that the flame pulsation frequency ( f fire ) can be obtained by way of the Fast Fourier Transform (FFT) method (with recorded RGB images being transformed into pseudo-gray images based on Ostu’s method) and the vent flow oscillatory frequency ( f vent ) can also be obtained using a similar processing method. The frequencies are found to vary in accordance with variation of the horizontal opening size. Through theoretical analysis, the relationship between the flame pulsation frequency and vent flow oscillatory frequency is investigated. Moreover, it is expected that the comprehensive frequency term would alter in alignment with the parameters of the horizontal opening, and this sufficiently fitted with the experimental data.

Explosive volcanism on Mercury: Analysis of vent and deposit morphology and modes of eruption

The MESSENGER mission revealed, for the first time, conclusive evidence of explosive volcanism on Mercury. Several previous works have cataloged the appearance and location of explosive volcanism on the planet using a variety of identifying characteristics, including vent presence and deposit color as seen in multispectral image mosaics. We present here a comprehensive catalog of vents of likely volcanic origin; our classification scheme emphasizes vent morphology. We have analyzed the morphologies of all vents in our catalog, and recognize three main morphologies: “simple vent”, “pit vent”, and “vent-with-mound”. The majority of vents we identify are located within impact craters. The spatial distribution of vents does not correlate with the locations of volcanic smooth plains deposits, in contrast to the Moon, nor do vents correlate with the locations of large impact basins (except for the Caloris and Tolstoj basins). Using the degradation state of the vent host crater as a proxy for maximum age, we suggest that vent formation has been active through the Mansurian and into the Kuiperian periods, although the majority of vents were likely formed much earlier in mercurian history. The morphologies and locations of vents are used to investigate a set of plausible formation geometries. We find that the most likely and most prevalent formation geometry is that of a dike, stalled at depth, which then explosively vents to the surface. We compare the vent and deposit size of mercurian pyroclastic deposits with localized and regional lunar pyroclastic deposits, and find a range of possible eruption energies and corresponding variations in eruption style. Localized lunar pyroclastic deposits and the majority of mercurian pyroclastic deposits show evidence for eruption that is consistent with the magmatic foam at the top of a dike reaching a critical gas volume fraction. A subset of mercurian vents, including the prominent Copland-Rachmaninoff vent to the northeast of the Rachmaninoff basin, indicates eruption at enhanced gas volume fractions. This subset of vents shows a similar eruptive behavior to the lunar Orientale dark mantle ring deposit, suggesting that the dikes that formed these vents and deposits on Mercury underwent some form of additional volatile build-up either through crustal volatile incorporation or magma convection within the dike. There also exists a population of mercurian vents that no longer retain a visible associated pyroclastic deposit; we hypothesize that the visible signature of the pyroclastic deposit has been lost through space weathering and regolith mixing processes. Together, these results provide a comprehensive analysis of explosive volcanism on Mercury, and inform continued research on the thermal history of Mercury and magma composition and evolution.

Adiabatic correction for the esterification of acetic anhydride by methanol via accurate kinetics

Abstract In the field of adiabatic correction for complex reactions, a simple one-stage kinetic model was used to estimate the real reaction kinetics. However, this assumption simplified the real process, inevitably generated inaccurate or even unsafe results. Therefore, it was necessary to find a new correction method for complex reactions. In this work, esterification of acetic anhydride by methanol was chosen as an object reaction of study. The reaction was studied under different conditions by Reaction Calorimeter (RC1). Then, Thermal Safety Software (TSS) was used to establish the kinetic model and estimate the parameters, where, activation energies for three stages were 67.09, 81.02, 73.77 kJˑmol− 1 respectively, and corresponding frequency factors in logarithmic form were 16.05, 19.59, 15.72 s− 1. In addition, two adiabatic tests were performed by Vent Sizing Package2 (VSP2). For accurate correction of VSP2 tests, a new correction method based on Enhanced Fisher method was proposed. Combined with kinetics, adiabatic correction of esterification reaction was achieved. Through this research, accurate kinetic parameters for a three-step kinetic model of the esterification reaction were acquired. Furthermore, the correlation coefficients between simulated curves and corrected curves were 0.976 and 0.968, which proved the accuracy of proposed new adiabatic correction method. Based on this new method, conservative corrected results were able to be acquired and be applied in safety assessment.

Design of flow configuration for parallel air-cooled battery thermal management system with secondary vent

Battery thermal management system (BTMS) is critical to dissipate the heat generated by the battery pack and guarantee the safety of the electric vehicles. Among the various battery thermal management technologies, the air cooling is one of the most commonly used solutions. In this paper, the cooling performance of the parallel air-cooled BTMS is improved through using the secondary vent. Computational fluid dynamics is introduced to calculate the flow field and the temperature field, finally evaluating the cooling performance of the BTMS. Mathematical analysis is conducted to explore the influences of the inlet air temperature and the heat generation rate on the battery cell temperature. The analysis results demonstrate that the temperature rise and the temperature difference of the battery pack are independent of the inlet air temperature, and are proportional to the heat generation rate for the situation of the constant heat generation rate. Subsequently, the influences of the position and the size of the secondary vent on the cooling performance of the BTMS are investigated through using the typical numerical cases. The results show that the position of the secondary vent strongly affects the maximum temperature and the maximum temperature difference of the battery pack. When the vent is on the convergence plenum, it is suggested to be located against the cooling channel around the battery cell with the maximum temperature. Compared to the vent located on the convergence plenum, the one against the outlet performs better. In this situation, the maximum temperature of the battery pack is reduced by 5K or more, and the maximum temperature difference is reduced by 60% or more compared to the BTMS without vent for the situation of the constant heat generation rate. Moreover, the cooling performance of the BTMS becomes better as the size of the secondary vent increased, and similar conclusion can be obtained when the heat generation rate is unsteady.

Ventilation optimization of solar greenhouse with removable back walls based on CFD

Ventilation is important for crop production and quality in greenhouse cultivation, and vent dimension and position are the basis of greenhouse design. In this study, the effect of the back wall vent dimension on solar greenhouse cooling was investigated by CFD (Computer Fluid Dynamics). The results showed that the average air temperature in a solar greenhouse with removable back walls (RG) was reduced by approximately 1.7°C and the highest temperature dropped by approximately 5.8°C compared with the traditional solar greenhouse with a brick back wall (TG). A 2-D CFD transient simulation model was developed to simulate the indoor temperature and airflow distributions in RGs with different back wall vent sizes. The results suggest that a back wall vent of 1.4m increased inside the ventilation efficiency in a solar greenhouse with removable back walls.

Evaluation of self-heating models for peracetic acid using calorimetry

Abstract Thermal analysis of peracetic acid (PAA) with respect to the explosive properties was performed using calorimetry. The exothermic characteristics and thermal runaway profiles of PAA solutions were acquired through differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2). The results revealed significant enthalpy changes and gas eruption for PAA solutions that were subjected to free-radical induced and autocatalytic reactions. The reaction kinetics and order of various PAA solutions were elucidated using calorimetry.

An experimental study to assess the effect of soffit louvered vents on wind loads and wind driven rain intrusion on low rise buildings

Wind-driven rain (WDR) intrusion in buildings during hurricanes often leads to significant damage to building interior and contents, causing major losses. Many buildings in hurricane-prone U.S. coastal states are fitted with soffit vents with louvers that are designed to close during high winds and reduce rain intrusion. This paper focuses on the topic of WDR intrusion through soffit vents and, in particular, studies the effects of louvered soffit vents on (i) reduction of water intrusion, and (ii) overall aerodynamic loading of buildings’ roofs. A gable and a hip roof building retrofitted with open and closed vents were tested at the Wall of Wind (WOW) experimental facility. WDR intrusion studies were carried out only on the hip roof building, while wind pressure distributions were estimated for the gable and hip roof buildings. Results from the WDR intrusion study indicate a marked reduction in water intrusion for the closed vent roofs. Moreover, the net mean and peak pressure coefficients for the closed vent roofs are reduced in magnitude (less suction) compared to the open vent roofs. Future research is recommended to study the effect of different vent sizes and locations, besides considering other roof types (e.g. mono-slope).

Effects of clinical hearing aid settings on sound localization cues

Sound localization cues, particularly interaural level difference (ILD) cues, are known to be affected by hearing aid processing such as wide-dynamic range compression and strong directional microphones. These distorted cues may negatively impact spatial awareness and communication in complex environments, two areas of challenge for new and experienced hearing aid users. Previously, we investigated frequency specific alterations to ILD and interaural time difference (ITD) cues using linear amplification in simulated reverberant rooms and with gaged vent sizes. In reverberation, ITD became erratic and ILD reduced; minimal effects of hearing aid venting were observed (Diedesch and Stecker, Am. Aud. Soc. 2016). Here, we applied that approach to hearing aid settings more typically encountered by clinical patients. Phonak Audeo receiver-in-the-canal (RIC) hearing aids were programmed to typical open-fit hearing impairments using clinically normal settings for compression algorithms and directional microphones. Recordings, collected using an acoustic manikin, were compared across hearing aid coupling (standard open and closed domes) in anechoic and simulated rooms. Frequency-specific ITD and ILD were quantified across coupling, room, and hearing aid settings. [Work supported by the F. V. Hunt Postdoctoral Research Fellowship, NIH R01-DC011548 (GCS), R01-DC011828 (FJG), and the VA RR&D NCRAR.]

Methane-induced explosions in vented enclosures

Explosions in enclosures leading to devastating accidents occur in various industrial, commercial, and residential occupancies. To relieve the effect of such explosions, vents of various sizes and geometry are designed. In this study, a computational model for gas explosions venting, developed and validated on hydrogen explosion by Ugarte et al. [Process Safety and Environmental Protection, 99, (2016) 167–174] is extended to vented explosion scenarios for methane. The model is based on a time-dependent set of ordinary differential equations whose solution allows prediction of temperature, pressure and vented mass transients resulting from the explosion of methane-air in vented enclosures. The model is compared to the experiments available in the literature and NFPA 68 standards at different vent areas and equivalent ratios. The influence of gas equivalence ratio and vent size on the rate of pressure rise is analyzed. A framework for the gas explosion vent design using the fundamental laminar burning velocity of a gas-air mixture is also discussed.

Analysis of thermal hazards of O,O-dimethylphosphoramidothioate by DSC, TG, VSP2, and GC/MS

O,O-dimethylphosphoramidothioate (DMPAT) is widely used as the vital intermediate in pesticides to synthesize acephate, chlorine methamidophos, and methamidophos. February, 2016, a serious explosion and fire occurred in Taichung, Taiwan, resulting from DMPAT decomposition, causing one death and injuring one employee. To explore the thermal hazard of DMPAT, we applied various instruments of thermal analysis. Combustion phenomena and decomposed products were identified by combustion test and gas chromatography-mass spectrometry. Differential scanning calorimetry and thermogravimetry were used to analyze the thermal stability parameters, and mass loss conditions under five heating rates illustrating decomposition. Vent sizing package 2 was used to simulate stirring or unstirring system failure in a practical process. The apparent activation energy of DMPAT and self-accelerating decomposition temperature were, respectively, 92.4±3.2kJ/mol calculated by Starink equation, and 66.0°C by simulated approach. The findings of these results are vital for inherently safer measures during production, storage, and transportation.

Design of silos for dust explosions: Determination of vent area sizes and explosion pressures

The “Eurocode 1 – Actions on structures – Part 4: Silos and tanks” EN 1991-4 includes dust explosions as an accidental action for load combination in some design situations. Venting is the most widely used method to mitigate the effects of explosions. The area size of the venting devices installed in the silo will determine the development of internal overpressures in the event of an explosion, and thus the structural design of the silo. Also, the inertia and the activation pressure of the venting elements can influence the explosion pressures. The Eurocode 1 suggests using the German DIN-Report 140 to design the venting devices. However, other methods exist, such as the European standard EN 14491 and the American standard NFPA 68, which were not specifically developed for silos. In this study, the DIN-Report 140 has been analysed by calculating a wide range of cases, including different silo dimensions, materials (barley and wheat flour) and values of inertia and activation pressure of the venting devices. Three types of venting systems have been considered: bursting panels, explosion doors and light-weight concrete slabs. In addition, the DIN-Report 140 has been compared with current European and American venting standards. The results obtained in this study indicate that there are marked differences between the three methods considered, and that vent areas calculated according to DIN-Report 140 for either bursting panels or explosion doors seem to be very conservative. Uncertainties and limitations of DIN-Report 140 have been detected and discussed. The final goals of this study are to provide guidance on the determination of explosion loads and to contribute to the development of a single common practice for venting in silos.