Suppression of flame propagation in a long duct by inertia isolation with inert gases

Experimental studies were done with a small pipe with a diameter of 0.043 m and a large pipe with a diameter of 0.49 m to demonstrate the flame propagation suppression with inertia isolation in a long duct. Tests were carried in an ignition section containing propylene/air mixture near stoichiometric concentration and generating a peak flame propagation speed of approximately 100 m/s. The ignition section is connected to a section filled with an inert gas, another section with flammable mixtures, and finally a sufficiently long, ambient section to accommodate flame propagation. The critical length of the inert gas section required for successful suppression of flame from the igniting the flammable section is found to be 0.6 m for CO₂ and 0.9 m for N₂ in the large pipe and 0.2 m for CO₂ and 0.3 m for N₂ in the small pipe. Additional tests with a 3 m of ignition section and peak flame propagation speed of 225 m/s showed that the critical length for successful suppression by CO₂ is only increased slightly to 0.9 m, confirming that the suppression is a result of inertia isolation rather than inert gas dilution. Finally, application of the results in responding to large-scale leak into a long, underground duct is discussed.     

Determination of Cd,Cr, Cu,Pb and Zn from various water samples with use of FAAS techniques after the solid phase extraction on rice bran

A facile and novel method has been developed for the determination of cadmium, chromium, copper, lead, and zinc from various water samples using FAAS. In the present investigation, a syringe was loaded with sorbent (rice bran) for the separation and enrichment of cadmium, chromium, copper, lead, and zinc, prior to their analysis by flame atomic absorption spectrometry which was described to substitute the batch and column techniques. The syringe was loaded with 2.0 g of sorbent in order to retain the analyte elements. Six milliliter of sample solution (pH 8.0 ± 0.2) was drawn into the syringe in 15 s and discharged over a period of 15 s. Then, 2.0 M HCl eluent was drawn into the syringe and ejected back to desorb the analyte elements. At the optimum conditions, the percentage recoveries of Cd, Cr, Cu, Pb, and Zn was in the range of 95.5–99.4% with SD of 0.10%. The elements could be concentrated by drawing and discharging several portions of sample successively. The detailed study of various interferences made the confirmation of the method highly selective. The risk of contamination is less than that with the column technique. The method was successfully applied for the determination of Cd, Cr, Cu, Pb, and Zn in spiked and natural water samples. The results obtained are in good agreement with the reported methods at the 95% confidence level.     

Separation of polycarbonate and acrylonitrile–butadiene–styrene waste plastics by froth flotation combined with ammonia pretreatment

The objective of this research is flotation separation of polycarbonate (PC) and acrylonitrile–butadiene–styrene (ABS) waste plastics combined with ammonia pretreatment. The PC and ABS plastics show similar hydrophobicity, and ammonia treatment changes selectively floatability of PC plastic while ABS is insensitive to ammonia treatment. The contact angle measurement indicates the dropping of flotation recovery of PC is ascribed to a decline of contact angle. X-ray photoelectron spectroscopy demonstrates reactions occur on PC surface, which makes PC surface more hydrophilic. Separation of PC and ABS waste plastics was conducted based on the flotation behavior of single plastic. At different temperatures, PC and ABS mixtures were separated efficiently through froth flotation with ammonia pretreatment for different time (13 min at 23 °C, 18 min at 18 °C and 30 min at 23 °C). For both PC and ABS, the purity and recovery is more than 95.31% and 95.35%, respectively; the purity of PC and ABS is up to 99.72% and 99.23%, respectively. PC and ABS mixtures with different particle sizes were separated effectively, implying that ammonia treatment possesses superior applicability.     

Ignition hazard evaluation on A2L refrigerants in situations of service and maintenance

To restrict the progress of the global warming, A2L refrigerants such as 2,3,3,3-tetrafluoroprop-1-ene (R1234yf), (Z/E)-1,3,3,3-tetrafluoroprop-1-ene (R1234ze), and difluoromethane (R32) have been expected of alternatives to the standard refrigerants currently in use. The ignition hazard of A2L refrigerants under plausible accident situations in service and maintenance was examined experimentally for two cases: leakage of an A2L refrigerant from a pinhole in a pipe or hose (Scenario 1), and leakage of an A2L refrigerant into an item of equipment used for service and maintenance, such as a collection device (Scenario 2). In Scenario 1, the location of the flammable zone and the possibility of a jet flame being formed instantaneously on contact with an ignition source were examined. Even when R1234yf leaked from a 4 mmϕ pinhole (corresponding to breakage of a pipe), the flammable zone extended only about 10 cm from the pinhole in the downstream region. In an ignition test with a continuous spark as the ignition source, a pale emission appeared only near the spark, and the flame did not propagate to the rest of the refrigerant jet. In Scenario 2, the accumulation and ignition behaviors of A2L refrigerants in a model collection device were examined experimentally. Ignition and flame propagation occurred in a test on a model collection device lacking slits, whereas when slits wider than 20 mm were present, ignition and flame propagation did not occur. Even if R1234yf leaked into the model collection device, provided that slits of an effective width were present, the R1234yf could diffuse through slits and barely accumulated, and no ignition or flame propagation occurred.     

Extinguishment of hydrogen laminar diffusion flames by water vapor in a cup burner apparatus

Transient computations with full hydrogen chemistry were performed to reveal the flame structure and extinguishment process of co-flow, hydrogen diffusion flame suppressed by water vapor. As the concentration of water vapor was increased, the flame detached away from the burner brim and formed an edge flame at the flame base. Water vapor showed larger chemical inhibition effect than nitrogen when extinguishing hydrogen flame, which was attributed to its enhanced third body effect in the reaction H + O₂ + M = HO₂ + M. The minimum extinguishing concentration (MEC) of water vapor and nitrogen was predicted by Senecal formula and perfectly stirred reactor (PSR) model respectively. The MECs predicted by PSR model agree with the MECs calculated by Fluent, which shows that 1) the flame extinction is controlled by the flame base, and 2) radiation absorption is negligible. The measured MECs are in a reasonable agreement with the values calculated by Fluent, which demonstrates the accuracy of the CFD model. A simple model was used to investigate the relative importance of extinguishing mechanisms of water vapor. The results show that in a co-flow configuration the thermal cooling and chemical inhibition effect are the main extinguishing mechanisms in suppressing hydrogen diffusion cup burner flame.     

Numerical modeling of water spray suppression of conveyor belt fires in a large-scale tunnel

Conveyor belt fires in an underground mine pose a serious life threat to miners. Water sprinkler systems are usually used to extinguish underground conveyor belt fires, but because of the complex interaction between conveyor belt fires and mine ventilation airflow, more effective engineering designs are needed for the installation of water sprinkler systems. A computational fluid dynamics (CFD) model was developed to simulate the interaction between the ventilation airflow, the belt flame spread, and the water spray system in a mine entry. The CFD model was calibrated using test results from a large-scale conveyor belt fire suppression experiment. Simulations were conducted using the calibrated CFD model to investigate the effects of sprinkler location, water flow rate, and sprinkler activation temperature on the suppression of conveyor belt fires. The sprinkler location and the activation temperature were found to have a major effect on the suppression of the belt fire, while the water flow rate had a minor effect.     

Propagation of ethylene–air flames in closed cylindrical vessels with asymmetrical ignition

A study of explosions in several elongated cylindrical vessels with length to diameter L/D = 2.4–20.7 and ignition at vessel's bottom is reported. Ethylene–air mixtures with variable concentration between 3.0 and 10.0 vol% and pressures between 0.30 and 1.80 bara were experimentally investigated at ambient initial temperature. For the whole range of ethylene concentration, several characteristic stages of flame propagation were observed. The height and rate of pressure rise in these stages were found to depend on ethylene concentration, on volume and asymmetry ratio L/D of each vessel. High rates of pressure rise were found in the early stage; in later stages lower rates of pressure rise were observed due to the increase of heat losses. The peak explosion pressures and the maximum rates of pressure rise differ strongly from those measured in centrally ignited explosions, in all examined vessels. In elongated vessels, smooth p(t) records have been obtained for the explosions of lean C₂H₄–air mixtures. In stoichiometric and rich mixtures, pressure oscillations appear even at initial pressures below ambient, resulting in significant overpressures as compared to compact vessels. In the stoichiometric mixture, the frequency of the oscillations was close to the fundamental characteristic frequency of the tube.     

Microtox assay to determine the toxicity of degradation products from degradable plastics

Six types of starch-polyethylene degradable plastics were evaluated for the release of water-soluble toxic compounds under accelerated degradation conditions. A plastic strip (2.5×15.2 cm) was placed in a 250-ml Erlenmeyer flask with 100 ml of ASTM type I water with or without trace element solutions and shaken at 65°C and 110 rpm for 20 weeks in replicates of two. High temperature was used to accelerate the oxidative degradation of polyethylene. Plastic degradation was measured by loss of tensile strength, percentage elongation, strain energy, and weight-average molecular weight. The most rapid period of polyethylene thermal degradation was complete for most materials by day 28. Ten-milliliter aqueous samples were removed from each flask at days 1, 7, 28, 56, 84, and 140 (water volumes were maintained at 100 ml with fresh type I water), filtered through glass filters, then evaluated by using the Microtox Toxicity Analyzer (Microbics Corporation, Carlsbad, CA). No water-soluble toxic compounds were detected during the period of rapid film degradation. Toxicity was observed at day 28 for one film and at day 84 for all films, which could possibly correlate with the release of small oxidative compounds such as formaldehyde and acetaldehyde. Because of the sensitivity of this assay, positive results must be confirmed by otherin vitro studies.Journal Paper No. J-14851 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Projects No. 2889 and 0178.     

Degradation studies of novel degradable starch-polyethylene plastics containing oxidized polyethylene and prooxidant

Linear low-density polyethylene films were prepared that contained native corn starch (7, 14, or 28%), low or high molecular weight oxidized polyethylene (15%), and a prooxidant mixture (18% POLYCLEAN II) that contains manganese and vegetable oil. For each mixture all components were first mixed at high temperatures in a twin-screw extruder and pelletized. The pellets were cast into films using a single-screw extruder. Oxidized-polyethylene addition did not impair the transparency and thickness of the films and did not reduce the percentage elongation, whereas significant reductions in film mechanical properties were observed. Thermal and photodegradation properties of each film were evaluated by 70°C forced-air oven treatment (20 days), by high-temperature, high-humidity treatment in a steam chamber (20 days), and by exposure to ultraviolet light (365 nm; 4 weeks). Changes in the mechanical properties of the films were determined by an Instron Universal Test Machine; in the carbonyl index, Fourier transform infrared spectroscopy; and in molecular weight, by high-temperature gel-permeation chromatography (HT-GPC). The addition of oxidized polyethylene, especially high molecular weight oxidized polyethylene, and up to 14% starch to the films significantly increased the rate of thermal and photodegradation.Journal Paper No. J-15363 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 0178 and 2889.