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Povzetek: 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.
Ključne besede: concurrent flame spread, microgravity, duct size, sample size, cellulose fabrics
Objavljeno v DiRROS: 08.01.2024; Ogledov: 165; Prenosov: 34
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Povzetek: This research study presents a heat transfer model aimed at estimating the thermal and physical response of intumescent coatings. The numerical model is inspired by the outcomes of an experimental study focused on analysing the insulating effectiveness of a commercial intumescent coating for a range of heating conditions and initial coating thickness. The model solves the one-dimensional heat conduction problem using the finite-difference Crank-Nicolson method, and it assumes that the effectiveness of intumescent coatings is mainly dependent on their ability to develop swelled porous char. The coating swelling is implemented in the model by adopting an approach based on expanding the mesh representing the physical domain in proximity to the substrate-coating interface. The model described herein offers researchers and engineers a tool to estimate the heat transfer of swelling intumescent coatings (i.e. in-depth thermal gradient). Outcomes of the analysis shown herein demonstrate that the heat conduction within intumescent coatings is governed by the physical coating swelling and the thermal conditions at the coating-substrate interface. The numerical model shows that its accuracy is highly influenced by the coating thickness ahead of the reaction zone. Consequently, the coating swelling rate plays a key role, while the thermo-physical properties of the intumescent coating have a secondary effect. According to its assumptions, the model defines a quasi-steady-state thermal problem: it is more accurate for conditions close to steady-state (e.g. high heat fluxes), but it loses accuracy for cases characterised by transient phenomena (e.g. phases prior to the onset of swelling and low heat fluxes).
Ključne besede: intumescent coatings, heat transfer, numerical model, swelling, fire safety
Objavljeno v DiRROS: 08.01.2024; Ogledov: 179; Prenosov: 34
Celotno besedilo (1,21 MB)
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Povzetek: Mineral wool, i.e. rock and glass wool, represents considerable challenge after its functional-time runs out due to its small density leading to large volume consumption during transport and in landfills where it usually ends. Because rock wool is mineralogically and chemically a promising precursor material for alkali-activation, it was milled from few centimetres-decimeters long fibres to micron-sized fibres. Since fibres in alkali-activated materials generally show an increase in mechanical strength, especially the bending strength, 1 m% of additional fibres (basalt, cellulose (2 types), glass, polypropylene, polyvinyl alcohol and steel fibres) was used in the alkali mixture, that was curred at 40 °C for 3 days. Time dependence of the mechanical strengths of alkali- activated materials with and without additional fibres was followed. Maximal increase of compressive and bending strength after 28 days was reached with polypropylene fibres, i.e. it was 20% and 30% higher than compressive and bending strength of alkali- activated material without additional fibres respectively.
Ključne besede: secondary raw material, alkali activated material, foaming, homogenization, mechanical strength
Objavljeno v DiRROS: 21.12.2023; Ogledov: 229; Prenosov: 78
Celotno besedilo (8,39 MB)
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Povzetek: In recent years great attention has been placed by the building sector on alkali-activated technology based on metakaolin, fly ash and ground granulated blast furnace slag (GGBFS), but also on emerging precursors such as by-products from non-ferrous metallurgy. The present work focuses on the development of alkali-activated binders from two slags, one from primary and one from secondary copper production, which were finely milled, blended with GGBFS, and activated with K-based alkali silicate solution with a 1.7 SiO2/K2O molar ratio. The aggregate to paste mass ratio was 2. The mixtures were cast, and cured for a designated time at room temperature and 60% RH. The so-obtained paving blocks were then tested in accordance with European standard for concrete paving blocks. The following properties were measured: splitting tensile strength, abrasion resistance, slip and skid resistance, resistance to freeze-thaw and resistance to freeze-thaw in the presence of de-icing salts. Their properties were compared to those of commercially available concrete paving blocks, and it was found that the performance of the alkali-activated pavers was generally comparable with the concrete pavers, while certain properties (e.g., abrasion resistance, freeze-thaw resistance and freeze-thaw resistance in presence of de-icing salts) were considerably better.
Ključne besede: slags, alkali activated pavers, properties
Objavljeno v DiRROS: 21.12.2023; Ogledov: 165; Prenosov: 62
Celotno besedilo (4,29 MB)
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Povzetek: Pri načrtovanju osvetlitve izračuni le delno napovejo vplive svetlobe na uporabnike prostorov. Svetloba ima namreč poleg dobro poznanih slikovnih učinkov, ki jih možgani interpretirajo na podlagi odzivov čepkov in paličic, tudi neslikovne učinke. Ti ne pripomorejo k orientaciji v prostoru, temveč sporočajo telesu ključne informacije, ki vplivajo na tvorbo hormonov. Vrh te zaznave je v modrem delu spektra vidne svetlobe. Žal delovanja teh fotoreceptorjev še ne opisujemo s parametri, ustaljenimi v praksi projektiranja, zato so vplivi na uporabnike pogosto prezrti. Dodaten izziv pomeni praksa, pri kateri svetlobne učinke preračunavamo v lukse, kar pomeni, da jih množimo s povprečnim človeškim dnevnim vidom. Tak pristop ni primeren za vrednotenje neslikovnih učinkov, ker imajo drugo akcijsko krivuljo. Izmerili smo spektralno sestavo odbitih dnevnih svetlob v modelnem prostoru, ker nas je zanimalo, kakšne razlike nastanejo v slikovni in neslikovni zaznavi, če pobarvamo stene z različnimi barvami. Modra in vijoličasta stena neslikovno stimulirata opazovalca bolj kot slikovno v obeh opazovanih smereh pogleda, oranžna v obeh primerih neslikovno vpliva manj, pri zeleni pa je bila neslikovna zaznava bolj stimulirana od slikovne pri pogledu naprej, pri pogledu v mizo pa je bilo obratno.
Ključne besede: svetloba, fotobiološki vpliv, spektralna sestava svetlobe, dnevna svetloba
Objavljeno v DiRROS: 21.12.2023; Ogledov: 193; Prenosov: 66
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