In order to reduce the uncertainty and risk in the design of spacecraft fire safety systems, a new experimental rig that allows the study of concomitant flames spreading over the coating of parallel cylindrical wires in an air flow parallel to the wires in microgravity has been developed. The parabolic flight experiments were conducted at small length-and timescales, i.e. typically over 10 cm long samples for up to 20 seconds. For the first time, the influence of neighboring spread on the mass burning rate was assessed in microgravity. The observations are contrasted with the influence characterized in normal gravity. The experimental results are expected to deliver meaningful guidelines for future, planned experiments at a larger scale.Arising from the current results, the issue of the potential interaction among spreading flames also needs to be carefully investigated as this interaction plays a major role in realistic fire scenarios, and therefore on the design of the strategies that would allow the control of such a fire. Once buoyancy has been removed, the characteristic length and time scales of the different modes of heat and mass transfer are modified. For this reason, interaction among spreading flames may be revealed in microgravity, while it would not at normal gravity, or vice versa. Furthermore, the interaction may lead to an enhanced spread rate when mutual preheating dominates or, conversely, a reduced spread rate when oxidizer flow vitiation is predominant.In more general terms, the current study supports both the SAFFIRE and the FLARE projects, which are large projects with international scientific teams. First, material samples will be tested in a series of flight experiments (SAFFIRE 1-3) conducted in Cygnus vehicles after they have undocked from the ISS. These experiments will allow the study of ignition and possible flame spread in real spacecraft conditions, i.e. over real length scale samples within real time scales. Second, concomitant research conducted within the FLARE project is dedicated to the assessment of new standard tests for materials that a spacecraft can be composed of. Finally, these tests aim to define the ambient conditions that will mitigate and potentially prohibit the flame spread in microgravity over the material studied.
We describe a novel technique based on the impact of a piston on a liquid confined in a vessel. Pressure measurements reveal that strong pressure variations (up to 100 atmospheres) with a rich content of frequencies are efficiently transmitted to the liquid. High-speed camera visualizations show that pre-existing millimetric bubbles always collapse during the first instants of the impact whereas the behavior of submillimetric bubbles depends on the features of the pressure evolution in the system. In addition to the impact velocity, the amount of * Corresponding author: fuster@dalembert.upmc.fr 1 gas/vapor trapped between the piston and the liquid's surface plays an important role on how pressure evolves. Only when negative pressure occurs bubbles grow significantly and collapse. The violent collapse of bubbles promote turbulence and mixing at very small length-scales which renders this technique interesting to intensify processes limited by heat and mass diffusion.
The sonocatalytic degradation of EDTA in aqueous solution was studied under ultrasound irradiation (345 kHz, 73 W, acoustic power 0.20 W•mL −1 , Ar and Ar/O 2 saturating gases, T = 20-50°C) in the presence of Co 3 O 4 /TiO 2 and Pt/TiO 2 nanocatalysts. About 90% of EDTA (C 0 = 5 10-3 M) was oxidized during ultrasonic treatment at 40°C in the presence of the Co 3 O 4 /TiO 2 catalyst and Ar/O 2 gas mixture. By contrast, Pt/TiO 2 catalyst exhibited much lower sonocatalytic activity in this system. Suggested mechanism of EDTA oxidation in the presence of Co 3 O 4 /TiO 2 catalyst involved the generation of oxidizing radicals by acoustic cavitation and Co(II)-Co(III) redox process. Quite low apparent activation energy of the sonocatalytic process (E a = 19 kJ mol −1) was attributed to diffusion of reagents in the vicinity of the active sites of catalyst. Sonocatalytic degradation of EDTA is accompanied by formation of iminodiacetic acid, formic acid, oxalic acid, glycolic acid and acetic acid as intermediate products in an agreement with radical-driven mechanism.
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