Home About us Contact
|
Home About us Contact | ||
|
|
||
Oxygen Ratio (oxygen + ratio)
Selected AbstractsPrediction of flammability speciation for the lower alkanes, carboxylic acids, and estersPROCESS SAFETY PROGRESS, Issue 1 2007M. Palucis Abstract A Gibbs energy minimization procedure is used to predict the flammability envelopes of alkanes, carboxylic acids, and acetates. In addition to providing the calculated adiabatic flame temperature (CAFT), the product profiles reveal regions of incomplete combustion products and the onset of methane formation above 0.0001 mole fraction. Temperatures at the predicted onset of methane production appear to be closely related to the temperature at the upper flammability limit (UFL). Although a fixed CAFT value could be related to the lower flammability limit (LFL), it was found that this was not the case with the UFL and only for acetic acid could a single CAFT value of 1200K be used to conservatively predict the flammable region. Rather, in general, a single CAFT value could not conservatively predict the upper flammable region. The predictions also reveal local maxima and minima in the concentrations of reaction products. These maps of incomplete combustion products for the flammability region predict that incomplete combustion products are produced at fuel/oxygen ratios significantly below the fuel/oxygen stoichiometric ratio. This region decreases as the limiting oxygen concentration is approached. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2006 [source] Pressure and gas composition effects on the operation of the pulsed flame photometric detectorISRAEL JOURNAL OF CHEMISTRY, Issue 2 2001Gad Frishman The effect of pressure and hydrogen/oxygen ratio of a burning gas mixture on pulsed flame emission time-dependence was investigated in the range of 0.1,5 atm using a specially designed pulsed flame photometric detector (PFPD). We studied the pressure and gas composition effect on the pulsed flame delayed light emission of sulfur, phosphorus, and nitrogen-containing organic compounds. The optimal pressure conditions for nitrogen detection, intensity, and emission time delay was found to be 0.4 bar, at which the detection sensitivity could be improved by a factor of 2. For phosphorus, the optimal pressure obtained was 1.3 bar with 40% sensitivity improvement (compared with 1 bar). In the case of sulfur detection, two emission maxima were obtained, at 1.1 and 0.6 bar, at H/O ratio of 5. Increasing the H/O ratio resulted in the appearance of only one peak at 1 bar, and enhancement of the sensitivity by a factor of 2.4 at H/O ratio of 10.3. From the analytical point of view, we found that emission intensity is practically unchanged by the pressure and the H/O ratio for all three elements investigated in the range of 0.8,1.1 bar and H/O of 5,6. Thus, in addition to excellent sensitivity and improved selectivity, the PFPD can be applied under a variety of atmospheric pressure conditions in field environmental applications. [source] Experimental investigation of the intermediates of isooctane during ignitionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2007X. He Direct measurements of intermediates of ignition are challenging experimental objectives, yet such measurements are critical for understanding fuel decomposition and oxidation pathways. In the current work, a new gas-sampling system is used to provide quantitative discrete measurements of 30 hydrocarbon and oxygenate species during rapid compression facility studies of isooctane ignition. Two target conditions and equivalence ratios (based on molar fuel to oxygen ratio) were studied (P = 5.2 atm, T = 1000 K, , = 0.4 and P = 4.8 atm, T = 975 K, , = 1.2). The results are compared with model predictions that use the detailed reaction mechanism developed by Curran et al. (Combust Flame 2002, 129, 253,280). In general, the model predictions are in excellent agreement with the experimental data, including several trace species. Isobutene (i-C4H8) and propene (C3H6) were the major olefin species identified in the experiments. The results are consistent with an intermediate temperature reaction path sequence, where isooctane is consumed by H-atom abstraction to yield isooctyl radicals that undergo ,-scission to form olefin and alkyl radical species. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 498,517, 2007 [source] Flame soot generated under controlled combustion conditions: Heterogeneous reaction of NO2 on hexane sootINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2002M. S. Salgado We used a Combustion Aerosol Standard burner unit that affords controlled and adjustable flame conditions, and adapted it for use with liquid fuel. We prepared samples of hexane soot under different well-defined combustion conditions, and probed the chemical properties of hexane soot by using its heterogeneous interaction with NO2 in a Knudsen flow reactor. Soot generated under conditions of fuel to oxygen ratio near stoichiometry (, = 0.82) produced HONO as the main product. Yields of HONO decreased for soot generated under lean conditions (, = 0.16). Finally, NO was the principal product of the reaction for soot generated under extremely lean conditions (, = 0.09) corresponding to the lower flammability limit. We may conclude that the combustion conditions determined surface properties gauged by the heterogeneous NO2,soot interaction. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 620,631, 2002 [source] Manual hyperinflation , Effects on respiratory parametersPHYSIOTHERAPY RESEARCH INTERNATIONAL, Issue 3 2000Shane Patman Abstract Background and Purpose Manual hyperinflation (MH) of the lungs is commonly used by physiotherapists in the treatment of intubated mechanically ventilated patients with the aim of increasing alveolar oxygenation, reversing atelectasis or mobilizing pulmonary secretions. However, the efficacy of MH, used in isolation, has not been clearly established. Method This randomized, controlled trial investigated the effects of MH on lung compliance (CL), the arterial oxygen to fraction of inspired oxygen ratio (PaO2:FIO2) and the alveolar,arterial oxygen tension difference (A,a)PO2 in 100 medically stable, mechanically ventilated subjects who had undergone coronary artery surgery (CAS). Post-CAS subjects were used for this study as they constitute a large, homogeneous and accessible group. Subjects were randomized to either a control group (non-MH group) or to a treatment group (MH group) which received MH within four hours of surgery. Results After four minutes of MH there were significant improvements in CL, PaO2:FIO2 and (A,a)PO2 with values remaining above baseline measures at 60 min post-intervention. The mean improvement in CL was 6 ml/cmH2O (approximately 15%), 56 mmHg for PaO2:FIO2 (approximately 17%) and 29 mmHg for (A,a)PO2 (approximately 17%) immediately post-intervention. No significant changes in mean CL, PaO2:FIO2 or (A,a)PO2 were seen in the non-MH group. Conclusions MH performed in the stable ventilated patient significantly increased CL and PaO2:FIO2 and decreased (A,a)PO2, but the clinical significance of this improvement is unclear. Further investigations are required to validate the findings of this study as well as to determine the therapeutic value of MH on patient outcome. Copyright © 2000 Whurr Publishers Ltd. [source] Influence of cultivation conditions on mechanical and morphological properties of bacterial cellulose tubesBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2007Aase Bodin Abstract Bacterial cellulose (BC) was deposited in tubular form by fermenting Acetobacter xylinum on top of silicone tubes as an oxygenated support and by blowing different concentrations of oxygen, that is, 21% (air), 35%, 50%, and 100%. Mechanical properties such as burst pressure and tensile properties were evaluated for all tubes. The burst pressure of the tubes increased with an increase in oxygen ratio and reached a top value of 880 mmHg at 100% oxygen. The Young's modulus was approximately 5 MPa for all tubes, irrespective of the oxygen ratio. The elongation to break decreased from 30% to 10,20% when the oxygen ratio was increased. The morphology of the tubes was characterized by Scanning Electron Microscopy (SEM). All tubes had an even inner side and a more porous outer side. The cross section indicated that the tubes are composed of layers and that the amount of layers and the yield of cellulose increased with an increase in oxygen ratio. We propose that an internal vessel wall with high density is required for the tube to sustain a certain pressure. An increase in wall thickness by an increase in oxygen ratio might explain the increasing burst pressure with increasing oxygen ratio. The fermentation method used renders it possible to produce branched tubes, tubes with unlimited length and inner diameters. Endothelial cells (ECs) were grown onto the lumen of the tubes. The cells formed a confluent layer after 7 days. The tubes potential as a vascular graft is currently under investigation in a large animal model at the Centre of Vascular Engineering, Sahlgrenska University Hospital, Gothenburg. Biotechnol. Bioeng. 2007;97: 425,434. © 2006 Wiley Periodicals, Inc. [source] Tubeless combined high-frequency jet ventilation for laryngotracheal laser surgery in paediatric anaesthesiaACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 4 2000G. Ihra Background: High-frequency jet ventilation (HFJV) is an alternative ventilatory approach in airway surgery and for facilitating gas exchange in patients with pulmonary insufficiency. We have developed a new technique of combined HFJV utilising two superimposed jet streams. In this study we describe the application of tubeless supralaryngeal HFJV during laryngotracheal laser surgery in infants and children. Methods: Tubeless combined HFJV characterised by the simultaneous supralaryngeal application of a low-frequency (LF) and a high-frequency (HF) jet stream was evaluated in a clinical study in 10 children undergoing elective laryngotracheal CO2 laser surgery. Additionally, pressure and flow characteristics were determined with the use of a paediatric test lung. HFJV was applied by means of a modified Kleinsasser laryngoscope with integrated metal injectors. In addition to pulse oximetry, monitoring of ECG, heart rate and blood pressure, supraglottic airway pressure was measured and arterial blood gases were analysed. Results: Tubeless combined HFJV was used in 10 infants and children (mean age 4.6 yr, range 2 months,10 years) undergoing 17 consecutive endoscopic procedures with CO2 laser microsurgery of the larynx or the trachea under general anaesthesia. The mean duration of supralaryngeal HFJV was 46 min (range 15,75 min). Mean driving pressures of the HF and the LF jet streams were 0.75 bar and 0.95 bar, respectively. Inspiratory oxygen ratios were in the range 0.4,1.0. HFJV resulted in mean PaO2 and PaCO2 values of 19.7 kPa and 6.1 kPa, respectively. No complications during HFJV were observed. In the test lung, combined HFJV applied with driving pressures of 0.7,1.0 bar and 0.9,1.2 bar for HF and LF jet ventilation, respectively, resulted in maximum peak and baseline distal airway pressures of 17.6 cm H2O and 5.4 cm H2O, respectively. Conclusion: The application of the combined double frequency HFJV was effective in maintaining gas exchange in the presence of laryngeal or tracheal stenoses. It provided good visibility of anatomical structures and offered space for surgical manipulation, avoiding the use of combustible material inside the larynx or trachea. [source] | |||||||||||||