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    The effect of duct size, sample size, and fuel composition on concurrent flame spread over large cellulose samples in microgravity

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    Concurrent flame spread data for thermally-thin charring solid fuels are presented from Saffire and BASS experiments performed in habitable spacecraft for three duct sizes, five sample sizes, two materials, and two atmospheres. The flame spread rates and flame lengths were strongly affected by duct size even for the relatively large ducts (> 30 cm tall). A transient excess pyrolysis length (i.e., flame length overshoot) was observed for the cotton fabric that burned away, which indicates that the transient excess pyrolysis length phenomenon is caused by more than just the flame moving into the developing boundary layer thickness as was the case with the SIBAL sample. A burnout time, defined as the pyrolysis length divided by the flame spread rate, normalized the pyrolysis length histories into a single curve with a steady burnout time of 22 s for the SIBAL fabric. The transient excess pyrolysis length is hypothesized to be a post-ignition flame growth transient for the essentially two-dimensional flames where the burnout time becomes very long until the preheat and pyrolysis lengths develop. The three-dimensional flames over narrow samples have lateral thermal expansion and lateral oxygen diffusion which allows them to transition to a steady state length without the transient excess pyrolysis length. Surface temperature profiles, nondimensionalized by the pyrolysis length, indicate that the temperature profiles exhibit the same shape across the pyrolysis zone. A surface energy balance calculation in the preheat region revealed that the heat flux increased rapidly at the pyrolysis front to near the critical heat flux for ignition. An estimate of the acceleration of the inviscid core flow in the duct due to thermal expansion and developing boundary layers on the duct walls and the SIBAL sample surface seems to explain the observed spread rate trends across three duct sizes and multiple sample sizes

    Flame spread behaviour of Polydimethylsiloxane (PDMS) membranes in 1 g and µg environments

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    Diffusion flame behaviour and silica ash (SiO2) production were experimentally studied for various Polydimethylsiloxane (PDMS) membrane thicknesses (0.125 mm to 1.0 mm) in normal gravity and during microgravity flight experiments. The flames were established on vertical samples (300 mm in length) and subjected to either opposed or concurrent forced flows (both laminar and turbulent), assimilating the NASA Test 1 that is in use for spacecraft material selection. The opposed flame spread rate was observed to be steady and could be estimated using classical theory. Under concurrent flow, the flame spread rate was only steady for very high forced flows. The opposed flame-spread rate ranged from 0.5 to 1.5 mm/s, while the concurrent case ranged between 0.1 and 12 mm/s. The transport of silica ash (SiO2) was found to affect the heat balance of the concurrent flame spread in a manner that resulted in unsteady flame spread. For opposed flame spread, on the other hand, the transport of silica ash showed to be irrelevant. The extinction behaviour for the concurrent flame spread was heavily dominated by the transport of silica-ash, while for opposed flames, extinction was due to kinetics (at high forced flows). In microgravity environments, the transport and deposition of silica ash is anticipated to dominate flame spread and near-limit as well. These results suggest that silica-based products might be less flammable in microgravity than other similar materials such as common thermoplastics (PP or PE) used as wire jackets

    Uspešno izvedeno 14. Državno tekmovanje gozdnih delavcev

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    Mesec požarne varnosti 2023: Požari v naravi

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    The corrosion properties of steel in pore solutions obtained from alkali‐activated mortars

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    Alkali‐activated materials (AAMs) are considered a promising alternative to materials made from ordinary Portland cement (OPC). Other than considering the durability of the material itself, the use of AAMs for reinforced concrete elements also raises the question of steel corrosion processes in these materials, which are still relatively unknown. Three different alkali‐activated mortars were prepared for this study, based on either fly ash, slag, or metakaolin. Pore solutions were then extracted from each mortar and chemically analyzed. Electrochemical techniques were used to study the corrosion of steel in synthetic pore solutions containing varying concentrations of chlorides. In parallel, the same corrosion tests were performed in a generic pore solution representing OPC mortar. It was shown that the chemical composition differed in each pore solution tested, thus affecting the corrosion properties of the steel. The addition of chloride also had a varying effect on the corrosion properties of the steel in each type of pore solution tested. This study provided a basic overview of the corrosion behavior and mechanisms of the various AAM environments in comparison to that of OPC

    Indikacije za slikovne preiskave pri raku dojk

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    Državni presejalni program za raka dojk Dora

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    Life IP CARE4CLIMATE - Action C8 and E3

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