Browsing by Author "Hashimoto, Nozomu"
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Item Effect of Flow Direction on the Extinction Limit for Flame Spread over Wire Insulation in Microgravity(47th International Conference on Environmental Systems, 2017-07-16) Nagachi, Masashi; Mitsui, Fumiya; Citerne, Jean-Marie; Dutilleul, Hugo; Guibaud, Augustin; Jomaas, Grunde; Legros, Guillaume; Hashimoto, Nozomu; Fujita, OsamuExperiments to determine the Limiting Oxygen Concentration (LOC) of a flame spreading over electric wire insulation were carried out in microgravity (parabolic flights) and in normal gravity, and the difference between the LOC in opposed and concurrent flows was evidenced under microgravity (μG). Polyethylene insulated Copper (Cu) wires and polyethylene insulated Nickel-Chrome (NiCr) wires with inner core diameter of 0.50 mm and insulation thickness of 0.30 mm were examined with external flow velocities ranging from 50mm/s to 200mm/s. The results for Copper wires show that with increasing external flow velocity, the LOC monotonically decreased in concurrent flow condition and the LOC first decreased and then increased (“U” trend) in opposed flow condition. These trends were similar to the results of the experiments with NiCr wires. Also, in terms of the minimum LOC value (MLOC), the MLOC for concurrent flow was about 1-2% lower in Oxygen concentration than that for opposed flow in both wires cases. Further, when comparing the MLOC of NiCr wires with the MLOC of Cu wires, it was found that the MLOC of the NiCr wires was close to that of Cu wires for concurrent flow conditions. However, the MLOC of the NiCr wires was about 1% lower in Oxygen concentration than that of Cu wires for opposed flow conditions. These results provide insight into the mechanism of extinction limit of flame spread over wire insulation, especially the effect of flow direction and core wire material, both of which will be useful for improving fire safety onboard spacecraft.Item Effect of the Ignition Method on the Extinction Limit for a Flame Spreading over Electric Wire Insulation(47th International Conference on Environmental Systems, 2017-07-16) Mitsui, Fumiya; Nagachi, Masashi; Citerne, Jean-Marie; Dutilleul, Hugo; Guibaud, Augustin; Jomaas, Grunde; Legros, Guillaume; Hashimoto, Nozomu; Fujita, OsamuExperiments for flame spreading over electric wire insulation were conducted in parabolic flights (microgravity) and on ground (normal gravity) to understand the effect of the ignition condition on the Limiting Oxygen Concentration (LOC) for electric wires under an external, opposed flow condition of 100 mm/s (typical flow velocity on ISS). Both the ignition power and the igniter heating time were varied ranging from 50 W to 110W and from 5 s to 15 s in order to investigate the ignition condition effect. Polyethylene-coated Nickel-Chrome wires with inner core diameter of 0.50 mm and insulation thickness of 0.30 mm were used as sample wires, and a 0.50 mm diameter coiled Kanthal wire was used as igniter. The experimental results show that the LOC assumes an almost constant value under normal gravity conditions once ignition occurred, whereas under microgravity conditions, the LOC gradually decreases as the ignition power or heating time increases and eventually it reaches an almost constant value. Thus, the effect of ignition condition on LOC is stronger in microgravity than in normal gravity. The difference in oxygen concentration between the maximum and the minimum LOC was about 2% within the tested range of ignition conditions. This means that additional heating is required after ignition occurs to obtain the correct LOC. Finally, the results suggest that there exists a minimum ignition power and heating time to obtain the correct LOC values for electric wire combustion, especially in microgravity. This result has the potential to improve safety aspects associated with the development of a fire safety standard for spacecrafts, and consequentially also to improve spacecraft fire safety in general.Item Evaluation of Buoyant Flow Velocity Induced by Centrifugal and Coriolis Acceleration During Downward Flame Spread Over Thin Wire in a Centrifuge(2023 International Conference on Environmental Systems, 2023-07-16) Konno, Yusuke; Ishikawa, Shoryu; Hashimoto, Nozomu; Fujita, OsamuCentrifuges are effective devices for observing physical phenomena in various gravitational fields. This study discusses the effectiveness of observing flame spread phenomena along the solid materials in centrifuges as a basis for spacecraft fire safety. Flame spread tests are carried out on the ground in the present study. Thin wires which consist of a metallic core and polymer insulation are used as test samples. A sample is supported vertically in a chamber at 120 mm apart from the axis of rotation. The upper end of the sample is ignited by a hot wire and subsequent downward flame spread under varied centrifugal force is observed. A spreading flame leans to the radial direction due to centrifugal force, but also to the circumferential direction due to the Coriolis force. By measuring the flame tilt angle, we attempt to predict the buoyant flow velocity affecting the spreading flame, based on the scale analysis at the location of sample. The buoyant flow velocities obtained in this study are similar to those reported in previous studies, indicating the validity of analysis method. Those results show that the centrifuge can be used not only to investigate the material flammability under arbitrary gravitational field, but also to evaluate the buoyant flow velocity that affects the flame spreading along the solid materials.Item Opposed Flame Spread over Polyethylene Insulated Wires under Varying External Radiations and Oxygen Concentrations(46th International Conference on Environmental Systems, 2016-07-10) Miyamoto, Kyosuke; Huang, Xinyan; Hashimoto, Nozomu; Fujita, Osamu; Fernandez-Pello, CarlosFuture space missions may require spacecraft cabin environments different than those used on the International Space Station (ISS). Environmental variables such as flow condition, oxygen concentration, ambient pressure, presence of an external radiant flux, partial or microgravity (µg), may change the material flammability and fire dynamics for any particular set of environmental conditions. Electrical cables and harnesses have been identified as a potential source of fires in spacecraft. In this work, the opposed flame spread behavior for polyethylene (PE) insulated wires are investigated under varying external irradiations and oxygen concentrations. Two wire dimensions with inner copper core/PE insulation outer diameters of 3.5/8.0 mm and 5.5/9.0 mm are selected. Three different insulations: (1) clear high-density (HDPE), (2) clear low-density polyethylene (LDPE), and (3) black LDPE are examined and compared. The work is part of a project in fire safety in space based installations and in particular electrical wire fire safety. The comparison of wire heating by the external radiant flux with core and no core reveals that the copper core acts as a heat sink. Moreover, different PE insulations (i.e. transparence and polymer microstructures) have an appreciable influence on the melting condition and flame spread rate. Phenomenological arguments are used to understand and explain the experimental observations. The result of this work provides information about the fire behavior of electrical wires in fire environments where external heating for an adjacent fire or heat source may be present thus they may be useful toward upgrading the fire safety design and standards of future space missions.