Heavy Vapor Research Articles

Теоретические основы оценки аэродинамического воздействия ветровых потоков на сооружения завода по подготовке и сжижению природного газа

Leaks (spills) of liquefied gases evaporate rapidly on the ground (water) and initially generate a cold plume of heavy vapors. The plume spreads fast downwind, heats up with time, and can become positively volatile in case the concentration of interest for the study (above the lower flammability limit) is reached; therefore, the plume can rise and transform into a vapor cloud. The plume or the vapor cloud can ignite in the flash form. Such situations are possible at liquefied natural gas production plants or regasification units where large amounts of explosive substances are handled involving changes in their aggregate state. The article analyses the significance of the wind impact on the facilities of natural gas liquefaction plants for regular operation and the potential consequences of emergencies. In order to assess the wind impact, the direct numerical modeling of the structure of local wind flows generated at the airflow around the plant facilities by vertical method is suggested. An example of numerical modeling for a natural gas liquefaction plant based on the modular constructions of the process line is provided.

Evaporation from a cylindrical cavity: effect of gravity on the vapour cloud

We examine the vapour cloud of a pure liquid evaporating from a millimetric cylindrical well/cavity/aperture. This is accomplished by injecting the liquid up a vertical pipe towards its outlet onto a horizontal substrate. The injection is halted before the liquid surpasses the substrate level. The resulting final state is a meniscus at or near the pipe's end. The analysis is realised by vapour interferometry (side view over the substrate) closely intertwined with simulations (including Stefan flow), which also help to fill up certain gaps in the measurements and provide computed evaporation rates. Comparison with experiment is facilitated by converting the computed vapour clouds into interferometric images, especially helpful when an inverse (Abel-type) conversion is difficult. Experiments are conducted in both microgravity (via parabolic flights) and ground conditions, thus enabling direct assessment of the role of gravity. The contrast is accentuated by a working liquid with heavy vapour (refrigerant HFE-7100), when instead of being flattened on ground the vapour cloud assumes a roughly hemispherical shape in microgravity. Furthermore, a non-trivial vapour-cloud response to the flight ${\rm g}$ -jitter (residual gravity oscillations) is unveiled, ${\rm g}$ -jitter vibrations posing a challenge for interferometry itself. A number of undesired but curious side issues are revealed. One concerns vapour formed deep inside the pipe during rapid injection and subsequently ejected into the field of view, which is detected experimentally and quantified in terms of vapour Taylor dispersion in the pipe. Others are an injection volume anomaly and parasitic postinjection specifically observed in microgravity conditions.

The “green” use of fluorocarbons in Cherenkov detectors and silicon tracker cooling systems: challenges and opportunities in an unfolding era of alternatives

Saturated fluorocarbons (SFCs) of form CnF(2n+2) are chosen for their optical properties as Cherenkov radiators, with C4F10 and CF4 currently used at CERN in the COMPASS and LHCb ring imaging Cherenkov detectors. Their non-conductivity, non-flammability and radiation-resistance also make SFCs ideal coolants: C6F14 liquid cooling is used in all LHC experiments, while C3F8 is used for the evaporative cooling of TOTEM and the ATLAS silicon tracker. These fluids, however, have high global warming potentials (5000–10000*GWPCO2), and represented around 36% of CERN’s CO2-equivalent emissions in 2018. There is thus an impetus to reduce their use, losses in purification and wastage through leaks, through improved monitoring and closed circulation system design. Newer spur-oxygenated fluoro-ketones, for example from the 3 M NOVEC® range, with CnF2nO structures, can offer similar performance to SFCs with but with very low, or zero GWP. Although these fluids do not yet exist in large quantities over the full CnF2 “matrix” the radiation tolerance and thermal performance of NOVEC 649 (C6F12O) was sufficiently promising for it to be chosen as a C6F14 replacement for cooling silicon photomultipliers. Additionally, subject to optical testing, NOVEC 5110 (C5F10O) could (if blended with nitrogen) replace both C4F10 and CF4 in Cherenkov detectors. Lighter molecules (for example C2F4O, with similar thermodynamics to C2F6)—if and when available in industrial quantities—might allow lower temperature operation than evaporative CO2 in future silicon trackers operated at very high luminosity. Ultrasonic gas mixture analysis is very sensitive to concentration changes of a heavy vapour in a light carrier, and is used—in the only such fluorocarbon coolant leak monitoring system operating at LHC—for real-time monitoring of C3F8 coolant leaks from the ATLAS pixel and SCT silicon trackers into their nitrogen-flushed environmental volumes. A typical C3F8 sensitivity of better than 10−5 is achieved. Advanced new ultrasonic algorithms allow measurement of the concentrations of a pair of gases of particular interest on top of a varying known baseline of other gases. The technique is thus of considerable value in leak monitoring and could be used to blend fluoro-ketones with nitrogen or argon to reduce the GWP “load” of large volume atmospheric pressure gas Cherenkov radiators without the recourse to higher-pressure noble gas approaches. This paper outlines an approach to GWP reduction with fluoro-ketone fluids and the blending of heritage SFCs or fluoro-ketones with lighter gases using ultrasonic monitoring and control. Possible avenues for the use of fluoro-ketones in liquid phase and evaporative cooling of silicon trackers are discussed.

Active Role of Vapor Clouds around Evaporating Sessile Droplets in Microgravity: Marangoni Jets and Electroconvection.

A benchmark microgravity experiment (dubbed "ARLES") is analyzed. It concerns evaporation of several-μL sessile droplets with a pinned millimetric circular contact line on a flat substrate into a vast calm (here nitrogen) atmosphere at nearly normal conditions. Hydrofluoroether (HFE-7100) is used as a working liquid whose appreciable volatility and heavy vapor accentuate the contrast between the micro- and normal gravity. A possibility of switching on a DC electric field (EF) of several kV/mm orthogonally to the substrate is envisaged. We here focus on the findings intimately associated with the visualization of the vapor cloud by means of interferometry and rationalized by means of extensive simulations. In particular, with different degrees of unexpectedness, we discover and explore a Marangoni jet (without EF) and electroconvection (with EF) in the gas, which would otherwise be masked by buoyancy convection. Using the same tools, we examine some malfunctions of the space experiment.

“Ayenst trauelynge fendys by nyghte”: Simple Medicines, Practical Innovation, and the Premodern Conceptualization of the Nightmare

ABSTRACTSleep paralysis, as it is known today, was one of the most remarked-upon maladies in premodern medicine. The feeling of being choked during sleep was usually seen by physicians as being caused by an abundance of melancholic humors. Others interpreted the experience as a supernatural attack. However, the distinctions between medical and “superstitious” remedies against nightmares were rarely so clear cut, especially given the belief that demons were able to manipulate the bodily humors. In this article I will chart the various substances—plant and stone—that were traditionally believed to assuage the symptoms of the nightmare. I will examine how “hot” herbs, such as peony, and minerals with occult heating properties, such as gagate, could rebalance the dangerously cold and heavy vapors that provoked a nightmare attack. It will be seen that even seemingly “magical” apotropaic practices were entirely rational within the milieu of humoral theory.

Experimental study on evaporation of droplets in microgravity and in the presence of electric field

One of the key limiting factors in the evaporation rate of sessile droplets is the evacuation of the generated vapour away from the liquid-air interface. In the absence of convection, the main driving mechanism is the vapour diffusivity: as mass diffusion is quite a slow process, this generally leads to small evaporation rates. For liquids with a heavy vapour, natural convection induced by density gradients in the vapour cloud can increase the evaporation rate significantly on ground. Nevertheless, this effect is absent in space and one therefore has to find alternative mechanisms to accelerate evaporation. The electric field may induce some convection and influence evaporation. This work describes experiments regarding evaporation of droplets in microgravity conditions performed during a sounding rocket campaign in June 2019. Microgravity allows to exclude the contribution of natural convection that otherwise prevails on the other effects. The electric field produces a clear change in the vapour concentration distribution surrounding the droplet and an increase of the evaporation rate with respect the case with no electric field. Moreover, in the absence of electric field, the Marangoni convection in the liquid has an effect on the vapour cloud too, preventing the pure diffusive behaviour.

Natural convection flows due to evaporation of heavier-than-air fluids: Flow direction and validity of using similarity of temperature and vapor density fields

Natural convection driven by evaporation of heavier-than-air fluids from the surface of the heated horizontal and vertical flat plates is studied both experimentally and numerically. The combined buoyancy effects of temperature and vapor density are shown to result in either downward or upward flow depending on the plate temperature and evaporating substance volatility and molar mass. For some substances (e.g., butanol) flow reversals are observed: solutal buoyancy is dominant for low and high temperatures of the heated plate leading to downward flow, whereas at moderate temperatures thermal buoyancy prevails resulting in upward convection. Refractive index fields are measured using Background Oriented Schlieren (BOS). Similarity between the temperature and vapor density fields associated with heat and mass transfer analogy is used to obtain temperature and vapor density fields from experimental data. The validity of this approach is analyzed. Good agreement between experimental temperature and vapor density distributions and numerical simulations is obtained for ethanol vapor, which has Lewis number about 1.8. For butanol vapor, which has Lewis number about 2.5, similarity is violated and temperature and vapor density contributions to refractive index cannot be separated. This is also true for validity of simplified modeling using total expansion coefficient. Similarity is also shown to be violated for hot liquid evaporation from a tank with conductive walls. In this case boundary conditions are dissimilar and upward convective flow of warm clean air near the outer surface of the tank walls is observed, which entrains the heavy vapor.

Ethanol and Methanol Burn Risks in the Home Environment.

Biofuel heaters and fireplaces have in recent years been introduced for indoor and outdoor use. Due to their simplicity, they are usually equipped with few or no safety features. Worldwide, incidents resulting in major skin burn injury and long hospitalization periods have occurred when using such biofuel units. The present study analyses the characteristics of the liquids ethanol and methanol to get a scientific background for understanding related accidents. The comparably heavy vapors, especially from ethanol, may generate a pillow of combustible gas in the vicinity of the unit, particularly in quiescent indoor air conditions. It is also revealed that these fuels represent a potential severe risk, since the equilibrium vapor pressures are close to the stoichiometric fuel–air composition at normal room temperatures. Selected incidents were reviewed to understand the mechanisms involved when severe burns were received by the users. It turns out that the most severe incidents were related to refilling operations and included ignition of the fuel container vapor phase. When ignited, the container gas phase expansion propelled burning fuel from the bottle or container onto the user or other persons in the vicinity. Similar incidents involving refilling methanol for chemistry demonstrations and ethanol for endodontic (dentistry) treatment were also studied and it was shown that these accidents followed similar accident mechanisms. It may be concluded that the main contributors to burn risk are the near-stoichiometric vapor pressure of these liquids at room temperature and the close proximity of the fuel container to burning fuel. Research needs and possible technical barriers are suggested to reduce this risk for the future.

Development of heavy vapour clouds in very low wind speeds

The majority of very large vapour cloud explosions occur in such low wind speeds that vapour flow is gravity-driven. The rate of stripping (or detrainment) of heavy gas by the wind is so low that almost all of the gas released remains in a gas “blanket”, which typically slumps in all directions around the source. Such gravity-driven flammable clouds may extend many hundreds of metres from the source in all directions without significant dilution: their development cannot be assessed with conventional windy dispersion models.Previous work on the basic problem of gravity-driven vapour transport on a flat open surface is reviewed. Existing methods suffer from a number of deficiencies including arbitrary specification of current height and velocity and the neglect of surface friction.A new method of analysis is presented. Close to the source the flow can be calculated from the initial conditions at the source by integration of momentum and continuity equations. Entrainment of fresh air and friction increase the stability of the flow (Richardson number) and the rate of dilution declines towards zero. When the Richardson number approaches unity the current becomes critical and further out from the source the flow is under downstream control.The new method is used to calculate the total dilution of a vapour cloud before entrainment of fresh air is completely suppressed. This determines whether clouds are flammable at long-range. The effects of surface roughness, bund height, vapour density etc. are described.Predictions are compared with data from incidents.

Heating rate effects on pyrolytic vapors from scrap truck tires

Powder of scrap truck tire was pyrolysed in a fixed bed reactor equipped with a water-cooled liquid recovery system and a gas sampling valve. A sampling system was set up and the quantitative and qualitative analyses of pyrolytic vapors were performed for heating rates (HR) ranging from 5 to 25°Cmin−1. HR which practically has no influence on the quality and yield of char (38wt%), has a significant effect on the pyrolytic vapors, especially on the cracking reactions of heavy vapors. By increasing HR from 5 to 25°Cmin−1, the gas yield increases from 7.24 to 18.04wt% at the expense of oil yield. The high heating rates favor production of CH4 and disadvantage production of C4H8. In addition, heating rates between 10 and 15°Cmin−1 minimize the H2, CO and CO2 concentrations and maximize the C2H6, C3H6, C4H6 and H2S concentrations. Its lower heating value is between 47 and 56MJNm−3. As regards the produced oils, they consist mainly of aromatic products whose higher heating value is about 40MJkg−1. Regardless of heating rates, around 97.15% of the energy contained in raw material (tire) is found in the three pyrolysis products. The sulfured organic compounds appear in forms of C7H5NS, C15H16O3S and C16H14O2N2S.

Investigation of the Sorption of Heavy Aromatic Compounds in Polymers: Application to the Cleaning of Synthesis Gas

Syngas from gasification contains heavy aromatic hydrocarbons, which must be removed because of condensation hazards. This work addresses the sorption of toluene and naphthalene in cross-linked poly(dimethylsiloxane) to explore the potential of vapor permeation to clean syngas. This topic is unusual for permeation in terms of temperature and heavy vapors and has never been investigated. The sorption of pure hydrocarbons was studied with vapor and liquid over the entire range of activities. The sorption of their mixtures was also investigated to explore synergetic effects. It was shown that the solubility of naphthalene is high and strongly variable with activity. However, the sorbed amounts of naphthalene were lower than those with toluene for the same activity. The isotherms were fitted with Flory–Huggins and ENSIC models. In the case of mixture sorption, strong coupling effects were revealed. A modified ENSIC model using a binary parameter of interaction between the hydrocarbons was developed to model t...

THE ENVIRONMENTAL SAFETY IMPROVING BY MODELING DISPERSION AND EMISSIONS REDUCING OF GAS STATIONS

The paper suggests the perspective ways of reduction emissions of dangerous pollutions on the gas stations. It compares the pollutant concentration values obtained by in environmental measurements and the modeling of dispersion of emissions from the gas stations located on the city territory. This paper concludes that there is the advisability to account of technology fuel filling process in tanks for the regulations of the sanitary protection zone size of gas station. Moreover it concludes that the calculations of heavy hydrocarbon vapor dispersion in the atmosphere for various physical parameters of the emissions source (gas station) are necessary. Therefore the installation of vapor trapping of heavy hydrocarbons to the gas station is necessary as well.

Density‐Driven Migration of Heavy NAPL Vapor in the Unsaturated Zone

Contaminant vapor (gas) plumes emanating from liquid sources migrate easily in the unsaturated zone. Heavy vapors preferentially migrate downward due to their greater density and thus pose a potential threat to underlying aquifers. Large‐scale column experiments and numerical simulations were conducted to investigate the density‐driven migration of carbon disulfide (CS2) vapor. Carbon disulfide, among others used to manufacture viscous rayon, is an industrial, non‐polar solvent. It is highly volatile and characterized by a very high density (1.6) relative to air when in a gaseous state. The experiments were conducted in large, vertical columns (i.d. = 0.109 m) of 4‐m length packed with a dry porous medium. Different types of glass beads were used to investigate the sensitivity of migration to permeability. The porous medium was kept dry to avoid partitioning effects into pore water. Gas samples were taken along the column throughout the experiment to quantify time and space dependent vapor migration. The experiments characterized the migration behavior of a heavy CS2 vapor plume injected in the middle of the column. The vapor plume steadily migrated downward dependent on the total mass of injected CS2 and permeability. The setup of the experiment was reproduced in a 1‐D, two‐phase, two‐component, isothermal, numerical model. Simulation results were compared with data from the vapor migration experiments. The results of the numerical model satisfactorily reproduced the migration behavior observed in the experiments but suggested slightly higher velocities than those observed. Thus the research presented improves the understanding of density driven, advective migration of a heavy contaminant vapor in a dry porous medium at a large scale. It provides valuable experimental data not only for future research but particularly for the transfer to field situations.

Condensation rate of light vapour molecules in the transition regime

In order to overcome uncertainties of semi-empirical models based on the flux matching theory and to resolve discrepancies between more accurate interpolation formulas, obtained from various solutions of the Boltzmann equation, a new approach, similar to that recently proposed by the authors to consideration of the heavy vapour molecules condensation, is applied to light vapours. In this limit the transport of light vapour molecules to the central particle can be strictly considered as specific random walks, characterized by the exponential distribution of the elementary displacement distances for each walker migrating with a fixed speed and changing direction randomly, whereas the condensation rate is related to the mean volume swept per unit time by the migrating effective particle of radius equal to the radius of the central particle. Results of numerical calculations of the condensation rate at different values of the Knudsen number are approximated by the interpolation expression with a relatively high accuracy in comparison with the traditional expressions.

Next approximation of the random walk theory for Brownian coagulation

The new approach to Brownian coagulation theory, developed in the authors’ previous papers and based on the simple random walk theory (with a fixed elementary walk distance of migrating particles), is further improved by more realistic consideration of random walks with stochastically distributed lengths. The interpolation expressions derived in the simple random walk approach avoiding semi-empirical assumptions of the traditional models, are justified (within the calculation accuracy) by new calculation results obtained in the next approximation of the random walk theory. The developed approach being applied to the problem of heavy vapour molecules condensation in a large trap, results in the improved description of the condensation rate in the transition regime.

Lithium isotope fractionation during magma degassing: Constraints from silicic differentiates and natural gas condensates from Piton de la Fournaise volcano (Réunion Island)

Recent volcanic products from the Piton de la Fournaise Volcano, Reunion, show pronounced depletion or enrichment in lithium and significant isotopic fractionation related to degassing. (1) trachytic pumices from the April 2007 eruption show extreme Li depletion (90%) and isotopic fractionation (δ 7Li of − 21‰). The depletion of water and volatiles (Cl, F, B, Cs) in these samples suggests that Li loss occurred in response to degassing, which most likely occurred as the small, isolated volume of magma underwent extensive differentiation near the surface. Because the pre-degassing composition is relatively well known, the composition of the degassed pumice constrains the partition coefficient to 60 < D V–M < 135 and the isotopic fractionation factor, α V–M, to 1.010 at magmatic temperatures. Unlike D V–M, α V–M does not depend on whether crystallization and degassing occurred successively or concomitantly. (2) basaltic samples from the interior wall of the long-lived 1998 Piton Kapor were extensively altered by acidic gas. They also show extreme Li depletion, but barely significant isotopic fractionation (δ 7Li = + 4.5‰), suggesting that high-temperature leaching of Li by volcanic gas does not significantly fractionate Li isotopes. (3) high-temperature (400–325 °C) gas condensates formed during degassing of the thick lava flow of April 2007 display high Li contents (50–100 ppm), which are consistent with Li being as volatile as Zn and Sn. Their isotopically light Li signature (average of − 1.7‰) is consistent with their derivation from isotopically heavy vapor (+ 13.5‰) if the factor of isotopic fractionation between condensate and vapor is less than 0.985. A degassing-crystallization model accounts for the evolution of trace species, which, like lithium, are volatile but also moderately incompatible.

Engineering predictions of explosive layer formation in flammable-liquid spills

A model is described to predict the evaporation of a flammable-liquid spill and the subsequent formation of an explosive layer by mixing of the vapors with surrounding air. The model is intended for use in engineering predictions and is, therefore, designed to be easy to use and to produce answers within a very short time. To achieve these goals, simplifying assumptions have been introduced, the most important being the treatment of the flow field as one-dimensional (i.e., only variations in the vertical direction are taken into account). Special adjustments are made through submodels for effects that would not be addressed with sufficient accuracy by neglecting horizontal gradients. This is done to deal with forced ventilation and to treat the case where the vaporizing pool occupies only a fraction of the floor area of the enclosure. The model has been validated by comparison with available data from vaporizing pools and for diffusing heavy vapors; some of these comparisons are presented. Overall, agreement with experiment is found to be satisfactory and generally on the conservative side. This evaluation has confirmed the suitability of the formulation for use as a component in a comprehensive hazard-analysis approach that includes methods to predict the pressure increase from combustion of the explosive layer. Development of an integrated tool is currently under way.

Development of an engineering tool to quantify the explosion hazard of flammable liquid spills

AbstractFlammable liquid spills, or slow heavy vapor releases, produce flammable layers which, if ignited, can cause damage to the enclosure containing the release. The question of pressure development in the ensuing explosion has been addressed in a previous paper. This paper describes a model to predict the fuel distribution in the flammable layer as a function of the parameters that define the spill (or fuel release) scenario. Since the model is intended for use in engineering predictions, it is designed to be easy to use and compatible with widely available computer resources. Accordingly, the flow field is treated as one‐dimensional taking only variations in the vertical direction into account.This simplifying assumption is supplemented by special adjustments for effects not accurately addressed without the horizontal gradients. This includes sub‐models to deal with forced ventilation and cases where the vaporizing pool occupies only a fraction of the floor area of the enclosure.The model has been validated by comparison with available data from vaporizing pools, and for diffusing heavy vapors. Overall agreement with the experiment is satisfactory, and generally on the conservative side. On the basis of these results, the formulation has been judged suitable for use in combination with the method to predict the pressure increase from combustion of the flammable layer. These two elements are part of an integrated tool developed for use by FM Global Loss Prevention Consultants. The paper discusses the implications of this modeling approach in terms of protection design.

Mixture reactivity in explosions of stratified fuel/air layers

The paper addresses one aspect of the definition of the explosion hazard from flammable liquid spills or slow heavy vapor releases in enclosures. In this type of accidents, the explosive mixture is typically confined to a layer near the floor. No methods are currently available for the sizing of explosion vents in these partial-volume deflagrations. Resolution of the issue was sought through tests carried out in a 63.7 m3 (2250 ft3) chamber with stratified mixtures of propane in air. The layers were formed by slowly injecting propane at the chamber floor through diffusers, at a rate of the order of the estimated rate of vaporization of a typical solvent such as acetone. The layer composition was carefully characterized through gas concentration measurements at twelve locations, using a single continuous analyzer connected to a multiplexed sampling system. Following ignition of the layers, data were obtained on the propagation velocity of the flame and on the pressure developed by the explosion in the room both with and without venting. The results of the experiments have been correlated using an existing model, modified to account for the cylindrical geometry of the system and for the dual-mode character of the combustion process (a premixed flame is typically followed by diffusive/ convective burning of the rich portion of the fuel/air layer). While confirming the conservatism of current design recommendations, which are based on the assumption of a full-volume explosion, the work has brought out the fact that the contributions to pressure development from the different portions of the layer must be properly taken into account. Work is currently in progress to predict the fuel distribution in the explosive layer as a function of the parameters that define the spill (or fuel release) scenario. This step is being done through modeling of the rate of vaporization of a liquid pool and the subsequent dispersion of the vapors in the surrounding area. The model, when combined with the already-developed treatment of the explosion problem, will provide an integrated tool for predicting the protection requirements of flammable liquid process/dispensing areas.

Mass transfer dominated by thermal diffusion in laminar boundary layers

The concentration distribution of massive dilute species (e.g. aerosols, heavy vapours, etc.) carried in a gas stream in non-isothermal boundary layers is studied in the large-Schmidt-number limit, Sc[Gt ]1, including the cross-mass-transport by thermal diffusion (Ludwig–Soret effect). In self-similar laminar boundary layers, the mass fraction distribution of the dilute species is governed by a second-order ordinary differential equation whose solution becomes a singular perturbation problem when Sc[Gt ]1. Depending on the sign of the temperature gradient, the solutions exhibit different qualitative behaviour. First, when the thermal diffusion transport is directed toward the wall, the boundary layer can be divided into two separated regions: an outer region characterized by the cooperation of advection and thermal diffusion and an inner region in the vicinity of the wall, where Brownian diffusion accommodates the mass fraction to the value required by the boundary condition at the wall. Secondly, when the thermal diffusion transport is directed away from the wall, thus competing with the advective transport, both effects balance each other at some intermediate value of the similarity variable and a thin intermediate diffusive layer separating two outer regions should be considered around this location. The character of the outer solutions changes sharply across this thin layer, which corresponds to a second-order regular turning point of the differential mass transport equation. In the outer zone from the inner layer down to the wall, exponentially small terms must be considered to account for the diffusive leakage of the massive species. In the inner zone, the equation is solved in terms of the Whittaker function and the whole mass fraction distribution is determined by matching with the outer solutions. The distinguished limit of Brownian diffusion with a weak thermal diffusion is also analysed and shown to match the two cases mentioned above.