Other affiliations: Tokyo University of Science, Nagoya University, National Institute of Standards and Technology ...read more
Bio: Yuji Nakamura is an academic researcher from Toyohashi University of Technology. The author has contributed to research in topics: Premixed flame & Combustion. The author has an hindex of 20, co-authored 148 publications receiving 1378 citations. Previous affiliations of Yuji Nakamura include Tokyo University of Science & Nagoya University.
Papers published on a yearly basis
••01 Jan 2009
TL;DR: In this paper, two kinds of sample wires, made by nickel-chrome (NiCr) and iron (Fe) as core metal, are used in the experiment to study the electric fire spread along a single wire harness in sub-atmospheric pressure.
Abstract: Flame spread along the single wire harness (thin-metal wire with coating of polyethylene film) in sub-atmospheric pressure has been examined experimentally to gain better understandings of the electric fire in the aircraft and space habitats. Two kinds of sample wires, made by nickel-chrome (NiCr) and iron (Fe) as core metal, are used in this study. Ambient gas is fixed as air and total pressure is varied from atmospheric to sub-atmospheric (100–20 kPa). As the pressure decreases, flame shape changes from typical “teardrop” to “oval” and flame becomes less-luminous irrespective of the materials of the wire. It turns out that the dependence of the spread rate on pressure varies with the materials of the wire; when the pressure decreases, the spread rate of NiCr-harness monotonically increases, whereas that of Fe-harness mostly remains as constant. From the simple thermal-length analysis, it is proposed that there are two modes in the spread depending on the controlling factor; one is “wire-driven mode” (the spread is mainly governed by the thermal input through the wire) and the other is “flame-driven mode” (the spread is mainly governed by the thermal input from the flame). Observed two cases (NiCr- and Fe-harness) would be categorized to the latter and former modes, respectively.
••01 Jan 2013
TL;DR: In this article, an ignition-to-spread model is developed to systematically explain electrical wire ignition and the following transition to spread, and experiments show that additional heating times after flash are required in order to fully pass the transition and achieve a spreading flame.
Abstract: Ignition of electrical wires by external heating is investigated in order to gain a better understanding of the initiation of electrical-wire fires. An ignition-to-spread model is developed to systematically explain ignition and the following transition to spread. The model predicts that for a higher-conductance wire it is more difficult to achieve ignition and the weak flame may extinguish during the transition phase because of a large conductive heat loss along the wire core. An experimental study was performed using several sample wires with different core metals, diameters and coating thicknesses of polyethylene. A coil heater was adopted as the ignition source, and both the heat flux and heating time were selected as the main parameters to identify the flashpoint and spread point of wire fires. Experiments show that additional heating times after flash are required in order to fully pass the transition and achieve a spreading flame, agreeing with model predictions. Finally, the effects of different heating lengths, environmental pressures, and oxygen concentration on wire ignition are discussed, which may be useful for upgrading the design and standards of future fire-safe wires.
TL;DR: In this article, the authors review the recent understandings of the fundamental combustion processes in wire fire over the last three decades and highlight the complex role of the metallic core in the ignition, flame spread, burning, and extinction of wire fire.
Abstract: Electrical wires and cables have been identified as a potential source of fire in residential buildings, nuclear power plants, aircraft, and spacecraft. This work reviews the recent understandings of the fundamental combustion processes in wire fire over the last three decades. Based on experimental studies using ideal laboratory wires, physical-based theories are proposed to describe the unique wire fire phenomena. The review emphasizes the complex role of the metallic core in the ignition, flame spread, burning, and extinction of wire fire. Moreover, the influence of wire configurations and environmental conditions, such as pressure, oxygen level, and gravity, on wire-fire behaviors are discussed in detail. Finally, the challenges and problems in both the fundamental research, using laboratory wires and numerical simulations, and the applied research, using commercial cables and empirical function approaches, are thoroughly discussed to guide future wire fire research and the design of fire-safe wire and cables.
••01 Jan 2011
TL;DR: In this article, a microgravity experiment was conducted at MGLAB (Micro Gravity Laboratory of Japan) to simulate the status of the circuit breaker shortly after the overload of a wire.
Abstract: Ignition phenomena of overloaded electric wires have been investigated in microgravity as basic information for fire safety in space. Microgravity experiments were conducted at MGLAB (Micro Gravity Laboratory of Japan) to provide 4.5 s of microgravity time. In the experiments the current supply duration was selected as the main test parameter to simulate the status of the circuit breaker shortly after the overload occurs. Other important test parameters were the surrounding oxygen concentration and the supplied electric current amount. The results showed that the microgravity environment significantly increases the ignition probability, including the occurrence of delayed ignition and extended ignition limits, with large electric currents when compared with the situation under normal earth based gravity. The increase in the ignition probability is explained by decreases in the minimum ignition energy in microgravity interacting with the ignition mechanism.
••01 Jan 2005
TL;DR: In this article, the properties of micro-scale hydrogen diffusion flames produced from sub-millimeter diameter (d ǫ = 0.2 and 0.48mm) tubes are investigated using nonintrusive UV Raman scattering coupled with LIPF technique.
Abstract: Characteristics of microscale hydrogen diffusion flames produced from sub-millimeter diameter ( d = 0.2 and 0.48 mm) tubes are investigated using non-intrusive UV Raman scattering coupled with LIPF technique. Simultaneous, temporally and spatially resolved point measurements of temperature, major species concentrations (O 2 , N 2 , H 2 O, and H 2 ), and absolute hydroxyl radical concentration (OH) are made in the microflames for the first time. The probe volume is 0.02 × 0.04 × 0.04 mm 3 . In addition, photographs and 2-D OH imaging techniques are employed to illustrate the flame shapes and reaction zones. Several important features are identified from the detailed measurements of microflames. Qualitative 2-D OH imaging indicates that a spherical flame is formed with a radius of about 1 mm as the tube diameter is reduced to 0.2 mm. Raman/LIPF measurements show that the coupled effect of ambient air leakage and pre-heating enhanced thermal diffusion of H 2 leads to lean-burn conditions for the flame. The calculated characteristic features and properties indicate that the buoyancy effect is minor while the flames are in the convection–diffusion controlled regime because of low Peclet number. Also, the effect of Peclet number on the flame shape is minor as the flame is in the convection–diffusion controlled regime. Comparisons between the predicted and measured data indicate that the trends of temperature, major species, and OH distributions are properly modeled. However, the code does not properly predict the air entrainment and pre-heating enhanced thermal-diffusive effects. Therefore, thermal diffusion for light species and different combustion models might need to be considered in the simulation of microflame structure.
01 Jan 2007
01 Jan 2016
TL;DR: The numerical heat transfer and fluid flow is universally compatible with any devices to read and is available in the authors' digital library an online access to it is set as public so you can get it instantly.
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••28 Jan 2005
TL;DR: The Q12-40 density: ρ ((kg/m) specific heat: Cp (J/kg ·K) dynamic viscosity: ν ≡ μ/ρ (m/s) thermal conductivity: k, (W/m ·K), thermal diffusivity: α, ≡ k/(ρ · Cp) (m /s) Prandtl number: Pr, ≡ ν/α (−−) volumetric compressibility: β, (1/K).
Abstract: Geometry: shape, size, aspect ratio and orientation Flow Type: forced, natural, laminar, turbulent, internal, external Boundary: isothermal (Tw = constant) or isoflux (q̇w = constant) Fluid Type: viscous oil, water, gases or liquid metals Properties: all properties determined at film temperature Tf = (Tw + T∞)/2 Note: ρ and ν ∝ 1/Patm ⇒ see Q12-40 density: ρ ((kg/m) specific heat: Cp (J/kg ·K) dynamic viscosity: μ, (N · s/m) kinematic viscosity: ν ≡ μ/ρ (m/s) thermal conductivity: k, (W/m ·K) thermal diffusivity: α, ≡ k/(ρ · Cp) (m/s) Prandtl number: Pr, ≡ ν/α (−−) volumetric compressibility: β, (1/K)
••01 Jan 2007
TL;DR: In this article, a review of the development of micro-power generators by focusing more on the advance in fundamental understanding of microscale combustion is presented, and the conventional concepts of combustion limits such as flammability limit, quenching diameter, and flame extinction and heat recirculation are revisited.