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| 2. |
- Fjellgaard Mikalsen, Ragni, et al.
(författare)
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Extinguishing smoldering fires in wood pellets through cooling
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Extinguishing smoldering fires is a severe challenge for fire brigades, and has proven to be difficult even on the lab scale. In this study, the influence of a closed water cooling loop located within the fuel bed was investigated experimentally. Increasing the cooling led to a system less prone to intense combustion at an early stage, and eventually to complete extinguishment of self-sustained smoldering fires. Extinguishment was obtained in half of the cases with maximum cooling. Extinguishment occurred soon after smoldering had been established, giving a significant reduction in fuel consumption compared to the self-sustained smoldering fires that continued to complete burn-out.
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| 3. |
- Fjellgaard Mikalsen, Ragni, et al.
(författare)
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Extinguishing Smoldering Fires in Wood Pellets with Water Cooling : An Experimental Study
- 2019
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Ingår i: Fire technology. - : Springer Science and Business Media LLC. - 0015-2684 .- 1572-8099. ; 25:1, s. 257-284
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Tidskriftsartikel (refereegranskat)abstract
- Smoldering fires in stored or transported solid biofuels are very difficult to extinguish. The current study has explored heat extraction from the combustion zone as a method for extinguishing such flameless fires. Heat extraction from the sample was made feasible using water flowing through a metal pipe located inside the sample. The fuel container was a steel cylinder with insulated side walls, open at the top and heated from below. Wood pellets (1.25 kg, 1.8 l) was used as fuel. Results from small-scale experiments provide proof-of-concept of cooling as a new extinguishing method for smoldering fires. During self-sustained smoldering with heat production in the range 0 W to 60 W, the heat loss to the cooling unit was in the range 5 W to 20 W. There were only marginal differences between non-extinguished and extinguished cases. Up-scaling is discussed, cooling could be feasible for preventing smoldering fires in silos.
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| 4. |
- Fjellgaard Mikalsen, Ragni
(författare)
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Fighting flameless fires : Initiating and extinguishing self-sustainedsmoldering fires in wood pellets
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Smoldering fires represent domestic, environmental and industrial hazards. This flameless form of combustion is more easily initiated than flaming, and is also more persistent and difficult to extinguish. The growing demand for non-fossil fuels has increased the use of solid biofuels such as biomass. This represents a safety challenge, as biomass self-ignition can cause smoldering fires, flaming fires or explosions.Smoldering and extinguishment in granular biomass was studied experimentally. The set-up consisted of a cylindrical fuel container of steel with thermally insulated side walls. The container was closed at the bottom, open at the top and heated from below by a hot surface. Two types of wood pellets were used as fuel, with 0.75-1.5 kg samples.Logistic regression was used to determine the transition region between non-smoldering and self-sustained smoldering experiments, and to determine the influence of parameters. Duration of external heating was most important for initiation of smoldering. Sample height was also significant, while the type of wood pellet was near-significant and fuel container height was not.The susceptibility of smoldering to changes in air supply was studied. With a small gap at the bottom of the fuel bed, the increased air flow in the same direction as the initial smoldering front (forward air flow) caused a significantly more intense combustion compared to the normal set-up with opposed air flow.Heat extraction from the combustion was studied using a water-cooled copper pipe. Challenges with direct fuel-water contact (fuel swelling, water channeling and runoff) were thus avoided. Smoldering was extinguished in 7 of 15 cases where heat extraction was in the same range as the heat production from combustion. This is the first experimental proof-of-concept of cooling as an extinguishment method for smoldering fires.Marginal differences in heating and cooling separated smoldering from extinguished cases; the fuel bed was at a heating-cooling balance point. Lower cooling levels did not lead to extinguishment, but cooling caused more predictable smoldering, possibly delaying the most intense combustion. Also observed at the balance point were pulsating temperatures; a form of long-lived (hours), macroscopic synchronization not previously observed in smoldering fires.For practical applications, cooling could be feasible for prevention of temperature escalation from self-heating in industrial storage units. This study provides a first step towards improved fuel storage safety for biomass.
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| 5. |
- Fjellgaard Mikalsen, Ragni, et al.
(författare)
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Smoldering combustion- from pulsations to extinguishment
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Smoldering is known as a slow, but unpredictable form of combustion. In this study we have looked at how smoldering is affected by water cooling of the fuel bed without direct contact between fuel and water flow. The study is a part of the EMRIS project, and its findings have possible implications for preventing and suppressing fires in industrial storage units.
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| 6. |
- Fjellgaard Mikalsen, Ragni, et al.
(författare)
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Synchronized smoldering combustion
- 2018
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 121:5, s. 50002-p1-50002-p2
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Tidskriftsartikel (refereegranskat)abstract
- Synchronized, pulsating temperatures are observed experimentally in smoldering fires.The entire sample volume (1.8 l) participates in the pulsations (pulse period 2–4 h). The synchronylasts up to 25 h and is followed by a spontaneous transition to either disordered combustion orself-extinguishment. The synchronization is obtained when the fuel bed is cooled to the brink ofextinguishment. Calculations for adiabatic conditions, including heat generation from combustion(nonlinear in temperature) and heat storage in sample (linear in temperature), predict divergingsample temperature. Experimentally, heat losses to surroundings (linear in temperature) preventtemperatures to increase without bounds and lead to pulsations.
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| 7. |
- Karyaparambil, Dheeraj Dilip, et al.
(författare)
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Flame heights and charring on a particle board – An experimental study
- 2022
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Ingår i: Fire Safety Journal. - : Elsevier BV. - 0379-7112. ; 134
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Tidskriftsartikel (refereegranskat)abstract
- Vertically oriented particle-board samples were exposed to external venting flames to study the fire spread and charring behaviour along a timber façade. Variation in flame height and the height, volume, area, density, and depth of the char layer were studied to determine the impact of heat-release rate and experiment duration. There was a peak flame height after which the flame returned to steady height approximately equal to the value before the ignition of the particle board and flame heights with inert panels. Flames did not spread to the top of the panel with increased experiment duration. Char height and area were found to increase with heat-release rate but were not affected significantly by experiment duration. Char depth and volume increased with both experiment duration and heat-release rates. Char density decreased with increased experiment duration and heat-release rate.
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| 8. |
- Villacorta, Edmundo, et al.
(författare)
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Onset of smoldering fires in storage silos : Susceptibility to design, scenario, and material parameters
- 2021
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Ingår i: Fuel. - : Elsevier Ltd. - 0016-2361 .- 1873-7153. ; 284
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Tidskriftsartikel (refereegranskat)abstract
- Biomass fuels in large storage units are prone to self-heating and ignition causing smoldering fires. Here, the susceptibility of such ignition processes to parameters is explored through small-scale experiments. In a silo geometry, wood pellets samples of size 0.75 to 1.5 kg were heated from below to initiate smoldering, while the top was open, allowing convective exchange of gases between the porous sample and the surroundings. The thermally insulated sidewalls reduce the heat flow in lateral direction in a similar way that additional pellets material would do in a larger set-up. Thus, the present experimental set-up mimics a much larger system in lateral direction. After heating was terminated, the procedure led to self-sustaining smoldering or spontaneous cooling, depending on parameters. The transition zone between smoldering and non-smoldering was explored under variation in sample size, imposed heating, pellets type, and height of sample container. Logistic regression was applied to fit the experimental data to a model. The model predicted the probability of an experiment to result in either smoldering or non-smoldering under variation in parameters – and the parameters were sorted according to importance. The duration of the external heating was found to be the most influential parameter. For risk assessments in connection with large biomass fuel storage units, this result indicates that the temperature increase could be more important than the size and geometry of the storage unit and the stored material type. © 2020 The Authors
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