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1436. Experimental study of the burning behavior and key parameters of gasoline pool fires with different ullage heightsJinlong Zhao, Xinjiang Li, Zhenqi Hu, Rongxue Kang, Grunde Jomaas, 2023, original scientific article Abstract: Pool fires with different ullage heights are a common type of fire accident. A series of gasoline pool fire ex- periments with two sizes (D = 40 cm, 60 cm) and six ullage heights (h = 0, 0.2D, 0.4D, 0.6D, 0.8D, 1.0D) are conducted. The burning process, axial temperature profile, radiative heat feedback, and burning rate are measured and analyzed. The result shows that the fuel vapor layer and the down-reaching flame layer are distinguished based on the axial temperature profile for the steady burning stage. Meanwhile, the down-reaching flame length (Ldown) increases more profoundly for large tank diameters under the same ullage height. Subse- quently, the dimensionless down-reaching flame length (Ldown* = Ldown/D) increases exponentially with the dimensionless ullage heights (h* = h/D). Finally, based on the classical burning rate model for the low ullage height and the heat transfer process from the flame to the fuel surface, a correlation with different ullage heights is established to calculate the burning rate, which is then validated against the experimental data in the paper and literature values. The results are of importance to understand the burning rate and the radiative heat feedback to the fuel surface for pool fires with different ullage heights.
Keywords: pool fires, ullage height, down-reaching flame, flame radiative heat feedback, burning rate correlation
Published in DiRROS: 08.01.2024; Views: 275; Downloads: 54
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1437. The effect of duct size, sample size, and fuel composition on concurrent flame spread over large cellulose samples in microgravitySandra L. Olson, Gary A. Ruff, Paul V. Ferkul, Jay C. Owens, John Easton, Ya-Ting T. Liao, James S. T'ien, Balazs Toth, Grunde Jomaas, A. Carlos Fernandez-Pello, Guillaume Legros, Augustin Guibaud, Osamu Fujita, Nikolay Smirnov, David L. Urban, 2023, original scientific article Abstract: 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.
Keywords: concurrent flame spread, microgravity, duct size, sample size, cellulose fabrics
Published in DiRROS: 08.01.2024; Views: 253; Downloads: 48
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1438. The microstructure, mechanical and electrochemical properties of 3D printed alloys with reusing powdersMirjam Bajt Leban, Miha Hren, Tadeja Kosec, 2023, original scientific article Abstract: CoCrMo and Ti6Al4V are widely used in medical, dental and 3D printing technology, allowing the accurate fabrication of geometrically complicated structures. In order to reduce the costs of printed objects, the reuse of powder is common daily practice. AQ1 When using 3D printing technology, the direct impact of elevated temperatures and the influence of the laser beam may change the properties of the powder when it is reused, thus affecting the final properties of the printed object. The main aim of the present study was to investigate the impact of reused powder on the mechanical, microstructural and electrochemical properties of 3D printed objects. 3D printed objects fabricated from virgin and reused powder of both alloys were analyzed by metallographic observation, computed tomography, XRD and electrochemical methods. The main finding of the study was that the use of reused powder (recycled 3 times) does not detrimentally affect the mechanical and corrosion integrity of 3D printed CoCr and Ti6Al4V alloys, especially for the purpose of applications in dentistry.
Keywords: additive manufacturing, selective laser melting, virgin powder, reused powder, microtomography
Published in DiRROS: 08.01.2024; Views: 328; Downloads: 135
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1439. Numerical heat transfer model for swelling intumescent coatings during heatingAndrea Lucherini, Juan P. Hidalgo, Jose L. Torero, Cristian Maluk, 2023, original scientific article Abstract: 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).
Keywords: intumescent coatings, heat transfer, numerical model, swelling, fire safety
Published in DiRROS: 08.01.2024; Views: 258; Downloads: 45
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1440. A new approach towards a user-driven coastal climate service to enhance climate resilience in European citiesRoberta Paranunzio, Iulia Anton, Elisa Adirosi, Tasneem Ahmed, Luca Baldini, Carlo Brandini, Filippo Giannetti, Cécil J. W. Meulenberg, Alberto Ortolani, Francesco Pilla, 2024, original scientific article Abstract: Coastal climate services play a crucial role in developing customised climate information for diverse end-users and stakeholders. To build climate-resilient societies, decision-makers should be empowered through easy access to powerful tools that enable timely adaptation to future and ongoing hazards. For this reason, fit-for-purpose climate services are needed to conduct accurate historical characterisation and projections for interpretative studies on climate- and water-related risks at the local coastal scale. The EU-funded SCORE project (Smart Control of Climate Resilience in European Coastal Cities) utilises climate and marine services for the development of smart technologies that support nature-based solutions to address specific concerns, including rising sea levels, coastal erosion, and coastal flooding due to extreme weather events. As part of the SCORE project, decision-makers will be able to address climate change-related coastal effects in their own cities through novel participatory approaches (Coastal City Living Labs—CCLLs). As part of this framework, this work (i) discusses the main requirements for the identification of fit-for-purpose coastal climate services for local-scale impact studies in European coastal cities based on CCLL requests and prior knowledge and (ii) provides relevant parameters and features that fulfil the users’ needs.
Keywords: ecosystem, ecosystem services, climate change adaptation, coastal climate service, urban areas, climate resilience, coastal hazards
Published in DiRROS: 05.01.2024; Views: 342; Downloads: 146
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