Large Vent Research Articles

Dynamics of fuel-lean and stoichiometric methane-air explosion venting: Experiments and simulations

The computational explosion venting analyzer (EVA), a zero-dimensional (0D) model based on the conservation of mass and energy, is being developed to model centrally- and rear-ignited explosions. For this purpose, a series of explosion venting experiments in a cylinder with vent areas of 132.7, 86.6, 67.9 cm2 (corresponding to the vent area ratios of K=0.47,0.31,0.24, respectively) is performed. Two equivalence ratios of ϕ=0.8 and 1 are considered to represent the fuel-lean and stoichiometric methane-air mixtures, respectively. The dynamics of explosions is studied through the observation of flame propagation and pressure measurements. In rear ignition experiments, laminar, so-called “finger flame” propagation is observed, while in the case of center ignition, a flame initially expands spherically and then is pulled by the vent, acquiring a half-elliptical and half-spherical shape. The peak pressures obtained from rear ignition exceed their counterparts in the center ignition experiments. The EVA is compared with the experimental matrix. No turbulence is implemented in stoichiometric simulations, and slight turbulence has been accounted for in the lean mixture simulations. It is found that the large vent, generally, imposes more disturbances on the flame shape and the fuel-lean mixtures are more prone to the diffusional-thermal instabilities. It is shown that such a simple numerical tool, as the EVA is, can estimate a complicated problem such as pressure evolution resulted from a vented gas explosion.

Numerical investigation of air demand by the free surface tunnel flows By WANGRU WEI, JUN DENG and WEILIN XU, J. Hydraulic Res. 59(1), 2021, 158--165, https://doi.org/10.1080/00221686.2020.1744747

The authors developed a novel design equation based on numerical model results by taking into account the effects of water velocity and residual tunnel cross-sectional area above the water surface. The discussers acknowledge the presented approach, but also express their concerns regarding the following points: (i) the validation of the numerical model is superficial as it is based on bulk parameters only and ignores known model limitations; (ii) effects of the air vent characteristics are not considered in the numerical model and consequently neither in the presented design approach; (iii) air entrainment is not considered in the authors' approach but may be important for Froude numbers above 6; and (iv) the general applicability of the design equation due to the small range of considered Froude numbers and the negligence of air vent characteristics which have been shown to significantly impact air demand in outlet tunnels. This discussion aims at clarifying some facts not clearly presented by the authors and identifying limitations of the authors' design equation. Overall, we highlight that the approach describes the unrestricted air discharge and should be limited to the parameter range and assumptions considered for its derivation, i.e. for large air vent parameters (A* > 0.1) and flows with Froude numbers below 10.

Improving small unmanned aerial vehicle flight endurance with cryo-compressed hydrogen vessels

Detailed analysis indicates that substantial increases (22–43%) in flight endurance of small unmanned aerial vehicles (UAVs) powered by liquid hydrogen (LH2) are possible by increasing the maximum allowable pressure of the cryogenic storage vessel beyond the critical point to contain evaporated hydrogen (H2) and mitigate vent losses to the environment. Taking an existing UAV (US Naval Research Laboratory's “Ion Tiger”) as a baseline, we consider the effect of increasing Dewar maximum allowable pressure on flight endurance, under two different scenarios. In Case 1, the weight of the H2 storage system (including H2) is kept equal to the baseline design to maintain flight conditions unchanged. In Case 2, the external volume of the Dewar is kept equal to the baseline design, and the weight of the Dewar (and UAV) increases when the maximum allowable pressure increases, with the result that the propulsion power for the heavier UAV increases.The results are favorable. Although the modified Dewars have smaller inner volume (Case 1) or greater weight (Case 2) than the original Ion Tiger, flight endurance increases by 22% (Case 1) and 43% (Case 2), because the large H2 vent losses (39%) of the original design are reduced to only 1.6% (Case 1) and 1% (Case 2). The much higher utilization efficiency of the H2 stored in these modified Dewars compensates for their volume and weight disadvantages, resulting in UAVs with superior endurance.

A Novel Design and Development of Mortice Tubular Deadbolt Latch Mechanism

Abstract: In order to protect individuals or secure items in a respected location or region, locks are devices that keep the door, gate, or drawer stable in its position when it is closed. These are the typical standard sorts that have been in use for a while; an innovative idea has been proposed to replace them with smart mechanisms. In order to lower the price and the size of the existing type by increasing the ease of operation and security. In this project, a brand-new latch mechanism is suggested as an alternate for primordial ones. Using a solenoid, the deadbolt will lock automatically when the door is closed, either from inside or outside; a keyless way can be used to open it from inside, and a key can be used to unlock it from outside. In comparison to previous mortice locks on the market, it only requires a small vent on a door, whereas the ubiquitous one requires a large vent. This may weaken the door and affect the door’s life. The installation is also a swift process, as it requires only a small vent and comes ready to install. This uses a constant power source and can be installed in any type of door. It also has a battery backup for the specified amount of time. Using Ansys, the lock's stress is computed and compared to the existing one

Temperature evolution, flame behavior and extinction inside compartment with a ceiling vent under the ambient wind

This article presents an experimental and CFD simulation investigation and analysis on temperature evolution and flame behavior inside compartment with a ceiling vent under ambient wind. Experiments were conducted employing a reduced-scale model containing a cubic fire compartment with a ceiling vent under the external wind generated by a wind tunnel. The temperature of windward and leeward inside compartment as well as the flame behavior were recorded for various vent dimensions, heat release rates and wind speeds for a total of 720 test conditions. Results show that there are two types of fire behavior regimes inside the compartment for relatively small- (Bernoulli flow regime) or large vents (oscillatory exchange flow regime). With a relatively small vent, the flame is located at the center of compartment and the temperatures of windward and leeward are almost the same with or without the ambient wind. Then the flame turns to extinct due to lack of oxygen with increasing of fuel supply. However, with a relatively large vent, there is a flame transition from windward to leeward accompanied by the transition of temperature distribution with increasing of fuel supply when subject to ambient wind. Such extinction and transition mechanisms are interpreted by the aid of CFD simulation of global equivalence ratio and flow/oxygen field inside compartment. The critical heat release rate for the occurrence of flame transition decreases with raising wind speed while increases with vent size. Their complex dependence is found to be well represented in terms of a non-dimensional heat release rate as a function of the wind Froude number, employing the vent area-equivalent characteristic diameter as length scale. These new findings facilitate the understanding of the compartment fire evolution with a ceiling vent subject to ambient wind.

Prominent volcanic source of volatiles in the south polar region of the Moon

Gas-rich discharges of magma produced pyroclastic vents on the lunar surface. Calculations suggest those pyroclastic vents repeatedly generated 1012 to 1015 g of H2O and CO + CO2 for pyroclastic volumes of 10 to 500 km3 early in lunar history, particularly during the first billion years of lunar history. Some of those volatiles migrated to the lunar poles where they could be trapped in permanently shadowed regions (PSRs). The largest indigenous source of volatiles in the south polar region was volcanism that occurred on the floor of the Schrödinger impact basin. Here a large pyroclastic vent ceased erupting ∼ 3.70 +0.02-0.03 Ga, releasing H2O, CO-CO2, F, S, and Cl vapor species, including calculated values of 3.0 × 1013 to 1.6 × 1014 g H2O. A transport and depositional model suggests 1.1 × 1010 kg (12%) of that water may have been trapped in the south polar region.

Evaluation of the marginal excess cement and retention force of implant-supported zirconia crowns with various vent designs under different cement application patterns.

To investigate the effects of implant-supported zirconia crowns with various vent designs on the marginal excess cement (MEC) and retention values under different cement application patterns. Cercon zirconia crowns (n=36) were divided into the following groups: no venting (NV group), a small occlusal vent hole (SOV group), a large occlusal vent hole (LOV group), and a small palatal-occlusal vent hole (SPV group). The cement was applied to the crowns with different methods: occlusally half axial walls (OH), cervically half axial walls (CH) and all axial walls (AA), and different amounts of cement were applied with a chosen method. The weight of the MEC was calculated, and the retention force was recorded. ANOVA was used to analyze the MEC weights and retention values. In all vented groups, the OH application method resulted in no MEC and the least retention force, and the AA method expressed significantly less MEC (p < 0.01) than the CH method without retention force reduction. At each amount of cement (5, 10, 20, 30 mg), all three venting designs significantly reduced the MEC by the AA method, and the mean MEC of the LOV group was lower than that of any other group. Applying a thin layer of cement evenly to all axial walls of vented zirconia crowns showed excellent clinical effects regarding the MEC and the retention force. Residual excess cement was identified as a possible risk indicator for peri-implant diseases. Simply and effectively minimizing marginal extrusions without reducing the retention force has clinical value. The results of this study indicate that applying a thin layer of cement evenly to all axial walls of vented zirconia crowns is an acceptable method.

Anatomical Details of Aetosauria (Archosauria: Pseudosuchia) as Revealed by an Articulated Posterior Skeleton from the Upper Triassic Ischigualasto Formation, San Juan Province, Argentina

Aetosaurs are an early-diverging clade of “crocodile-line” archosaurs whose oldest records come from Argentina and Brazil. Articulated skeletons of aetosaurs are rare, but offer insight into their paleobiology. We describe here an incomplete, articulated posterior skeleton of an aetosaur from the Upper Triassic Ischigualasto Formation of San Juan Province, Argentina. It resembles Aetosauroides, the only aetosaur genus currently recognized from the Ischigualasto Formation, but lacks apomorphies that would allow us to assign it to that taxon, appears to be more robust than the holotype of A. scagliai, and preserves a different tail morphology. We identify the specimen as a basal aetosaur in part because the few exposed dorsal and lateral osteoderms have a typical ornamentation of radially distributed pits, grooves, and ridges emanating from a “center of ossification”. Although the specimen is incomplete and exposed primarily in ventral view from the sacrum posteriorly, it preserves many anatomical features not often preserved in aetosaurs, including extensive appendicular armor and a well-preserved caudal ventral carapace. The latter apparently consists of only two columns of ventral osteoderms, and preserves a large cloacal vent proximally. Posteriorly, the ventral paramedian osteoderms fuse to form a single element, something that has not previously been demonstrated in aetosaurs. The arrangement of osteoderms around the vent is distinct from that seen in A. scagliai. The ventral caudal osteoderms differ from many other aetosaurs in that they do not transition from wider than long to longer than wide, indicating that the specimen had a relatively abbreviated tail.

Stress concentration factors of RHS T-connections with galvanizing holes under in-plane bending

The hot spot stress method recommended by the CIDECT Design Guide 8 cannot be directly used in the fatigue design of galvanized tubular steel connections since: (1) the hot-dipping process can sometimes significantly change the residual stress magnitude and distribution at the welded joint; and (2) sufficiently large vent and drain holes must be specified at the welded joint location prior to galvanizing, and quite often at the locations recommended by the design guide for calculation of hot spot stresses. Hence, the existing formulae and charts for determination of Stress Concentration Factors (SCFs) may not be applicable. In this study, Finite Element (FE) modelling was performed to examine the existing SCF formulae for welded rectangular hollow section (RHS) T-connections under brace in-plane bending. The FE models were validated by comparison of the experimental results from six large-scale connection tests. A parametric study including 192 FE models with varied hole locations, brace-to-chord width ratios, chord wall slendernesses, and brace-to-chord thickness ratios, shows that the existing SCF formulae can lead to unsafe predictions. Critical hot spot stress locations are thus identified. The effects of both brace in-plane bending and chord loading were studied. New design formulae that take the vent and drain holes into account are proposed. These formulae are shown to provide more accurate predictions of SCFs in such connections.

Numerical Simulation of the Influence of Vent Conditions on Hydrogen Flame Propagation

ABSTRACT In order to reduce the damage caused by a gas explosion in a ventilation duct, a Large Eddy Simulation (LES) model was used to simulate the hydrogen/air explosion process in the ventilation duct under different side vent. The results show that in the process of flame propagation, the large size side vent near the ignition end produces a larger discharge effect, which causes more serious distortion and longer time for the flame front passing through the side vents. The influence mechanism of the side vent on the flame propagation is different at different stages of flame propagation. When the flame front is behind the side vent, the positive flow field traction on the flame front increases the contact area between the flame front and unburned gas, and thus accelerates the flame propagation. When the side vent is 1 m away from the ignition end, with the side vent diameter increasing from 40 mm to 80 mm, the peak flame propagation speed increases by 19.02% before the flame reaches the vent. When the flame front passes through the side vent, the exhaust of the side vent and the disturbance of the vertical flow field can restrain the flame propagation. However, when the flame front is in front of the vent, the synergistic effect between turbulent vortex and reverse flow field causes the flame propagation speed to fluctuate greatly. The influence of the side vent size on the explosion relief effect is restricted by the side vent position. When the side vent is located in the pressure rising section, the pressure relief effect of the side vents with different sizes is very great and is almost unaffected by the size of the side vent. When the side vent is 1 m away from the ignition end, the peak overpressure in the tube decreased by 50.75%, 52.88% and 55.43%, respectively, when the diameter of the side vent was 40 mm, 60 mm and 80 mm. On the contrary, when the side vent is outside the pressure rising section, the pressure relief effect of the side vent will be weakened, and vents with different sizes have a great alteration to pressure relief effect. For the side vent being 5 m from the ignition end, the peak overpressure in the tube decreased by 4.49%, 13.41%, and 35.51%, respectively, when the diameter of the side vent was 40 mm, 60 mm, and 80 mm.

Effects of hydrogen concentration, non-homogenous mixtures and obstacles on vented deflagrations of hydrogen-air mixtures in a 27 m3 chamber

Experimental data from vented hydrogen deflagrations with concentrations from 15% to 21% are presented. The experiments were performed in a 27 m3 cubic chamber with a vent area of either 0.78 or 1.76 m2. Uniform and stratified mixtures were used in the test matrix, and the obstacle configuration also varied to achieve different volumetric blockage ratios. The purpose of this study was to investigate the effect of hydrogen concentration, vent area, non-homogeneous mixtures and obstacles on the explosion venting for lean hydrogen-air mixtures, and to evaluate the performance of an analytical model for calculating the maximum reduced overpressure. The results show that the maximum overpressure measured inside the empty chamber increases from 3 kPa to 28.5 kPa as hydrogen concentration increases from 15.3% to 20.2%. The raised vent location may affect the pressure development during explosion venting, and a third pressure peak caused by the occurrence of the maximum flame surface area could appear in the pressure profile when a large vent is located on the upper part of the side wall. Higher volumetric blockage ratio leads to higher maximum overpressure and flame velocity, and the increment of each pressure peak with the blockage ratio is more pronounced for the back ignition. Furthermore, when comparing with the volume of unburnt gases, the obstacles have a greater effect on the flame. However, the obstructions have a limited effect on the non-homogenous hydrogen deflagration, whose combustion behaviour is governed by the maximum hydrogen concentration in the chamber. Molkov’ best-fit model over-predicts the maximum reduced overpressure measured inside the empty chamber, but the predictions are relatively acceptable for the center ignition.

Upgrade of the Cryogenic Control System for SRF Modules at the Taiwan Light Source

An upgrade of the cryogenic control system for superconducting radio-frequency (SRF) modules of the Taiwan Light Source (TLS) has been completed. The biggest challenge was to recover all protection and operational functions, while minimizing the quantity of vented helium from SRF modules while replacing valve controllers. Gradually, this work was finished within several one- and ten-day scheduled machine shutdown periods for accelerator maintenance. No large helium vent nor pollution of the cryogenic system occurred during all component replacements and function verifications. Functions of the cryogenic electronics were improved, whereas the valve controllers are upgraded to new versions to increase reliability and availability. Communications with the data acquisition system was also secured by buffered signal processing module so that device shutdown of the data acquisition system will not interrupt the cryogenic valve operation.

Pressure-induced dipole theory and pressure pulsation in shallow urban road tunnels with top vents

Shallow urban road tunnels with top vents represent environmentally friendly and energy-saving technology. To date, four such tunnels are operational in Nanjing, and their intra-tunnel air quality has been widely acclaimed. However, no prescriptive design methods have been developed for this technology. Natural ventilation at the top of the tunnels is caused by the pressure difference inside and outside the top vents. Thus, a prerequisite to the development of scientific design methods for such tunnels is a complete understanding and representation of the pressure wave distribution pattern in the tunnels. Based on an analogy with an electric dipole, we propose a pressure-induced dipole theory and construct an intra-tunnel pressure distribution model. An experimental platform is developed to evaluate the pressure distribution inside tunnels under 6 operational conditions. The results suggest the following. (1) The proposed pressure-induced dipole theory can well describe and explain the pressure wave distribution rules in road tunnels. (2) With a uniform and continuous traffic flow, the real-time pressure on each point in the tunnels demonstrates periodical asymmetrical quasi-sinusoidal pulsation, where the cycle is given as T = (S + L)/v. (3) Periodical pressure pulsation with decaying amplitude exists around the top vents. With large top vents, the pressure exchange between the inside and outside of the tunnels is significant.

The Apparent Absence of Kilometer‐Sized Pyroclastic Volcanoes on Mercury: Are We Looking Right?

AbstractSpacecraft data reveal that volcanism was active on Mercury. Evidence of large‐volume effusive and smaller‐scale explosive eruptions has been detected. However, only large (&gt;~15 km) volcanic features or vents have been found so far, despite abundant high‐resolution imagery. On other volcanic planets, the size of volcanoes is anticorrelated with their frequency; small volcanoes are much more numerous than large ones. Here we present results of a numerical model that predicts the shapes of ballistically emplaced volcanic edifices and hence can explain the lack of kilometer‐sized constructional explosive volcanoes on the surface of Mercury. We find that due to the absence of the atmosphere, particles are spread on this planet over a larger area than is typical for Earth or Mars. Erupted volumes are likely insufficient to build edifices with slope angles that enable their easy recognition with currently available data or that could survive destruction by subsequent impact bombardment.

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.

Experimental study of geysers through a vent pipe connected to flowing sewers.

Geysers of air-water mixtures in urban drainage systems is receiving considerable attention due to public safety concerns. However, the geyser formation process and its relation with air release from pressurized pipes are still relatively little known. A large-scale physical model, that consisted of a main tunnel with a diameter of 270 mm and a length of 25 m connecting two reservoirs and a vertical vent pipe, was established to investigate geyser evolution and pressure transients. Experimental results including dynamic pressure data and high speed videos were analysed in order to characterize geysering flow through the vent pipe. Pressure transients were observed during geysering events. Their amplitudes were found to be about three times the driving pressure head and their periods were close to the classic surge tank predictions. The influence of flow rate and vent pipe size were examined: geyser heights and pressure peaks decreased for small flow rate and large diameter vent pipe. It is suggested that geyser heights are related with the pressure head and the density of the air-water mixture.

Numerical simulations of vented hydrogen deflagration in a medium-scale enclosure

A validation study was performed to investigate the ability of Computational Fluid Dynamics (CFD) models to predict hydrogen deflagrations in vented enclosures. The validation exercise was aimed at assessing the suitability of CFD as a reliable tool for explosion safety assessments and involved comparing CFD predictions with measurements from an experiment carried out by FM Global in a 64 m3 enclosure. The enclosure included a large square vent located in the center of one of its walls. The enclosure was filled with a homogenous hydrogen-air mixture of 18% v/v composition before ignition at its center. In this paper, CFD model predictions of the transient pressure and the flame speed are compared against experimental measurements. Additionally, peak overpressure predictions are compared against empirical correlations and the NFPA 68 vent sizing standard. The study focuses on the prediction of the first overpressure peak that is generated by external explosion. The agreement between the models’ predictions and experimental results is found to be satisfactory, which suggests that CFD models have the potential to predict explosion phenomena with reasonable accuracy. However, more extensive model validation and sensitivity studies are required before CFD models can be used with confidence in explosion safety assessments.

Effect of sampling density on the reliability of airflow rate measurements in a naturally ventilated animal mock-up building

Measuring natural ventilation rates in buildings with large vents with high accuracy and precision is not straight forward due to high spatial and temporal variabilities in the velocity distribution. Simplification of airflow rate measurements are mostly effectuated by lowering sampling density. Different sampling densities were investigated for both direct and tracer gas methods and compared with a detailed direct measurement method were in a naturally ventilated animal mock-up building. The results obtained by the reference method indicated that using only sampling locations in the middle of the side openings overestimated the airflow rate. In view of wind variations, better accuracy, precision and lower coefficients of variation were obtained with a higher number of sampling locations. The coefficients of variation varied between 5% for the reference and 29% using only one sampling location in the side outlet. In the ridge opening, only one middle sampling location was sufficient for an accuracy of 2% and a precision of 3%. The indirect tracer gas method gave varying concentrations with high confidence intervals resulting in non-significantly different measurement results between the different sampling strategies. The pattern of sampling locations was found to be very important resulting in different accuracies for a given sampling density.

Constraints on density changes in the funnel-shaped caldera inferred from gravity monitoring of the Lusi mud eruption

From its inception May 29, 2006, the Lusi mud eruption has continuously erupted fluids, boiling mud and clasts through large active vents approximately 100 m in diameter. In 2016, we conducted a Dynamic Gravity survey (DG) using a network built over four locations and two Continuous Gravity-monitoring (CG) experiments to monitor the eruption activity. The CG was done for 8 days from June 2nd to June 10th, and for 9 days from August 20th to August 29th, 2016. Atmospheric pressure and atmospheric temperature variations were recorded during each experiment to constrain potential environmental effects, and Earth and oceanic tide effects were removed from gravity signals (CG and DG). Atmospheric pressure effects were removed from CG gravity signals. At the station, closest to the hydrothermal pond, the DG survey results show a gravity increase of ∼0.009 mGal month−1, which we interpret as the growth of the mud edifice in the central area. CG-monitoring shows that gravity variations occur at a period of 12–13 h, with amplitudes reaching up to 0.020 mGal. We interpret this as relating to density variation of the rising mud mixture (fluids + coarse mud + clasts). The observed 12–13 h period variations appear to indicate that tides may have some control on the density change of rising mud mixture by triggering the release of gas trapped at depth. Our 3D gravity results around the Lusi vents show that density variations range from 100 kg m−3 to 775 kg m−3. Similarly, vent diameters better constrain density contrasts occurring within the caldera zone, which is more likely to range between 400 and 450 kg m−3, and is equivalent respectively to 27% and 31% of gas ratio change over time.

Experimental Analysis on the Critical smoke exhaust rate for Large Vent in Tunnel concerning for Plug-holing Phenomenon

For different combinations of fire heat release rate and longitudinal velocity, a series of experimental tests concerning for plug-holing phenomenon have been carried out on a 1/20 reduced scale model tunnel. Firstly the smoke temperature distribution beneath the tunnel ceiling was given out. And based on the temperature profiles of pile A, B and C, the air-smoke interfaces for three locations were accordingly labeled and flow patterns below the vent were given out. Secondly with the augment of the smoke exhaust rate, the smoke layer decreased. For the case (Q=4.68MW, v=0.33m/s), the stability of upper smoke layer had been broken, when the smoke flow rate increased to 58m3/s corresponding to plug-holing phenomenon. Lastly for different combinations of fire heat release rate and longitudinal velocity, the critical smoke exhaust rate can be obtained. And a simple dimensionless correlation, suitable for practical application, was given out.