Detonation limits in mixtures of oxygen and homologous hydrocarbons

1970 ◽  
Vol 319 (1539) ◽  
pp. 461-477 ◽  
Keyword(s):  
Homologous Series ◽  
Ambient Pressure ◽  
Oxygen Mixture ◽  
Critical Rate ◽  
Mole Percent ◽  
Detonation Parameters ◽  
Detonation Limits ◽  
Hydrocarbon Molecules ◽  
Cracking Mechanism ◽  
Cracking Products

Detonation parameters have been determined for fuel+ oxygen mixtures for ambient pressure and temperature in a 1 in (2.54 cm) diameter tube, with initiating impact from a detonating stochiometric hydrogen + oxygen mixture. Detonation limits in mole percent fuel are : methane 8.25 and 55.80 n -propane 2.50 and 42.50 n -butane 2.05 and 37.95 neopentane 1.50 and 33.00 propylene 2.50 and 50.00 These data have been matched with comparable results for the systems oxygen + ethane and oxygen + ethylene, obtained in other researches, in order to establish behaviour in homologous series of com pounds. For all compositions, propagation of detonation can usefully be correlated to the Mach product v M 2 . Far-reaching correlations are found for different hydrocarbon molecules, when the data are transformed on a homology basis. This suggests that the structure of the fuel molecules has only a secondary influence. At the fuel-lean limits, marginal behaviour can be interpreted in terms of a critical tem­perature rise which may be related to a critical rate of an initial cracking mechanism . Near the fuel-rich limits it seems more likely that stability depends on the condensation of (carbonaceous) solids from a mixture of cracking products.

scholarly journals The Effect of Pre-Ozonation of Natural Bitumen on the Rate of Cracking Reactions

2020 ◽  
pp. 78-88
Author(s):  
Nikita N. Sviridenko ◽  
Anatoly K. Golovko
Keyword(s):  
Rate Constants ◽  
Raw Materials ◽  
Thermal Transformation ◽  
Raw Material ◽  
Oxygen Mixture ◽  
Natural Bitumen ◽  
Molecular Components ◽  
Cracking Products

The effect of bitumen ozone-oxygen mixture pretreatment followed by cracking on thermolysis processes was investigated. Pretreatment of natural bitumen allowed to intensify the process of destruction of high-molecular components of raw materials, the content of which decreased by 8–15% wt. In the resulting liquid cracking products, oils predominate from 70 to 80% wt. Based on the formalized model of the thermal transformation of high-molecular components of the raw material, the rate constants of the bitumen thermolysis reactions (k) and the effect of pretreatment of the ozoneoxygen bitumen mixture on the cracking reactions are calculated

Visualization and Parametric Study of Reaction Propagation in Meso-Scale Tubes

2009 ◽  
Author(s):  
Chan-Yu Wang ◽  
Jun-Kai Wang ◽  
Ming-Hsun Wu
Keyword(s):  
High Speed ◽  
Initial Pressure ◽  
Transition Process ◽  
Ambient Condition ◽  
Oxygen Mixture ◽  
Reaction Fronts ◽  
Detonation Limits ◽  
High Speed Cinematography ◽  
Deflagration Wave ◽  
Meso Scale

Reaction propagation of ethylene/oxygen and methane/oxygen mixtures in capillary tubes of 1 and 2 mm in diameters with initial pressure and temperature at ambient condition were experimentally visualized and analysed using high speed cinematography. Deflagrative flame was initiated in middle of the smooth tube, and the reaction fronts accelerated as they propagated towards the exits in the opposite directions. Lengths of the tubes investigated ranged from 0.4 to 1 m (one side), and deflagration-to-detonation transitions were observed for equivalence ratios between 0.5 and 3. The visible reaction front propagates at speeds approach Chapman-Jouguet speed for ethylene/oxygen mixture in the 1 mm and 2 mm tubes. An overshoot in propagation velocity was found during transition process. For leaner and richer mixtures beyond the detonation limits, steady deflagration wave propagation was observed. Reaction propagation in methane/oxygen mixture was also investigated. Several near-limit propagation modes were found.

scholarly journals Effect of helium preconditioning on neurological decompression sickness in rats

2019 ◽  
Vol 126 (4) ◽  
pp. 934-940 ◽  
Author(s):  
Rongjia Zhang ◽  
Yongchao Yu ◽  
Anatol Manaenko ◽  
Hongda Bi ◽  
Ning Zhang ◽  
...  
Keyword(s):  
Evoked Potential ◽  
Decompression Sickness ◽  
Ambient Pressure ◽  
Spinal Cord Ischemia ◽  
Neurological Deficits ◽  
Oxygen Mixture ◽  
Sprague Dawley ◽  
Spinal Lesions ◽  
Sprague Dawley Rats ◽  
Grip Test

Decompression sickness (DCS) occurs because of an excessively rapid and extensive reduction of the ambient pressure. Bubble-induced spinal cord ischemia is generally considered as a part of neurological DCS pathogenesis. Because helium preconditioning (HPC) recently demonstrated beneficial properties against ischemic damage, we hypothesized that HPC may decrease the neurological deficits of DCS in rats. Seventy-five male Sprague-Dawley rats were divided into a non-HPC group ( n = 25) and a HPC group ( n = 25) and 25 naive animals that were euthanized for histological examination ( n = 5) or anesthetized for baseline somatosensory evoked potential (SSEP) recordings ( n = 20). To induce DCS, rats were compressed with air to a pressure of 709 kPa for 60 min and decompressed at a rate of 203 kPa/min. HPC was administered as three episodes of 79% helium-21% oxygen mixture inhalation for 5 min interspersed with 5 min of air breathing. We found that HPC resulted in significantly decreased DCS incidence and delay of DCS onset. HPC also improved animal performance on the grip test after decompression and significantly ameliorated decompression-induced decrease of platelet number. Furthermore, the incidence of abnormal SSEP waves and histological spinal lesions was significantly reduced by HPC. We conclude that HPC can decrease the occurrence of DCS and ameliorate decompression-induced neurological deficits. NEW & NOTEWORTHY Helium preconditioning ameliorates decompression-induced neurological deficits in rats. Helium breathing before air dives may prevent neurological deficit and attenuate symptoms after decompression.

An Attack on the Contamination Problem in the Electron Microscope

1967 ◽  
Vol 25 ◽  
pp. 368-368
Author(s):  
J. J. Kelsch ◽  
A. Holtz
Keyword(s):  
Electron Microscope ◽  
Pressure Gradient ◽  
Ionization Potential ◽  
Simple Solution ◽  
Specimen Surface ◽  
Contamination Rate ◽  
Local Pressure ◽  
High Ionization ◽  
Hydrocarbon Molecules ◽  
Contamination Problem

A simple solution to the serious problem of specimen contamination in the electron microscope is presented. This is accomplished by the introduction of clean helium into the vacuum exactly at the specimen position. The local pressure gradient thus established inhibits the migration of hydrocarbon molecules to the specimen surface. The high ionization potential of He permits the use of relatively large volumes of the gas, without interfering with gun stability. The contamination rate is reduced on metal samples by a factor of 10.

New replica method with plasma polymerized film by glow discharge

1988 ◽  
Vol 46 ◽  
pp. 414-415
Author(s):  
A. Tanaka ◽  
M. Yamaguchi ◽  
T. Hirano
Keyword(s):  
Power Supply ◽  
Plasma Polymerization ◽  
Vacuum Chamber ◽  
Complex Surface ◽  
Replica Method ◽  
Metal Extraction ◽  
High Voltage Power Supply ◽  
Negative Glow ◽  
Hydrocarbon Gas ◽  
Hydrocarbon Molecules

The plasma polymerization replica method and its apparatus have been devised by Tanaka (1-3). We have published several reports on its application: surface replicas of biological and inorganic specimens, replicas of freeze-fractured tissues and metal-extraction replicas with immunocytochemical markers.The apparatus for plasma polymerization consists of a high voltage power supply, a vacuum chamber containing a hydrocarbon gas (naphthalene, methane, ethylene), and electrodes of an anode disk and a cathode of the specimen base. The surface replication by plasma polymerization in negative glow phase on the cathode was carried out by gassing at 0.05-0.1 Torr and glow discharging at 1.5-3 kV D.C. Ionized hydrocarbon molecules diffused into complex surface configurations and deposited as a three-dimensionally polymerized film of 1050 nm in thickness.The resulting film on the complex surface had uniform thickness and showed no granular texture. Since the film was chemically inert, resistant to heat and mecanically strong, it could be treated with almost any organic or inorganic solvents.

Reduction of Specimen Contamination in Electron-Beam Instruments

1976 ◽  
Vol 34 ◽  
pp. 576-577
Author(s):  
G. Lehmpfuhl ◽  
P. J. Smith
Keyword(s):  
Electron Beam ◽  
Cold Trap ◽  
Beam Diameter ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Hydrocarbon Molecules ◽  
Electron Microscopes ◽  
Combination Of Methods ◽  
Convergent Beam ◽  
Very High

Specimens being observed with electron-beam instruments are subject to contamination, which is due to polymerization of hydrocarbon molecules by the beam. This effect becomes more important as the size of the beam is reduced. In convergent-beam studies with a beam diameter of 100 Å, contamination was observed to grow on samples at very high rates. Within a few seconds needles began forming under the beam on both the top and the underside of the sample, at growth rates of 400-500 Å/s, severely limiting the time available for observation. Such contamination could cause serious difficulty in examining a sample with the new scanning transmission electron microscopes, in which the beam is focused to a few angstroms.We have been able to reduce the rate of contamination buildup by a combination of methods: placing an anticontamination cold trap in the sample region, preheating the sample before observation, and irradiating the sample with a large beam before observing it with a small beam.

A theory of contamination in electron microscopes by surface diffusion

1978 ◽  
Vol 36 (1) ◽  
pp. 116-117
Author(s):  
J.T. Fourie
Keyword(s):  
Electron Beam ◽  
Surface Diffusion ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Physical Parameters ◽  
Carbon Compounds ◽  
Hydrocarbon Molecules ◽  
Electron Microscopes ◽  
Primary Electrons ◽  
Long Chain

Contamination in electron microscopes can be a serious problem in STEM or in situations where a number of high resolution micrographs are required of the same area in TEM. In modern instruments the environment around the specimen can be made free of the hydrocarbon molecules, which are responsible for contamination, by means of either ultra-high vacuum or cryo-pumping techniques. However, these techniques are not effective against hydrocarbon molecules adsorbed on the specimen surface before or during its introduction into the microscope. The present paper is concerned with a theory of how certain physical parameters can influence the surface diffusion of these adsorbed molecules into the electron beam where they are deposited in the form of long chain carbon compounds by interaction with the primary electrons.

Environmental microscopy of capillary stress-induced strain behavior in ambient-pressure aerogels

1996 ◽  
Vol 54 ◽  
pp. 850-851
Author(s):  
Sudeep M. Rao ◽  
Joshua Samuel ◽  
Sai S. Prakash ◽  
C. Jeffrey Brinker
Keyword(s):  
Silica Aerogel ◽  
Ambient Pressure ◽  
Drying Shrinkage ◽  
Pore Filling ◽  
Silica Network ◽  
Strain Behavior ◽  
Partially Saturated ◽  
Capillary Stress ◽  
Wetting Liquid ◽  
Aerogel Films

Ambient pressure silica aerogel thin films have recently been prepared by exploiting reversible drying shrinkage caused by derivatization of the internal gel surface. Aerogels have porosities of upto 99.9% and due to the small size of the pores (few nanometers), large capillary stresses are produced in gels that are partially saturated with a wetting liquid. As a result of these capillary stresses, the flexible silica network undergoes strain which has been observed using environmental microscopy. This technique allows variation of the equilibrium vapor pressure and temperature, and a simultaneous monitoring of the deformation of the unconstrained film thickness. We have observed >600% deformation during the pore-filling and pore-emptying cycles. In this presentation, we discuss the unique stress-strain behavior of these films.Ref.: Sai S. Prakash, C. Jeffrey Brinker, Alan J. Hurd & Sudeep M. Rao, "Silica aerogel films prepared at ambient pressure by using surface derivatization to induce reversible drying shrinkage", Nature. Vol. 374, 30 March, 1995, 439-443.

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