Experimental study on the characteristics of horizontal flame spread over XPS surface on plateau.
A series of comparative laboratory-scale experiments were carried out in the Lhasa plateau and the Hefei plain respectively to investigate the characteristics of flame spread over the extruded polystyrene (XPS) foam, a typical thermal insulation material. Flame shape and the temperature profile in solid phase were monitored, and the effects of altitude on the heat transfer process were analyzed. The results show that the temperature rise with time undergoes three stages: the preheating stage, the melting stage and the pyrolysis stage. The durations of the melting and pyrolysis stages on plateau are longer than that in plain, which sequentially results in a lower flame spread rate on plateau. Comparing of the temperature change rate curve on plateau with that in plain, it is found that the peak characteristics of the curves in the pyrolysis stage changed from single peak to multi-peaks, which suggests that the altitude difference might change the pyrolysis mechanisms of XPS material. Moreover, the sample scale effects on flame spread are also explored. Two different regimes are found in flame spread behavior with sample scale at the both altitudes. The spread rate drops with sample scale in convection regime and rises in radiation regime.
Native Bacterial Mixed Culture: A Proportionate Solution for Refinery and Petrochemical Wastewaters
Background: Heat, chemical and organic pollution are three types of environmental pollution, caused by refinery and petrochemical industries. Problems caused by hear and chemical pollutants are currently resolved to some extent but organic pollution such as Poly Aromatic Hydrocarbons (PAHs) are still considered as important problems of industry and environment. Objectives: A laboratory study was carried out to investigate the effects of native bacterial mixed culture (BMC) isolated from mixtures of refinery and petrochemical wastewaters for treatment of wastewaters of refinery and petrochemical industries. Materials and Methods: All bacteria were isolated from two refineries and two petrochemical plants of Iran. Several bacterial strains from both kinds of wastewater were mixed and two final stock culture collections (BMC a and BMC b ), showed the ability to improve the growth among strains. BMC a was added to the refinery wastewater (activated sludge influent sample) and BMC b was added to petrochemical wastewater (activated sludge influent sample). The effects of continuous and non-continuous aeration at high and low pressures, along with the effects of nutrient addition in the beginning of experiment versus sequential addition at specific time intervals, were studied. Results: Native BMC, when continuous high level aeration was used, decreased chemical oxygen demand (COD) in refinery and petrochemical wastewaters for about 81% and 63%, respectively. Gradual addition of nutrients increased COD removal of refinery and petrochemical wastewaters to 85% and 87%, respectively. Conclusions: Native BMCs from mixture of refineries and petrochemical wastewaters can be an effective method of wastewater treatment of both regional refinery and petrochemical plants. High pressure continuous aeration and gradual nutrient addition to the native BMCs can improve bioremediation of organic wastewater in different industries.
Ionization by drift and ambipolar electric fields in electronegative capacitive radio frequency plasmas.
Unlike α- and γ-mode operation, electrons accelerated by strong drift and ambipolar electric fields in the plasma bulk and at the sheath edges are found to dominate the ionization in strongly electronegative discharges. These fields are caused by a low bulk conductivity and local maxima of the electron density at the sheath edges, respectively. This drift-ambipolar mode is investigated by kinetic particle simulations, experimental phase-resolved optical emission spectroscopy, and an analytical model in CF(4). Mode transitions induced by voltage and pressure variations are studied.