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  • 1.
    Försth, Michael
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SP – Sveriges Tekniska Forskningsinstitut / Brandteknik, material (BRm).
    Radiation emission from a heating coil or a halogen lamp on a semitransparent sample2014In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 77, no Mar, p. 223-232Article in journal (Refereed)
    Abstract [en]

    The radiation emission of the heating coil of a Cone Calorimeter and the one of the halogen lamp of a Fire Propagation Apparatus have been studied experimentally for varying power settings. These are two standard apparatuses used for fire calorimetry. The objective is to characterize and compare the radiative flux spectrum received by a fuel sample during pyrolysis experiments. The deviation from the standard assumption of black or gray emission is discussed. It is observed that the emission of the heating coil can be approximated well to an ideal blackbody, especially in the infrared range. On the contrary, the halogen lamp emission is more complex, non gray, with an important contribution in the visible and in the near infrared ranges. The flux received by a sample exposed to these emitters is predicted using ray tracing simulations. This shows that the irradiation flux and spectrum from the cone can be accurately calculated if the coil temperature is known. The non Lambertian irradiation flux from the lamp is modeled with a combination of diffuse and collimated intensities, representing the direct emission from the lamp itself and the reflection by the mirror at the rear side. For both emitters, the irradiation is confirmed to be approximately uniform over the surface of a sample 5 cm large (maximum deviation of ±2% on the incident flux). The uniformity decreases for larger samples, but the ratio of the flux at the center to average flux is still 1.04 for standard 10 cm × 10 cm samples under the cone. For illustration purposes, the influence of the spectral characteristics of the emitter is studied in the case of a sample of PMMA, a non gray translucent medium. Using recently published measurements of PMMA absorptivity, the absorbed flux by a 3 cm thick sample is predicted. In the case of an incident flux of 20 kW/m2, the calculated average absorptivity of the sample is 0.91 under the cone, while it is 0.32 under the FPA lamp. These calculations involve absorption data of a virgin sample at room temperature and consequently the numerical results only hold for the initial instants of irradiation. However, the very large differences in radiative behavior show that important discrepancies in the pyrolysis behavior are expected between the two emitters. This might have consequences for fire testing and inter comparisons of flammability results worth further investigation. 

  • 2.
    Yao, Yongzhenh
    et al.
    RISE - Research Institutes of Sweden, Safety and Transport, Safety. University of Science and Technology of China, China.
    Li, Ying Zhen
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Ingason, Haukur
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Cheng, X.
    University of Science and Technology of China, China.
    Numerical study on overall smoke control using naturally ventilated shafts during fires in a road tunnel2019In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 140, p. 491-504Article in journal (Refereed)
    Abstract [en]

    This paper studies the overall smoke control of natural ventilation systems with vertical shafts during fires in a common road tunnel by numerical modelling. The variables studied include the heat release rate, longitudinal fire location along the tunnel, length of shafts and the interval between two shafts. Simulation results indicate that the total smoke spread length on both sides of fire source is closely independent of the heat release rate and longitudinal fire locations. For a given dimensionless shaft interval (the ratio of the shaft interval to shaft length), with the increase of shaft length, the smoke spread length firstly increases, reaching a maximum at 12 m, and then decreases significantly until 18 m. For a fire less than 30 MW, the first shaft pair on both sides of fire source prevents the critical-temperature smoke (270 °C) from spreading beyond this shaft. For a 100 MW fire, in the cases with shorter shaft lengths (L shaft ≤9 m), the critical-temperature smoke can't be controlled between the first shaft pair. The gas temperature at human height (1.8 m) is less than 60 °C in all cases with shafts. Downdraught occurs when the smoke front stabilizes at the bottom of a shaft and the buoyancy force could be too low to overcome the kinetic pressure of the air flow flowing into this shaft, consequently destroying the structure of smoke layer. In most scenarios, the total exhaust area of shafts that is required to exhaust all the smoke is about 100 m 2 . The first shaft pair plays a critical role to exhaust the smoke, and its exhaust efficiency is also affected significantly by the shaft length. This study investigates how to control the smoke by using vertical shafts in a road tunnel fire and the conclusions are useful to tunnel fire protection engineering.

  • 3.
    Zhao, Shengzhong
    et al.
    RISE - Research Institutes of Sweden, Safety and Transport, Safety. Chongqing University, China.
    Li, Y. Z.
    Chongqing University, China.
    Ingason, Haukur
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Liu, F.
    Chongqing University, China.
    A theoretical and experimental study on the buoyancy-driven smoke flow in a tunnel with vertical shafts2019In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 141, p. 33-46Article in journal (Refereed)
    Abstract [en]

    In this study, a series of small-scale experiments was carried out in a model scale tunnel with dimensions of 20 m (Length) × 2 m (Width) × 1 m (Height) to investigate the characteristics of buoyancy-driven smoke flow in a tunnel with vertical shafts. Different shaft settings and four different longitudinal ventilation velocities were tested in the experiments. A theoretical model for the mass flow rate of buoyancy-driven smoke flow in the shaft was developed and validated. The gas temperature along the tunnel ceiling and smoke stratification were subsequently analyzed and discussed. The results showed that more shafts, greater shaft heights and greater shaft cross sectional areas can significantly increase the smoke extraction rate, and the total smoke mass flow rate in the shafts increases with the increasing ventilation velocity. The local pressure loss coefficient at the shaft inlet may not be a fixed value. An average value of 1.0 for this coefficient was recommended for engineering estimation and design of rectangular-shaped natural shafts. The presence of vertical shaft is beneficial to the smoke stratification and could increase the height of the smoke layer interface, especially for the downstream of the shaft.

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